# Single-byte XOR cipher

The hex encoded string:

    1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736

... has been XOR'd against a single character. Find the key, decrypt
the message.

You can do this by hand. But don't: write code to do it for you.

How? Devise some method for "scoring" a piece of English plaintext.
Character frequency is a good metric. Evaluate each output and choose
the one with the best score.

## Achievement Unlocked

You now have our permission to make "ETAOIN SHRDLU" jokes on Twitter.