24-02-2012, 04:46 PM
Cryptography issues
[attachment=17710]
Confidentiality: only sender, intended receiver should “understand” message contents
sender encrypts message
receiver decrypts message
End-Point Authentication: sender, receiver want to confirm identity of each other
Message Integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection
Polyalphabetic encryption
n monoalphabetic cyphers, M1,M2,…,Mn
Cycling pattern:
e.g., n=4, M1,M3,M4,M3,M2; M1,M3,M4,M3,M2;
For each new plaintext symbol, use subsequent monoalphabetic pattern in cyclic pattern
dog: d from M1, o from M3, g from M4
Key: the n ciphers and the cyclic pattern
Block ciphers
Message to be encrypted is processed in blocks of k bits (e.g., 64-bit blocks).
1-to-1 mapping is used to map k-bit block of plaintext to k-bit block of ciphertext
[attachment=17710]
Confidentiality: only sender, intended receiver should “understand” message contents
sender encrypts message
receiver decrypts message
End-Point Authentication: sender, receiver want to confirm identity of each other
Message Integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection
Polyalphabetic encryption
n monoalphabetic cyphers, M1,M2,…,Mn
Cycling pattern:
e.g., n=4, M1,M3,M4,M3,M2; M1,M3,M4,M3,M2;
For each new plaintext symbol, use subsequent monoalphabetic pattern in cyclic pattern
dog: d from M1, o from M3, g from M4
Key: the n ciphers and the cyclic pattern
Block ciphers
Message to be encrypted is processed in blocks of k bits (e.g., 64-bit blocks).
1-to-1 mapping is used to map k-bit block of plaintext to k-bit block of ciphertext
