signaling traffic based online topology reconstruction and...

Eötvös Loránd University

Faculty of Informatics

Signaling traffic based online

topology reconstruction and

visualization in mobile networks

Bálint Molnár Lídia Boglárka Torma

Associate professor at ELTE Computer Science

Bruno Crispo

Associate Professor at University

of Trento, Italy

László Kottyán

Software Developer at Ericsson

Hungary Ltd.

Budapest, 2016.

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1 Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Historical background . . . . . . . . . . . . . . . . . . . . . . 3

1.2 About VoLTE . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Before starting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1 The used topology . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 What a network monitoring tool needs to have . . . . . . . . . 10

3 Diameter protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1 Packet format . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 Diameter Source and destination identi�cation methodology . 18

3.3 Targeted messages, interfaces, and nodes . . . . . . . . . . . . 19

4 S1AP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5 GTPv2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5.1 Targeted interfaces and nodes using GTPv2 . . . . . . . . . . 30

5.2 Methodology for GTPv2 . . . . . . . . . . . . . . . . . . . . . 31

6 Concluding passive methods on the investigated interfaces . . . . . . 37

7 Anonymization and de-anonymization . . . . . . . . . . . . . . . . . . 39

7.1 Anonymization . . . . . . . . . . . . . . . . . . . . . . . . . . 39

7.2 De-anonymization . . . . . . . . . . . . . . . . . . . . . . . . . 43

8 Security issues with web applications . . . . . . . . . . . . . . . . . . 47

9 Access control: Authentication and authorization . . . . . . . . . . . 51

9.1 Authorization methods . . . . . . . . . . . . . . . . . . . . . . 51

9.2 Authentication in general . . . . . . . . . . . . . . . . . . . . 54

9.3 Authentication in a single page web application (SPA) . . . . 55

9.4 User handling in a Network Monitoring Tool . . . . . . . . . . 59

10 Security Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

i

List of Figures

1 Network functions and interfaces under investigation . . . . . . . . . 9

2 Summary of the Diameter header format[10] . . . . . . . . . . . . . . 13

3 Summary of the Diameter AVP header format[10] . . . . . . . . . . . 14

4 An example for Diameter protocol. The lime brace stands for the

Request �ag, the orange for the Command Code and the dark green

for the Application Id. . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5 Example for S1AP codes . . . . . . . . . . . . . . . . . . . . . . . . . 23

6 GTP-U encapsulation of UE user plane tra�c[15] . . . . . . . . . . . 29

7 Secret key generation for each security classes[22] . . . . . . . . . . . 42

8 Double Submit Cookie[43] . . . . . . . . . . . . . . . . . . . . . . . . 48

9 The basic RBAC model with sessions[34] . . . . . . . . . . . . . . . . 52

10 Authentication with password . . . . . . . . . . . . . . . . . . . . . . 55

11 Responsibilities of the database, server, and client[42] . . . . . . . . . 56

ii

List of Tables

1 Common Diameter command codes . . . . . . . . . . . . . . . . . . . 16

2 Diameter Attribute-names and codes[10] . . . . . . . . . . . . . . . . 17

3 Diameter interfaces and network functions . . . . . . . . . . . . . . . 20

4 Diameter commands with the corresponding interfaces, network func-

tions and directions 1/2 . . . . . . . . . . . . . . . . . . . . . . . . . 21

5 Diameter commands with the corresponding interfaces, network func-

tions and directions 2/2 . . . . . . . . . . . . . . . . . . . . . . . . . 22

6 S1AP procedure codes 1/2 . . . . . . . . . . . . . . . . . . . . . . . . 25

7 S1AP procedure codes 2/2 . . . . . . . . . . . . . . . . . . . . . . . . 26

8 S1AP messages and initiators 1/2 . . . . . . . . . . . . . . . . . . . . 27

9 S1AP messages and initiators 2/2 . . . . . . . . . . . . . . . . . . . . 28

10 GTPv2 messages and corresponding interfaces 1/3 . . . . . . . . . . . 34



iii

Introduction

The 4G Telecommunication network's complexity lies not only in the numerous

interconnected elements but also in the various protocols used in the communication.

To secure the superior performance of these complex networks, it is essential to

monitor them e�ectively. One of the monitoring methods is to capture all the

messages between network functions (NF). A monitoring system has to gather and

analyze all the relevant messages transmitted between network functions to be able

to point out errors and misbehavior.

In a typical case, the architecture of the network is given as an input for the anal-

ysis of the captured tra�c. The input consists of the network functions, connections

between them and their IP addresses. The description format of the network ar-

chitecture is not standardized and the topology information is not always available,

therefore, it is important to �nd a way to automate the network topology discovery,

in order to construct the topology without prespeci�ed input.

The main problem which is investigated and shall be resolved is to �nd the most

appropriate logic or algorithm which is proper to discover all network functions and

connections among them by using passive methods. Messages transmitted between

network functions using diameter, S1AP, and GTPv2 protocols are to be examined

thoroughly, aiming to �nd a logic or algorithm to clearly specify the sender and

receiver function. Hence, the previously gathered IP addresses can be matched to

the right nodes.

While analyzing the transmitted messages, a monitoring tool user can access

sensitive data which he or she does not have the privilege to see. Hence, anonymiza-

tion and encryption are necessary. That implies a problem which has to be resolved,

that is the need of an extensive security plan and a comprehensive view on security

and privacy issues in a web application, including authentication and authorization,

concerning security issues in web applications and anonymization techniques.

In Section 1 a brief introduction to the evolution of the telecommunication net-

work and VoLTE can be found.

In Section 2 I de�ne the used topology including the network functions and

interfaces. I will also introduce a network monitoring tool in general with some

features and properties they need to have, namely topology reconstruction feature

and secure private data handling with authentication and authorization methods.

In the later sections, I investigate the question how a network topology can be

reconstructed by using passive methods. For this I introduce the protocols S1AP,

1

Diameter, and GTPv2, aiming to �nd a way or logic to clearly identify the source

and destination node of each transmitted message.

In Section 7 I introduce anonymization methods. This section also provides an

overview on the users' privacy details and data handling.

In Section 8 I discuss possible attacks a web application can su�er, like SQL-

injection, XSS and password issues.

Section 9 introduces authorization and authentication. More speci�cally, it dis-

cusses monitoring tool users' access rights and the accessibility of information with

di�erent privacy levels. This section also includes a brief overview of single page

applications and possible authentication problems, paying special attention to the

requirements of a network monitoring tool.

Finally, in Section 10 a summary of the investigated security issues and remedies

is provided.

2

1. LITERATURE 3

1 Literature

1.1 Historical background

A telecommunication network is a collection of network functions and links which are

connected so as to enable telecommunication between the terminals. For instance,

such networks are public switched telephone networks. In my thesis I work with one

of its varieties, namely mobile networks.

The history of mobile telephony dates back to the early twentieth century when

the American Telephone & Telegraph company �rst discussed developing a wireless

phone in 1915.[1] Since then by outgrowing its boundaries a great evolution has

occurred and today's network communication emerged.

The �rst system of mobile communication, the so-called GSM, is a standard

developed by the European Telecommunications Standards Institute (ETSI) to de-

scribe the protocols for second-generation (2G) digital cellular networks used by

mobile phones.[2, p. 529]

To replace �rst generation (1G) analog cellular networks the 2G digital networks

were developed, and by 2014 it has become the default global standard for mo-

bile communications. To include data communications, �rst circuit-switched then

packet-switched data transport was used via GPRS (General Packet Radio Services)

and EDGE (Enhanced Data rates for GSM Evolution or EGPRS). The latter along

with UMTS (Universal Mobile Telecommunications System) and HSPA (High-Speed

Packet Access) form the so-called 3G (digital voice and data) which is developed

and maintained by the 3GPP (3rd Generation Partnership Project).[4, Chapter

2.7] WCDMA (Wideband Code Division Multiple Access) also found in 3G mobile

telecommunications networks and is used in Japan. This is the most commonly used

member of the UMTS family.

At the end of 2004, the 3GPP Standardization Forum started to evaluate a new

radio technology as a successor for WCDMA (Wideband Code Division Multiple

Access). The new approach, the fourth generation (4G), was called Long Term

Evolution (LTE) advanced standards, which do not form part of the ETSI GSM

standard. In 2012 it was the fastest developing mobile system technology ever.[5,

VoLTE]

4

1.2 About VoLTE

But the story does not end here. As subscribers demand more services for less

money, it is vitally important for telecom operators to protect their pro�tability by

reducing delivery costs. The answer is to eliminate the need for separate voice and

data networks.

On the 19th of May in 2014 in Singapore, Singtel, in collaboration with Samsung

and Ericsson, unveiled 4G ClearVoice, the world's �rst commercial full-featured

Voice over LTE (VoLTE) service.[3]

It is a standardized IP Multimedia System (IMS)-based Voice Over IP (VoIP)

service and is designed to replace existing circuit-switched voice. While VoIP is

a generic term for any voice over IP service, VoLTE is a speci�c implementation

in the LTE standards, based on IMS. It unlocks richer conversation services and

lays a foundation for operators to o�er toll-grade quality using well-de�ned quality

of service (QoS) mechanisms.[6] VoLTE is expected to o�er operators a chance to

produce better service quality compared to OTT (Over-the-Top, such as Skype,

GTalk) competitors.

As written in [6, Validating VoLTE 2nd ed.] VoLTE is not just an upgrade, but

a whole new deal. Until it is not supported by all mobile phones in use, operators

need to provide seamless fallback to 2G/3G networks where LTE is not available.

However, VoLTE provides better quality, 3 times more capacity than 3G and

o�ers rich IP communications, including video calling and content sharing[7], the

circuit-switched fallback (CSFB) solution is still preferred by most of the mobile

operators because deploying a completely new system is expensive. CSFB is a

golden mean in a sense that operators use LTE for data tra�c while turning o� the

3G and 2G radios, and switch them on again only for incoming and outcoming calls.

Although this topology can reduce radio units' battery consumption in smartphones,

but call initiation is longer than in fully IP-based systems.[8]

Anite, a part of Keysight Technologies, developed a network monitoring system

called Nemo. In [9] they showed that according to their measurements, circuit-

switched networks deliver very good performance and excellent reliability. In the

case of WCDMA, the average value is slightly better than with GSM. As it was

expected, LTE CS fallback call set-up takes more seconds to establish a call. While

the WCDMA and GSM averages are between 2.4s and 3.3s, the CSFB is constantly

above 3.3s. VoLTE was also tested in di�erent maturity phases. The results show

vast improvement when the technology had been optimized further. The average

1. LITERATURE 5

duration of VoLTE call establishment with the latest version was around 3.2 seconds.

Validating VoLTE

Ensuring a high-quality VoLTE rollout requires end-to-end validation that begins

in the lab and continues into the live network. Throughout the chapters of [6,

Validating VoLTE 2nd ed.] the whole VoLTE network, its elements, the nodes and

certain messages between them are detailed along with the test con�guration for

each partition. The book outlines a VoLTE test plan that ensures a correct, stable,

and e�ective VoLTE deployment.

