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#
# Util/PEM.py : Privacy Enhanced Mail utilities
#
# ===================================================================
#
# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# 1. Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in
# the documentation and/or other materials provided with the
# distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
# ===================================================================
__all__ = ['encode', 'decode']
import re
from binascii import a2b_base64, b2a_base64, hexlify, unhexlify
from Crypto.Hash import MD5
from Crypto.Util.Padding import pad, unpad
from Crypto.Cipher import DES, DES3, AES
from Crypto.Protocol.KDF import PBKDF1
from Crypto.Random import get_random_bytes
from Crypto.Util.py3compat import tobytes, tostr
def encode(data, marker, passphrase=None, randfunc=None):
"""Encode a piece of binary data into PEM format.
Args:
data (byte string):
The piece of binary data to encode.
marker (string):
The marker for the PEM block (e.g. "PUBLIC KEY").
Note that there is no official master list for all allowed markers.
Still, you can refer to the OpenSSL_ source code.
passphrase (byte string):
If given, the PEM block will be encrypted. The key is derived from
the passphrase.
randfunc (callable):
Random number generation function; it accepts an integer N and returns
a byte string of random data, N bytes long. If not given, a new one is
instantiated.
Returns:
The PEM block, as a string.
.. _OpenSSL: https://github.com/openssl/openssl/blob/master/include/openssl/pem.h
"""
if randfunc is None:
randfunc = get_random_bytes
out = "-----BEGIN %s-----\n" % marker
if passphrase:
# We only support 3DES for encryption
salt = randfunc(8)
key = PBKDF1(passphrase, salt, 16, 1, MD5)
key += PBKDF1(key + passphrase, salt, 8, 1, MD5)
objenc = DES3.new(key, DES3.MODE_CBC, salt)
out += "Proc-Type: 4,ENCRYPTED\nDEK-Info: DES-EDE3-CBC,%s\n\n" %\
tostr(hexlify(salt).upper())
# Encrypt with PKCS#7 padding
data = objenc.encrypt(pad(data, objenc.block_size))
elif passphrase is not None:
raise ValueError("Empty password")
# Each BASE64 line can take up to 64 characters (=48 bytes of data)
# b2a_base64 adds a new line character!
chunks = [tostr(b2a_base64(data[i:i + 48]))
for i in range(0, len(data), 48)]
out += "".join(chunks)
out += "-----END %s-----" % marker
return out
def _EVP_BytesToKey(data, salt, key_len):
d = [ b'' ]
m = (key_len + 15 ) // 16
for _ in range(m):
nd = MD5.new(d[-1] + data + salt).digest()
d.append(nd)
return b"".join(d)[:key_len]
def decode(pem_data, passphrase=None):
"""Decode a PEM block into binary.
Args:
pem_data (string):
The PEM block.
passphrase (byte string):
If given and the PEM block is encrypted,
the key will be derived from the passphrase.
Returns:
A tuple with the binary data, the marker string, and a boolean to
indicate if decryption was performed.
Raises:
ValueError: if decoding fails, if the PEM file is encrypted and no passphrase has
been provided or if the passphrase is incorrect.
"""
# Verify Pre-Encapsulation Boundary
r = re.compile(r"\s*-----BEGIN (.*)-----\s+")
m = r.match(pem_data)
if not m:
raise ValueError("Not a valid PEM pre boundary")
marker = m.group(1)
# Verify Post-Encapsulation Boundary
r = re.compile(r"-----END (.*)-----\s*$")
m = r.search(pem_data)
if not m or m.group(1) != marker:
raise ValueError("Not a valid PEM post boundary")
# Removes spaces and slit on lines
lines = pem_data.replace(" ", '').split()
# Decrypts, if necessary
if lines[1].startswith('Proc-Type:4,ENCRYPTED'):
if not passphrase:
raise ValueError("PEM is encrypted, but no passphrase available")
DEK = lines[2].split(':')
if len(DEK) != 2 or DEK[0] != 'DEK-Info':
raise ValueError("PEM encryption format not supported.")
algo, salt = DEK[1].split(',')
salt = unhexlify(tobytes(salt))
padding = True
if algo == "DES-CBC":
key = _EVP_BytesToKey(passphrase, salt, 8)
objdec = DES.new(key, DES.MODE_CBC, salt)
elif algo == "DES-EDE3-CBC":
key = _EVP_BytesToKey(passphrase, salt, 24)
objdec = DES3.new(key, DES3.MODE_CBC, salt)
elif algo == "AES-128-CBC":
key = _EVP_BytesToKey(passphrase, salt[:8], 16)
objdec = AES.new(key, AES.MODE_CBC, salt)
elif algo == "AES-192-CBC":
key = _EVP_BytesToKey(passphrase, salt[:8], 24)
objdec = AES.new(key, AES.MODE_CBC, salt)
elif algo == "AES-256-CBC":
key = _EVP_BytesToKey(passphrase, salt[:8], 32)
objdec = AES.new(key, AES.MODE_CBC, salt)
elif algo.lower() == "id-aes256-gcm":
key = _EVP_BytesToKey(passphrase, salt[:8], 32)
objdec = AES.new(key, AES.MODE_GCM, nonce=salt)
padding = False
else:
raise ValueError("Unsupport PEM encryption algorithm (%s)." % algo)
lines = lines[2:]
else:
objdec = None
# Decode body
data = a2b_base64(''.join(lines[1:-1]))
enc_flag = False
if objdec:
if padding:
data = unpad(objdec.decrypt(data), objdec.block_size)
else:
# There is no tag, so we don't use decrypt_and_verify
data = objdec.decrypt(data)
enc_flag = True
return (data, marker, enc_flag)