Here is the opening stanza of an important work of the English language:

Burning 'em, if you ain't quick and nimble
I go crazy when I hear a cymbal

Encrypt it, under the key “ICE”, using repeating-key XOR.

In repeating-key XOR, you’ll sequentially apply each byte of the key; the first byte of plaintext will be XOR’d against I, the next C, the next E, then I again for the 4th byte, and so on.

It should come out to:

0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272
a282b2f20430a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f

Encrypt a bunch of stuff using your repeating-key XOR function. Encrypt your mail. Encrypt your password file. Your .sig file. Get a feel for it. I promise, we aren’t wasting your time with this.

code:


In [10]: text = b"Burning 'em, if you ain't quick and nimble I go crazy when I hear a cymbal"
    ...: key = b"ICE"
    ...: 
    ...: ans = bytes(
    ...:     text[i] ^ key[i % len(key)]
    ...:     for i in range(len(text))
    ...: )
    ...: 
    ...: print(ans.hex())
    ...: 
0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272a282b2f20690a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f