Exam 1 Flashcards
name an advantage of perfect secrecy
key cannot be cracked or discovered
name a disadvantage of perfect secrecy
difficult to communicate the key pad/ difficult to maintain syncronization
what does the CIA stand for
Confidentiality
integrity
authentication
what properties should and ideal block cipher have?
- encryption should be reversible ( Decryption should always return the original message and have a one to one mapping)
-encryption/decryption should be easy with key and difficult otherwise
-computing the mapping should be efficient
what is a pseudo-random permutaion
key defines the permutation
permutation is random-looking
efficient ot compute
what is the feistel network and how many block bits and key bits dows it require
A method of turning astrong PRF to a strong PRP in 4 easy steps
uses a 64 bit block and 56 bit ke
what did claude shannon introduce
a substitution-permutation (S-P)
what did claude shannon achieve
Confusion through substittion
Diffusion through permutation
what is confusion and diffusion
confusion is obscuring the local correlation between plaintext and ciphertext
diffusion is hiding the plaintext statististics by spreading it oer a larger area of ciphertext
what is the main limitation of ECB and what is the cause for this limitation?
message repetitions may show in cipher text due to the encrypted message blocks being independent
what is CBC
Cipher Block Chaining breaks up repetition in plaintext by XORing each block with a random-looking value
it uses an initialization vector which is a one time vector sent along with ciphertext and gets sent unencrypted. it needs to be unpredictable
what are the advantages of ECB
parallel encryption of blocks of bits
simple way of block cipher
what is the main disadvantage of CBC
parallel encryption is not possible since every encryption requires a previous cipher
what are the advantages of CTR
there is no relationship between cipher text and plain text
parallel execution of encryption is still possible
what are the disadvantages of CTR
requires a lot of synchronisation for maintaining counters
can’t be used safely with small block length ciphers (3DES for example)
what are osme otehr encryption modes (besides ECB, CTR, CBC)
Cipher feedback mode (CFB
output feedback mode (OFB)
XTS for random access applications
Offset codebook (OCD and Galios/counter (GCM for authenticated encryyption
what are teh bit distributions for the rijndael AES cipher
128/192/256 bit keys
10/12/14 rounds
128 bit data
what is the main difference between the AES and feistel network
unlike the feistel network, hte AES encryption uses the PRP round function
what is the main similarity between AES and Feistel network
similar to feistel, AES uses a key schedule to make each round effectively different
what are the 4 security services
authentication: assurance that the communicating entity is the one claimed
access control: prevention of the unauthorized use of a resource
data confidentiality: protection of data from authorised disclosure
data integrity: assurance that the data received is as sent by an authorized entity
non-repudiation: protection against denial by one of the parties in a communication
what are some active attacks
masquerade: takes place when one entity pretends to be a different entity by capturing and replaying an authentication sequence
replay is the passive capture of a data unit and its subsequent retransmission
modification of messages
denial of service
what are the 3 goals of crypto system designers
key space exponential in key length
infusible to brute force
make brute force the best strategy to crack the cipher