2. BEFORE STARTING 7

2 Before starting

2.1 The used topology

VoLTE, like other networks, consists of network elements: functions and interfaces.

My thesis mainly focuses on the nodes

• eNodeB (E-UTRAN Node B, also known as Evolved Node B)

• MME (Mobility Management Entity)

• S-GW (Serving Gateway)

• P-GW/PDN-GW (Packet Data network Gateway)

• PCRF (Policy Charging and Rules Function)

• HSS (Home Subscriber Server)

• SLF (Subscriber Location Function)

• P-CSCF (Proxy Call Session Control Function)

• I/S-CSCF (Interrogating/Serving Call Session Control Function)

• E-CSCF (Emergency � Call Session Control Function)

• MMTelAS and SCCAS (Multimedia Telephony Application Server and Service

Centralization and Continuity Application Server)

• ePDG (evolved Packet Data Gateway)

• TWAN (Trusted WLAN Access Network)

• 3GPP AAA (3GPP Authentication, Authorization, and Accounting)

• GMLC (Gateway Mobile Location Centre) and

• AP (Application Protocol).

The investigated protocols are Diameter, S1AP, and GTPv2.

Figure 1 shows the above-listed network functions with the interfaces among

them. In this thesis, the mainly targeted nodes are colored in blue, while the green

ones are for further future investigation. The green color is also used to indicate

interfaces which have importance for later jobs. For other interfaces three types of

8

color representations are used: yellow for S1AP, purple for diameter and brown for

GTPv2 protocol (see the bottom right corner for the legend).

There is one more node included in the diagram but not mentioned, yet: SGSN.

We will see in Section 5 that though it is not part of VoLTE, it has importance in

3G, and is possible to get messages sent via GTPv2 interfaces: S3, S4, and S16.

They are highlighted by using gray letters.

2.BEFORESTARTING

9

Figure 1: Network functions and interfaces under investigation

10

2.2 What a network monitoring tool needs to have

Among several properties a network monitoring tool needs to have automated con-

�guration and has to handle private user data.

Methods and environment

For the con�guration, a topology reconstruction algorithm needs to be de�ned.

For this two kinds of network discovery methods exist: active and passive. With

active methods the network can be discovered by sending additional messages in

order to collect IP addresses, and if possible, to discover Network Functions. Passive

monitoring method is used to capture all the messages between network functions,

analyze them, extract the information elements contained by the packages and decide

which IP address corresponds to which sender and receiver node.

In this Thesis, passive methods are investigated. The input consists of a trace

�le with the extension of .pcap, for which we use the program WireShark to open.

It provides a clear view of each message contained by the .pcap �le.

Security in a network monitoring tool

While analyzing the messages and collecting information, a network monitoring tool

user can have access to private data for which he or she does not have the privilege.

For instance, among GTPv2 messages, there are several which contains or condi-

tionally contains IMSI and MSISDN, which are two private data and not to reveal

publicly. Just for a few example, Create Session Request, Delete Session Request,

Downlink Data Noti�cation Acknowledge, Create Indirect Data Forwarding Tunnel

Request, Stop Paging Indication and many other messages contain this information

element.

Other types of sensitive private data can be found in diameter messages mainly

in the AVP header. For instance in User Data Request message contains

� Session-ID

� Origin-Realm

� Origin-Host

� Destination-Realm

� Destination-Host

� User-Identity.

2. BEFORE STARTING 11

Moreover, User Data Answer contains User-Data, and Subscriber Data Request en-

compasses User-Name and Subscription-Data. Most of the messages enclose Origin-

Host and Origin-Realm as well as User-Identity, which is also commonly present.

These pieces of information should be anonymized using cryptographic encryp-

tion functions. A privileged network monitoring tool user needs to see the existence

of these data but can carry out his duties without knowing them, hence, they can

work with encrypted information.

Revealing these private data without any restriction is dangerous. Unauthorized

access can lead to misuse of personal information including but not limited to ha-

rassment, espionage, and impersonation. Also, patterns of user behavior can be

created aiming to track the user and commit varied malicious actions.

Therefore, it is inevitable to deal with security issues, encrypt user data and

store them safely. However encryption can make attackers' job harder, penetration

is still possible and should be preceded by using input sanitization wherever user

input can be submitted, thus prevent unauthorized access to the databases. There

are also several �tricks� and attacks which can lead to unauthorized access.

Next to the above mentioned private data, that is IMSI and MSISDN, there are

equally important sensitive pieces of information that can be found in the network

monitoring tool users' account. For instance, the successful reconstruction of the

topology reveals the detailed structure of the inner network. A broad picture can

be seen by many, but the details like IP addresses and ports should be shown only

for network monitoring tool users who actually use these data for their work.

Therefore, a proper access handout implies the inevitability of an e�ective au-

thentication scheme. Comprehensive authorization and authentication in web ap-

plications are important tasks and needed to be handled.

3. DIAMETER PROTOCOL 13

3 Diameter protocol

Diameter is an Authentication, Authorization, and Accounting (AAA) protocol. It

is a message (packet) based protocol, where AAA nodes exchange messages and

receive Positive or Negative acknowledgment for each message exchanged between

nodes. Diameter was initially developed to overcome the limitations of RADIUS,

which is also an AAA protocol, but it had issues with reliability, scalability, security

and �exibility because it supports UDP, that does not use implicit hand-shaking

mechanism for providing the above-mentioned issues. Instead of UDP, Diameter

uses the TCP and SCTP for message exchange, which makes it reliable.[10][11]

3.1 Packet format

There are two types of messages: Request and Answer. Each message consists of a

Diameter header and a variable number of Attribute-Value Pairs (AVPs).

Diameter Header

As is shown in Figure 2, the header �elds are the following:

Figure 2: Summary of the Diameter header format[10]

• Version, to indicate Diameter Version. Now it must be set to 1.

• Message Length, to indicate the message length of the Diameter message in-

cluding the header �elds and the padded AVPs.

14

• Flags : the assigned bits are R (Request), P (Proxiable), E (Error), T (Poten-

tially re-transmitted message) and r (reserved). If the Request bit is set, that

is, R=1, then the message is a request. If cleared, that is, R=0, it indicates

an answer.

• Command code is a unique identi�er for each message. It is di�erent for each

type of request. Though the corresponding answer has the same command

code, the request �ag R is set to 0. The three columns of Table 1 shows the

listed message types, their abbreviations, and the command codes.

• Hop-by-Hop (H2H) Identi�er is a unique integer that aids in matching requests

and replies. The sender of an answer message MUST ensure that the H2H

Identi�er �eld contains the same value that was found in the corresponding

request.

• End-to-End (E2E) Identi�er is used to detect duplicate messages.

Note that the header �elds are mandatory to be present and �lled.

Diameter AVP header

Diameter AVPs carry speci�c authentication, accounting, authorization, and routing

information as well as con�guration details for the request and reply.

Figure 3: Summary of the Diameter AVP header format[10]

Figure 3 shows the format of the AVP header. One message can include several

AVPs, di�erentiated by the Attribute-name or code. Table 2 contains the possible

attribute values.

In my thesis, the most important AVPs are the Origin-Host and Origin-Realm.

These values are mandatory to be present in all Diameter messages. Similar to


the origin values, Destination-Host and Destination-Realm AVPs are also useful

but usually are not contained in the diameter messages. Destination-Host must

be present in all unsolicited agent initiated messages, and may be present in other

request messages, but - along with Destination-Realm - it is forbidden for answers

to contain it.

• Origin-Host identi�es the endpoint that originated the Diameter message. Its

value is guaranteed to be unique within a single host.

• The Origin-Realm contains the Realm of the originator of any Diameter mes-

sage.

• The absence of Destination-Host will cause a message to be sent to any Diame-

ter server supporting the application within the realm speci�ed in Destination-

Realm AVP.

• When Destination-Realm present, the Destination-Realm AVP is used to per-

form message routing decisions.

16

Command name abbr Code Command name abbr Code

AA-Request AAR 265 User-Data-Request UDR 306

AA-Answer AAA 265 User-Data-Answer UDA 306

Diameter-EAP-Request DER 268 Profile-Update-Request PUR 307

Diameter-EAP-Answer DEA 268 Profile-Update-Answer PUA 307

Abort-Session-Request ASR 274 Subscribe-Notifications-Request SNR 308

Abort-Session-Answer ASA 274 Subscribe-Notifications-Answer SNA 308

Accounting-Request ACR 271 Push-Notification-Request PNR 309

Accounting-Answer ACA 271 Push-Notification-Answer PNA 309

Credit-Control-Request CCR 272 Bootstrapping-Info-Request BIR 310

Credit-Control-Answer CCA 272 Bootstrapping-Info-Answer BIA 310

Capabilities-Exchange-Request CER 257 Message-Process-Request MPR 311

Capabilities-Exchange-Answer CEA 257 Message-Process-Answer MPA 311

Device-Watchdog-Request DWR 280 Update-Location-Request ULR 316

Device-Watchdog-Answer DWA 280 Update-Location-Answer ULA 316

Disconnect-Peer-Request DPR 282 Cancel-Location-Request CLR 317

Disconnect-Peer-Answer DPA 282 Cancel-Location-Response CLA 317

Re-Auth-Request RAR 258 Authentication-Information-Request AIR 318

Re-Auth-Answer RAA 258 Authentication-Information-Answer AIA 318

Session-Termination-Request STR 275 Insert-Subscriber-Data-Request IDR 319

Session-Termination-Answer STA 275 Insert-Subscriber-Data-Response IDA 319

User-Authorization-Request UAR 300 Delete-Subscriber-Data-Request DSR 320

User-Authorization-Answer UAA 300 Delete-Subscriber-Data-Response DSA 320

Server-Assignment-Request SAR 301 Purge-UE-Request PUR 321

Server-Assignment-Answer SAA 301 Purge-UE-Response PUA 321

Location-Info-Request LIR 302 Reset-Request RSR

Location-Info-Answer LIA 302 Reset-Answer RSA

Multimedia-Auth-Request MAR 303 Notify-Request NR 323

Multimedia-Auth-Answer MAA 303 Notify-Answer NA 323

Registration-Termination-Request RTR 304 Provide-Location-Request PLR 8388620

Registration-Termination-Answer RTA 304 Provide-Location-Answer PLA 8388620

Push-Profile-Request PPR 305 Routing-Info-Request RIR 8388622

Push-Profile-Answer PPA 305 Routing-Info-Answer RIA 8388622

Table 1: Common Diameter command codes


Attribute-Name Code Firmware-Revision 267Acct-Interim-Interval 85 Host-IP-Address 257Accounting-Realtime-Required 483 Inband-Security-Id 299Acct-Multi-Session-Id 50 Multi-Round-Time-Out 272Accounting-Record-Number 485 Origin-Host 264Accounting-Record-Type 480 Origin-Realm 296Accounting-Session-Id 44 Origin-State-Id 278Accounting-Sub-Session-Id 287 Product-Name 269Acct-Application-Id 259 Proxy-Host 280Auth-Application-Id 258 Proxy-Info 284Auth-Request-Type 274 Proxy-State 33Authorization-Lifetime 291 Redirect-Host 292Auth-Grace-Period 276 Redirect-Host-Usage 261Auth-Session-State 277 Redirect-Max-Cache-Time 262Re-Auth-Request-Type 285 Result-Code 268Class 25 Route-Record 282Destination-Host 293 Session-Id 263Destination-Realm 283 Session-Timeout 27Disconnect-Cause 273 Session-Binding 270E2E-Sequence 300 Session-Server-Failover 271Error-Message 281 Supported-Vendor-Id 265Error-Reporting-Host 294 Termination-Cause 295Event-Timestamp 55 User-Name 1Experimental-Result 297 Vendor-Id 266Experimental-Result-Code 298 Vendor-Specific-Application-Id 260Failed-AVP 279

Table 2: Diameter Attribute-names and codes[10]

18

3.2 Diameter Source and destination identi�cation method-

ology

To �nd a way or logic to clearly identify the source and destination network function

(NF), we mainly use the Application-ID. As is said in the beginning of this subsec-

tion, it is mandatory to be included in the diameter header. From the Application-

ID, we clearly can tell on which interface the message was transmitted. An example

for the Application-ID format is

ApplicationId: 3GPP Gx (16777238),

where '3GPP Sh` is the full name and 16777238 is the Application-ID, see Figure 4.

