identification authentication. 2 authentication allows an entity (a user or a system) to prove its...
TRANSCRIPT
IdentificationAuthentication
2
Authentication Allows an entity (a user or a system) to prove its
identity to another entity Typically, the entity whose identity is verified
reveals knowledge of some secret S to the verifier
Strong authentication: the entity reveals knowledge of S to the verifier without revealing S to the verifier
3
Authentication Information
Must be securely maintained by the
system.
4
Elements of Authentication Person/group/code/system: to be authenticated Distinguishing characteristic: differentiates the
entities to be authenticated Proprietor/system owner/administrator: responsible
for the system Authentication mechanism: verify the distinguishing
characteristic Access control mechanism: grant privileges upon
successful authentication
5
Authentication Requirements Network must ensure
Data exchange is established with addressed peer entity not with an entity that masquerades or replays previous messages
Network must ensure data source is the one claimed Authentication generally follows identification
Establish validity of claimed identity Provide protection against fraudulent transactions
6
User Authentication What the user knows
Password, personal information What the user possesses
Physical key, ticket, passport, token, smart card What the user is (biometrics)
Fingerprints, voiceprint, signature dynamics
7
Passwords Commonly used method For each user, system stores (user name, F(password)),
where F is some transformation (e.g., one-way hash) in a password file F(password) is easy to compute From F(password), password is difficult to compute Password is not stored in the system
When user enters the password, system computes F(password); match provides proof of identity
8
Vulnerabilities of Passwords Inherent vulnerabilities
Easy to guess or snoop No control on sharing
Practical vulnerabilities Visible if unencrypted in distributed and network
environment Susceptible for replay attacks if encrypted naively
Password advantage Easy to modify compromised password.
9
Weak Passwords Bell Labs study (Morris and Thompson, 1979), 3289
passwords were examined 15 single ASCII characters, 72 two ASCII characters, 464
three ASCII characters, 477 four ASCII characters, 706 five letters (all lower case or all upper case), 605 six letters, all lower case, 492 week passwords (name, dictionary words, etc.)
Summary: 2831 passwords (86% of the sample) were weak, i.e., either too easy to predict or too short
10
Attacks on Password Guessing attack/dictionary attack Social Engineering Sniffing Trojan login Van Eck sniffing
11
Guessing Attack Exploits human nature to use easy to
remember passwords Trial-and-error attack Easy to detect (failed logins) and block Need audit mechanism
12
Social Engineering Attacker asks for password by masquerading
as somebody else (not necessarily an authenticated user)
May be difficult to detect Protection against social engineering: strict
security policy and users’ education
13
Dictionary Attacks on Passwords
Attack 1: Create dictionary of common words and names and their simple
transformations Use these to guess password
Attack 2: Usually F is public and so is the password file (encrypted) Compute F(word) for each word in dictionary Find match
Attack 3: Pre-compute dictionary Look up matches
14
Password Salt Used to make dictionary attack more difficult Salt is a 12 bit number between 0 and 4095 It is derived from the system clock and the process identifier Compute F(password+salt); both salt and F(password+salt) are
stored in the password table User: gives password, system finds salt and computes
F(password+salt) and check for match Note: with salt, the same password is computed in 4096 ways
15
Password Management Policy Educate users to make better choices Define rules for good password selection and
ask users to follow them Ask or force users to change their password
periodically Actively attempt to break user’s passwords
and force users to change broken ones Screen password choices
16
One-time Password
Use the password exactly once!
17
Lamport’s scheme Doesn’t require any special hardware System computes F(x),F2(x),…, F100(x) (this allows 100
logins before password change) System stores user’s name and F100(x) User supplies F99(x) the first time If the login is correct, system replaces F100(x) with F99(x) Next login: user supplies F98(x) … and so on User calculates Fn(x) using a hand-held calculator, a
workstation, or other devices
18
Time Synchronized There is a hand-held authenticator
It contains an internal clock, a secret key, and a display Display outputs a function of the current time and the key It changes about once per minute
User supplies the user id and the display value Host uses the secret key, the function and its clock to
calculate the expected output Login is valid if the values match
19
Time Synchronized
Secret key
Time
One Time PasswordDES
20
Challenge Response
Work station Host
Network
• Non-repeating challenges from the host is used• The device requires a keypad
User ID
Challenge
Response
21
Challenge Response
Secret key
Challenge
One Time PasswordDES
22
Devices with Personal Identification Number (PIN) Devices are subject to theft, some devices
require PIN (something the user knows) PIN is used by the device to authenticate the user Problems with challenge/response schemes
Key database is extremely sensitiveThis can be avoided if public key algorithms are used
23
Smart Cards Portable devices with a CPU, I/O ports, and
some nonvolatile memory Can carry out computation required by public
key algorithms and transmit directly to the host
Some use biometrics data about the user instead of the PIN
24
Biometrics Fingerprint Retina scan Voice pattern Signature Typing style
25
Problems with Biometrics Expensive
Retina scan (min. cost) about $ 2,200 Voice (min. cost) about $ 1,500 Signature (min. cost) about $ 1,000
False readings Retina scan 1/10,000,000+ Signature 1/50 Fingerprint 1/500
Can’t be modified when compromised