Vigenere system – polyalphabetic substitution cipher, key is a word
Vernan cipher – one-time pad, key is the length of the message
- randomly generated
- physically protected against disclosure
- used only once
- key at least as long as the message
Running key cipher (book cipher) – use a book text as the running key
Confusion – complicated relationship between plain and cipher text
Diffusion – one change in plain text = several changes in cipher text
Keys required: n = number of participants
- Symmetric = (n * (n-1)) / 2
- Asymmetric = 2 * n
Data Encryption Standard (DES) – 56-bit key, 16 rounds of XOR
- Electronic codebook (ECB) – encrypts each block with the same key
- Cipher Block Chaining (CBC) – each new block is XORed with previous block of cipher text before being encrypted (con: errors propagate)
- Cipher Feedback (CFB) – streaming version of CBC – data collects in a buffer until full, then encrypts – uses Initialization Vector (IV)
- Output Feedback (OFB) – similar to CFB but XORs with a seed value instead of previous cipher text – prevents error propagaion
- Counter (CTR) – stream cipher, XOR with simple counter – no propagation errors – allows encryption to be broken into parts, so good for parallel computing
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