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Many Cleanups to vault

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* Make is_encrypted_file handle both files opened in text and binary mode
  On python3, by default files are opened in text mode.  Since we know
  the encoding of vault files (and especially the header which is the
  first set of bytes) we can decide whether the file is an encrypted
  vault file in either case.
* Fix is_encrypted_file not resetting the file position
* Update is_encrypted_file to check that all the data in the file is ascii
* For is_encrypted_file(), add start_pos and count parameters
  This allows callers to specify reading vaulttext from the middle of
  a file if necessary.
* Combine VaultLib.encrypt() and VaultLib.encrypt_bytestring()
* Change vault's is_encrypted() to take either text or byte strings and to return False if any part of the data is non-ascii.
* Remove unnecessary use of six.b
* Vault Cipher: mark a few methods as private.
* VaultAES256._is_equal throws a TypeError if given non byte strings
* Make VaultAES256 methods that don't need self staticmethods and classmethods
* Mark VaultAES and is_encrypted as deprecated
* Get rid of VaultFile (unused and feature implemented in a different way)
* Normalize variable and parameter names on plaintext, ciphertext, vaulttext
* Normalize variable and parameter names on "b_" prefix when dealing with bytes
* Test changes:
  * Remove redundant tests( both checking the same byte string)
  * Fix use of format string without format operator
  * Enable vault editor tests on python3
  * Initialize the vault_cipher for VaultAES256 testing in setUp()
  * Make assertTrue and assertFalse take the actual method calls for
    better error messages.
  * Test that non-ascii byte strings compare correctly.
  * Test that unicode strings and ints raise TypeError

* Test-specific:
  * Removed test_methods_exist().  We only have one VaultLib so the
    implementation is the assurance that the methods exist. (Can use an abc for
    this if it changes).
  * Add tests for both byte string and text string input where the API takes either.
  * Convert "assert" to unittest assert functions or add a custom message where
    that will make failures easier to debug.
  * Move instantiating the VaultLib into setUp().
This commit is contained in:
Toshio Kuratomi 2016-09-13 07:30:17 -07:00
commit e70066a6f7
4 changed files with 383 additions and 366 deletions
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366
lib/ansible/parsing/vault/__init__.py
View file

@ -1,4 +1,6 @@
# (c) 2014, James Tanner <tanner.jc@gmail.com>
# (c) 2016, Adrian Likins <alikins@redhat.com>
# (c) 2016, Toshio Kuratomi <tkuratomi@ansible.com>
#
# Ansible is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
@ -25,7 +27,6 @@ import tempfile
import random
from io import BytesIO
from subprocess import call
from ansible.errors import AnsibleError
from hashlib import sha256
from binascii import hexlify
from binascii import unhexlify
@ -61,7 +62,9 @@ try:
except ImportError:
HAS_AES = False
from ansible.compat.six import PY3
from ansible.compat.six import PY3, binary_type
from ansible.compat.six.moves import zip
from ansible.errors import AnsibleError
from ansible.module_utils._text import to_bytes, to_text
try:
@ -84,14 +87,13 @@ except Exception as e:
import traceback
display.debug("Traceback from import of cryptography was {0}".format(traceback.format_exc()))
HAS_ANY_PBKDF2HMAC = HAS_PBKDF2 or HAS_PBKDF2HMAC
CRYPTO_UPGRADE = "ansible-vault requires a newer version of pycrypto than the one installed on your platform." \
" You may fix this with OS-specific commands such as: yum install python-devel; rpm -e --nodeps python-crypto; pip install pycrypto"
b_HEADER = b'$ANSIBLE_VAULT'
HEADER = '$ANSIBLE_VAULT'
CIPHER_WHITELIST = frozenset((u'AES', u'AES256'))
CIPHER_WRITE_WHITELIST = frozenset((u'AES256',))
# See also CIPHER_MAPPING at the bottom of the file which maps cipher strings
@ -108,32 +110,56 @@ class AnsibleVaultError(AnsibleError):
pass
def is_encrypted(b_data):
def is_encrypted(data):
""" Test if this is vault encrypted data blob
:arg data: a python2 str or a python3 'bytes' to test whether it is
recognized as vault encrypted data
:arg data: a byte or text string to test whether it is recognized as vault
encrypted data
:returns: True if it is recognized. Otherwise, False.
