def decrypt(data, passphrase):
"""Decrypt a piece of data using a passphrase and *PBES2*.
The algorithm to use is automatically detected.
:Parameters:
data : byte string
The piece of data to decrypt.
passphrase : byte string
The passphrase to use for decrypting the data.
:Returns:
The decrypted data, as a binary string.
"""
enc_private_key_info = DerSequence().decode(data, nr_elements=2)
enc_algo = DerSequence().decode(enc_private_key_info[0])
encrypted_data = DerOctetString().decode(
enc_private_key_info[1]).payload
pbe_oid = DerObjectId().decode(enc_algo[0]).value
if pbe_oid != _OID_PBES2:
raise PbesError("Not a PBES2 object")
pbes2_params = DerSequence().decode(enc_algo[1], nr_elements=2)
### Key Derivation Function selection
kdf_info = DerSequence().decode(pbes2_params[0], nr_elements=2)
kdf_oid = DerObjectId().decode(kdf_info[0]).value
kdf_key_length = None
# We only support PBKDF2 or scrypt
if kdf_oid == _OID_PBKDF2:
pbkdf2_params = DerSequence().decode(kdf_info[1],
nr_elements=(2, 3, 4))
salt = DerOctetString().decode(pbkdf2_params[0]).payload
iteration_count = pbkdf2_params[1]
left = len(pbkdf2_params) - 2
idx = 2
if left > 0:
try:
kdf_key_length = pbkdf2_params[idx] - 0
left -= 1
idx += 1
except TypeError:
pass
# Default is HMAC-SHA1
pbkdf2_prf_oid = "1.2.840.113549.2.7"
if left > 0:
pbkdf2_prf_algo_id = DerSequence().decode(pbkdf2_params[idx])
pbkdf2_prf_oid = DerObjectId().decode(
pbkdf2_prf_algo_id[0]).value
elif kdf_oid == _OID_SCRYPT:
scrypt_params = DerSequence().decode(kdf_info[1],
nr_elements=(4, 5))
salt = DerOctetString().decode(scrypt_params[0]).payload
iteration_count, scrypt_r, scrypt_p = [
scrypt_params[x] for x in (1, 2, 3)
]
if len(scrypt_params) > 4:
kdf_key_length = scrypt_params[4]
else:
kdf_key_length = None
else:
raise PbesError("Unsupported PBES2 KDF")
### Cipher selection
enc_info = DerSequence().decode(pbes2_params[1])
enc_oid = DerObjectId().decode(enc_info[0]).value
if enc_oid == _OID_DES_EDE3_CBC:
# DES_EDE3_CBC
ciphermod = DES3
key_size = 24
elif enc_oid == _OID_AES128_CBC:
# AES128_CBC
ciphermod = AES
key_size = 16
elif enc_oid == _OID_AES192_CBC:
# AES192_CBC
ciphermod = AES
key_size = 24
elif enc_oid == _OID_AES256_CBC:
# AES256_CBC
ciphermod = AES
key_size = 32
else:
raise PbesError("Unsupported PBES2 cipher")
if kdf_key_length and kdf_key_length != key_size:
raise PbesError("Mismatch between PBES2 KDF parameters"
" and selected cipher")
IV = DerOctetString().decode(enc_info[1]).payload
# Create cipher
if kdf_oid == _OID_PBKDF2:
if pbkdf2_prf_oid == _OID_HMAC_SHA1:
hmac_hash_module = SHA1
elif pbkdf2_prf_oid == _OID_HMAC_SHA224:
hmac_hash_module = SHA224
elif pbkdf2_prf_oid == _OID_HMAC_SHA256:
hmac_hash_module = SHA256
elif pbkdf2_prf_oid == _OID_HMAC_SHA384:
hmac_hash_module = SHA384
elif pbkdf2_prf_oid == _OID_HMAC_SHA512:
hmac_hash_module = SHA512
else:
raise PbesError("Unsupported HMAC %s" % pbkdf2_prf_oid)
key = PBKDF2(passphrase,
salt,
key_size,
iteration_count,
hmac_hash_module=hmac_hash_module)
else:
key = scrypt(passphrase, salt, key_size, iteration_count, scrypt_r,
scrypt_p)
cipher = ciphermod.new(key, ciphermod.MODE_CBC, IV)
# Decrypt data
pt = cipher.decrypt(encrypted_data)
return unpad(pt, cipher.block_size)
def encrypt(data, passphrase, protection, prot_params=None, randfunc=None):
"""Encrypt a piece of data using a passphrase and *PBES2*.
