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# -*- coding: ascii -*-
#
# Util/PEM.py : Privacy Enhanced Mail utilities
#
# ===================================================================
# The contents of this file are dedicated to the public domain. To
# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
# non-exclusive license to exercise all rights associated with the
# contents of this file for any purpose whatsoever.
# No rights are reserved.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
# ===================================================================
"""Set of functions for encapsulating data according to the PEM format.
PEM (Privacy Enhanced Mail) was an IETF standard for securing emails via a
Public Key Infrastructure. It is specified in RFC 1421-1424.
Even though it has been abandoned, the simple message encapsulation it defined
is still widely used today for encoding *binary* cryptographic objects like
keys and certificates into text.
"""
__all__ = ['encode', 'decode']
import sys
if sys.version_info[0] == 2 and sys.version_info[1] == 1:
from Crypto.Util.py21compat import *
from Crypto.Util.py3compat import *
import re
from binascii import hexlify, unhexlify, a2b_base64, b2a_base64
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
def encode(data, marker, passphrase=None, randfunc=None):
"""Encode a piece of binary data into PEM format.
:Parameters:
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: http://cvs.openssl.org/fileview?f=openssl/crypto/pem/pem.h&v=1.66.2.1.4.2
"""
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))
# 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 decode(pem_data, passphrase=None):
"""Decode a PEM block into binary.
:Parameters:
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("\s*-----BEGIN (.*)-----\n")
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("-----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))
if algo == "DES-CBC":
# This is EVP_BytesToKey in OpenSSL
key = PBKDF1(passphrase, salt, 8, 1, MD5)
objdec = DES.new(key, DES.MODE_CBC, salt)
elif algo == "DES-EDE3-CBC":
# Note that EVP_BytesToKey is note exactly the same as PBKDF1
key = PBKDF1(passphrase, salt, 16, 1, MD5)
key += PBKDF1(key + passphrase, salt, 8, 1, MD5)
objdec = DES3.new(key, DES3.MODE_CBC, salt)
elif algo == "AES-128-CBC":
key = PBKDF1(passphrase, salt[:8], 16, 1, MD5)
objdec = AES.new(key, AES.MODE_CBC, salt)
else:
raise ValueError("Unsupport PEM encryption algorithm.")
lines = lines[2:]
else:
objdec = None
# Decode body
data = a2b_base64(b(''.join(lines[1:-1])))
enc_flag = False
if objdec:
data = unpad(objdec.decrypt(data), objdec.block_size)
enc_flag = True
return (data, marker, enc_flag)
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