By knowing the interface we know the two nodes the message is transmitted

across. Most of the messages can be sent by only one of the endpoints. In this case

by knowing the Command Code, the value of �ag bit R and the Application-ID, we

can determine the source and destination unequivocally.

As shown in Figure 4, the Command Code is 272, which stands for Credit Con-

trol. The Request bit is not set, thus, the message is an Answer. As we know, Credit

Control Answer can be transmitted in multiple interfaces, hence, we need to know,

which one was used. From Application ID, we can read that the used interface is

Gx. From that it is obvious that the source NF is PGW and the destination node

is PCRF.

Figure 4: An example for Diameter protocol. The lime brace stands for the Request

�ag, the orange for the Command Code and the dark green for the Application Id.

In other cases, when in the same interface both directions or multiple senders

are possible, other methods are needed.


With the help ofOrigin-Host andOrigin-Realm, by subtracting the Origin-Realm

name from the Origin-Host, we can �nd the remaining part useful. In most cases it

contains information concerning network functions or corresponding company prod-

uct's name, so we can �lter by these values.

For instance, let us consider the message 'Insert-Subscriber-Data-Request`. A

possible host value is 'hss.tcu.ics.se` and the corresponding realm is 'tcu.ics.se`, so

the result of the subtraction is 'hss`, which matches its unique possible sender.

3.3 Targeted messages, interfaces, and nodes

Targeted diameter messages

Now let us take a look at the targeted messages. In Table 1 we already could see all

the possible command codes, but not all of them are important for us.

The excluded messages are

• Device-Watchdog-Request (DWR),

• Device-Watchdog-Answer (DWA),

• Capabilities-Exchange-Request (CER),

• Capabilities-Exchange-Answer (CEA),

• Disconnect-Peer-Request (DPR) and

• Disconnect-Peer-Answer (DPA).

DWR and DWA are irrelevant because they do not contain any relevant infor-

mation. Their only purpose is to keep the connection alive.

CER, CEA, DPR and DPA messages have signi�cance only when initiating and

aborting a connection.

20

Targeted diameter interfaces and nodes

The targeted messages use the interfaces, which are listed in the �rst column, be-

tween the network functions in the second column:

Rx: P-CSCF - PCRF

Gx/Gx+: PCRF - PGW

Cx: I-CSCF - HSS

Dx: I-CSCF - SLF

Dh: MMTelAS (or E-CSCF) - SLF

S6a: MME - HSS

Sh: MMTelAS (or E-CSCF) - HSS

(a) First priority

S6b: PGW - 3GPP AAA

Sx: MME - PCRF

SWx: 3GPP AAA - HSS

SLg/SLh: GMLC - MME

Zx: AP - HSS

Dzx: AP - SLF

(b) Second priority

Table 3: Diameter interfaces and network functions

Remark 1. The interfaces targeted in my thesis are listed in Table 3a. The ones

listed in Table 3b are for further investigation.

Remark 2. In the case of Sh and Dh, the sender can be E-CSCF and MMTelAS if

the command name is User-Data. This is the only relevant diameter message type

where Origin-Host is necessary to denominate the sender.

To �nd the list of message type with the corresponding functions and directions

see Table 4 and 5.

3.DIAMETERPROTOCOL

21

abbr Command name Code Interface Source Dest Interface2 Source2 Dest2 Interface Source DestAAR AA-Request 265 P-CSCF PCRF PGW 3GPP AAAAAA AA-Answer 265 PCRF P-CSCF 3GPP AAA PGWASR Abort-Session-Request 274 PCRF P-CSCF PCRF PGWASA Abort-Session-Answer 274 P-CSCF PCRF PGW PCRFCCR Credit-Control-Request 272 PGW PCRF MME PCRFCCA Credit-Control-Answer 272 PCRF PGW PCRF MMERAR Re-Auth-Request 258 PCRF P-CSCF PCRF PGWRAA Re-Auth-Answer 258 P-CSCF PCRF PGW PCRFSTR Session-Termination-Request 275 P-CSCF PCRF PGW 3GPP AAASTA Session-Termination-Answer 275 PCRF P-CSCF 3GPP AAA PGWUAR User-Authorization-Request 300 I-CSCF HSS I-CSCF SLFUAA User-Authorization-Answer 300 HSS I-CSCF SLF I-CSCFSAR Server-Assignment-Request 301 S-SCSF HSS S-SCSF SLF 3GPP AAA HSSSAA Server-Assignment-Answer 301 HSS S-SCSF SLF S-SCSF HSS 3GPP AAALIR Location-Info-Request 302 I-CSCF HSS I-CSCF SLFLIA Location-Info-Answer 302 HSS I-CSCF SLF I-CSCFMAR Multimedia-Auth-Request 303 S-SCSF HSS S-SCSF SLFMAA Multimedia-Auth-Answer 303 HSS S-SCSF SLF S-SCSFMAR Multimedia-Auth-Request 303 3GPP AAA HSS AP HSS AP SLFMAA Multimedia-Auth-Answer 303 HSS 3GPP AAA HSS AP SLF APRTR Registration-Termination-Request 304 HSS S-SCSF HSS 3GPP AAARTA Registration-Termination-Answer 304 S-SCSF HSS 3GPP AAA HSSPPR Push-Profile-Request 305 HSS S-SCSF HSS 3GPP AAAPPA Push-Profile-Answer 305 S-SCSF HSS 3GPP AAA HSSUDR User-Data-Request 306 MTAS/E-CSHSS MTAS/E-CSSLFUDA User-Data-Answer 306 HSS MTAS/E-CS SLF MTAS/E-CSCFPUR Profile-Update-Request 307 MTAS HSS MTAS SLFPUA Profile-Update-Answer 307 HSS MTAS SLF MTASSNR Subscribe-Notifications-Request 308 MTAS HSS MTAS SLFSNA Subscribe-Notifications-Answer 308 HSS MTAS SLF MTASPNR Push-Notification-Request 309 HSS MTASPNA Push-Notification-Answer 309 MTAS HSS

Rx S6b

Rx Gx

Gx/Gx+ Sx

Cx Dx

Rx Gx/Gx+

Rx S6b

Cx Dx

Cx Dx SWx

Cx Dx

SWx Zx Dzx

Cx SWx

Cx SWx

Sh Dh

Sh Dh

Sh Dh

Sh

Table 4: Diameter commands with the corresponding interfaces, network functions and directions 1/2

22

ULR Update-Location-Request 316 MME HSSULA Update-Location-Answer 316 HSS MMECLR Cancel-Location-Request 317 HSS MMECLA Cancel-Location-Response 317 MME HSSAIR Authentication-Information-Request 318 MME HSSAIA Authentication-Information-Answer 318 HSS MMEIDR Insert-Subscriber-Data-Request 319 HSS MMEIDA Insert-Subscriber-Data-Response 319 MME HSSDSR Delete-Subscriber-Data-Request 320 HSS MMEDSA Delete-Subscriber-Data-Response 320 MME HSSPUR Purge-UE-Request 321 MME HSSPUA Purge-UE-Response 321 HSS MMERSR Reset-Request 322 HSS MMERSA Reset-Answer 322 MME HSSNR Notify-Request 323 MME HSSNA Notify-Answer 323 HSS MMEPLR Provide-Location-Request 8388620 GMLC MMEPLA Provide-Location-Answer 8388620 MME GMLCRIR Routing-Info-Request 8388622 MME GMLCRIA Routing-Info-Answer 8388622 GMLC MME

Legend:

S6a

S6a

S6a

S6a

S6a

S6a

S6a

S6a

SLg

SLh

Everything is known just by looking at the command codeApplicationID is needed to know the interfaceUseful in the future, but now we do not need themCannot tell anything about it, maybe Origin host-Origin realm

Table 5: Diameter commands with the corresponding interfaces, network functions and directions 2/2

4. S1AP 23

4 S1AP

S1AP provides the signaling service between E-UTRAN and the evolved packet core

(EPC) that is required to ful�ll the S1AP functions

• E-RAB management function,

• Initial Context Transfer function,

• UE Capability Info Indication function,

• Mobility Functions,

• S1 interface management functions,

• NAS Signaling transport function,

• S1 UE context Release function,

• UE Context Modi�cation function,

• Status Transfer,

• Trace function,

• Location Reporting,

• S1 CDMA2000 Tunneling function,

• Warning message transmission function,

• RAN Information Management (RIM) function and

• Con�guration Transfer function.[12]

Basically, in this protocol, there is only one interface, S1-MME. Hence, it is not

hard to �nd the sender and the receiver NF, since the messages are transmitted

between eNodeB and MME. Most of the messages are one-directional, so the sender

is clear. The possible messages and the corresponding initiators are listed in Table 8

and in Table 9.

In each message the procedure name and message type is denoted by codes.

Table 6 and 7 show the logic how we can match them. The �rst two columns

list the procedure names and the corresponding codes. The third, fourth and �fth

columns show the message type: S1AP-PDU initiating Message has the number 0,

S1AP-PDU successful Outcome has 1 and S1AP-PDU Unsuccessful Outcome has 2.

Figure 5: Example for S1AP codes

24

For instance, if the procedure code is 23 and the S1AP-PDU number is 1 then

the message is UE CONTEXT RELEASE COMPLETE, as Figure 5 shows.

The problematic messages are

• RESET,

• RESET ACKNOWLEDGE and

• ERROR INDICATION.

By only taking these messages we cannot determine the direction, we need the

context. They appear only in case of error or misbehavior, therefore, in 90% of

the cases we can see other messages which can clearly determine the sender and

receiver. Apart from these three, the determination is straightforward for all the

other messages.

