Bruteforce 4 byte XOR encryption. Made for HMGCC's BLK_BOX challenge.

4byte-xor-bruteforce.py

alphabet = [i for i in range(32, 127)]+[10]
getEnglish = lambda text: list(filter(lambda c: c in alphabet, text))
isEnglish = lambda text: len(getEnglish(text)) == len(text)

with open('msg', 'rb') as f:
    encrypted = f.read()
    samples = []
    for i in range(4):
        samples.append([val for index, val in enumerate(encrypted) if index % 4 == i])

keysFound = []
for a in range(256):
    decryptAttempt = [val ^ a for val in samples[0]]
    if isEnglish(decryptAttempt):
        for b in range(256):
            decryptAttempt = [val ^ b for val in samples[1]]
            if (isEnglish(decryptAttempt)):
                for c in range(256):
                    decryptAttempt = [val ^ c for val in samples[2]]
                    if (isEnglish(decryptAttempt)):
                        for d in range(256):
                            decryptAttempt = [val ^ d for val in samples[3]]
                            if (isEnglish(decryptAttempt)):
                                keysFound.append([a, b, c, d])
                            
for keyset in keysFound:
    print(keyset)
    print(''.join(chr(c ^ keyset[i%4]) for i, c in enumerate(encrypted)))