Exam 1 Flashcards
Security Attack
Any action that compromises the security of information
Security Mechanism
A mechanism that is designed to detect, prevent, or recover from a security attack
Security Service
A service that enhances the security of data processing systems and information transfers. A security service makes use of one or more security mechanisms
What are some examples of Passive Threats?
- Release of message content
- Traffic analysis
What are some examples of Active Threats?
- Masquerade
- Replay
- Modification of message contents
- Denial of service
Name some security services
- Confidentiality (privacy)
- Authentication (who created or sent the data)
- Integrity (has not been altered)
- Non-repudiation (the order is final)
- Access control (prevent misuse of resources)
- Availability (permanence, non-erasure)
- Denial of service attack
- Virus that deletes files
Methods of Defense
- Encryption
- Software control (access limitations in a data base, in operating system protect each user from other users)
- Hardware Controls (smartcard)
- Policies (frequent changes of passwords)
- Physical Controls
What are Specific Security Mechanisms?
- May be incorporated into the appropriate protocol layer in order to provide some of the OSI security services
- Encipherment
- Digital Signature
- Access Control
- Data Integrity
- Authentication Exchange
- Traffic Padding
- Routing Control
- Notarization
Encipherment
The use of mathematical algorithms to transform data into a form that is not readily intelligible. The transformation and subsequent recovery of the data depend on an algorithm and zero or more encryption keys.
Digital Signature
Data appended to, or a cryptographic transformation of, a data unit that allows a recipient of the data unit to prove the source of integrity of that data unit and protect against forgery (e.g. by the recipient)
Access Control
A variety of mechanisms that enforce access rights to resources.
Data Integrity
A variety of mechanisms used to assure the integrity of a data unit or stream of data units.
Authentication Exchange
A mechanism intended to ensure the identity of an entity be means of information exchange
Traffic Padding
The insertion of bits into gaps in a data stream of frustrate traffic analysis attempts
Routing Control
Enables selection of particular physically secure routes for certain data and allows routing changes, especially when a breach of security is suspected
Notarization
The use of a trusted third party to assure certain properties of a data exchange
Conventional Encryption Principles
- An encryption scheme has five ingredients:
- Plaintext
- Encryption algorithm
- Secret Key
- Ciphertext
- Decryption algorithm
- Security depends on the secrecy of the key, not the secrecy of the algorithm
Cryptography
- Classified along three independent dimensions:
- The type of operations used for transforming plaintext to ciphertext
- Substitution: Each element (bit, letter) in the plaintext is mapped to another element (e.g., B -> F)
- Transposition: Elements in the plaintext are re-arranged (change locations)
- The type of operations used for transforming plaintext to ciphertext
- The number of keys used
- Symmetric (singe key)
- Asymmetric (two keys, or public-key encryption)
- The way in which the plaintext is processed
- One block at a time - block cipher
- Element by element, continuously - stream cipher
Feistel Cipher Structure: Block Size
Larger block sized means greater security
Feistel Cipher Structure: Key Size
Larger key size means greater security
Feistel Cipher Structure: Number of Rounds
Multiple rounds offer increasing security
Feistel Cipher Structure: Subkey Generation Algorithm
Greater complexity will lead to greater difficulty of cryptanalysis
Feistel Cipher Structure: Fast Software Encryption/Decryption
The speed of the execution of the algorithm becomes a concern
XOR
0 XOR 0 = 0
0 XOR 1 = 1
1 XOR 0 = 1
1 XOR 1 = 0
DES
- Data Encryption Standard
- Block cipher
- Plaintext is processed in 64-bit blocks
- The key is 56-bits in length
- When following the Fesitel structure it is 16 rounds
DES Process
- L[i] = R[i-1]
- R[i] - L[i-1] XOR F(R[i-1], K[i])
Cipher Block Chaining (CBC) Mode
- Message is divided into several blocks
- The input to the encryption algorithm is the XOR of the current plaintext block and the preceding ciphertext block
- Repeating pattern of the 64-bits are not exposed
MAKE SURE TO INCLUDE EQUATIONS AND DIAGRAM ON CHEAT SHEET
Location of Encryption Devices
- Link encryption
- End-to-end encryption
- High Security
Link Encryption
- A lot of encryption devices
- High level of security
- Decrypt each packet at every switch
End-to-End Encryption
- The source of encrypt and the receiver decrypts
- Payload encrypted
- Header in the clear
High Security
Both link and end-to-end encryption are needed
Authentication - Requirements
Must be able to verify that
- Message came from apparent source or author
- Contents have not been altered
- Sometimes, it was sent at a certain time or sequence
- Offer protection against active attack (falsification of data or transactions)
Approaches to Message Authentication - Authentication Using Conventional Encryption
Only the sender and receiver should know the shared key
Approaches to Message Authentication - Message Authentication without Message Encryption
An authentication tag us generated and appended to each message
- e.g. Hash without encryption
Approaches to Message Authentication - Message Authentication Code (MAC)
- Calculate the MAC as a function of the message and the key.