"""
try:
# Make sure we have a byte string and that it only contains ascii
# bytes.
b_data = to_bytes(to_text(data, encoding='ascii', errors='strict', nonstring='strict'), encoding='ascii', errors='strict')
except (UnicodeError, TypeError):
# The vault format is pure ascii so if we failed to encode to bytes
# via ascii we know that this is not vault data.
# Similarly, if it's not a string, it's not vault data
return False
if b_data.startswith(b_HEADER):
return True
return False
def is_encrypted_file(file_obj):
def is_encrypted_file(file_obj, start_pos=0, count=-1):
"""Test if the contents of a file obj are a vault encrypted data blob.
The data read from the file_obj is expected to be bytestrings (py2 'str' or
python3 'bytes'). This more or less expects 'utf-8' encoding.
:arg file_obj: A file object that will be read from.
:returns: True if the file is a vault file. Otherwise, False.
:kwarg start_pos: A byte offset in the file to start reading the header
from. Defaults to 0, the beginning of the file.
:kwarg count: Read up to this number of bytes from the file to determine
if it looks like encrypted vault data. The default is -1, read to the
end of file.
:returns: True if the file looks like a vault file. Otherwise, False.
"""
# read the header and reset the file stream to where it started
current_position = file_obj.tell()
b_header_part = file_obj.read(len(b_HEADER))
file_obj.seek(current_position)
return is_encrypted(b_header_part)
try:
file_obj.seek(start_pos)
vaulttext = file_obj.read(count)
try:
b_vaulttext = to_bytes(to_text(vaulttext, encoding='ascii', errors='strict'), encoding='ascii', errors='strict')
except (UnicodeError, TypeError):
# At present, vault files contain only ascii characters. The encoding is utf-8
# without BOM (for future expansion). If the header does not
# decode as ascii then we know we do not have proper vault
# encrypted data.
return False
finally:
file_obj.seek(current_position)
return is_encrypted(b_vaulttext)
class VaultLib:
@ -143,11 +169,11 @@ class VaultLib:
self.cipher_name = None
self.b_version = b'1.1'
# really b_data, but for compat
def is_encrypted(self, data):
@staticmethod
def is_encrypted(data):
""" Test if this is vault encrypted data
:arg data: a python2 utf-8 string or a python3 'bytes' to test whether it is
:arg data: a byte or text string or a python3 to test for whether it is
recognized as vault encrypted data
:returns: True if it is recognized. Otherwise, False.
"""
@ -155,36 +181,29 @@ class VaultLib:
# This could in the future, check to see if the data is a vault blob and
# is encrypted with a key associated with this vault
# instead of just checking the format.
display.deprecated(u'vault.VaultLib.is_encrypted is deprecated. Use vault.is_encrypted instead', version='2.4')
return is_encrypted(data)
def is_encrypted_file(self, file_obj):
@staticmethod
def is_encrypted_file(file_obj):
display.deprecated(u'vault.VaultLib.is_encrypted_file is deprecated. Use vault.is_encrypted_file instead', version='2.4')
return is_encrypted_file(file_obj)
def encrypt(self, data):
def encrypt(self, plaintext):
"""Vault encrypt a piece of data.
:arg data: a PY2 unicode string or PY3 string to encrypt.
:arg plaintext: a text or byte string to encrypt.
:returns: a utf-8 encoded byte str of encrypted data. The string
contains a header identifying this as vault encrypted data and
formatted to newline terminated lines of 80 characters. This is
suitable for dumping as is to a vault file.
The unicode or string passed in as data will encoded to UTF-8 before
encryption. If the a already encoded string or PY2 bytestring needs to
be encrypted, use encrypt_bytestring().
If the string passed in is a text string, it will be encoded to UTF-8
before encryption.
"""
plaintext = data
plaintext_bytes = plaintext.encode('utf-8')
b_plaintext = to_bytes(plaintext, errors='surrogate_or_strict')
return self.encrypt_bytestring(plaintext_bytes)
def encrypt_bytestring(self, plaintext_bytes):
'''Encrypt a PY2 bytestring.
