Cryptography Flashcards
(41 cards)
Cryptography
The study of mathematical techniques related to aspects of information security such as confidentiality, data integrity, entity authentication, and data authentication
Data integrity
A service which addresses the unauthorised alteration of data.
Entity authentication
A service that determines if an entity is who it claims to be.
Data origin authentication
A service that determines if an entity claiming to be the sender of a message really is the one from whom it originates.
Non-reputation
A service that prevents an entity from denying previous commitments or actions.
A
alphabet of definition
M
Message space
plaintext
Element of the message space
C
Ciphertext space
ciphertext
Element of the ciphertext space, or element of key space
K
Key space
Encryption function E_e
Bijection from M to C
Decryption function
Bijection from C to M
Symmetric-key
The encryption scheme is symmetric-key if for each associated encryption/ decryption key pair (e; d), if is computationally “easy” to determine d knowing only e, and to determine e from d.
Block cipher
An encryption scheme which breaks up the plaintext messages to be transmitted into strings of a fixed length t over an alphabet A and encrypts one block at a time.
Stream ciphers
Very simple block ciphers having block length equal to one.
Public-key
For each associated encryption/ decryption key pair (e, d). if given e it is infeasible to determine the corresponding decryption key d.
Equivaltence class
Set of numbers all equivalent to a modulo n
The integers modulo n
The set of all equivalence classes of integers in {0, …, n-1}
Binary operation (on a set S)
A function f:SxS->S, implies closure
A group satisfies…
Associativity, Identity, Inverse
COmmutative/ abelian
ad = da
Homomorphism
(G,) and (H,.) groups A function h: G -> H such that h(ab) = h(a).h(b) for all a, b in G
Isomorphism
A bijective homomorphism
