Symmetric encryption in pure Python (Blowfish)

For a project at work, it became obvious that I would need to implement some form of partial encryption between hosts in a self-configuring network. Nothing super-extreme, of course, since all traffic will exist within a closed environment; I just need enough protection to prevent casual observers from finding out enough about the protocol to inject malicious packets and provide some simple handshaking between the components of the system.

Blowfish came to mind as a good scheme for handling this (each host and operator can be considered sufficiently secure, so sharing an application-specific pass-phrase via config-file is an acceptable solution), and a small amount of Googling turned up http://ivoras.sharanet.org/projects/blowfish.html (based on http://felipetonello.com/scripts/python/blowfish.txt, though I doubt that’s the original site), which I ended up using as the basis for my implementation. Actually, ‘basis’ isn’t the right word, since I didn’t change any logic at all. Rather, I just replaced the more antiquated data-types and access methods with more modern equivalents, restructured the layout, and sought to bring things more in line with PEP 8. The result being a slightly faster, leaner implementation that’s a bit more readable.

My code, with an identical interface to Ivan Voras’s version, dual-licensed under the GPLv1 and Artistic Licenses, like the original, is reproduced below:

[python]
#!/usr/bin/env python
# -*- coding: utf-8 -*-

# blowfish.py
# Copyright (C) 2002 Michael Gilfix <mgilfix@eecs.tufts.edu>
#
# This module is open source; you can redistribute it and/or
# modify it under the terms of the GPL or Artistic License.
# These licenses are available at http://www.opensource.org
#
# This software must be used and distributed in accordance
# with the law. The author claims no liability for its
# misuse.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#

# This software was modified by Ivan Voras: CTR cipher mode of
# operation was added, together with testing and example code.
# These changes are (c) 2007./08. Ivan Voras <ivoras@gmail.com>
# These changes can be used, modified ad distributed under the
# GPL or Artistic License, the same as the original module.
# All disclaimers of warranty from the original module also
# apply to these changes.

# Further modifications by Neil Tallim <flan@uguu.ca> to make use
# of more modern Python practises and features, improving
# performance and, in this maintainer’s opinion, readability.
#
# New changes implemented (and copyrighted, I suppose),
# June 13, 2010, subject to the terms of the original module.
"""
Blowfish Encryption

This module is a pure python implementation of Bruce Schneier’s
encryption scheme ‘Blowfish’. Blowish is a 16-round Feistel Network
cipher and offers substantial speed gains over DES.

The key is a string of length anywhere between 64 and 448 bits, or
equivalently 8 and 56 bytes. The encryption and decryption functions operate
on 64-bit blocks, or 8-byte strings.
"""
import array
import struct

class Blowfish:
"""
Implements the encryption and decryption functionality of the Blowfish
cipher, as well as CTR processing for arbitrary-length strings.
"""
# Key restrictions
KEY_MIN_LEN = 8 #64 bits
KEY_MAX_LEN = 56 #448 bits

# Cipher directions
ENCRYPT = 0
DECRYPT = 1

# For _round()
_MODULUS = 2L ** 32

# CTR constants
_BLOCK_SIZE = 8

def __init__(self, key):
"""
Creates an instance of blowfish using ‘key’ as the encryption key.

Key is a string of bytes, used to seed calculations.
Once the instance of the object is created, the key is no longer necessary.
"""
if not self.KEY_MIN_LEN <= len(key) <= self.KEY_MAX_LEN:
raise ValueError("Attempted to initialize Blowfish cipher with key of invalid length: %(len)i" % {
‘len’: len(key),
})

self._p_boxes = array.array(‘I’, [
0x243F6A88, 0x85A308D3, 0x13198A2E, 0x03707344,
0xA4093822, 0x299F31D0, 0x082EFA98, 0xEC4E6C89,
0x452821E6, 0x38D01377, 0xBE5466CF, 0x34E90C6C,
0xC0AC29B7, 0xC97C50DD, 0x3F84D5B5, 0xB5470917,
0x9216D5D9, 0x8979FB1B
])