4. S1AP 25

S1AP-PDU initiaing Message

S1AP-PDU successful Outcome

S1AP-PDU Unsuccessful

OutcomeProcedure Procedure Code 0 1 2Handover Preparation 0 HANDOVER REQUIRED HANDOVER HANDOVER Handover Resource Allocation

1 HANDOVER REQUESTHANDOVER REQUEST ACKNOWLEDGE

HANDOVER FAILURE

Handover Notification 2

Path Switch Request 3 PATH SWITCH REQUESTPATH SWITCH REQUEST

PATH SWITCH REQUEST FAILURE

Handover Cancellation 4 HANDOVER CANCELHANDOVER CANCEL ACKNOWLEDGE

E-RAB Setup 5 E-RAB SETUP REQUEST E-RAB SETUP E-RAB Modify 6 E-RAB MODIFY REQUEST E-RAB MODIFY E-RAB Release 7 E-RAB RELEASE E-RAB RELEASE E-RAB Release Indication

8

Initial Context Setup 9INITIAL CONTEXT SETUP REQUEST

INITIAL CONTEXT SETUP RESPONSE

INITIAL CONTEXT SETUP FAILURE

Paging 10Downlink NAS Transport 11Initial UE Message 12Uplink NAS Transport 13Reset 14 RESET RESET ACKNOWLEDGEError Indication 15NAS non delivery indication 16S1 Setup 17 S1 SETUP REQUEST S1 SETUP RESPONSE S1 SETUP FAILUREUE Context Release Request 18DownlinkS1 CDMA2000 Tunnelling 19Uplink S1 CDMA2000 Tunnelling

20

UE Context Modification 21

UE CONTEXT MODIFICATION REQUEST

UE CONTEXT MODIFICATION

UE CONTEXT MODIFICATION

UE Capability Info Indication

22

UE Context Release 23UE CONTEXT RELEASE COMMAND

UE CONTEXT RELEASE COMPLETE

eNB Status Transfer 24MME Status Transfer 25Deactivate Trace 26Trace Start 27

Trace Failure Indication 28eNB Configuration Update

29ENB CONFIGURATION UPDATE

ENB CONFIGURATION UPDATE

ENB CONFIGURATION UPDATE FAILURE

Table 6: S1AP procedure codes 1/2

26

MME Configuration Update 30

MME CONFIGURATION UPDATE

MME CONFIGURAION UPDATE

MME CONFIGURATION

Location Reporting Control 31Location Reporting Failure Indication 32Location Report 33Overload Start 34Overload Stop 35

Write-Replace Warning 36WRITE-REPLACE WARNING REQUEST

WRITE-REPLACE WARNING RESPONSE

eNB Direct Information Transfer 37MME Direct Information Transfer

38

eNB Configuration Transfer 40MME Configuration Transfer 41Cell Traffic Trace 42Kill 43 KILL REQUEST KILL RESPONSEDownlink UE Associated LPPa Transport 44Uplink UE Associated LPPa Transport 45Downlink Non UE Associated LPPa Transport 46Uplink Non UE Associated LPPa Transport

47

PWS Failure Indication

PWS Restart Indication

Reroute NAS Request

UE Context Modification Indication

UE CONTEXT MODIFICATION INDICATION

UE CONTEXT MODIFICATION CONFIRM

UE Radio Capability Match

UE RADIO CAPABILITY MATCH REQUEST

UE RADIO CAPABILITY MATCH RESPONSE

PrivateMessage 39

E-RAB MODIFICATION INDICATION

E-RAB MODIFICATION INDICATION

E-RAB MODIFICATION CONFIRM

Table 7: S1AP procedure codes 2/2

4. S1AP 27

S1AP message groups message InitiatorE-RAB Setup Request MMEE-RAB Setup Response eNBE-RAB Modify Request MMEE-RAB Modify Response eNBE-RAB Release Command MMEE-RAB Release Response eNBE-RAB Release Indication eNBE-RAB Modification Indication eNBE-RAB Modification Confirm MMEInitial Context Setup Request MMEInitial Context Setup Response eNBInitial Context Setup Failure eNBUE Context Release Request eNBUE CONTEXT RELEASE COMMAND MMEUE Context Release Complete eNBUE Context Modification Request MMEUE Context Modification Response eNBUE Context Modification Failure eNBUE Radio Capability Match Request MMEUE Radio Capability Match Response eNBUE Context Modification Indication eNBUE Context Modification Confirm MMEHandover Required eNBHandover Command MMEHandover Preparation Failure MMEHANDOVER REQUEST MMEHandover Request Acknowledge eNBHANDOVER FAILURE eNBHandover Notify eNBPATH SWITCH REQUEST eNBPath Switch Request Acknowledge MMEPath Switch Request Failure MMEHandover Cancel eNBHndover Cancel Acknowledge MMEeNB Status Transfer eNBMME Status Transfer MME

Paging PAGING MMEINITIAL UE MESSAGE eNBDownlink NAS Transport MMEUplink NAS Transport eNBNAS Non Delivery Indication eNBReroute NAS Request MMERESET MME/eNBRESET ACKNOWLEDGE eNB/MMEError Indication MME/eNBS1 SETUP REQUEST eNBS1 SETUP RESPONSE MMES1 SETUP FAILURE MMEENB CONFIGURATION UPDATE eNB

NAS transport Messages

Handover Signalling Messages

Context Management Messages

E-RAB management Messages

Management Messages

Table 8: S1AP messages and initiators 1/2

28

S1AP message groups message InitiatorENB CONFIGURATION UPDATE ACKNOWLEDGE MMEENB CONFIGURATION UPDATE FAILURE MMEMME CONFIGURATION UPDATE MMEMME CONFIGURATION UPDATE ACKNOWLEDGE eNBMME CONFIGURATION UPDATE FAILURE eNBOVERLOAD START MMEOVERLOAD STOP MMEDownling S1 CDM2000 Tunneling MMEUplink S1 CDMA2000 Tunneling eNB

UE Capability Info Indication UE Capability Info Indication eNBTrace Start MMETrace Failure Indication eNBDeactivate Trace MMELocation Reporting Control MMELocation Report Failure Indication eNBLocation Report eNBWRITE-REPLACE WARNING REQUEST MMEWRITE-REPLACE WARNING RESPONSE eNBKILL REQUEST MMEKILL RESPONSE eNBPWS Restart Indication eNBPWS Failure Indication eNB

eNB Direct Information Transfer eNB DIRECT INFORMATION TRANSFER eNBMME direct Information Transfer MME DIRECT INFORMATION TRANSFER MME

eNB Configuration Transfer eNB CONFIGURATION TRANSFER eNBMME Configuration Transfer MME CONFIGURATION TRANSFER MME

Cell Traffic Trace Cell Traffic Trace eNBDownlink UE Associated LPPA Transport MMEUplink UE Associated LPPA Tranport eNBDOWNLINK NON UE ASSOCIATED LPPA TRANSPORT MMEUPLINK NON UE ASSOCIATED LPPA TRANSPORT eNB

S1 CDMA2000 Tunneling Messages

Trace Messages

Location Reporting Messages

Warning message transmission Messages

LPPa transport Messages

Management Messages

Table 9: S1AP messages and initiators 2/2

5. GTPV2 29

5 GTPv2

GPRS Tunneling Protocol (GTP) is present at all levels of LTE.

GTP is an important IP/UDP-based communications protocol used in GSM,

UMTS, and LTE core networks. It is used to encapsulate user data when pass-

ing through core network and also carries bearer speci�c signaling tra�c between

various core network entities.[15] GTP tunnels are used between two nodes commu-

nicating over a GTP based interface, to separate tra�c into di�erent communication

�ows.[14]

The advantages of GTP and one of the reasons why is used in LTE is the mobility.

In particular, when the User Equipment (UE) is mobile, the IP address remains the

same and packets are still forwarded since tunneling is provided between PGW and

eNB via SGW. Another bene�t is that multiple tunnels (bearers) can be used by the

same UE to obtain di�erent network QoS. Moreover, to provide security the main

IP address remains hidden.

Figure 6: GTP-U encapsulation of UE user plane tra�c[15]

For better understanding, it works as follows. Look at the case when an IP packet

generated by UE reaches to eNodeB and is then forwarded to SGW. Consider that

any application on UE creates an IP/TCP packet. This packet consists of actual

data by application, TCP or UDP header and the IP �eld information which has

source address of UE and destination address of application server.

As Figure 6 shows, when the eNodeB receives this packet it will put the IP packet

inside the GTP header. Then it is encapsulated inside the UDP and IP header and

forwarded as Ethernet frame toward the SGW. Here the IP header contains eNodeB

IP as a source address and SGW IP as a destination address.[15]

30

There are three GPRS Tunneling Protocol Types:

• GTP-C, the control part of GTP. Used for core network speci�c signaling in

GPRS, UMTS and LTE networks.

• GTP-U, used in user plane to carry user data tra�c in GPRS, UMTS and

LTE networks.

• GTP', it has the same message structure as GTP-C and GTP-U, but its pur-

pose is to carry charging data from the CDF of the GSM or UMTS to the

CGF.[15]

Today GTP has two versions. In LTE, GTPv2 is used for GTP-C on S5, S11,

S2a and S2b, and GTPv1 for GTP-U on S1-U, S5 and X2-U interfaces. Moreover,

S3, S4, S8, S10, S12 and S16 interfaces also utilize GTP protocols.

5.1 Targeted interfaces and nodes using GTPv2

In my thesis I focus on version 2, thus, I am investigating mainly interfaces between

nodes and control part of the signaling, for which GTP-C is used. These nodes and

interfaces are

• MME � MME (S10),

• MME � SGW (S11),

• SGW � PGW (S5/S8),

• ePDG � PGW (S2b) and

• TWAN � PGW (S2a).

However SGSN is not contained in the topology described in Section 2, it is still

likely to get a �le that contains messages sent by/to the SGSN on interfaces S3

(SGSN � MME), S4 (SGSN � SGW) and S16 (SGSN � SGSN). It is possible since

SGSN is not a part of VoLTE but has importance in 3G. To preclude the chance of

mistreating a message, two options are possible:

1. pre�ltering the list of messages before feeding the network discovery algorithm

in order to obtain messages sent only on the supported interfaces;

2. the network discovery method should be intelligent enough to recognize these

messages and handle them properly.

5. GTPV2 31

5.2 Methodology for GTPv2

The di�culty is that most of the messages do not contain any information about

the used interface, hence, each message requires di�erent logic to decide.

But before a deeper explanation, �rst a short introduction on TEID and F-TEID

is needed.

GTP Tunnel, TEID, F-TEID

To fully understand these abbreviations, a few de�nitions are necessary to be dis-

cussed.

De�nition 1 ([13]). A GTP tunnel is a communication tunnel between two GTP

nodes. It is used to separate tra�c into di�erent communication �ows.

De�nition 2 ([13]). A tunnel endpoint is identi�ed with a TEID, an IP address

and a UDP port number.

De�nition 3 ([13]). Tunnel Endpoint Identi�er (TEID) unambiguously iden-

ti�es a tunnel endpoint in scope of a path.

A GTP tunnel is identi�ed in each node by a TEID, an IP address, and a UDP

port number. The receiving end side of a GTP tunnel locally assigns the TEID value

that the transmitting side has to use. For the value exchange, GTP-C messages are

used.

The TEID-C shall be unique per PDN-Connection on GTP based S2a, S2b, S5

and S8 interfaces, and there shall be only one pair of TEID-Cs per UE on each of

the S11, S4, S3, S10 and S16 interfaces.

