personal cloud using bittorrent sync

7/24/2019 Personal Cloud using Bittorrent Sync

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Personal Cloud using Bittorrent Sync

Flavio Martins Marcos Vit

Faculdade de Engenharia Eltrica e de Computao Universidade Estadual de

Campinas (UNICAMP)

Av. James Maxwell 30, Cidade Universitria Zeferino Vaz, Distrito Baro Geraldo

CEP 13083-852 - Campinas-SP Brasil

[email protected]

Abstract.The BitTorrent peer-to-peer protocol has proved to be very efficient

for sharing files in a network without the coordination of central servers.There are currently several cloud storage solutions such as Dropbox but

recent events involving USA government, private data leakage and spying

motivated the development ofBittorrent Syncfor offering a personal cloud for

data storage.

1

Introduction

Bittorrent Sync[1] by Bittorrent, Inc[2] is a proprietary solution for sharing files among

other computers or mobile devices based on the Bittorrent peer-to-peer protocol, whichwas adapted for this purpose. It is currently in Beta phase and it is available for

Windows, Mac, Linux, BSD, iOS and Android.

The files are shared only with the devices specified by the user. It requires no cloud and

it is fully independent of any servers.

Figure 1. BitTorrent Sync Data sharing only among users devices


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There is no data size limitation or subscription fees that come with traditional cloud

based solutions such as Dropbox[3].

This work will depict this new application checking its performance, security, usability

and possible new applications.

2

Background

Bram Cohen developed the Bittorrent protocol and released the first version in 2001. It

proved along the last years to be a successful solution for sharing large volumes of files

using peer-to-peer networks.

There are available in the market many solutions for storing data remotely but all of

them relies on central sever for storing the data.

There was a gap for an application able to automatically sync files without the

dependency of a central coordination and not storing the files outside the user domain.

Bittorrent Sync was conceived to fulfilling this gap ensuring the user could have total

control of what is being shared.

2.1 P2P Protocol

BitTorrent Sync synchronizes your files using a peer-to-peer (P2P) protocol. This

protocol is very effective for transferring large files across multiple devices, and is very

similar to the powerful protocol used by applications like Torrent and BitTorrent.

The data is transferred in pieces from each of the syncing devices, and BitTorrent Sync

chooses the optimal algorithm to make sure you have a maximum download and upload

speed during the process.

The devices chosen to be synched are connected directly using UDP, NAT traversal and

UPnP port mapping. It is also provided additional methods of ensuring connectivity as

relay and tracker servers. If the devices are on the same local network, BitTorrent Syncwill use the client LAN for faster synchronization.

2.2 Security

BitTorrent Sync was designed with focus on privacy and security. The system uses SRP[4] for mutual authentication and for generating session keys that ensure Perfect

Forward Secrecy. All traffic between devices is encrypted with AES-128 in counter

mode, using a unique session key. Modification requests are all verified using Ed25519

[5] signatures and only systems with full access keys can generate valid modificationrequests.


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2.3 Secret

The secret is a randomly generated 20-byte key. It is Base32-encoded in order to bereadable by humans. BitTorrent Sync uses /dev/random (Mac, Linux) and the Crypto

API (Windows) in order to produce a completely random string. This authentication

approach is significantly stronger than a login/password combination used by other

services. That's why using a secret generated by BitTorrent Sync is very safe and

secure.

The secret can be shared using copy and paste or using QR code and a camera from the

mobile device.

Figure 2. Using a QR code for connecting a mobile device to a sync folder

2.4 Peer Discovery

In order to find proper peers that have the same secret, Sync uses:

Local peer discovery. Sending broadcast packets discovers all peers inside local

network. If there are peers with the same secret they respond to the broadcast

message and connect.

Peer exchange (PEX). When two peers are connected, they exchange

information about other peers they know.

Known hosts (folder settings). If there is a known host with a static ip:port, it

is possible to specify this in Sync client, so that it connects to the peer using this

information.


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DHT. Sync uses DHT to distribute information about itself and obtain theinformation about other peers with this secret. Sync sends

SHA1(Secret):ip:portto DHT to announce itself and will get a list of peers by

asking DHT for the following key SHA1(Secret)

BitTorrent tracker. BitTorrent Sync can use a specific tracker server tofacilitate peer discovery. The tracker server sees the combination of

SHA1(secret):ip:port and helps peers connect directly. The BitTorrent Sync

tracker also acts like a STUN server [6] and can help do a NAT traversal for

peers so that they can establish a direct connection even behind a NAT.

2.5 Traffic Relay

There are rare cases when peers cant talk directly. This usually happens when devices

are in an office behind strong firewalls. In such a case BitTorrent provides a relay server

to route traffic between peers. All traffic is AES encrypted with your secret, so there is

no chance for us to see any of your data.

3

Developer API

It is available an API for developing new applications based on BitTorrent Sync. It

offers to developers a wide range of possibilities. It is possible to integrate Sync intonew apps, build, improve, and change the way Sync works on the devices, or use the

API to automate workflows.

This API is based on JSON and gives almost full flexibility to customize Sync

behaviors, as examples below:

Get folders and the secrets if available

Add folders to sync

Remove folder from sync process

Get files from a synced folder

Set synced files preferences, allowing to selectively allow or not a file to be

synced

Get the folders peers which are currently connected to the P2P network

Set folder hosts instead using the tracker and relay server form BitTorrent Inc

Get download and upload speed

Shutdown gracefully


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4

BitTorrent Sync Setup and Tests

The following test environment was setup for verifying and measuring Bittorrent Syncusability and performance:

OSX MacBook Pro

Android Sony Xperia L mobile phone

Windows 7 notebook

802.11g WIFI D-LINK DIR-655 router connected to the Internet via DSL

(10Mbps connection)

The first 2 devices above were connected to same local network connected the WIFI

router. The Windows notebook was located in other network reachable through theInternet.