self._s_boxes = (
array.array(‘I’, [
0xD1310BA6, 0x98DFB5AC, 0x2FFD72DB, 0xD01ADFB7,
0xB8E1AFED, 0x6A267E96, 0xBA7C9045, 0xF12C7F99,
0x24A19947, 0xB3916CF7, 0x0801F2E2, 0x858EFC16,
0x636920D8, 0x71574E69, 0xA458FEA3, 0xF4933D7E,
0x0D95748F, 0x728EB658, 0x718BCD58, 0x82154AEE,
0x7B54A41D, 0xC25A59B5, 0x9C30D539, 0x2AF26013,
0xC5D1B023, 0x286085F0, 0xCA417918, 0xB8DB38EF,
0x8E79DCB0, 0x603A180E, 0x6C9E0E8B, 0xB01E8A3E,
0xD71577C1, 0xBD314B27, 0x78AF2FDA, 0x55605C60,
0xE65525F3, 0xAA55AB94, 0x57489862, 0x63E81440,
0x55CA396A, 0x2AAB10B6, 0xB4CC5C34, 0x1141E8CE,
0xA15486AF, 0x7C72E993, 0xB3EE1411, 0x636FBC2A,
0x2BA9C55D, 0x741831F6, 0xCE5C3E16, 0x9B87931E,
0xAFD6BA33, 0x6C24CF5C, 0x7A325381, 0x28958677,
0x3B8F4898, 0x6B4BB9AF, 0xC4BFE81B, 0x66282193,
0x61D809CC, 0xFB21A991, 0x487CAC60, 0x5DEC8032,
0xEF845D5D, 0xE98575B1, 0xDC262302, 0xEB651B88,
0x23893E81, 0xD396ACC5, 0x0F6D6FF3, 0x83F44239,
0x2E0B4482, 0xA4842004, 0x69C8F04A, 0x9E1F9B5E,
0x21C66842, 0xF6E96C9A, 0x670C9C61, 0xABD388F0,
0x6A51A0D2, 0xD8542F68, 0x960FA728, 0xAB5133A3,
0x6EEF0B6C, 0x137A3BE4, 0xBA3BF050, 0x7EFB2A98,
0xA1F1651D, 0x39AF0176, 0x66CA593E, 0x82430E88,
0x8CEE8619, 0x456F9FB4, 0x7D84A5C3, 0x3B8B5EBE,
0xE06F75D8, 0x85C12073, 0x401A449F, 0x56C16AA6,
0x4ED3AA62, 0x363F7706, 0x1BFEDF72, 0x429B023D,
0x37D0D724, 0xD00A1248, 0xDB0FEAD3, 0x49F1C09B,
0x075372C9, 0x80991B7B, 0x25D479D8, 0xF6E8DEF7,
0xE3FE501A, 0xB6794C3B, 0x976CE0BD, 0x04C006BA,
0xC1A94FB6, 0x409F60C4, 0x5E5C9EC2, 0x196A2463,
0x68FB6FAF, 0x3E6C53B5, 0x1339B2EB, 0x3B52EC6F,
0x6DFC511F, 0x9B30952C, 0xCC814544, 0xAF5EBD09,
0xBEE3D004, 0xDE334AFD, 0x660F2807, 0x192E4BB3,
0xC0CBA857, 0x45C8740F, 0xD20B5F39, 0xB9D3FBDB,
0x5579C0BD, 0x1A60320A, 0xD6A100C6, 0x402C7279,
0x679F25FE, 0xFB1FA3CC, 0x8EA5E9F8, 0xDB3222F8,
0x3C7516DF, 0xFD616B15, 0x2F501EC8, 0xAD0552AB,
0x323DB5FA, 0xFD238760, 0x53317B48, 0x3E00DF82,
0x9E5C57BB, 0xCA6F8CA0, 0x1A87562E, 0xDF1769DB,
0xD542A8F6, 0x287EFFC3, 0xAC6732C6, 0x8C4F5573,
0x695B27B0, 0xBBCA58C8, 0xE1FFA35D, 0xB8F011A0,
0x10FA3D98, 0xFD2183B8, 0x4AFCB56C, 0x2DD1D35B,
0x9A53E479, 0xB6F84565, 0xD28E49BC, 0x4BFB9790,
0xE1DDF2DA, 0xA4CB7E33, 0x62FB1341, 0xCEE4C6E8,
0xEF20CADA, 0x36774C01, 0xD07E9EFE, 0x2BF11FB4,
0x95DBDA4D, 0xAE909198, 0xEAAD8E71, 0x6B93D5A0,
0xD08ED1D0, 0xAFC725E0, 0x8E3C5B2F, 0x8E7594B7,
0x8FF6E2FB, 0xF2122B64, 0x8888B812, 0x900DF01C,
0x4FAD5EA0, 0x688FC31C, 0xD1CFF191, 0xB3A8C1AD,
0x2F2F2218, 0xBE0E1777, 0xEA752DFE, 0x8B021FA1,
0xE5A0CC0F, 0xB56F74E8, 0x18ACF3D6, 0xCE89E299,
