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Crypto challenges

The cryptopals crypto challenges site is here. I have finished the first set of challenges.

Set 1

  • Number 1. Convert a hex string to base 64.
  • Discussion of base64
  • Number 2. XOR two hex-encoded strings.
  • Number 3. Check all 256 possible repeated one-byte keys against a ciphertext. This is called single-character XOR.

For number 3 and 4, I developed three tests of English:

  • Number of characters on a whitelist.
  • A scoring function that uses letter frequencies
  • Look up "words" in a dictionary of English words

The last one works really well, but is slow.

  • Number 4. Find the string encrypted by single-character XOR