TEID is compulsory for most of the messages. In GTPv2 header, a �ag T

indicates its presence. The most common message among the exceptions, where T

should be set to 0, is Create Session Request. This is the one which includes the �S11

MME DL TEID� and the �S5 SGW DL TEID�, which are generated and included by

MME and SGW respectively. As an answer, the Create Session Response includes

the �S5 PGW UL TEID� and the �S11 SGW UL TEID�, which are generated and

included by PGW and SGW respectively.

The TEID value itself does not provide any information, we need the Fully-

quali�ed TEID (F-TEID) to match the TEID value to the corresponding IP address.

32

Luckily, F-TEID-type IEs are included in several messages, like

• Sender F-TEID for Control Plane,

• S1-U eNodeB F-TEID,

• S5/S8-U PGW FTEID,

• S2a-U PGW F-TEID,

• S2b-U PGW F-TEID,

• S4-U SGSN F-TEID,

• S12 RNC F-TEID.

Except for the �rst and third item, if one of the rest appears in the message, we

immediately can tell which interface was used. �Sender F-TEID for Control Plane�

carries useful information about the sender node, therefore, it can be used to decide

if the sender was MME or SGSN.

If �S1-U eNodeB F-TEID� is present, the interface is S11. With the same logic,

�S2a-U PGW F-TEID�, �S2b-U PGW F-TEID�, �S4-U SGSN F-TEID� and �S12

RNC F-TEID� indicate interface S2a, S2b, S4 and also S4, respectively.

�S5/S8-U PGW F-TEID� is slightly di�erent: in messages Create Session Re-

quest, Create Session Response, and Create Bearer Request if this Information Ele-

ment (IE) is not present, then the used interface had to be S2a or S2b. The expla-

nation is that on S2a/b the communication is carried out between TWAN/ePDG

and PGW, thus, there is no need to send any messages between SGW and PGW on

S5/S8.

But F-TEID type information elements are useful not just to draw conclusion

about the particular message but to obtain NF-IP pairs which can be used for further

identi�cations.

Additionally, there are other IEs, which if included, the used interface is known.

In particular in Bearer Resource Command �Tra�c Aggregate Description (TAD)� is

present only on S11, in Context Request �Routeing Area Identity (RAI)� and �GUTI�

indicates S3 and S10, respectively. The same is true for Identi�cation Request.

Another unusual utilization of TEID is the condition of T=0 or T=1. It is a

unique, not too e�ective but interesting solution. In Suspend Noti�cation message

if TEID is set to 0, the source is SGSN. The explanation lays in the condition that

5. GTPV2 33

if TEID is 0, the interface is S3 or S16, and if 1, the interface is S11/S4 or S3. With

the help of mathematical logic we can formalize this as follows:

S3 ∨ S4/S11 → SGSN ∨ (MME ∨ SGSN) = SGSN ∨MME

S3 ∨ S16 → SGSN ∨ SGSN = SGSN,

where the �rst line shows the sources in case of T=1 and the second in T=0.

Similar to the above case, with the same logic we can conclude that in case of

Suspend Acknowledge message the destination node is SGSN when T=0.

Table 10, 11 and 12 show the decision criteria of each message being sent on

interface GTPv2.

In these tables, if a network function is highlighted in light green, it signi�es that

we can clearly assign an IP address to it, without even looking at the content of the

message. If the message name itself is highlighted in light green it signi�es that the

information elements provided by this exact message are enough for the matching.

Fortunately, these messages are very common in any .pcap �le, therefore, other

messages are not required any more. There are also cases when the only problem is

the inability to di�erentiate between SGSN and MME. This to be resolved requires

other logic and technique which is for further future investigation. It also concerns

the decision problem between TWAN and ePDG.

For more coloring de�nitions see the legend in Table 12.

34

GTPv2 message Interface source dest Interfa source dest Interface source destECHO REQUESTECHO RESPONSEVersion Not Supported IndicationCreate Session Request S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWCreate Session Response S11/S4 SGW MME/SGSN S2a/b PGW TWAN/ePDG S5/S8 PGW SGWCreate Bearer Request S11/S4 SGW MME/SGSN S2a/b PGW TWAN/ePDG S5/S8 PGW SGWCreate Bearer Response S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWBearer Resource Command S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWBearer Resource Failure Indication S11/S4 SGW MME/SGSN S2b PGW TWAN/ePDG S5/S8 PGW SGWModify Bearer Request S11/S4 MME/SGSN SGW S5/S8 SGW PGWModify Bearer Response S11/S4 SGW MME/SGSN S5/S8 PGW SGWDelete Session Request S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWDelete Session Response S11/S4 SGW MME/SGSN S2a/b PGW TWAN/ePDG S5/S8 PGW SGWDelete Bearer Request S11/S4 SGW MME/SGSN S2a/b PGW TWAN/ePDG S5/S8 PGW SGWDelete Bearer Response S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWDownlink Data Notification S11/S4 SGW MME/SGSNDownlink Data Notification Acknowledge S11/S4 MME/SGSN SGWDownlink Data Notification Failure Indication S11/S4 MME/SGSN SGWDelete Indirect Data Forwarding Tunnel S11/S4 MME/SGSN SGWDelete Indirect Data Forwarding Tunnel Response S11/S4 SGW MME/SGSNModify Bearer Command S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWModify Bearer Failure Indication S11/S4 SGW MME/SGSN S2a/b PGW TWAN/ePDG S5/S8 PGW SGWUpdate Bearer Request S11/S4 SGW MME/SGSN S2a/b PGW TWAN/ePDG S5/S8 PGW SGWUpdate Bearer Response S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWDelete Bearer Command S11/S4 MME/SGSN SGW S5/S8 SGW PGWDelete Bearer Failure Indication S11/S4 SGW MME/SGSN S5/S8 PGW SGWCreate Indirect Data Forwarding Tunnel S11/S4 MME/SGSN SGWCreate Indirect Data Forwarding Tunnel Response S11/S4 SGW MME/SGSNRelease Access Bearers Request S11/S4 MME/SGSN SGWRelease Access Bearers Response S11/S4 SGW MME/SGSNStop Paging Indication S11/S4 SGW MME/SGSNModify Access Bearers Request S11 MME SGWModify Access Bearers Response S11 SGW MMERemote UE Report Notification S11 MME SGW S5/S8 SGW PGWRemote UE Report Acknowledge S11 SGW MME S5/S8 PGW SGWForward Relocation Request S10/S3/S16 MME SGSN (in S3 the direction is MME->SGSN)

Table 10: GTPv2 messages and corresponding interfaces 1/3

5.GTPV2

35

Forward Relocation Response S10/S3/S16 SGSN MME (in S3 the direction is SGSN->MME)Forward Relocation Complete Notification S10/S3/S16 SGSN MME (in S3 the direction is SGSN->MME)Forward Relocation Complete Acknowledge S10/S3/S16 MME SGSN (in S3 the direction is MME->SGSN)Context Request S10/S3/S16 MME/SGSN SGSN/MMEContext Response S10/S3/S16 MME/SGSN SGSN/MMEContext Acknowledge S10/S3/S16 SGSN/MME MME/SGSNIdentification Request S10/S3/S16 MME/SGSN SGSN/MMEIdentification Response S10/S3/S16 SGSN/MME MME/SGSNForward Access Context Notification S10/S16 MME/SGSN MME/SGSNForward Access Context Acknowledge S10/S16 MME/SGSN MME/SGSNDetach Notification S3 MME/SGSN SGSN/MMEDetach Acknowledge S3 SGSN/MME MME/SGSNChange Notification Request S11/S4 MME/SGSN SGW S5/S8 SGW PGWChange Notification Response S11/S4 SGW MME/SGSN S5/S8 PGW SGWRelocation Cancel Request S10/S3/S16 MME/SGSN SGSN/MMERelocation Cancel Response S10/S3/S16 SGSN/MME MME/SGSNConfiguration Transfer Tunnel S10 MME MMERAN Information Relay S3 MME/SGSN SGSN/MMEISR Status Indication S3 MME/SGSN SGSN/MMEUE Registration Query Request S3 SGSN MMEUE Registration Query Response S3 MME SGSNSuspend Notification S11/S4 MME/SGSN SGW S3/S16 SGSN MME S5/S8 SGW PGWSuspend Acknowledge S11/S4 SGW MME/SGSN S3 MME SGSN S5/S8 PGW SGWResume Notification S11/S4 MME/SGSN SGW S5/S8 SGW PGWResume Acknowledge S11/S4 SGW MME/SGSN S5/S8 PGW SGWCS Paging Indication S3 MME SGSNAlert MME Notification S3 MME SGSNAlert MME Acknowledge S3 SGSN MMEUE Activity Notification S3 SGSN MMEUE Activity Acknowledge S3 MME SGSNCreate Forwarding Tunnel Request S11 MME SGWCreate Forwarding Tunnel Response S11 SGW MMEDelete PDN Connection Set Request S11 MME/SGW SGW/MME S2a/b TWAN/ePDG/PGW PGW/TWAN/ePDG S5/S8 PGW/SGW SGW/PGWDelete PDN Connection Set Response S11 SGW/MME MME/SGW S2a/b PGW/TWAN/ePDG TWAN/ePDG/PGW S5/S8 SGW/PGW PGW/SGWUpdate PDN Connection Set Request S5/S8 SGW PGWUpdate PDN Connection Set Response S5/S8 PGW SGWPGW Restart Notification S11/S4 SGW MME/SGSNPGW Restart Notification Acknowledge S11/S4 MME/SGSN SGW


36

PGW Downlink Triggering Notification S11/S4 SGW MME/SGSNPGW Downlink Triggering Acknowledge S11/S4 MME/SGSN SGWTrace Session Activation S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWTrace Session Deactivation S11/S4 MME/SGSN SGW S2a/b TWAN/ePDG PGW S5/S8 SGW PGWMBMS Session Start Request Sm/Sn MBMS GW MME/SGSNMBMS Session Start Response Sm/Sn MME/SGSN MBMS GWMBMS Session Update Request Sm/Sn MBMS GW MME/SGSNMBMS Session Update Response Sm/Sn MME/SGSN MBMS GWMBMS Session Stop Request Sm/Sn MBMS GW MME/SGSNMBMS Session Stop Response Sm/Sn MME/SGSN MBMS GW

Legend:We know all NEsOptional IEs + MME/SGSN decision problemMME/SGSN decision problem onlyWe know at least one NEOptional IEs but known MME/SGSNOptional IEs Cannot tell anything about itNot relevant


6. CONCLUDING PASSIVE METHODS 37

6 Concluding passive methods on the investigated

interfaces

While the passive method works pretty well on Diameter and S1AP, the way how

to exploit Information Elements embedded in GTPv2 messages probably not really

e�ective.

For S1AP messages we only need to know the name of the message, and choose

the corresponding row from Table 8 and 9 to get the initiator node.