0xB4A84FE0, 0xFD13E0B7, 0x7CC43B81, 0xD2ADA8D9,
0x165FA266, 0x80957705, 0x93CC7314, 0x211A1477,
0xE6AD2065, 0x77B5FA86, 0xC75442F5, 0xFB9D35CF,
0xEBCDAF0C, 0x7B3E89A0, 0xD6411BD3, 0xAE1E7E49,
0x00250E2D, 0x2071B35E, 0x226800BB, 0x57B8E0AF,
0x2464369B, 0xF009B91E, 0x5563911D, 0x59DFA6AA,
0x78C14389, 0xD95A537F, 0x207D5BA2, 0x02E5B9C5,
0x83260376, 0x6295CFA9, 0x11C81968, 0x4E734A41,
0xB3472DCA, 0x7B14A94A, 0x1B510052, 0x9A532915,
0xD60F573F, 0xBC9BC6E4, 0x2B60A476, 0x81E67400,
0x08BA6FB5, 0x571BE91F, 0xF296EC6B, 0x2A0DD915,
0xB6636521, 0xE7B9F9B6, 0xFF34052E, 0xC5855664,
0x53B02D5D, 0xA99F8FA1, 0x08BA4799, 0x6E85076A
]),
array.array(‘I’, [
0x4B7A70E9, 0xB5B32944, 0xDB75092E, 0xC4192623,
0xAD6EA6B0, 0x49A7DF7D, 0x9CEE60B8, 0x8FEDB266,
0xECAA8C71, 0x699A17FF, 0x5664526C, 0xC2B19EE1,
0x193602A5, 0x75094C29, 0xA0591340, 0xE4183A3E,
0x3F54989A, 0x5B429D65, 0x6B8FE4D6, 0x99F73FD6,
0xA1D29C07, 0xEFE830F5, 0x4D2D38E6, 0xF0255DC1,
0x4CDD2086, 0x8470EB26, 0x6382E9C6, 0x021ECC5E,
0x09686B3F, 0x3EBAEFC9, 0x3C971814, 0x6B6A70A1,
0x687F3584, 0x52A0E286, 0xB79C5305, 0xAA500737,
0x3E07841C, 0x7FDEAE5C, 0x8E7D44EC, 0x5716F2B8,
0xB03ADA37, 0xF0500C0D, 0xF01C1F04, 0x0200B3FF,
0xAE0CF51A, 0x3CB574B2, 0x25837A58, 0xDC0921BD,
0xD19113F9, 0x7CA92FF6, 0x94324773, 0x22F54701,
0x3AE5E581, 0x37C2DADC, 0xC8B57634, 0x9AF3DDA7,
0xA9446146, 0x0FD0030E, 0xECC8C73E, 0xA4751E41,
0xE238CD99, 0x3BEA0E2F, 0x3280BBA1, 0x183EB331,
0x4E548B38, 0x4F6DB908, 0x6F420D03, 0xF60A04BF,
0x2CB81290, 0x24977C79, 0x5679B072, 0xBCAF89AF,
0xDE9A771F, 0xD9930810, 0xB38BAE12, 0xDCCF3F2E,
0x5512721F, 0x2E6B7124, 0x501ADDE6, 0x9F84CD87,
0x7A584718, 0x7408DA17, 0xBC9F9ABC, 0xE94B7D8C,
0xEC7AEC3A, 0xDB851DFA, 0x63094366, 0xC464C3D2,
0xEF1C1847, 0x3215D908, 0xDD433B37, 0x24C2BA16,
0x12A14D43, 0x2A65C451, 0x50940002, 0x133AE4DD,
0x71DFF89E, 0x10314E55, 0x81AC77D6, 0x5F11199B,
0x043556F1, 0xD7A3C76B, 0x3C11183B, 0x5924A509,
0xF28FE6ED, 0x97F1FBFA, 0x9EBABF2C, 0x1E153C6E,
0x86E34570, 0xEAE96FB1, 0x860E5E0A, 0x5A3E2AB3,
0x771FE71C, 0x4E3D06FA, 0x2965DCB9, 0x99E71D0F,
0x803E89D6, 0x5266C825, 0x2E4CC978, 0x9C10B36A,
0xC6150EBA, 0x94E2EA78, 0xA5FC3C53, 0x1E0A2DF4,
0xF2F74EA7, 0x361D2B3D, 0x1939260F, 0x19C27960,
0x5223A708, 0xF71312B6, 0xEBADFE6E, 0xEAC31F66,
0xE3BC4595, 0xA67BC883, 0xB17F37D1, 0x018CFF28,
0xC332DDEF, 0xBE6C5AA5, 0x65582185, 0x68AB9802,
0xEECEA50F, 0xDB2F953B, 0x2AEF7DAD, 0x5B6E2F84,
0x1521B628, 0x29076170, 0xECDD4775, 0x619F1510,
0x13CCA830, 0xEB61BD96, 0x0334FE1E, 0xAA0363CF,
