This is for a modern cryptography class that I am currently taking.

The challenge is the cryptopals challenge 3: Single-Byte XOR Cipher, and I am trying to use python 3 to help complete this.

I know that I am supposed to XOR the string and converted to English. The hex string is "1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736" which converts to "806748453371902409051174291875458592743800337585421566549206796642836053682239286" in decimal form.

I have XOR'd this against multiple hex byte combinations (2 hex digits), but I do not know how to convert this into English. Is it just brute force and educated guessing at this point?

I know about ETAOIN SHRDLU, but this hasn't really been that helpful.

Thank you for your time and help.

ADDED: Additionally, I tried Challenge #4 but this code does not seem to work. But it did work for Challenge #3 so I am confused.

Challenge #3 Challenge #4

You can use binascii.hexlify, binascii.unhexlify to convert byte strings to hexadecimals or vice versa:

>>> import binascii
>>> binascii.hexlify(b'HELLO')  # to Hex
b'48454c4c4f'
>>> binascii.unhexlify('48454c4c4f')  # from Hex
b'HELLO'

Using str.isprintable, you can filter out non-printable candidates:

>>> 'abcd'.isprintable()
True
>>> '\x00'.isprintable()
False
>>> '\x7f'.isprintable()
False

import binasciiencoded = binascii.unhexlify('1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736')
for xor_key in range(256):decoded = ''.join(chr(b ^ xor_key) for b in encoded)if decoded.isprintable():print(xor_key, decoded)