User authentication

COMPUTER SECURITY
USERAUTHENTICATION
Mr. RAJASEKAR RAMALINGAM
Faculty - Department of IT
College of Applied Sciences – Sur,
Sultanate of Oman.
vrrsekar@yahoo.com

CONTENT
• USER AUTHENTICATION
• MEANS OF USER AUTHENTICATION
• PASSWORD AUTHENTICATION
• PASSWORD VULNERABILITIES
• USE OF HASHED PASSWORDS – IN UNIX
• PASSWORD CRACKING TECHNIQUES
• USING BETTER PASSWORDS
• TOKEN AUTHENTICATION
• BIOMETRIC AUTHENTICATION
USER AUTHENTICATION 2

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1. USER AUTHENTICATION
• RFC 2828 defines user authentication as:
• “The process of verifying an identity claimed by or for a system
entity.
• Fundamental security building block
• Basis of most types of access control & for user accountability.
• User authentication is distinct from message authentication.
• User authentication process consists of two steps:
1. Identification: Presenting an identifier to the security system.
2. Verification: Binding entity (person) and identifier
USER AUTHENTICATION

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2. MEANS OF USER AUTHENTICATION
• Four general means of authenticating a user's identity are
• Individual knows: Includes a password, a personal identification
number (PIN), or answers to a prearranged set of questions.
• Individual possesses: Includes electronic keycards, smart cards, and
physical keys. Also known as a token.
• Individual is (static biometrics): Includes recognition by fingerprint,
retina, and face.
• Individual does (dynamic biometrics): Examples include recognition
by voice pattern, handwriting characteristics, and typing rhythm.
• can use alone or combined
• all can provide user authentication & have issues.
USER AUTHENTICATION

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3. PASSWORD AUTHENTICATION
• Widely used user authentication method
– User provides name/login and password
– System compares password with that saved for specified
login
• Authenticates ID of user logging and
– That the user is authorized to access system
– Determines the user’s privileges
– Is used in Discretionary Access Control
USER AUTHENTICATION

4. PASSWORD VULNERABILITIES
Offline
dictionary
attack
Specific
account
attack
Popular
password
attack
Password
guessing
against
single user
Workstation
hijacking
Exploiting
user
mistakes
Exploiting
multiple
password
use
Eectronic
monitoring

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Following are the attack strategies:
1. Offline dictionary attack:
• A hacker gain access to the system password file.
• Compares the password hashes against hashes of commonly used
passwords.
2. Specific account attack:
• Attacker targets a specific account &submits password guesses until the
correct password is discovered.
3. Popular password attack / Against single user:
• The attacker chooses a popular password and tries it.
• Attacker attempts to gain knowledge about the account holder and system
password policies and uses that knowledge to guess the password.
USER AUTHENTICATION

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4. Workstation hijacking:
• The attacker waits until a logged-in workstation is unattended.
5. Exploiting user mistakes:
• User is more likely to write it down passwords, because it is
difficult to remember.
6. Exploiting multiple password use.
• Similar password for a many applications
7. Electronic monitoring:
• If a password is communicated across a network to log on to a
remote system, it is vulnerable to eavesdropping.
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5. USE OF HASHED PASSWORDS – IN UNIX
USER AUTHENTICATION

• A widely used password security technique.
• Use of hashed passwords and a salt value.
• Found on all UNIX and other operating systems.
1. Loading a new password:
• The user selects or is assigned a password.
• Password combined with a fixed-length salt value.
• Salt is a pseudorandom or random number.
• PW & salt serve as inputs to a hashing algorithm to produce a fixed-length
hash code.
• Hashed password then stored, together with a plaintext copy of the salt, in
the password file for the corresponding user ID.
2. Verifying a password:
• When a user attempts to log on to a system, the user provides an ID and a
password.
• OS uses the ID to retrieve the plaintext salt and the encrypted password.
• The salt and user-supplied password are used as input to the encryption
routine.
• If the result matches the stored value, the password is accepted.
10USER AUTHENTICATION

