def chall_four(unknown_string):
unknown_hex = base64.b64decode(unknown_string).hex()
found_block_sizes = find_cipher_block_size(unknown_hex)
block_size = found_block_sizes[1] - found_block_sizes[0]
my_string = ("A" * block_size * 3).encode().hex(
) # want to pad >2 block lengths to detect repetition (i.e. force message to have 2 equivalent blocks)
padded_msg = pkcs7_pad(my_string + unknown_hex, block_size)
(ciphertext,
CipherObj) = aes_ecb_encrypt_with_key(bytes.fromhex(padded_msg),
bytes.fromhex(key))
ciphertext = ciphertext.hex()
ecb_detected = detect_ecb(ciphertext)
if not ecb_detected:
print("ECB not detected; not exploitable")
return
# now we know the block size, and it's in ECB
decrypted_blocks = ''.join([
padding_oracle(unknown_hex[i:i + block_size * 2], block_size, '')
for i in range(0, len(unknown_hex), block_size * 2)
])
#unpad string
padding = ord(decrypted_blocks[-1])
decrypted_blocks = decrypted_blocks[:-padding]
return decrypted_blocks
def find_cipher_block_size(unknown_string):
padded_lengths = []
for i in range(0, 64):
rand_str = ("A" * i).encode().hex()
try:
(ciphertext, CipherObj) = aes_ecb_encrypt_with_key(
bytes.fromhex(rand_str + unknown_string), bytes.fromhex(key))
padded_lengths.append(i)
except ValueError:
pass #print(f"Invalid block length {i}; trying next length")
return padded_lengths
def aes_ctr_operation(key, data, nonce):
ctr_output = ''
ctr = 0
block = data[ctr*32:(ctr+1)*32]
while block:
ctr_data = pack('<QQ', int(nonce, 16), ctr) # see struct library for packing formatting
aes_out = aes_ecb_encrypt_with_key(ctr_data, bytes.fromhex(key))
temp_output = xor_hex_strings(aes_out[0].hex()[:len(block)], block)
if len(temp_output) % 2: temp_output = '0' + temp_output
ctr_output += temp_output
ctr += 1
block = data[ctr*32:(ctr+1)*32]
return ctr_output
def encryption_oracle(msg):
rand_count = random.randint(5, 10)
prepad_msg = get_random_int(
rand_count * 8) + msg.encode().hex() + get_random_int(rand_count * 8)
padded_msg = pkcs7_pad(prepad_msg.encode().hex(), 16)
#print(padded_msg)
ciphertext = ''
key = get_random_int(128)
iv = get_random_int(128)
if random.getrandbits(1):
ciphertext = cbc_encrypt(padded_msg, key, iv)
else:
(ciphertext,
CipherObj) = aes_ecb_encrypt_with_key(bytes.fromhex(padded_msg),
bytes.fromhex(key))
ciphertext = ciphertext.hex()
return ciphertext
def generic_encrypt_ecb(msg, key, block_size):
(ciphertext, CipherObj) = aes_ecb_encrypt_with_key(
bytes.fromhex(pkcs7_pad(msg, block_size)), bytes.fromhex(key))
return ciphertext.hex()
def encrypt_profile(input_string):
padded_string = pkcs7_pad(input_string.encode().hex(), 16)
return aes_ecb_encrypt_with_key(bytes.fromhex(padded_string), bytes.fromhex(key))