MAC = F(K,M)
Properties of a Secure HASH Function
To produce a “fingerprint”
Properties of a Secure HASH Function H
- H can be applied to any block of data at any size
- H produces a fixed length output
- H(x) is easy to compute for any given x
- For any given h, it is computationally infeasible to find x such that H(x) = h (one way property)
- For any given x, it is computationally infeasible to find y not equal to x with H(y) = H(x) (weak collision property)
- It is computationally infeasible to find any pair (x,y) such that H(x) = H(y) (strong collision property)
SHA-1 Steps
- Append padding bits - the length is 64-bits less than a multiple of 512-bits
- Append message length field (64-bits) - The total length is Lx512 bits
- Initialize message digest (MD) buffer - A 160-bit buffer is used to hold intermediate and final results of the hash function. The buffer can be represented as five 32-bit registers (A,B,C,D,E), which are initialized to some constant (32-bit integers)
- Process message in 512-bit blocks. The heart of the algorithm is a module - compression function, that consists of four rounds of processing, and each round has 20 steps.
HMAC (Hash MAC)
- Instead of using encryption algorithms, one may develop a MAC derived from a hash function, such as SHA-1
- A hash function was note designed for use as a MAC and can not be used directly to create a MAC since it does not rely on a secret key
- HMAC was proposed, which can create a MAC using a hash function and a secret key
- HMAC has been used in IP-Security, SSL/TLS, etc.
HMAC Motivations
- Faster in software than encryption algorithms such as DES
- Library code for has functions is widely available
- No export restrictions on hash functions from the US
HMAC Design Objectives
- To use available hash functions
- To allow for easy replace-ability if the embedded hash function
- To preserve the original performance of the hash function
- To use and handle keys in a simple way
- To have a well-understood cryptographic analysis of the strength of the authorization mechanism
Categories of Applications for Public-Key Cryptosystems
- Encryption/decryption: The sender encrypts a message with the recipient’s public key
- Digital Signature: The sender’s “signs” a message with its private key
- Key Exchange: Two sides cooperate to exchange a session key
RSA Encryption Overview
- Plaintext: M < n
- Ciphertext: C = M^e(mod(n))
RSA Decryption Overview
- Ciphertext: C
- Plaintext: M = C^d(mod(n)) = M^ed(mod(n))
Requirements for KERBEROS
- Secure: An eavesdropper should not be able to obtain the necessary information to impersonate a user
- Reliable: Kerberos should be highly reliable and should employ a distributed architecture
- When Kerberos system itself is under attack, it can still provide authentication service
- Transparent: Ideally, the user should not be aware that authentication is taking place
- Scalable: The system should be capable of supporting the large number of clients and servers
KERBEROS Realm Requirements
- A server
- A number of clients
- A few application servers
Purpose of X.509
X.509 defines a framework (certificate structure) for authentication services by the X.500 directory to its users
- The directory may serve as a database of public-key certificate
- Each certificate contains the public key of a user and is signed with the private key of a trusted Certificate Authority (CA)
- The heart of X.509 is the public-key certificate associated with each user
