def aes_ctr_encryption_oracle(plaintext, key, blocksize=16):
suffix = ";comment2=%20like%20a%20pound%20of%20bacon"
prefix = "comment1=cooking%20MCs;userdata="
plaintext = clean(plaintext)
iv = Random.new().read(blocksize)
nonce = form_nonce(0)
return aes_ctr_encrypt_decrypt(prefix + plaintext + suffix, key, nonce)
def test_ch18(self):
cipher = b64decode(
"L77na/nrFsKvynd6HzOoG7GHTLXsTVu9qvY/2syLXzhPweyyMTJULu/6/kXX0KSvoOLSFQ=="
)
key = "YELLOW SUBMARINE"
nonce = form_nonce(0)
self.assertEqual(
aes_ctr_encrypt_decrypt(cipher, key, nonce),
"Yo, VIP Let's kick it Ice, Ice, baby Ice, Ice, baby ")
def test_ch25(self):
key = generate_random_key(16)
with open('static/25.txt', 'r') as myfile:
cipher = b64decode(myfile.read())
plaintext = unpadpkcs7(aes_ecb_decrypt(cipher, "YELLOW SUBMARINE"))
nonce = form_nonce(0)
ciphertext = aes_ctr_encrypt_decrypt(plaintext, key, nonce)
edit_func = partial(edit_ciphertext, key=key)
# test edit_ciphertext function
result = edit_ciphertext(ciphertext, key, 32, "YELLOW")
self.assertEquals(
result,
aes_ctr_encrypt_decrypt(plaintext[:32] + "YELLOW" + plaintext[38:],
key, nonce))
# break it
self.assertEquals(break_edit_ciphertext(ciphertext, edit_func),
plaintext)
def test_ch20(self):
plaintexts = []
ciphertexts = []
key = generate_random_key(16)
with open('static/19.txt', 'r') as myfile:
for line in myfile.read().splitlines():
plaintexts.append(b64decode(line))
for plaintext in plaintexts:
nonce = form_nonce(0)
ciphertexts.append(aes_ctr_encrypt_decrypt(plaintext, key, nonce))
raise NotImplementedError
def test_ch19(self):
# this is a many time pad problem
plaintexts = []
ciphertexts = []
key = generate_random_key(16)
with open('static/19.txt', 'r') as myfile:
for line in myfile.read().splitlines():
plaintexts.append(b64decode(line))
for plaintext in plaintexts:
nonce = form_nonce(0)
ciphertexts.append(aes_ctr_encrypt_decrypt(plaintext, key, nonce))
break_ctr_reused_nonce_substitutions(ciphertexts)
raise NotImplementedError
def edit_ciphertext(ciphertext, key, offset, newtext):
nonce = form_nonce(0)
f = aes_ctr_encrypt_decrypt(
ciphertext[:offset] + newtext + ciphertext[offset + len(newtext):],
key, nonce)[offset:offset + len(newtext)]
return ciphertext[:offset] + f + ciphertext[offset + len(newtext):]