0xB5735C90, 0x4C70A239, 0xD59E9E0B, 0xCBAADE14,
0xEECC86BC, 0x60622CA7, 0x9CAB5CAB, 0xB2F3846E,
0x648B1EAF, 0x19BDF0CA, 0xA02369B9, 0x655ABB50,
0x40685A32, 0x3C2AB4B3, 0x319EE9D5, 0xC021B8F7,
0x9B540B19, 0x875FA099, 0x95F7997E, 0x623D7DA8,
0xF837889A, 0x97E32D77, 0x11ED935F, 0x16681281,
0x0E358829, 0xC7E61FD6, 0x96DEDFA1, 0x7858BA99,
0x57F584A5, 0x1B227263, 0x9B83C3FF, 0x1AC24696,
0xCDB30AEB, 0x532E3054, 0x8FD948E4, 0x6DBC3128,
0x58EBF2EF, 0x34C6FFEA, 0xFE28ED61, 0xEE7C3C73,
0x5D4A14D9, 0xE864B7E3, 0x42105D14, 0x203E13E0,
0x45EEE2B6, 0xA3AAABEA, 0xDB6C4F15, 0xFACB4FD0,
0xC742F442, 0xEF6ABBB5, 0x654F3B1D, 0x41CD2105,
0xD81E799E, 0x86854DC7, 0xE44B476A, 0x3D816250,
0xCF62A1F2, 0x5B8D2646, 0xFC8883A0, 0xC1C7B6A3,
0x7F1524C3, 0x69CB7492, 0x47848A0B, 0x5692B285,
0x095BBF00, 0xAD19489D, 0x1462B174, 0x23820E00,
0x58428D2A, 0x0C55F5EA, 0x1DADF43E, 0x233F7061,
0x3372F092, 0x8D937E41, 0xD65FECF1, 0x6C223BDB,
0x7CDE3759, 0xCBEE7460, 0x4085F2A7, 0xCE77326E,
0xA6078084, 0x19F8509E, 0xE8EFD855, 0x61D99735,
0xA969A7AA, 0xC50C06C2, 0x5A04ABFC, 0x800BCADC,
0x9E447A2E, 0xC3453484, 0xFDD56705, 0x0E1E9EC9,
0xDB73DBD3, 0x105588CD, 0x675FDA79, 0xE3674340,
0xC5C43465, 0x713E38D8, 0x3D28F89E, 0xF16DFF20,
0x153E21E7, 0x8FB03D4A, 0xE6E39F2B, 0xDB83ADF7
]),
array.array(‘I’, [
0xE93D5A68, 0x948140F7, 0xF64C261C, 0x94692934,
0x411520F7, 0x7602D4F7, 0xBCF46B2E, 0xD4A20068,
0xD4082471, 0x3320F46A, 0x43B7D4B7, 0x500061AF,
0x1E39F62E, 0x97244546, 0x14214F74, 0xBF8B8840,
0x4D95FC1D, 0x96B591AF, 0x70F4DDD3, 0x66A02F45,
0xBFBC09EC, 0x03BD9785, 0x7FAC6DD0, 0x31CB8504,
0x96EB27B3, 0x55FD3941, 0xDA2547E6, 0xABCA0A9A,
0x28507825, 0x530429F4, 0x0A2C86DA, 0xE9B66DFB,
0x68DC1462, 0xD7486900, 0x680EC0A4, 0x27A18DEE,
0x4F3FFEA2, 0xE887AD8C, 0xB58CE006, 0x7AF4D6B6,
0xAACE1E7C, 0xD3375FEC, 0xCE78A399, 0x406B2A42,
0x20FE9E35, 0xD9F385B9, 0xEE39D7AB, 0x3B124E8B,
0x1DC9FAF7, 0x4B6D1856, 0x26A36631, 0xEAE397B2,
0x3A6EFA74, 0xDD5B4332, 0x6841E7F7, 0xCA7820FB,
0xFB0AF54E, 0xD8FEB397, 0x454056AC, 0xBA489527,
0x55533A3A, 0x20838D87, 0xFE6BA9B7, 0xD096954B,
0x55A867BC, 0xA1159A58, 0xCCA92963, 0x99E1DB33,
0xA62A4A56, 0x3F3125F9, 0x5EF47E1C, 0x9029317C,
0xFDF8E802, 0x04272F70, 0x80BB155C, 0x05282CE3,
0x95C11548, 0xE4C66D22, 0x48C1133F, 0xC70F86DC,
0x07F9C9EE, 0x41041F0F, 0x404779A4, 0x5D886E17,
0x325F51EB, 0xD59BC0D1, 0xF2BCC18F, 0x41113564,
0x257B7834, 0x602A9C60, 0xDFF8E8A3, 0x1F636C1B,
0x0E12B4C2, 0x02E1329E, 0xAF664FD1, 0xCAD18115,
0x6B2395E0, 0x333E92E1, 0x3B240B62, 0xEEBEB922,