6. PASSWORD CRACKING TECHNIQUES
Dictionary attacks
• Develop a large dictionary of possible passwords and try
each against the password file
• Each password must be hashed using each salt value and
then compared to stored hash values
Rainbow table attacks
• Pre-compute tables of hash values for all salts
• A mammoth table of hash values
• Can be countered by using a sufficiently large salt value
and a sufficiently large hash length

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7. USING BETTER PASSWORDS
• Clearly have problems with passwords
• Goal to eliminate guessable passwords
• At the same time, easy for user to remember
• Four basic techniques:
1. User education
2. Computer-generated passwords
3. Reactive password checking
4. Proactive password checking
1. User education:
• Users can be told the importance of using hard-to-guess passwords.
• Provide users with guidelines for selecting strong passwords.
• Can be problematic when have a large user population.
• Because many users will simply ignore the guidelines.
USER AUTHENTICATION

2. Computer-generated passwords:
• Poor acceptance by users.
• Random in nature, users will not remember.
3. Reactive password checking:
• System periodically runs its own password cracker to
find guessable passwords.
• The system cancels any passwords that are guessed and
notifies the user.
• Can be costly in resources to implement.
4. Proactive password checking:
• User selects own password which the system then
checks to see if it is allowable and, if not, rejects it.

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8. TOKEN AUTHENTICATION
• Objects that a user possesses for the purpose of user
authentication are called tokens.
• Token are of different forms, they are:
1. Embossed: Raised characters only, on front, e.g. Old credit
card.
2. Magnetic stripe: Magnetic bar on back, characters on front,
e.g. Bank card.
3. Memory: Has Electronic memory inside, e.g. Prepaid phone
card.
4. Smartcard: Has Electronic memory and processor inside, e.g.
Biometric ID card
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8.1 MEMORY CARD / MAGNETIC STRIPS
• Store but do not process data
• Magnetic stripe card, e.g. bank card
• Electronic memory card
• Used alone for physical access
• With password/PIN for computer use
• Drawbacks of memory cards include:
– Need special reader
– Loss of token issues
– User dissatisfaction
USER AUTHENTICATION

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8.2 SMARTCARD / EMBOSED
• Credit-Card like
• Has own processor, memory, I/O ports
– Wired or wireless access by reader
– May have crypto co-processor
– ROM, EEPROM, RAM memory
• Executes protocol to authenticate with reader/computer
• Also have USB dongles
USER AUTHENTICATION

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9. BIOMETRIC AUTHENTICATION
• Authenticate user based on one of their physical
characteristics
• Biometric authentication system authenticates an
individual based on unique
• Physical characteristics like Fingerprints, hand
geometry, facial characteristics, and retinal and iris
patterns.
• Dynamic characteristics like voiceprint and signature.
USER AUTHENTICATION

1. Facial characteristics:
Characteristics based on location and shape of key facial features,
such as eyes, eyebrows, nose, lips, and chin shape.
2. Fingerprints:
The pattern of ridges and furrows on the surface of the fingertip.
3. Hand geometry:
Identify features of hand,: e.g. shape, lengths & widths of fingers.
4. Retinal pattern:
Formed by veins beneath the retinal surface is unique.
Uses digital image of the retinal pattern by projecting a low-
intensity beam of visual or infrared light into the eye.
5. Signature: Each individual has a unique style of handwriting,
especially in signature.

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9.1 OPERATION OF A BIOMETRIC SYSTEM
USER AUTHENTICATION

Operation of a biometric system.
• Each users must first be enrolled in the system.
• For biometric system, the user presents a name and a password or
PIN.
• System senses some biometric characteristic of this user (e.g.
fingerprint of right index finger).
• The system digitizes the input and then extracts a set of features that
can be stored as a number or set of numbers.
• This set of numbers is referred to as the user’s template.
• User authentication on a biometric system involves either
verification or identification.
• Verification is similar to a user logging on to a system by using a
memory card or smart card coupled with a password or PIN.
• In Identification process, the individual uses the biometric sensor
but presents no additional information.
• The system then compares the presented template with the set of
stored templates. If there is a match, then this user is identified.
Otherwise, the user is rejected. 20USER AUTHENTICATION

User authentication

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