Module 13: Cryptography in Network Security Flashcards
(20 cards)
Requirements that cryptography can fulfill
Authentication
Privacy
Integrity (message unaltered)
Non-repudiation (message received)
Secret-key (symmetric) cryptography
Encryption and decryption use the same key. Usually faster/more efficient for encrypting.
Public-key (asymmetric) cryptography
Different keys used for encryption and decryption. Can scale more easily.
4 main components in cryptography for any “practical systems”
Cryptosystems (algorithms)
Modes (how algorithms initialized and used to manage messages longer than one block)
Protocols (how algorithms composed and applied to real problems)
Key management (creating, distributing, storing, updating keys)
Common key length
128-bit for symmetric algorithms, 1024 bits for asymmetric algorithms
MIC (Message Integrity Code)
Cryptographic checksum, used to confirm data in file has not been maliciously changed
Block cipher algorithm
Takes fixed-length block of plaintext, encrypts to a fixed-length block of cipher text. Cons: repetitions are noticed. Solution: CBC (Cipher block chaining)
Stream cipher algorithm
Uses key to make pseudorandom key stream, XOR-ed with plaintext to make ciphertext. Con: simple cipher algorithm makes same key stream with each new messsage (solution: use Initialization Vector and key)
DES (Data Encryption Standard) (private-key)
Block cipher algorithm
Triple DES (private-key)
Uses three 56-bit DES keys to encrypt each block
Blowfish (private-key)
Cipher block algorithm, uses variable key lengths
AES (Advanced Encryption Standard) (private-key)
Attempt to replace DES
What does public key do for authentication?
Digital signature applied to message using private keys
How does public key solve security of key directory?
Public-key certificates. CA (certificate authorities) organized in a hierarchy.
RSA (named after creators) algorithm
best known public-key cryptosystem.
Mode of operation
Method of combining executions of cipher algorithms, for when message is longer than block length of the cipher.
ECB (Electronic Codebook) Mode
Encryption algorithm applied independently to each block of message. Cons: same input block always encrypted as same ciphertext block, attacker can substitute blocks to alter part of a message
CBC (Cipher Block Chaining) Mode
Each plaintext block XOR-ed with preceding ciphertext block. “bootstrapped” with Initialization Vector (IV)
Protocol
Series of steps take to accomplish a task. Used to refer to attainment of user-visible results such as secret communication and digital signatures.
Two methods for generating keys
User input
Pseudorandom