For Diameter messages, the �rst step is obtaining the command code, with a

help of the Request �ag deciding whether it is an answer or request type, then by

using the color representation from Table 5 deciding among the three cases:

1. Command Code is enough;

2. Application ID check is needed;

3. Cannot tell anything about the message.

In case 1 choose the corresponding row from Table 4 and 5. In case 2 �nd the

used interface in Application ID �eld, then choose the corresponding row from the

table and �nd the matching interface. In case 3 skip the message.

For GTPv2 it is di�erent. The useful information elements found in the packets

most of the times are not mandatory, and we cannot be sure that we can use them

for further investigation. Hence, if we receive a trace �le which does not start with

a Create Session Request, probably we will not be able to tell anything about the

source and destination node. Perhaps, in this case, the active method can help and

provide a much more comprehensive solution, which I will not detail in my thesis.

7. ANONYMIZATION AND DE-ANONYMIZATION 39

7 Anonymization and de-anonymization

7.1 Anonymization

As for many systems which gather messages containing user data, a network monitor-

ing tool (NMT) also needs to have a secure environment to handle private informa-

tion. Security does not only consist of anonymization, but it is one of its important

branches. Likewise, it is a recent topic in the world of security and privacy.

In a .pcap �le which is loaded in a network monitoring tool, the main private data

types are MSISDN (Mobile Station International Subscriber Directory Number) and

IMSI (International mobile subscriber identity), but there are other sensitive pieces

of information like IPv4 and IPv6, which needs to be handled carefully. The �rst

two are important numbers used for identifying a mobile subscriber, and are saved

in an encrypted database. There is also a uniquely assigned UserID for each of the

pairs. None of the private data listed in Section 2 should be revealed in the NMT

interface, therefore, they should be encrypted before being stored, hence, risks from

security leaks can be eliminated.

The storing mechanism works as follows:

1. reading .pcap �le,

2. collecting private data (MSISDN, IMSI, IPv4 & IPv6, etc.),

3. encrypting private data,

4. assigning a unique UserID,

5. storing encrypted MSISDN and IMSI in database with the corresponding

UserID,

6. exchanging private data values (except for MSISDN and IMSI) for their en-

crypted form in the loaded .pcap �le,

7. exchanging MSISDN and IMSI for UserID in the loaded .pcap �le.

Encryption schemes

Many good and robust encryption schemes are known and applied for securing

databases, which have to meet security requirements that normally include

• prevention of unauthorized disclosure of information,

• prevention of unauthorized modi�cation of information,

40

• prevent denial of service,

• prevent system penetration by unauthorized person and

• prevent the abuse of special privileges.[21]

Hybrid cryptography

A possible encryption method can be based on hybrid cryptography, a quite attrac-

tive database encryption technique with added security by use of two encryption

algorithms.

In 2010, Xing-hui and Xiu-jun[24] came up with an encryption system based

on International Data Encryption Algorithm (IDEA) combined with the Rivest-

Shamir-Adleman cryptosystem (RSA). This hybrid scheme in 2015 has still been

considered as safe and e�ective in a cryptographic manner.[23]

Hybrid cryptography is widely used nowadays because it combines the conve-

nience of a public-key cryptosystem with the e�ciency of a symmetric-key cryp-

tosystem in the following way: data encapsulation is done by symmetric-key, while

public-key cryptography is used as the key exchange mechanism.

Because of the huge amount of data we have to consider that the encryption

algorithm should be e�ective in the sense of preventing data reconstruction, and

fast at the same time. In 2010, Sharif and Mansoor[25] have done performance

analysis to compare stream and block cipher algorithms. Among block ciphers, they

tested IDEA, Serpent, CAST-5, RC2, RC5 and Blow�sh. Considering the speed

IDEA produced the worst result out of all the algorithms. Though IDEA is slower,

it is cryptographically more secure.

The proposition is, that instead of IDEA, use its successor IDEA NXT from 2003

(used to call FOX). It is also a symmetric block cipher that was developed to have

high-security level and large implementation possibilities. In [26] O'Kee� et.al tried

di�erent strategies for IDEA NXT implementation to test network performance pa-

rameters and found a way which resulted in increased speed and decreased memory

requirements while making no changes in power consumed.

Another possible choice for private key cryptography is AES. In [27], Nadeem

and Javed implemented four block cipher algorithms in order to compare their per-

formance. These four standards were DES, Triple DES, AES, and Blow�sh. What

they found is that the fastest was Blow�sh, then DES, AES and the slowest was

Triple DES. According to their results on the average execution times, AES is two

times slower than Blow�sh, which means that taking the values from [25] we can


conclude that AES is performing better than IDEA, which was four times slower

than Blow�sh.

The reason why DES or Blow�sh are not considered as a possibility is that

both are proved to be insecure. Against DES brute-force attack is e�ective. As for

Blow�sh it is known to be susceptible to attacks on re�ectively weak keys.[28][29]

IPv4 & IPv6 encryption can be done by using hybrid cryptography immediately

and substituting the encrypted values for the raw values in the .pcap �le right after.

If an NMT user wants to see the real data, by clicking on the encryption button,

the decryption is being performed and the raw data is revealed. This works only if

the current user has the access right to the corresponding data.

Attribute-based Encryption (ABE)

By going further, the question arises: is it possible to assign di�erent security level

to the di�erent types of data? The answer is yes, with the help of a cryptographic

encryption method, Attribute-based Encryption (ABE) schemes.

In a network monitoring tool, there are two di�erent types of data: classi�ed and

unclassi�ed. Unclassi�ed data can be stored in the clear without encryption, but

the sensitive data should be encrypted. Sensitive data is the above mentioned IMSI

and MSISDN, as well the monitoring tool users' personal data, such like settings,

results, and loaded �les, also shared �les when working in groups. To assign a

security level to each user of the tool, there are several schemes and methods which

can be chosen, including but not limited to RBAC, MAC, DAC, and TBAC. More

about them can be found in Section 9.1. Their implementation is based on attribute-

based encryption.

ABE is widely used for big data storage encryption, and makes it possible to

generate a public key for encrypting data and have been used as an access policy to

control users' access by exploiting attributes.[30]

In practice it is used as in hybrid cryptography: encrypt the database using

symmetric key cryptography, then encrypt the keys with ABE scheme. It is logical

since when encrypting a huge dataset like in a case of a network monitoring tool,

too many primes and therefore too much computation is needed.

For an example of a strong ABE algorithm, in 2012, Hwang and Yang[22] pro-

posed a multilevel database encryption system with subkeys. Their method allows

administrators to assign di�erent security level to the objects (e.g., �les, messages,

data, etc.) and distinct clearance to each subject (e.g., user, program, etc.). It

means that the decryption is permitted only in the security class higher than or

42

equal to that of the encrypted �eld-subkeys.

The used multilevel database system is a partially-ordered hierarchy (see Fig-

ure 7b), where an object with a particular security class can be accessed only by

subjects in the same or a higher security class. It also allows the encryption and de-

cryption of �elds within the same records. Not to reveal all the data corresponding

to the same user is smart.

The algorithm itself looks as follows.

(a) Totally-ordered hierarchy (b) Partially-ordered hierarchy

Figure 7: Secret key generation for each security classes[22]

Algorithm Key-Generation for Totally-Ordered Hierarchy [22]

Step 1 Get a node Sij from the hierarchy Hi by preorder traversal.

Step 2 Assigns sij a large prime pij randomly.

Step 3 Computes the secure key kij for sij using the formula

kij =∏

sil≥sij

pil.

Step 4 Repeat from Step 1 until all nodes of the hierarchy Hi are completely

examined.

Algorithm Key-Generation for Partially-Ordered Hierarchy [22]

Step 1 Get a node Sij from the hierarchy Hi by preorder traversal.

Step 2 Assigns sij two large primes pij and p′ij randomly.

Step 3 Computes the secure key kij for sij as follows:


Step 3.1 If sij is a root node, then kij = pij.

Step 3.2 If sij is not a root node, then

kij =∏

sil≥sij

pil∏

sil≥sij

p′il.

Step 4 Repeat from Step 1 until all nodes of the hierarchy Hi are completely

examined.

The system also provides fast update of records, in case of changing the sym-

metric key.

This method guarantees a high level of security thanks to the construction which

is mainly based on the Chinese remainder theorem. Hence, the security of the scheme

is equivalent to factoring a large composed prime.

7.2 De-anonymization

Other user data can be username, user location and time of call. During analyzation

most of the data got from the messages are dropped, but the last two are stored

and used for further, mainly statistical analysis. Though these datasets considered

as anonymous and safe, we still have to face the possibility of de-anonymization

attacks. According to the research papers from the last ten years, there are various

techniques and algorithms which can be used to build models of user behavior out

of these sets of information.

De�nition 4 (De-anonymization[16]). For the released data D, de-anonymization

of D is to connect its contained sensitive information to known user IDs.

By de�nition, there are basically two ways to commit de-anonymization, i.e. to

connect sensitive information to known IDs:

1. mapping users with known IDs to vertices in D, and

2. re-identifying the IDs of vertices in D.

Both ways can reveal sensitive information of users. However, in the former case,

mapping IDs to D does not always re-identi�es the mapped vertices.[16]

Nothing proves better its importance than the increasing number of publication

on de-anonymization, link prediction, and cross-reference among micro data, that

is, information about speci�c individuals.[17] It was possible due to the increasing

44

number of public datasets in response to �open government� laws and to support

data mining research.

In 2008 Narayanan and Shmatikov[17] came up with a de-anonymization method-

ology for sparse micro-data, and demonstrated its practical applicability on movie

viewing records. Their algorithm works under very general assumptions about the

distribution from which the data are drawn, and is robust to data perturbation.

Later, closely followed [17], in 2011 also Narayanan with Shi and Rubinstein[18]

published a paper about how they had won the Kaggle Social Network Challenge.

The goal of this machine learning competition was to promote research on link

prediction. The contest dataset was based on a large online social network (Flickr).

Then the obtained edge set was partitioning into a large training set and a smaller

test set, augmented with an equal number of fake edges. Using their own crawl of

Flickr, they were able to successfully de-anonymize 64.7% of the test edge-set.

In 2013, Gambs, Killijian, and Cortez[19] applied a de-anonymization attack

on geologicated datasets. They showed that the argument that, by itself location

data was anonymous and thus could be collected from users without violating their

privacy, was fallacious. They also showed that with high success rate the attack

could re-identify the individuals whose movements were contained in a provided

anonymous dataset. The adversary can use it as background information with some

mobility traces of the same individuals that he has been able to observe during the

training phase. From these traces, the adversary could build a Mobility Markov

Chain (MMC) that models in a compact and precise way the mobility behavior of

an individual. The de-anonymization attack was very accurate with a success rate

of up to 45% on large-scale real datasets.

A predecessor of the previous case was a closely related research by Mulder

et al.[20] on identi�cation via Location-Pro�ling in GSM networks. Their dataset

comes from a cellular network, i.e. a list of records of the movement of each device,

and probably its owner. This represents a serious privacy threat. In their work,

they showed techniques to build pro�les based on some user's locations, and then

techniques to match those pro�les with anonymized location data. For this identi�-

cation process, they used two methods: one based on simple �rst-order Markovian

chains, and another based on sequence of cell-IDs. The �rst one performed poorly:

slightly more than a third of the original mobile users could be correctly identi�ed,

while the latter performed well: around 80% of the original mobile users could be

properly identi�ed.


