def chal6():
"""
The text in input/6.txt has been base64 encoded after being
encrypted with repeating-key XOR. Decrypt it.
"""
f = open('input/6.txt')
ciphertext = utils.base64_to_bytes(f.read())
best_english_score = 0
result = ''
keysizes = utils.find_possible_keysizes(ciphertext, 3, 2, 40)
for keysize in keysizes:
key = [0] * keysize
# Split the ciphertext into blocks of length keysize
blocks = [ciphertext[i:i+keysize] for i in range(0,
len(ciphertext), keysize)]
# Transpose the blocks
transposed = [bytes(t) for t in zip_longest(*blocks,
fillvalue=0)]
# Treat each block as if it's been encrypted with a
# repeating-key XOR
for i in range(0, len(transposed)-1):
key[i] = utils.get_popular_byte(transposed[i])
plaintext = _crypto.xor_repeating_key(ciphertext, bytes(key))
english_score = utils.english_score(plaintext.decode('utf-8'))
if english_score > best_english_score:
result = plaintext.decode('utf-8')
res.append(xor(aes_ecb_decode(block, password), blocks[i - 1]))
return b''.join(res)
def aes_cbc_encode(plaintext: bytes, password: bytes, iv: bytes) -> bytes:
blocks = split_into_groups(plaintext, 16)
res = []
prev_block = iv
for block in blocks:
prev_block = aes_ecb_encode(xor(prev_block, block), password)
res.append(prev_block)
return b''.join(res)
print('Set 2')
print('Challenge 9')
res9 = pad_with_pkcs7(b'YELLOW SUBMARINE', 20)
assert res9 == b'YELLOW SUBMARINE\x04\x04\x04\x04'
print(res9)
print('Challenge 10')
ciphertext10 = base64_to_bytes(get_file('10.txt'))
password10 = b'YELLOW SUBMARINE'
iv = b'\x00' * 16
res10 = aes_cbc_decode(ciphertext10, password10, iv).decode('ascii')
assert res10.startswith("I'm back and I'm ringin' the bell")
print(res10)
# Check that encrypting is the opposite of decrypting
test_ciphertext10 = aes_cbc_encode(res10.encode('ascii'), password10, iv)
assert test_ciphertext10 == ciphertext10
def main():
res1 = hex_to_base64(
'49276d206b696c6c696e6720796f757220627261696e206c6'
'96b65206120706f69736f6e6f7573206d757368726f6f6d')
print('Task 1')
print(res1)
assert res1 == (b'SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc'
b'29ub3VzIG11c2hyb29t')
print('Task 2')
x = hex_to_bytes('1c0111001f010100061a024b53535009181c')
y = hex_to_bytes('686974207468652062756c6c277320657965')
res2 = bytes_to_hex(xor(x, y))
print(res2)
assert res2 == '746865206b696420646f6e277420706c6179'
print('Task 3')
ciphertext = hex_to_bytes('1b37373331363f78151b7f2b783431333d78397828372d'
'363c78373e783a393b3736')
res3 = decode_1_byte_xor(ciphertext)
print(res3[1])
assert res3[1] == "Cooking MC's like a pound of bacon"
print('Task 4')
ciphertexts = get_file('4.txt').split('\n')
res4 = find_and_decrypt_ciphertexts(ciphertexts)
print('Key: {0}\nPlaintext: {1}'.format(*res4))
assert res4[1] == 'Now that the party is jumping\n'
print('Task 5')
plaintext5 = ("Burning 'em, if you ain't quick and nimble\n"
"I go crazy when I hear a cymbal""")
key = "ICE"
correct_answer = ("0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343"
"c2a26226324272765272a282b2f20430a652e2c652a3124333a653e"
"2b2027630c692b20283165286326302e27282f")
res5 = bytes_to_hex(repeating_key_xor(text_to_bytes(plaintext5),
text_to_bytes(key)))
print(res5)
assert res5 == correct_answer
print('Task 6')
string1 = b'this is a test'
string2 = b'wokka wokka!!!'
print('Hamming Distance Check:', hamming_distance(string1, string2))
ciphertext6 = get_file('6.txt')
ciphertext6 = base64_to_bytes(ciphertext6)
res6 = decode_repeating_byte_xor(ciphertext6)
assert res6[0] == 'Terminator X: Bring the noise'
print('Key:', res6[0])
print('Plaintext:')
print(res6[1])
print('Task 7')
ciphertext7 = get_file('7.txt')
ciphertext7 = base64_to_bytes(ciphertext7)
password = b"YELLOW SUBMARINE"
res7 = aes_ecb_decode(ciphertext7, password).decode('ascii')
assert res7.startswith("I'm back and I'm ringin' the bell ")
print(res7)
print('Task 8')
ciphertexts8 = get_file('8.txt').split('\n')
ciphertexts8 = [bytes.fromhex(x) for x in ciphertexts8 if x]
res8 = detect_aes_ecb_encrypted_texts(ciphertexts8)
assert len(res8[1]) == 1
print('Most likely string:', bytes_to_hex(res8[1][0]))
print('Max no. of repeats of a 16byte chunk found:', res8[0])