Like encrypt(), except plaintext_bytes is not encoded to UTF-8
before encryption.'''
if self.is_encrypted(plaintext_bytes):
if is_encrypted(b_plaintext):
raise AnsibleError("input is already encrypted")
if not self.cipher_name or self.cipher_name not in CIPHER_WRITE_WHITELIST:
@ -197,32 +216,35 @@ class VaultLib:
this_cipher = Cipher()
# encrypt data
ciphertext_bytes = this_cipher.encrypt(plaintext_bytes, self.b_password)
b_ciphertext = this_cipher.encrypt(b_plaintext, self.b_password)
# format the data for output to the file
ciphertext_envelope = self._format_output(ciphertext_bytes)
return ciphertext_envelope
b_vaulttext = self._format_output(b_ciphertext)
return b_vaulttext
def decrypt(self, data, filename=None):
def decrypt(self, vaulttext, filename=None):
"""Decrypt a piece of vault encrypted data.
:arg data: a string to decrypt. Since vault encrypted data is an
:arg vaulttext: a string to decrypt. Since vault encrypted data is an
ascii text format this can be either a byte str or unicode string.
:kwarg filename: a filename that the data came from. This is only
used to make better error messages in case the data cannot be
decrypted.
:returns: a byte string containing the decrypted data
"""
b_data = to_bytes(data, errors='strict', encoding='utf-8')
b_vaulttext = to_bytes(vaulttext, errors='strict', encoding='utf-8')
if self.b_password is None:
raise AnsibleError("A vault password must be specified to decrypt data")
if not self.is_encrypted(b_data):
if not is_encrypted(b_vaulttext):
msg = "input is not vault encrypted data"
if filename:
msg += "%s is not a vault encrypted file" % filename
raise AnsibleError(msg)
# clean out header
b_data = self._split_header(b_data)
b_vaulttext = self._split_header(b_vaulttext)
# create the cipher object
cipher_class_name = u'Vault{0}'.format(self.cipher_name)
@ -233,20 +255,20 @@ class VaultLib:
else:
raise AnsibleError("{0} cipher could not be found".format(self.cipher_name))
# try to unencrypt data
b_data = this_cipher.decrypt(b_data, self.b_password)
if b_data is None:
# try to unencrypt vaulttext
b_plaintext = this_cipher.decrypt(b_vaulttext, self.b_password)
if b_plaintext is None:
msg = "Decryption failed"
if filename:
msg += " on %s" % filename
raise AnsibleError(msg)
return b_data
return b_plaintext
def _format_output(self, b_data):
def _format_output(self, b_ciphertext):
""" Add header and format to 80 columns
:arg b_data: the encrypted and hexlified data as a byte string
:arg b_vaulttext: the encrypted and hexlified data as a byte string
:returns: a byte str that should be dumped into a file. It's
formatted to 80 char columns and has the header prepended
"""
@ -254,38 +276,37 @@ class VaultLib:
if not self.cipher_name:
raise AnsibleError("the cipher must be set before adding a header")
b_header = HEADER.encode('utf-8')
header = b';'.join([b_header, self.b_version,
header = b';'.join([b_HEADER, self.b_version,
to_bytes(self.cipher_name,'utf-8', errors='strict')])
tmpdata = [header]
tmpdata += [b_data[i:i + 80] for i in range(0, len(b_data), 80)]
tmpdata += [b'']
tmpdata = b'\n'.join(tmpdata)
b_vaulttext = [header]
b_vaulttext += [b_ciphertext[i:i + 80] for i in range(0, len(b_ciphertext), 80)]
b_vaulttext += [b'']
b_vaulttext = b'\n'.join(b_vaulttext)
return tmpdata
return b_vaulttext
def _split_header(self, b_data):
"""Retrieve information about the Vault and clean the data
def _split_header(self, b_vaulttext):
"""Retrieve information about the Vault and clean the data
When data is saved, it has a header prepended and is formatted into 80
character lines. This method extracts the information from the header
and then removes the header and the inserted newlines. The string returned
is suitable for processing by the Cipher classes.
:arg b_data: byte str containing the data from a save file
:arg b_vaulttext: byte str containing the data from a save file
:returns: a byte str suitable for passing to a Cipher class's
decrypt() function.
