- 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