the cryptopals crypto challenges

Crypto Challenge Set 4

This is the last set of block cipher cryptography challenges, and also our coverage of message authentication.

This set is much easier than the last set. We introduce some new concepts, but the attacks themselves involve less code than, say, the CBC padding oracle.

Things get significantly trickier in the next two sets. A lot of people drop off after set 4.

  1. Break "random access read/write" AES CTR
  2. CTR bitflipping
  3. Recover the key from CBC with IV=Key
  4. Implement a SHA-1 keyed MAC
  5. Break a SHA-1 keyed MAC using length extension
  6. Break an MD4 keyed MAC using length extension
  7. Implement and break HMAC-SHA1 with an artificial timing leak
  8. Break HMAC-SHA1 with a slightly less artificial timing leak
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