:Parameters:
data : byte string
The piece of data to encrypt.
passphrase : byte string
The passphrase to use for encrypting the data.
protection : string
The identifier of the encryption algorithm to use.
The default value is '``PBKDF2WithHMAC-SHA1AndDES-EDE3-CBC``'.
prot_params : dictionary
Parameters of the protection algorithm.
+------------------+-----------------------------------------------+
| Key | Description |
+==================+===============================================+
| iteration_count | The KDF algorithm is repeated several times to|
| | slow down brute force attacks on passwords |
| | (called *N* or CPU/memory cost in scrypt). |
| | |
| | The default value for PBKDF2 is 1 000. |
| | The default value for scrypt is 16 384. |
+------------------+-----------------------------------------------+
| salt_size | Salt is used to thwart dictionary and rainbow |
| | attacks on passwords. The default value is 8 |
| | bytes. |
+------------------+-----------------------------------------------+
| block_size | *(scrypt only)* Memory-cost (r). The default |
| | value is 8. |
+------------------+-----------------------------------------------+
| parallelization | *(scrypt only)* CPU-cost (p). The default |
| | value is 1. |
+------------------+-----------------------------------------------+
randfunc : callable
Random number generation function; it should accept
a single integer N and return a string of random data,
N bytes long. If not specified, a new RNG will be
instantiated from ``crypto.Random``.
:Returns:
The encrypted data, as a binary string.
"""
if prot_params is None:
prot_params = {}
if randfunc is None:
randfunc = Random.new().read
if protection == 'PBKDF2WithHMAC-SHA1AndDES-EDE3-CBC':
key_size = 24
module = DES3
cipher_mode = DES3.MODE_CBC
enc_oid = _OID_DES_EDE3_CBC
elif protection in ('PBKDF2WithHMAC-SHA1AndAES128-CBC',
'scryptAndAES128-CBC'):
key_size = 16
module = AES
cipher_mode = AES.MODE_CBC
enc_oid = _OID_AES128_CBC
elif protection in ('PBKDF2WithHMAC-SHA1AndAES192-CBC',
'scryptAndAES192-CBC'):
key_size = 24
module = AES
cipher_mode = AES.MODE_CBC
enc_oid = _OID_AES192_CBC
elif protection in ('PBKDF2WithHMAC-SHA1AndAES256-CBC',
'scryptAndAES256-CBC'):
key_size = 32
module = AES
cipher_mode = AES.MODE_CBC
enc_oid = _OID_AES256_CBC
else:
raise ValueError("Unknown PBES2 mode")
# Get random data
iv = randfunc(module.block_size)
salt = randfunc(prot_params.get("salt_size", 8))
# Derive key from password
if protection.startswith('PBKDF2'):
count = prot_params.get("iteration_count", 1000)
key = PBKDF2(passphrase, salt, key_size, count)
kdf_info = DerSequence([
DerObjectId(_OID_PBKDF2), # PBKDF2
DerSequence([DerOctetString(salt),
DerInteger(count)])
])
else:
# It must be scrypt
count = prot_params.get("iteration_count", 16384)
scrypt_r = prot_params.get('block_size', 8)
scrypt_p = prot_params.get('parallelization', 1)
key = scrypt(passphrase, salt, key_size, count, scrypt_r, scrypt_p)
kdf_info = DerSequence([
DerObjectId(_OID_SCRYPT), # scrypt
DerSequence([
DerOctetString(salt),
DerInteger(count),
DerInteger(scrypt_r),
DerInteger(scrypt_p)
])
])
# Create cipher and use it
cipher = module.new(key, cipher_mode, iv)
encrypted_data = cipher.encrypt(pad(data, cipher.block_size))
enc_info = DerSequence([DerObjectId(enc_oid), DerOctetString(iv)])
# Result
enc_private_key_info = DerSequence([
# encryptionAlgorithm
DerSequence([
DerObjectId(_OID_PBES2),
DerSequence([kdf_info, enc_info]),
]),
DerOctetString(encrypted_data)
])
return enc_private_key_info.encode()