"""
# used by decrypt
tmpdata = b_data.split(b'\n')
tmpheader = tmpdata[0].strip().split(b';')
b_tmpdata = b_vaulttext.split(b'\n')
b_tmpheader = b_tmpdata[0].strip().split(b';')
self.b_version = tmpheader[1].strip()
self.cipher_name = to_text(tmpheader[2].strip())
clean_data = b''.join(tmpdata[1:])
self.b_version = b_tmpheader[1].strip()
self.cipher_name = to_text(b_tmpheader[2].strip())
b_ciphertext = b''.join(b_tmpdata[1:])
return clean_data
return b_ciphertext
class VaultEditor:
@ -400,7 +421,7 @@ class VaultEditor:
# A file to be encrypted into a vaultfile could be any encoding
# so treat the contents as a byte string.
plaintext = self.read_data(filename)
ciphertext = self.vault.encrypt_bytestring(plaintext)
ciphertext = self.vault.encrypt(plaintext)
self.write_data(ciphertext, output_file or filename)
def decrypt_file(self, filename, output_file=None):
@ -533,47 +554,6 @@ class VaultEditor:
return editor
class VaultFile(object):
def __init__(self, password, filename):
self.password = password
self.filename = filename
if not os.path.isfile(self.filename):
raise AnsibleError("%s does not exist" % self.filename)
try:
self.filehandle = open(filename, "rb")
except Exception as e:
raise AnsibleError("Could not open %s: %s" % (self.filename, str(e)))
_, self.tmpfile = tempfile.mkstemp()
# TODO:
# __del__ can be problematic in python... For this use case, make
# VaultFile a context manager instead (implement __enter__ and __exit__)
def __del__(self):
self.filehandle.close()
os.unlink(self.tmpfile)
def is_encrypted(self):
return is_encrypted_file(self.filehandle)
def get_decrypted(self):
check_prereqs()
if self.is_encrypted():
tmpdata = self.filehandle.read()
this_vault = VaultLib(self.password)
dec_data = this_vault.decrypt(tmpdata)
if dec_data is None:
raise AnsibleError("Failed to decrypt: %s" % self.filename)
else:
self.tmpfile.write(dec_data)
return self.tmpfile
else:
return self.filename
########################################
# CIPHERS #
########################################
@ -591,76 +571,84 @@ class VaultAES:
if not HAS_AES:
raise AnsibleError(CRYPTO_UPGRADE)
def aes_derive_key_and_iv(self, password, salt, key_length, iv_length):
def _aes_derive_key_and_iv(self, b_password, b_salt, key_length, iv_length):
""" Create a key and an initialization vector """
d = d_i = b''
while len(d) < key_length + iv_length:
text = b''.join([d_i, password, salt])
d_i = to_bytes(md5(text).digest(), errors='strict')
d += d_i
b_d = b_di = b''
while len(b_d) < key_length + iv_length:
b_text = b''.join([b_di, b_password, b_salt])
b_di = to_bytes(md5(b_text).digest(), errors='strict')
b_d += b_di
key = d[:key_length]
iv = d[key_length:key_length+iv_length]
b_key = b_d[:key_length]
b_iv = b_d[key_length:key_length+iv_length]
return key, iv
return b_key, b_iv
def encrypt(self, data, password, key_length=32):
def encrypt(self, b_plaintext, b_password, key_length=32):
""" Read plaintext data from in_file and write encrypted to out_file """
raise AnsibleError("Encryption disabled for deprecated VaultAES class")
def decrypt(self, data, password, key_length=32):
def decrypt(self, b_vaulttext, b_password, key_length=32):
""" Read encrypted data from in_file and write decrypted to out_file """
""" Decrypt the given data and return it
:arg b_data: A byte string containing the encrypted data
:arg b_password: A byte string containing the encryption password
:arg key_length: Length of the key
:returns: A byte string containing the decrypted data
"""
display.deprecated(u'The VaultAES format is insecure and has been'
' deprecated since Ansible-1.5. Use vault rekey FILENAME to'
' switch to the newer VaultAES256 format', version='2.3')
# http://stackoverflow.com/a/14989032
data = unhexlify(data)
