rsa_source/rsa/bigfile.py

   1 # -*- coding: utf-8 -*-
   2 #
   3 #  Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
   4 #
   5 #  Licensed under the Apache License, Version 2.0 (the "License");
   6 #  you may not use this file except in compliance with the License.
   7 #  You may obtain a copy of the License at
   8 #
   9 #      http://www.apache.org/licenses/LICENSE-2.0
  10 #
  11 #  Unless required by applicable law or agreed to in writing, software
  12 #  distributed under the License is distributed on an "AS IS" BASIS,
  13 #  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14 #  See the License for the specific language governing permissions and
  15 #  limitations under the License.
  16 '''Large file support
  17
  18     - break a file into smaller blocks, and encrypt them, and store the
  19       encrypted blocks in another file.
  20
  21     - take such an encrypted files, decrypt its blocks, and reconstruct the
  22       original file.
  23
  24 The encrypted file format is as follows, where || denotes byte concatenation:
  25
  26     FILE := VERSION || BLOCK || BLOCK ...
  27
  28     BLOCK := LENGTH || DATA
  29
  30     LENGTH := varint-encoded length of the subsequent data. Varint comes from
  31     Google Protobuf, and encodes an integer into a variable number of bytes.
  32     Each byte uses the 7 lowest bits to encode the value. The highest bit set
  33     to 1 indicates the next byte is also part of the varint. The last byte will
  34     have this bit set to 0.
  35
  36 This file format is called the VARBLOCK format, in line with the varint format
  37 used to denote the block sizes.
  38
  39 '''
  40
  41 from rsa import key, common, pkcs1, varblock
  42
  43 def encrypt_bigfile(infile, outfile, pub_key):
  44     '''Encrypts a file, writing it to 'outfile' in VARBLOCK format.
  45
  46     :param infile: file-like object to read the cleartext from
  47     :param outfile: file-like object to write the crypto in VARBLOCK format to
  48     :param pub_key: :py:class:`rsa.PublicKey` to encrypt with
  49
  50     '''
  51
  52     if not isinstance(pub_key, key.PublicKey):
  53         raise TypeError('Public key required, but got %r' % pub_key)
  54
  55     key_bytes = common.bit_size(pub_key.n) // 8
  56     blocksize = key_bytes - 11 # keep space for PKCS#1 padding
  57
  58     # Write the version number to the VARBLOCK file
  59     outfile.write(chr(varblock.VARBLOCK_VERSION))
  60
  61     # Encrypt and write each block
  62     for block in varblock.yield_fixedblocks(infile, blocksize):
  63         crypto = pkcs1.encrypt(block, pub_key)
  64
  65         varblock.write_varint(outfile, len(crypto))
  66         outfile.write(crypto)
  67
  68 def decrypt_bigfile(infile, outfile, priv_key):
  69     '''Decrypts an encrypted VARBLOCK file, writing it to 'outfile'
  70
  71     :param infile: file-like object to read the crypto in VARBLOCK format from
  72     :param outfile: file-like object to write the cleartext to
  73     :param priv_key: :py:class:`rsa.PrivateKey` to decrypt with
  74
  75     '''
  76
  77     if not isinstance(priv_key, key.PrivateKey):
  78         raise TypeError('Private key required, but got %r' % priv_key)
  79
  80     for block in varblock.yield_varblocks(infile):
  81         cleartext = pkcs1.decrypt(block, priv_key)
  82         outfile.write(cleartext)
  83
  84 __all__ = ['encrypt_bigfile', 'decrypt_bigfile']
  85