To obviate these kinds of attacks in 2011 Al Buona et.al[31] proposed de-

linkability, a privacy-preserving algorithm, that allows to sanitize multimedia doc-

uments' content and at the same time preserve their utility in order to achieve the

de-linkability.

These above examples of attacks show that revealing these datasets are very

dangerous and can easily fall into wrong hands. By anonymization, we only can

minimize the risk and possible harm of any data leakage.

8. SECURITY ISSUES WITH WEB APPLICATIONS 47

8 Security issues with web applications

Security mistakes are very easy to make and a simple one-line error can lead to catas-

trophic events included but not limited to dataset leakage, authentication problems,

cross-site-scripting (XSS) and cross-site-request-forgery (CSRF). Malicious actions

can be performed by leveraging weaknesses and vulnerabilities in a program code.

No programming language can protect from attacks, the code itself has to be able

to circumvent them.

Hereby I list and shortly introduce possible web client vulnerabilities which a

web application has to be aware of, as well remedies to avoid them. The Open Web

Application Security Project (OWASP) pages are excellent resources for gathering

information about this topic.

• Cross-Site Scripting (XSS) Attacks occur when user input is directly displayed

in an output web page, without any sanitization. With other words, anything

that is put into the input �eld is sent back to the page and rendered ver-

batim. Hence, the attacker can create a URL that submits malicious input

to the attacked website and tries to induce the victim to click on the link.

If he succeeds, the website response page includes malicious links or mali-

cious JavaScript code which are executed on the victim's browser. To prevent

these actions the programmer should make sure to 1. sanitize any user input

which might reach output statements (including statements that write to a

database or that save cookies), and 2. encode the output using HTML encod-

ing so that any malicious link or JavaScript code remains uninterpreted by the

browser.[39]

• Cross-Site Request Forgery (CSRF) occurs when a malicious website, email,

blog, instant message, or program causes a user's web browser to perform an

unwanted action on a trusted site for which the user is currently authenticated.

Owasp has two general recommendation for automated CSRF defense: 1. check

standard headers to verify the request is same origin and 2. Using Synchronizer

Token or Double Submit Cookie.

All requests should include Origin header and/or Referer header. If the Origin

header is present, its value should match the site's origin. If the Origin header

is not present, the hostname should be veri�ed in the Referer header if it

matches the site's origin. If both of these headers are missing, the more secure

way is to block the request.[40]

48

With the Synchronizer Token approach, the server embeds a dynamic hidden

variable in an input form. When the form is submitted, the server can check

if the hidden variable is present and is correct. This token can be reused, but

it is better to make it a one-time token by using nonces. They also protect

against replay attacks.[43]

The alternative defense is to use double submit cookie, which means that a

random value is sent in a cookie and also as a request parameter. Then the

server veri�es if the cookie value and request value match (see Figure 8).[40]

Figure 8: Double Submit Cookie[43]

• SQL injection occurs when the user provided data is used to form an SQL

query. The attacker provides malformed data to change the semantics of the

query. To mitigate this attack 1. always validate input that goes into an

SQL query, 2. use prepared or parametrized SQL queries instead of queries

formed by string concatenation or replacement and 3. grant access to tables

only through stored procedure.[39]

• Authentication issues

� Re�ection Attacks can be used for authentication, too. If the authentica-

tion is made by using hash function after a Di�e-Hellman key exchange

scheme, the two parties can authenticate themselves by sending to-be-

hashed messages, and if the received and the self-computed hash values

agree then the authentication worked. Therefore, as a malicious user, by

8. SECURITY ISSUES WITH WEB APPLICATIONS 49

sending random value r to the server, gets back its hashed value hash(r)

along with the message m to be hashed and sent back to the server.

At this point, the malicious user opens another session, sends m to the

server, and gets back hash(m). Then he can reuse it and send back to the

server to complete the �rst session. To mitigate this attack use direction

bits or di�erent keys in di�erent directions.[41]

� Password problems: A password has to ful�ll certain formal requirements.

Most applications do not allow users to set empty string as password, for

understandable reasons. The problem with weak passwords is that they

can be easily guessed (eg. pwd, password, secret, etc.. Short passwords

or ones with a limited variety of characters can su�er brute-force attacks.

On the other hand, using too di�cult and random passwords are safe but

hard to remember, hence the users can forget them.[39]

• Authorization issues

� File Access Race Condition or TOCTOU (time-of-check, time-of-use)

race conditions occur, when the program checks a property of a �le, ref-

erencing it by name. Then the program later performs a �lesystem oper-

ation using the same �lename and assumes that the previously-checked

property still holds. But in the meantime, if an attacker replaces the

�lename with a symbolic link to a di�erent �le, the program will use its

root privileges to operate on the �le, even though the attacker would be

unable to modify it.[36] To circumvent this, it is highly recommended to

use �lehandles instead of �lenames.[41]

� Least Privilege Violation Principle: When a program calls a privileged

function, it must �rst acquire root privilege. As soon as the privileged

operation has completed, the program should drop root privilege and

return to the privilege level of the invoking user.

Misused Privilege Management: Failure to adhere to the principle of least

privilege.[37][38]

9. ACCESS CONTROL: AUTHENTICATION AND AUTHORIZATION 51

9 Access control: Authentication and authorization

Accessing data is one of the key points in any system with stored sensitive informa-

tion. Con�dentiality, integrity and availability (abbreviated as �CIA�) are the three

types that information security risks can be categorized into. Access control is only

one aspect of a comprehensive computer security solution, but one of the most visi-

ble. It is critical to preserve the con�dentiality and integrity of information, so that

only authorized users can read information and can alter them in authorized ways.

There are two concepts which are fundamental to access control: authorization

and authentication. Although many people confuse them, they are not synonyms.

However, proper authorization is dependent on authentication.

In plain words, authentication is a process of determining who you are, autho-

rization determines what you are allowed to do.[33]

The following two de�nitions give a more sophisticated phrasing.

De�nition 5 ([35]). Authorization is a security mechanism used to determine

user/client privileges or access levels related to system resources, including computer

programs, �les, services, data and application features.

During authorization, a system veri�es an authenticated user's access rules and

either grants or refuses resource access.

De�nition 6 ([33]). Authentication is the process of determining that a user's

claimed identity is legitimate.

Remark 3 ([33],[35]). Authorization is normally preceded by authentication for user

identity veri�cation.

Authorization necessarily depends on proper authentication. If the system cannot

be certain of a user's identity, there is no valid way of determining if the user should

be granted access.

9.1 Authorization methods

There are several authorization management systems which exist and can be used

to allot di�erent access rights to users. There are early approaches like Manda-

tory Access Control (MAC) and Discretionary Access Control (DAC), which can be

enforced by Role-based access control (RBAC) without any complication, however,

RBAC is di�erent from them.

Restricting system access to authorized users and building a hierarchy is not

new and widely used in big companies with employees over 500. On average, these

52

organizations expended $241.01 per employee to implement RBAC.[32] RBAC is a

policy neutral access control mechanism which greatly simpli�es security adminis-

tration by using roles, hierarchies, and constraints to organize privileges. It attracts

a great deal of attention, particularly for commercial reasons, because it reduces the

complexity and cost of security administration in large networked applications. The

basic idea behind RBAC is that it takes into account that employees change much

more frequently than the duties within positions. If an employee moves within an

organization, only his or her role assignment is changed, revoking his or her existing

privileges and assigning a completely new set of privileges are unnecessary.[33]

RBAC has three primary rules:

1. Role assignment: A subject can execute a transaction only if the subject has

selected, or been assigned to, a role (i.e. has an active role).

2. Role authorization: A subject's active role must be an authorized role for that

subject.

3. Transaction authorization: A subject can execute a transaction only if the

transaction is authorized for one of the subject's active roles.

[49, Lecture 26][33]]

Remark 4 ([33]). Rule 1 and 2 ensure that users can take on a role only if they

are authorized for it. All the three rules together ensure that users can execute a

transaction only if they are authorized for it.

Figure 9: The basic RBAC model with sessions[34]

The basic idea of role-based access control is to cut the connection between the

user and the permission and connect them again with the insertion of another level

of indirection, namely the Roles. As Figure 9 illustrates, roles break this mapping


into two: users to roles and roles to privileges. Moreover, they introduced sessions

to extend the support for least privilege. Sessions are used on a particular occasion

when a user signs on the system to carry out some activity, hence, this means

another level of indirection between Roles and Users. So users activate roles within

the frame of a session.[34]

There are also other approaches like Task-based Access Control (TBAC) intro-

duced by Thomas and Sandhu[48] in 1997. TBAC is an active approach and a

family of models for authorization management. It is di�erent than the passive

subject-object model like RBAC. The di�erence is that permissions are turned on

only in a just-in-time fashion and synchronized with the processing of authorization

in progressing tasks. Basically, the granted access is based on a task, and the access

check compares it to the roles which contain that task, and then the users who are

part of at least one of those rules. TBAC can be considered as an extended form of

RBAC. However, it is not as widespread as RBAC and quite unknown.

Access control in practice

RBAC implementation can be done in two ways: implicitly and explicitly.

De�nition 7 ([50]).

Implicit access control: �Permissions granted or denied from users and groups�

Explicit access control: �Access Control applied directly to controllable objects�

In [51] they show the di�erence between these two types applied on RBAC.

Implicit access control is done by granting and revoking privileges to users. For

each transaction (resource) a set of roles is assigned directly in the program code.

For instance, the condition of the if statement contains the name of the roles which

have the access right.

The problem starts with the change of the security requirements. If the if

statement condition is changed, like granting access to another set of roles, the test

cases needs to be updated, the software to be rebuilt and a re-deployment to be

scheduled to production.

In the contrary, explicit access control applied in RBAC enables the security

policy change while the application is running. It can be done by not specifying in

the program code which role has the right privilege, but check if the current user

is permitted to commit to the current resource. Here the code is based on what is

being protected instead of who has the ability.

54

In the above mentioned article[51] they provided a list of the numerous bene�ts

of using explicit RBAC policy, including but not limited to the

• reduction of code refactoring by basing the code on the resources because they

change less frequently,

• increased �exibility of the security model and

• externalized security policy management: security policy changes can be done

by another person, bypassing the software developer.

9.2 Authentication in general

Authentication is based on one or more of the following factors:

• Something you know, such as the password, personal identi�cation number

(PIN), or lock combination;

• Something you have, such as a smart card, automatic teller machine (ATM)

card, or key;

• Something you are, or a physical characteristic, such as a �ngerprint or retinal

pattern, or a facial characteristic.[33]

The most popular and widely used authentication method is password based:

if for a given username the stored and the typed passwords match, the user is

authenticated.

Usually, username-password pairs stored in databases are not in plain but in

encrypted form. For this cryptographic hash functions are used. Its main properties,

namely pre-image resistance, second preimage resistance and collision resistance,

make it so widespread. In practice, it means that �nding another password which

has the same hash value is more than unlikely. Also, it is unfeasible to generate a

password from its hash value except by trying all possible messages. Hence, if the

table falls into wrong hands the passwords are not revealed.