b_ciphertext = unhexlify(b_vaulttext)
in_file = BytesIO(data)
in_file = BytesIO(b_ciphertext)
in_file.seek(0)
out_file = BytesIO()
bs = AES.block_size
tmpsalt = in_file.read(bs)
salt = tmpsalt[len(b'Salted__'):]
key, iv = self.aes_derive_key_and_iv(password, salt, key_length, bs)
cipher = AES.new(key, AES.MODE_CBC, iv)
next_chunk = b''
b_tmpsalt = in_file.read(bs)
b_salt = b_tmpsalt[len(b'Salted__'):]
b_key, b_iv = self._aes_derive_key_and_iv(b_password, b_salt, key_length, bs)
cipher = AES.new(b_key, AES.MODE_CBC, b_iv)
b_next_chunk = b''
finished = False
while not finished:
chunk, next_chunk = next_chunk, cipher.decrypt(in_file.read(1024 * bs))
if len(next_chunk) == 0:
b_chunk, b_next_chunk = b_next_chunk, cipher.decrypt(in_file.read(1024 * bs))
if len(b_next_chunk) == 0:
if PY3:
padding_length = chunk[-1]
padding_length = b_chunk[-1]
else:
padding_length = ord(chunk[-1])
padding_length = ord(b_chunk[-1])
chunk = chunk[:-padding_length]
b_chunk = b_chunk[:-padding_length]
finished = True
out_file.write(chunk)
out_file.write(b_chunk)
out_file.flush()
# reset the stream pointer to the beginning
out_file.seek(0)
out_data = out_file.read()
b_out_data = out_file.read()
out_file.close()
# split out sha and verify decryption
split_data = out_data.split(b"\n", 1)
this_sha = split_data[0]
this_data = split_data[1]
test_sha = to_bytes(sha256(this_data).hexdigest())
b_split_data = b_out_data.split(b"\n", 1)
b_this_sha = b_split_data[0]
b_plaintext = b_split_data[1]
b_test_sha = to_bytes(sha256(b_plaintext).hexdigest())
if this_sha != test_sha:
if b_this_sha != b_test_sha:
raise AnsibleError("Decryption failed")
return this_data
return b_plaintext
class VaultAES256:
@ -678,17 +666,19 @@ class VaultAES256:
check_prereqs()
def create_key(self, password, salt, keylength, ivlength):
@staticmethod
def _create_key(b_password, b_salt, keylength, ivlength):
hash_function = SHA256
# make two keys and one iv
pbkdf2_prf = lambda p, s: HMAC.new(p, s, hash_function).digest()
derivedkey = PBKDF2(password, salt, dkLen=(2 * keylength) + ivlength,
b_derivedkey = PBKDF2(b_password, b_salt, dkLen=(2 * keylength) + ivlength,
count=10000, prf=pbkdf2_prf)
return derivedkey
return b_derivedkey
def gen_key_initctr(self, password, salt):
@classmethod
def _gen_key_initctr(cls, b_password, b_salt):
# 16 for AES 128, 32 for AES256
keylength = 32
@ -700,79 +690,80 @@ class VaultAES256:
kdf = PBKDF2HMAC(
algorithm=c_SHA256(),
length=2 * keylength + ivlength,
salt=salt,
salt=b_salt,
iterations=10000,
backend=backend)
derivedkey = kdf.derive(password)
b_derivedkey = kdf.derive(b_password)
else:
derivedkey = self.create_key(password, salt, keylength, ivlength)
b_derivedkey = cls._create_key(b_password, b_salt, keylength, ivlength)
key1 = derivedkey[:keylength]
key2 = derivedkey[keylength:(keylength * 2)]
iv = derivedkey[(keylength * 2):(keylength * 2) + ivlength]
b_key1 = b_derivedkey[:keylength]
b_key2 = b_derivedkey[keylength:(keylength * 2)]
b_iv = b_derivedkey[(keylength * 2):(keylength * 2) + ivlength]
return key1, key2, hexlify(iv)
return b_key1, b_key2, hexlify(b_iv)
def encrypt(self, data, password):
salt = os.urandom(32)
key1, key2, iv = self.gen_key_initctr(password, salt)
def encrypt(self, b_plaintext, b_password):
b_salt = os.urandom(32)
b_key1, b_key2, b_iv = self._gen_key_initctr(b_password, b_salt)
# PKCS#7 PAD DATA http://tools.ietf.org/html/rfc5652#section-6.3
bs = AES.block_size
padding_length = (bs - len(data) % bs) or bs
data += to_bytes(padding_length * chr(padding_length), encoding='ascii', errors='strict')
padding_length = (bs - len(b_plaintext) % bs) or bs
b_plaintext += to_bytes(padding_length * chr(padding_length), encoding='ascii', errors='strict')