0x85B2A20E, 0xE6BA0D99, 0xDE720C8C, 0x2DA2F728,
0xD0127845, 0x95B794FD, 0x647D0862, 0xE7CCF5F0,
0x5449A36F, 0x877D48FA, 0xC39DFD27, 0xF33E8D1E,
0x0A476341, 0x992EFF74, 0x3A6F6EAB, 0xF4F8FD37,
0xA812DC60, 0xA1EBDDF8, 0x991BE14C, 0xDB6E6B0D,
0xC67B5510, 0x6D672C37, 0x2765D43B, 0xDCD0E804,
0xF1290DC7, 0xCC00FFA3, 0xB5390F92, 0x690FED0B,
0x667B9FFB, 0xCEDB7D9C, 0xA091CF0B, 0xD9155EA3,
0xBB132F88, 0x515BAD24, 0x7B9479BF, 0x763BD6EB,
0x37392EB3, 0xCC115979, 0x8026E297, 0xF42E312D,
0x6842ADA7, 0xC66A2B3B, 0x12754CCC, 0x782EF11C,
0x6A124237, 0xB79251E7, 0x06A1BBE6, 0x4BFB6350,
0x1A6B1018, 0x11CAEDFA, 0x3D25BDD8, 0xE2E1C3C9,
0x44421659, 0x0A121386, 0xD90CEC6E, 0xD5ABEA2A,
0x64AF674E, 0xDA86A85F, 0xBEBFE988, 0x64E4C3FE,
0x9DBC8057, 0xF0F7C086, 0x60787BF8, 0x6003604D,
0xD1FD8346, 0xF6381FB0, 0x7745AE04, 0xD736FCCC,
0x83426B33, 0xF01EAB71, 0xB0804187, 0x3C005E5F,
0x77A057BE, 0xBDE8AE24, 0x55464299, 0xBF582E61,
0x4E58F48F, 0xF2DDFDA2, 0xF474EF38, 0x8789BDC2,
0x5366F9C3, 0xC8B38E74, 0xB475F255, 0x46FCD9B9,
0x7AEB2661, 0x8B1DDF84, 0x846A0E79, 0x915F95E2,
0x466E598E, 0x20B45770, 0x8CD55591, 0xC902DE4C,
0xB90BACE1, 0xBB8205D0, 0x11A86248, 0x7574A99E,
0xB77F19B6, 0xE0A9DC09, 0x662D09A1, 0xC4324633,
0xE85A1F02, 0x09F0BE8C, 0x4A99A025, 0x1D6EFE10,
0x1AB93D1D, 0x0BA5A4DF, 0xA186F20F, 0x2868F169,
0xDCB7DA83, 0x573906FE, 0xA1E2CE9B, 0x4FCD7F52,
0x50115E01, 0xA70683FA, 0xA002B5C4, 0x0DE6D027,
0x9AF88C27, 0x773F8641, 0xC3604C06, 0x61A806B5,
0xF0177A28, 0xC0F586E0, 0x006058AA, 0x30DC7D62,
0x11E69ED7, 0x2338EA63, 0x53C2DD94, 0xC2C21634,
0xBBCBEE56, 0x90BCB6DE, 0xEBFC7DA1, 0xCE591D76,
0x6F05E409, 0x4B7C0188, 0x39720A3D, 0x7C927C24,
0x86E3725F, 0x724D9DB9, 0x1AC15BB4, 0xD39EB8FC,
0xED545578, 0x08FCA5B5, 0xD83D7CD3, 0x4DAD0FC4,
0x1E50EF5E, 0xB161E6F8, 0xA28514D9, 0x6C51133C,
0x6FD5C7E7, 0x56E14EC4, 0x362ABFCE, 0xDDC6C837,
0xD79A3234, 0x92638212, 0x670EFA8E, 0x406000E0
]),
array.array(‘I’, [
0x3A39CE37, 0xD3FAF5CF, 0xABC27737, 0x5AC52D1B,
0x5CB0679E, 0x4FA33742, 0xD3822740, 0x99BC9BBE,
0xD5118E9D, 0xBF0F7315, 0xD62D1C7E, 0xC700C47B,
0xB78C1B6B, 0x21A19045, 0xB26EB1BE, 0x6A366EB4,
0x5748AB2F, 0xBC946E79, 0xC6A376D2, 0x6549C2C8,
0x530FF8EE, 0x468DDE7D, 0xD5730A1D, 0x4CD04DC6,
0x2939BBDB, 0xA9BA4650, 0xAC9526E8, 0xBE5EE304,
0xA1FAD5F0, 0x6A2D519A, 0x63EF8CE2, 0x9A86EE22,
0xC089C2B8, 0x43242EF6, 0xA51E03AA, 0x9CF2D0A4,
0x83C061BA, 0x9BE96A4D, 0x8FE51550, 0xBA645BD6,
0x2826A2F9, 0xA73A3AE1, 0x4BA99586, 0xEF5562E9,
0xC72FEFD3, 0xF752F7DA, 0x3F046F69, 0x77FA0A59,
