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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 Cryptodome.Hash import MD5
+from Cryptodome.Util.Padding import pad, unpad
+from Cryptodome.Cipher import DES, DES3, AES
+from Cryptodome.Protocol.KDF import PBKDF1
+from Cryptodome.Random import get_random_bytes
+from Cryptodome.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)