# COUNTER.new PARAMETERS
# 1) nbits (integer) - Length of the counter, in bits.
# 2) initial_value (integer) - initial value of the counter. "iv" from gen_key_initctr
# 2) initial_value (integer) - initial value of the counter. "iv" from _gen_key_initctr
ctr = Counter.new(128, initial_value=int(iv, 16))
ctr = Counter.new(128, initial_value=int(b_iv, 16))
# AES.new PARAMETERS
# 1) AES key, must be either 16, 24, or 32 bytes long -- "key" from gen_key_initctr
# 1) AES key, must be either 16, 24, or 32 bytes long -- "key" from _gen_key_initctr
# 2) MODE_CTR, is the recommended mode
# 3) counter=<CounterObject>
cipher = AES.new(key1, AES.MODE_CTR, counter=ctr)
cipher = AES.new(b_key1, AES.MODE_CTR, counter=ctr)
# ENCRYPT PADDED DATA
cryptedData = cipher.encrypt(data)
b_ciphertext = cipher.encrypt(b_plaintext)
# COMBINE SALT, DIGEST AND DATA
hmac = HMAC.new(key2, cryptedData, SHA256)
message = b'\n'.join([hexlify(salt), to_bytes(hmac.hexdigest()), hexlify(cryptedData)])
message = hexlify(message)
return message
hmac = HMAC.new(b_key2, b_ciphertext, SHA256)
b_vaulttext = b'\n'.join([hexlify(b_salt), to_bytes(hmac.hexdigest()), hexlify(b_ciphertext)])
b_vaulttext = hexlify(b_vaulttext)
return b_vaulttext
def decrypt(self, data, password):
def decrypt(self, b_vaulttext, b_password):
# SPLIT SALT, DIGEST, AND DATA
data = unhexlify(data)
salt, cryptedHmac, cryptedData = data.split(b"\n", 2)
salt = unhexlify(salt)
cryptedData = unhexlify(cryptedData)
key1, key2, iv = self.gen_key_initctr(password, salt)
b_vaulttext = unhexlify(b_vaulttext)
b_salt, b_cryptedHmac, b_ciphertext = b_vaulttext.split(b"\n", 2)
b_salt = unhexlify(b_salt)
b_ciphertext = unhexlify(b_ciphertext)
b_key1, b_key2, b_iv = self._gen_key_initctr(b_password, b_salt)
# EXIT EARLY IF DIGEST DOESN'T MATCH
hmacDecrypt = HMAC.new(key2, cryptedData, SHA256)
if not self.is_equal(cryptedHmac, to_bytes(hmacDecrypt.hexdigest())):
hmacDecrypt = HMAC.new(b_key2, b_ciphertext, SHA256)
if not self._is_equal(b_cryptedHmac, to_bytes(hmacDecrypt.hexdigest())):
return None
# SET THE COUNTER AND THE CIPHER
ctr = Counter.new(128, initial_value=int(iv, 16))
cipher = AES.new(key1, AES.MODE_CTR, counter=ctr)
ctr = Counter.new(128, initial_value=int(b_iv, 16))
cipher = AES.new(b_key1, AES.MODE_CTR, counter=ctr)
# DECRYPT PADDED DATA
decryptedData = cipher.decrypt(cryptedData)
b_plaintext = cipher.decrypt(b_ciphertext)
# UNPAD DATA
try:
padding_length = ord(decryptedData[-1])
except TypeError:
padding_length = decryptedData[-1]
if PY3:
padding_length = b_plaintext[-1]
else:
padding_length = ord(b_plaintext[-1])
decryptedData = decryptedData[:-padding_length]
return decryptedData
b_plaintext = b_plaintext[:-padding_length]
return b_plaintext
def is_equal(self, a, b):
@staticmethod
def _is_equal(b_a, b_b):
"""
Comparing 2 byte arrrays in constant time
to avoid timing attacks.
@ -780,16 +771,19 @@ class VaultAES256:
It would be nice if there was a library for this but
hey.
"""
if not (isinstance(b_a, binary_type) and isinstance(b_b, binary_type)):
raise TypeError('_is_equal can only be used to compare two byte strings')
# http://codahale.com/a-lesson-in-timing-attacks/
if len(a) != len(b):
if len(b_a) != len(b_b):
return False
result = 0
for x, y in zip(a, b):
for b_x, b_y in zip(b_a, b_b):
if PY3:
result |= x ^ y
result |= b_x ^ b_y
else:
result |= ord(x) ^ ord(y)
result |= ord(b_x) ^ ord(b_y)
return result == 0