In this case the authentication process works as follows (see Figure 10:

1. User requests content which needs permission

2. Server requests user name and password = p1

3. User provides credentials: user name = u1 and password = p1


4. Server compute the hash value of the given user name and password: hash(u1)

and hash(p1)

5. If the computed hash value pair is matching with a pair stored in the database:

(a) checks if the user owns the proper access rights

(b) if yes, the server provides the requested content.

6. If the computed hash value pair is not matching with any pair in the database:

(a) the server returns with a 401 error message.

Figure 10: Authentication with password

9.3 Authentication in a single page web application (SPA)

What is an SPA?

De�nition 8 ([42]). A single page web application (SPA) is an application delivered

to the browser that does not reload the page during use. Like all applications, it is

intended to help the user complete a task, such as �write a document� or �administer

a web server.� We can think of an SPA as a fat client that is loaded from a web

server.

Figure 11 illustrates how the business logic and generation of HTML migrate

between the server and the client.

The primary bene�t of an SPA over a traditional website is that it provides a

better user experience. An SPA can deliver the best of both worlds: the immediacy

of a desktop application and the portability and accessibility of a website. More

speci�cally, an SPA

• can render like a desktop application,

• can respond like a desktop application,

• can notify users of its state like a desktop application,

• is nearly universally accessible like a website,

• can be instantly updated and distributed like a website and

• is cross-platform like a website.[42]

56

Figure 11: Responsibilities of the database, server, and client[42]

Security concerns for SPAs

However a SPA has many bene�ts over the traditional approach, authentication is

still rising issues and presents new security challenges. These types of applications

are �untrusted clients� since the server-side code has no control over the environment

they run in. Through the developer console, one can alter or inject JavaScript code

on a page. Mobile applications are also can be decompiled and inspected, hence, a

developer has to avoid embedding sensitive information like secret keys or passwords

in these type of clients. [43]

The primary goal of web application security is to

• prevent malicious code from running (eg. XSS attacks),

• ensure that user credentials are sent to the server in a secure way,

• secure API endpoints (eg. CSRF attacks) and

• expose access control rules to the client (eg. session ID challenges).[43]

Section 8 addresses each of these concerns.


JSON Web Tokens (JWT)

An approach to secure user authentication in a single page web application is using

tokens for authentication instead of cookies. JSON Web Tokens (JWT) give a

structured way to declare a user's identity and its access privileges.

De�nition 9 ([46]). JSON Web Token (JWT, pronounced jot) is a relatively new

token format used in space-constrained environments such as HTTP Authorization

headers. JWT is architected as a method for transferring security claims between

parties.

JWT is a great authentication mechanism which provides a structured and state-

less way to declare users and their access rights in a cryptographically signed and

encrypted way.

A token consists of three separate sections. The �rst is a header that describes

the token: contains the metadata for the token and at a minimal contains the type

of the signature and/or the encryption algorithm. The second is called claims, a

payload which contains the valuable bits, i.e. the information which is to be signed.

The third and last is the JSON Web Signature, a signature hash that can be used

to verify the integrity of the token by using the secret key.[45][44]

A token is a Base64 encoded string, which after breaking it apart the three

sections can be separated from each other. After decoding the second section it

looks as follows:

{

"sub": "users/TzMUocMF4p",

"name": "Edward Example",

"scope": "self groups/admins",

"exp": "1300819380"

}

where sub stands for the URI to the user resource, name refers to the user, scope

indicates the person's access right and exp is the expiration date.

Tokens are given to the users after they present some hard credentials, typically a

username and password, but they can also provide API keys or tokens from another

service.

JWT's are great for SPAs mainly because of their portability. In an SPA access

control logic is built in the frontend as well the backend. Because tokens contain all

information that is needed for authorization, hence they are very portable and can

58

be used by both the frontend and the backend to make decisions. Also, they can be

shared with partner services.

To achieve high-level security, tokens must be protected against the event of

getting stolen: they should be endowed with signatures. Tokens must be signed

with a strong key that is available only to the authentication service. Signature

veri�cation must be checked each time a token is used to authenticate a user. Also,

tokens have to be in an encrypted form if they contain non-opaque information.

Least but not last they have to be transmitted over HTTPS connection and never

over a non-HTTPS one.[44]

Tokens have to be stored in order to keep them in case of refreshing the browser.

It can be a web Storage (localStorage/sessionStorage) or a client-side cookie.

When using browser storage (localStorage or sessionStorage) for a JWT to ex-

change username and password, the response body contains the JWT as an access

token. On the client side, the token is stored in HTML5 web storage. To pass the

access token back to the protected APIs, the HTTP Authorization Header and the

Bearer scheme are used.

Cookies can be used for the same reason. In this case the response use the

Set-Cookie HTTP header. To pass the access token back to the protected APIs on

the same domain, the browser automatically includes the cookie value.[47]

Among the possible storage types, storing tokens in HTTPS-only cookies is the

best way. The local storage area is very vulnerable to XSS attacks. Storing them

in secure cookies protects against being exposed to the JavaScript environment in

the browser, which is vulnerable to XSS attacks. Man-in-the-middle attacks can be

prevented by not transmitting tokens over non-HTTPS connections.

Because cookies are used only as a storage mechanism, not as an authentication

mechanism, they do not require state to be stored on the server if JWT is being

stored in the cookie. This is because the JWT encapsulates everything the server

needs in order to serve the request.[47]

However secure cookies are used for storing they are still vulnerable to CSRF

Attacks, hence it is important to implement a CSRF token strategy to combat this

issue.[44] More about these strategies can be found in Section 8.


9.4 User handling in a Network Monitoring Tool

Authorization in a network monitoring tool is an important issue which needs to be

resolved. On one hand, as is mentioned in Section 7, there are sensitive pieces of

information like IMSI and MSISDN which should not be available for each person

who uses the tool. But on the other hand, there are other aspects which have to be

considered.

The structure of the inner network. First of all, not all the users need to

get the permission to have an inside view into the network. The details should be

hidden for certain group of users, such like the information of what ports are used

for communication. As is also mentioned in Section 7, IPv4, and IPv6 should be

hidden.

Personalized user account. Each authorized user has to be able to create his

or her own account, save and retrieve the previously loaded data, and share them

with other authorized users. Anything which was created by that particular user

can be shared, but the default is that he or she is the only one who has access to it.

Working in groups. Having an individual account implies the possibility of

working in groups and sharing the latest updates manually or automatically between

the members.

The program itself. A network monitoring tool itself should not be a free

application, hence, it requires protection against unauthorized downloads and usage,

aiming to save this intellectual property.

Possible requirements and approaches to resolve them

In the aspect of security, since a network monitoring tool is an SPA, the requirements

are similar to the ones described in Section 8. Taking steps to mitigate penetra-

tion against attacks, including but not limited to CSRF attacks, XSS attacks, SQL

injection, re�ection attack and password issues is inevitable.

Using JSON Web Tokens (JWT), mentioned in this subsection earlier, is great

to easily implement protection against CSRF attacks. Moreover, using HTTPS-only

cookies for storing can mitigate XSS attacks.

Authentication method should be strong enough, but at the same time not too

di�cult, in order to make the system usable.

To mitigate unauthorized download, secure keys should be assign to each poten-

tial user with which they can download the application and register.

10. SECURITY PLAN 61

10 Security Plan

In the previous sections, problems and various techniques of remedies were intro-

duced and compared, providing a comprehensive view on security and privacy issues

which can occur in a web application. Hereby this section is devoted to summa-

rize what has being discussed and create a concept of a security plan for a network

monitoring tool.

In the �rst place, there should be emphasized that only privileged users have

access to the tool, and can operate only after they authenticated themselves.

Authentication

Authentication is a key point in a web application, mainly because of its complexity.

In a user point of view authentication in our network monitoring tool will be

password-based. It ful�lls the requirements of implementing a strong but not di�cult

authentication method.

Requirements for a strong password:

� longer than 8 character

� include symbols: (e.g. # $%)

� include numbers: (e.g. 123456)

� include lowercase characters: (e.g. abcdefgh)

� include uppercase characters: (e.g. ABCDEFGH)

� exclude similar characters: (e.g. i, l, 1, L, o, 0, O)

� exclude ambiguous characters: ({ } [ ] ( ) / \ ' " ` � , ; : . < >).

Each authorized user is provided a private 16 character long key, consists of

numbers and uppercase letters, with which they can authenticate themselves and

install the software.

In a developer point of view, the authentication system should ful�ll the require-

ments stated in the end of Subsection 9.3. To do so, JSON Web Tokens has to

be used, stored in HTTPS-only cookies. It guarantees a fundament of implement-

ing a secure authentication scheme. As is also discussed in the Section 9.3, taking

steps to mitigate penetration is inevitable and can be done by applying the remedies

discussed in Section 8.

62

Authorization

Assigning access rights will be based on Externalized RBAC. Hence, security policy

is not the duty of the developer, and the implementation is not hampered by dealing

with the di�erent roles and possible changes. Moreover, sessions can be used when

granting temporary access and working in groups as well. For more details see

Subsection 9.1.

Anonymization and data encryption

After a successful login, a network monitoring tool user (NMT-user) can start op-

erations like loading data from .pcap �les. These �les consist of messages which

possibly contain private information about telecom subscribers (s-user). For the list

of sensitive and to-be-encrypted data see Section 2. When the .pcap �le is loaded,

data is stored in the database with access only for the current NMT-user (or in case

of working in groups, with access for the group members). Right before storing, s-

user data listed in Section 2 will be encrypted using hybrid cryptography combining

AES or IDEA NXT with RSA.

Hence, s-user data will appear on the screen in encrypted form. If the NMT-

user is privileged, there is a decrypt and a decrypt all button appeared on the user

interface, make it possible for the original values to be seen.

10. SECURITY PLAN 63

Conclusion

In my Thesis, two main questions were investigated, namely how the sender and

receiver network functions can be identi�ed by analyzing messages transmitted on

interfaces using protocols diameter, S1AP and GTPv2; and providing an overall

picture of the security requirements in a network monitoring tool.

We concluded that the passive method works pretty well on diameter and S1AP

interfaces. S1AP messages can be transmitted between eNodeB and MME, hence

is enough to know the initiator node. Each diameter message contains information

about the used interface, hence by taking the Command Code and the Application-

ID we can clearly determine the sender and receiver node, except for one message

type. GTPv2 messages are di�erent in the aspect of clarity: the useful information

elements found in the packets in most cases are not mandatory, hence are not present.

Though there are several messages from which we can determine clearly at least one

end of the communication, and a .pcap �le is long, hence, with high probability,

there can be found a matching for each IP address and network function.

In the latter sections, an overall picture on security was given paying special

attention to the requirements regarding a network monitoring tool. With respect to

the authentication, the requirements for a single page application were followed. As

for a big company with employees over 500, using externalized RBAC is proposed.

For the protection of telecom subscriber data, encryption is needed. For this, hybrid

cryptography is suggested.

By using the security plan described in Section 10 a fundament of a secure

authentication scheme implementation can be guaranteed.

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