The Matasano crypto challenges are a set of increasingly difficult coding challenges in cryptography; not puzzles, but designed to show you how crypto fits together and why all the parts are important. Cheers to Maciej Ceglowski of pinboard.in for bringing them to my attention.
49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d should produce
1c0111001f010100061a024b53535009181c xored with
686974207468652062756c6c277320657965 should produce
1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736 has been xored with a single byte from an English message.
One of the 60-character strings in the file has been encrypted by single-character XOR.
Burning 'em, if you ain't quick and nimble I go crazy when I hear a cymbal
when XORed with repeating key "ICE", should equal
Break the encoded file, which is base64ed after being encrypted with repeating key XOR.