0x80E4A915, 0x87B08601, 0x9B09E6AD, 0x3B3EE593,
0xE990FD5A, 0x9E34D797, 0x2CF0B7D9, 0x022B8B51,
0x96D5AC3A, 0x017DA67D, 0xD1CF3ED6, 0x7C7D2D28,
0x1F9F25CF, 0xADF2B89B, 0x5AD6B472, 0x5A88F54C,
0xE029AC71, 0xE019A5E6, 0x47B0ACFD, 0xED93FA9B,
0xE8D3C48D, 0x283B57CC, 0xF8D56629, 0x79132E28,
0x785F0191, 0xED756055, 0xF7960E44, 0xE3D35E8C,
0x15056DD4, 0x88F46DBA, 0x03A16125, 0x0564F0BD,
0xC3EB9E15, 0x3C9057A2, 0x97271AEC, 0xA93A072A,
0x1B3F6D9B, 0x1E6321F5, 0xF59C66FB, 0x26DCF319,
0x7533D928, 0xB155FDF5, 0x03563482, 0x8ABA3CBB,
0x28517711, 0xC20AD9F8, 0xABCC5167, 0xCCAD925F,
0x4DE81751, 0x3830DC8E, 0x379D5862, 0x9320F991,
0xEA7A90C2, 0xFB3E7BCE, 0x5121CE64, 0x774FBE32,
0xA8B6E37E, 0xC3293D46, 0x48DE5369, 0x6413E680,
0xA2AE0810, 0xDD6DB224, 0x69852DFD, 0x09072166,
0xB39A460A, 0x6445C0DD, 0x586CDECF, 0x1C20C8AE,
0x5BBEF7DD, 0x1B588D40, 0xCCD2017F, 0x6BB4E3BB,
0xDDA26A7E, 0x3A59FF45, 0x3E350A44, 0xBCB4CDD5,
0x72EACEA8, 0xFA6484BB, 0x8D6612AE, 0xBF3C6F47,
0xD29BE463, 0x542F5D9E, 0xAEC2771B, 0xF64E6370,
0x740E0D8D, 0xE75B1357, 0xF8721671, 0xAF537D5D,
0x4040CB08, 0x4EB4E2CC, 0x34D2466A, 0x0115AF84,
0xE1B00428, 0x95983A1D, 0x06B89FB4, 0xCE6EA048,
0x6F3F3B82, 0x3520AB82, 0x011A1D4B, 0x277227F8,
0x611560B1, 0xE7933FDC, 0xBB3A792B, 0x344525BD,
0xA08839E1, 0x51CE794B, 0x2F32C9B7, 0xA01FBAC9,
0xE01CC87E, 0xBCC7D1F6, 0xCF0111C3, 0xA1E8AAC7,
0x1A908749, 0xD44FBD9A, 0xD0DADECB, 0xD50ADA38,
0x0339C32A, 0xC6913667, 0x8DF9317C, 0xE0B12B4F,
0xF79E59B7, 0x43F5BB3A, 0xF2D519FF, 0x27D9459C,
0xBF97222C, 0x15E6FC2A, 0x0F91FC71, 0x9B941525,
0xFAE59361, 0xCEB69CEB, 0xC2A86459, 0x12BAA8D1,
0xB6C1075E, 0xE3056A0C, 0x10D25065, 0xCB03A442,
0xE0EC6E0E, 0x1698DB3B, 0x4C98A0BE, 0x3278E964,
0x9F1F9532, 0xE0D392DF, 0xD3A0342B, 0x8971F21E,
0x1B0A7441, 0x4BA3348C, 0xC5BE7120, 0xC37632D8,
0xDF359F8D, 0x9B992F2E, 0xE60B6F47, 0x0FE3F11D,
0xE54CDA54, 0x1EDAD891, 0xCE6279CF, 0xCD3E7E6F,
0x1618B166, 0xFD2C1D05, 0x848FD2C5, 0xF6FB2299,
0xF523F357, 0xA6327623, 0x93A83531, 0x56CCCD02,
0xACF08162, 0x5A75EBB5, 0x6E163697, 0x88D273CC,
0xDE966292, 0x81B949D0, 0x4C50901B, 0x71C65614,
0xE6C6C7BD, 0x327A140A, 0x45E1D006, 0xC3F27B9A,
0xC9AA53FD, 0x62A80F00, 0xBB25BFE2, 0x35BDD2F6,
0x71126905, 0xB2040222, 0xB6CBCF7C, 0xCD769C2B,
0x53113EC0, 0x1640E3D3, 0x38ABBD60, 0x2547ADF0,
0xBA38209C, 0xF746CE76, 0x77AFA1C5, 0x20756060,
0x85CBFE4E, 0x8AE88DD8, 0x7AAAF9B0, 0x4CF9AA7E,
0x1948C25C, 0x02FB8A8C, 0x01C36AE4, 0xD6EBE1F9,
0x90D4F869, 0xA65CDEA0, 0x3F09252D, 0xC208E69F,
0xB74E6132, 0xCE77E25B, 0x578FDFE3, 0x3AC372E6
])
)