Bittorrent Sync was installed on each device. The user interfaces were slightly different

among each other but in general it was straightforward to install and setup.

The usage of Bittorrent Sync is also very similar in each distribution.

It will be described in the following sections the test scenarios, results and network

packets analysis using Wireshark 1.10.3.

4.1 Configuring the Bittorrent Sync

Basically the synching setup is very similar on all operating system. It is needed to

specify a synching folder and generate a shared secret key, or it is possible to get the

secret key from someone else who want to share data content.

It is also possible to define if the sync will allow full access or read only permissions to

the folders.

For more details about Bittorrent Sync configuration and setup please refer to its online

documentation [1].

4.2 Synching Devices Connected to LAN

The following test scenario was executed with devices connected to a LAN with no

Internet connection:

1) An empty sync folder was defined in the MAC Book Pro (IP address

192.168.0.106)

2) A newly shared secret was generated for this folder.

3) Wireshark was used for capturing network traffic for further analysis.


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4) A new sync folder was setup on the Xperia L mobile phone (IP address192.168.0.101) and configured the sharing secret from step 2) using the QR code

and the mobile phone camera.

5)

A test file was created in the Mac Book Pro executing the command below inthe sync folder defined in the step 1)

dd if=/dev/zero of=test_file_512kB bs=500k count=1

6) After some seconds (folder scan interval set to 60 seconds by default) the test

file was synched with the mobile phone.

7) The observed transfer rate was closer to the limit of the WIFI connection used in

the test (average speed around 6~8Mbps).

4.3 Synching Devices Connected through Internet

This test scenario was similar to the previous one despite the fact that the Windows

notebook was located on the Internet instead the local area network.

5 Results

The tests results indicated that Bittorrent Sync performed very well enabling the sharing

of files among several devices (PCs and mobile phone). The installation and

configuration is straightforward. The synchronization process was tested on a local

network and also with a PC in the Internet. On both scenarios the synchronization wassuccessful and it was noticed data transfer rates closer to the limit of the router and

Internet connection used in the tests.

The captured data from Wireshark was analyzed and the following results were

obtained:

1. The first interesting package sent from the MacBook was a multicast UDP with

the message ping4:peer. BitTorrent Sync was trying to locate peers in thelocal network that have folders configured with the same secret.

2. During the folder sync setup it was noticed communication with IP address

54.225.92.50, which it is under Amazon domain. This indicated that BitTorrent

Sync is using services in Amazon for hosting its tracker or relay servers for

enabling the peer discovery over the Internet. The protocol used was DIS[7] and

it was possible to check that message get_peers4:peer was used. A response

was received back with message peers which seems to be the information

about the available peers for the configured folder.


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3. The data transfer synchronization was done among the peers using UDP.

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Conclusions

BitTorrent Sync demonstrated to offer a very innovative solution for sharing content

using an efficient P2P protocol and highly secure data transmission, allowing the user to

create a personal cloud for data storage, free of subscription fees, disk space limitation

and able to run even when not connected to the Internet.

This solution also offers a very flexible developer API that enables the development of

other applications on top of BitTorrent Sync.

However, it was noticed the following negative points:

1) It could be unsafe to share the folder secret key with full access permission with

someone else. There is a risk of compromising the user data if the secret is

forwarded to unreliable parties.

2) The user must be very careful when defining full access directories since an

accidental content change or deletion will be synched among all devices,

affecting the data permanently.

3) As noticed on Wireshark capture logs during the tests, there is some

communication being performed from BitTorrent Sync to some external IPs.When a sync folder is created, it is enabled by default the relay and tracker

server offered by BitTorrent Inc. Those servers are used by the P2P protocol forenabling peers discover and communication through the Internet. Case those

servers are down the sync process will not work over Internet. In other hands, it

is possible to disable the tracker and relay servers, so the user can define any

other server than those offered by BitTorrent Inc. for acting as tracker and relay

servers.

4) It was checked in the BitTorrent forum a comment from a developer who worksfor BitTorrent Inc. explaining that the sync process sends some data to

BitTorrent servers but it is just for statistics purposes and no user content data is

exposed. Looking in the Wireshark capture data it was not possible to check

what information is being transferred since the data was encrypted.

7

References

1. BitTorrent Sync

http://www.bittorrent.com/sync/

2. BitTorrent

http://www.bittorrent.com/

3. DropBox


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https://www.dropbox.com/

4. Secure Remote Password Protocol

http://www.ietf.org/rfc/rfc2945.txt5. Ed25519: high-speed high-security signatures

Daniel J. Bernstein, Niels Duif, Tanja Lange, Peter Schwabe, Bo-Yin Yang.

High-speed high-security signatures. Journal of Cryptographic Engineering 2

(2012), 7789. Document ID: a1a62a2f76d23f65d622484ddd09caf8.

http://cr.yp.to/papers.html#ed25519

6. Session Traversal Utilities for NAT

RFC 5389, J. Rosenberg, R. Mahy, P. Matthews, D. Wing

7. IEEE Standard for Distributed Interactive Simulation--Application Protocols

IEEE Std 1278.1-1995

personal cloud using bittorrent sync

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