CS 4363, Spring 2007
Lecture 2 Notes, 12 April 2007
- Student evaluation (at start of class).
- Attacks on a cryptosystem (cryptanalysis)
- Attacks based on different available information:
- Known ciphertext attack. This is the weakest condition,
since you will usually have ciphertext available.
- Known plaintext attack: the opponent knows a
sequence: M1, ..., Mq of messages,
not of his choosing.
- Plaintext/ciphertext pairs: the opponent knows a
sequence of pairs:
<M1, C1>, ...,
<Mq, Cq>, where each
Ci = ENC(Mi).
- Chosen plaintext attack: the opponent can choose
a plaintext and get the corresponding ciphertext.
- Chosen ciphertext attack: the opponent can choose
either plaintext or ciphertext and get the corresponding item.
- In item 1 above, can use brute force if the messages have
a known format.
- In item 2 above, can use brute force even if q = 1.
- Block ciphers (See
Lecture 9: Symmetric Encryption,
slides 34-70.
Revision date: 2007-04-11.
(Please use ISO
8601, the International Standard.)