# Cycle through the p-boxes and round-robin XOR the
# key with the p-boxes
key_len = len(key)
index = 0
for i in xrange(len(self._p_boxes)):
self._p_boxes[i] = self._p_boxes[i] ^ (
(ord(key[index % key_len]) << 24) +
(ord(key[(index + 1) % key_len]) << 16) +
(ord(key[(index + 2) % key_len]) << 8) +
(ord(key[(index + 3) % key_len]))
)
index += 4

# For the chaining process
l = r = 0

# Begin chain replacing the p-boxes
for i in xrange(0, len(self._p_boxes), 2):
(l, r) = self.cipher(l, r, self.ENCRYPT)
self._p_boxes[i] = l
self._p_boxes[i + 1] = r

# Chain replace the s-boxes
for i in xrange(len(self._s_boxes)):
for j in xrange(0, len(self._s_boxes[i]), 2):
(l, r) = self.cipher(l, r, self.ENCRYPT)
self._s_boxes[i][j] = l
self._s_boxes[i][j + 1] = r

def initCTR(self, iv=0):
"""
Initializes CTR engine for encryption or decryption.
"""
if not struct.calcsize("Q") == self._BLOCK_SIZE:
raise ValueError("Struct-type ‘Q’ must have a length of %(target-len)i bytes, not %(q-len)i bytes; this module cannot be used on your platform" % {
‘target-len’: self._BLOCK_SIZE,
‘q-len’: struct.calcsize("Q"),
})

self._ctr_iv = iv
self._calcCTRBuf()

def cipher(self, xl, xr, direction):
"""
Encrypts a 64-bit block of data where xl is the upper 32 bits and xr is
the lower 32-bits.

‘direction’ is the direction to apply the cipher, either ENCRYPT or
DECRYPT class-constants.

Returns a tuple of either encrypted or decrypted data of the left half
and right half of the 64-bit block.
"""
if direction == self.ENCRYPT:
for i in self._p_boxes[:16]:
xl = xl ^ i
xr = self._round(xl) ^ xr
(xl, xr) = (xr, xl)
(xl, xr) = (xr, xl)
xr = xr ^ self._p_boxes[16]
xl = xl ^ self._p_boxes[17]
else:
for i in reversed(self._p_boxes[2:18]):
xl = xl ^ i
xr = self._round(xl) ^ xr
(xl, xr) = (xr, xl)
(xl, xr) = (xr, xl)
xr = xr ^ self._p_boxes[1]
xl = xl ^ self._p_boxes[0]
return (xl, xr)

def encrypt(self, data):
"""
Encrypt an 8-byte (64-bit) block of text where ‘data’ is an 8 byte
string.

