def padding_oracle(ciphertext):
key, iv = deterministic_random_key_and_iv()
try:
challenge_10.AES_CBC(key, iv).decrypt(ciphertext)
except challenge_09.PaddingError:
return False
return True
def encryption_oracle(plaintext):
key = random_key_or_iv()
plaintext = random_padding() + plaintext + random_padding()
# Use ECB half the time and CBC the other half of the time
if secrets.randbelow(2) == 1:
return AES_ECB(key).encrypt(plaintext)
else:
iv = random_key_or_iv()
return challenge_10.AES_CBC(key, iv).encrypt(plaintext)
def read_comment(ciphertext):
key = deterministic_random_key()
comment = challenge_10.AES_CBC(key, key).decrypt(ciphertext)
# Verify ASCII compliance. Any character >= 0x80 will throw an exception
# containing the plaintext.
try:
return comment.decode('ascii')
except UnicodeDecodeError:
error_msg = comment.decode('iso-8859-1')
raise Exception("Invalid Message: {}".format(error_msg)) from None
def get_ciphertext_and_iv():
key, iv = deterministic_random_key_and_iv()
ciphertext = challenge_10.AES_CBC(key, iv).encrypt(select_random_string())
return ciphertext, iv
def is_admin_comment(ciphertext):
key, iv = deterministic_random_key_and_iv()
plaintext = challenge_10.AES_CBC(key, iv).decrypt(ciphertext)
return b";admin=true;" in plaintext
def new_comment(user_input):
key, iv = deterministic_random_key_and_iv()
comment = comment_for(user_input)
return challenge_10.AES_CBC(key, iv).encrypt(comment)