← Back
Editing: PEM.py
# # 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)
Save File
Cancel