Returns an 8-byte encrypted string.
"""
if not len(data) == 8:
raise ValueError("Attempted to encrypt data of invalid block length: %(len)i" % {
‘len’: len(data),
})

# Use big endianess since that’s what everyone else uses
xl = (ord(data[3])) | (ord(data[2]) << 8) | (ord(data[1]) << 16) | (ord(data[0]) << 24)
xr = (ord(data[7])) | (ord(data[6]) << 8) | (ord(data[5]) << 16) | (ord(data[4]) << 24)

(cl, cr) = self.cipher(xl, xr, self.ENCRYPT)
chars = ”.join ([
chr((cl >> 24) & 0xFF), chr((cl >> 16) & 0xFF), chr((cl >> 8) & 0xFF), chr(cl & 0xFF),
chr((cr >> 24) & 0xFF), chr((cr >> 16) & 0xFF), chr((cr >> 8) & 0xFF), chr(cr & 0xFF)
])
return chars

def decrypt(self, data):
"""
Decrypt an 8 byte (64-bit) encrypted block of text, where ‘data’ is the
8-byte encrypted string.

Returns an 8-byte string of plaintext.
"""
if not len(data) == 8:
raise ValueError("Attempted to encrypt data of invalid block length: %(len)i" % {
‘len’: len(data),
})

# Use big endianess since that’s what everyone else uses
cl = (ord(data[3])) | (ord(data[2]) << 8) | (ord(data[1]) << 16) | (ord(data[0]) << 24)
cr = (ord(data[7])) | (ord(data[6]) << 8) | (ord(data[5]) << 16) | (ord(data[4]) << 24)

(xl, xr) = self.cipher (cl, cr, self.DECRYPT)
return ”.join ([
chr((xl >> 24) & 0xFF), chr((xl >> 16) & 0xFF), chr((xl >> 8) & 0xFF), chr(xl & 0xFF),
chr((xr >> 24) & 0xFF), chr((xr >> 16) & 0xFF), chr((xr >> 8) & 0xFF), chr(xr & 0xFF)
])

def encryptCTR(self, data):
"""
Encrypts an arbitrary string and returns the encrypted string.

This method can be called successively for multiple string blocks.
"""
if not type(data) is str:
raise TypeError("Only 8-bit strings are supported")

return ”.join([chr(ord(ch) ^ self._nextCTRByte()) for ch in data])

def decryptCTR(self, data):
"""
Decrypts a string encrypted with encryptCTR() and returns the original
string.
"""
return self.encryptCTR(data)

def _calcCTRBuf(self):
"""
Calculates one block of CTR keystream.
"""
self._ctr_cks = self.encrypt(struct.pack("Q", self._ctr_iv)) # keystream block
self._ctr_iv += 1
self._ctr_pos = 0

def _nextCTRByte(self):
"""
Returns one byte of CTR keystream.
"""
b = ord(self._ctr_cks[self._ctr_pos])
self._ctr_pos += 1

if self._ctr_pos >= len(self._ctr_cks):
self._calcCTRBuf()
return b

def _round(self, xl):
"""
Performs an obscuring function on the 32-bit block of data, ‘xl’, which
is the left half of the 64-bit block of data.

Returns the 32-bit result as a long integer.
"""
# Perform all ops as longs then and out the last 32-bits to
# obtain the integer
f = long(self._s_boxes[0][(xl & 0xFF000000) >> 24])
f +=long(self._s_boxes[1][(xl & 0x00FF0000) >> 16])
f %= self._MODULUS
f ^= long(self._s_boxes[2][(xl & 0x0000FF00) >> 8])
f += long(self._s_boxes[3][(xl & 0x000000FF)])
f %= self._MODULUS
return f & 0xFFFFFFFF

# Sample usage
##############
if __name__ == ‘__main__’:
import time

def _demo(heading, source, encrypted, decrypted):
print heading
print "\tSource: %(source)s" % {
‘source’: source,
}
print "\tEncrypted: %(encrypted)s" % {
‘encrypted’: encrypted,
}
print "\tDecrypted: %(decrypted)s" % {
‘decrypted’: decrypted,
}
print

key = ‘This is a test key’
cipher = Blowfish(key)

# Encryption processing
(xl, xr) = (123456L, 654321L)
(cl, cr) = cipher.cipher(xl, xr, cipher.ENCRYPT)
(dl, dr) = cipher.cipher(cl, cr, cipher.DECRYPT)
_demo("Testing encryption", (xl, xr), (cl, cr), (dl, dr))

# Block processing
text = ‘testtest’
crypted = cipher.encrypt(text)
decrypted = cipher.decrypt(crypted)
_demo("Testing block encrypt", text, repr(crypted), decrypted)

# CTR ptocessing
cipher.initCTR()
text = "The quick brown fox jumps over the lazy dog"
crypted = cipher.encryptCTR(text)
cipher.initCTR()
decrypted=cipher.decryptCTR(crypted)
_demo("Testing CTR logic", text, repr(crypted), decrypted)

# Test speed
print "Testing speed"
test_strings = [”.join(("The quick brown fox jumps over the lazy dog", str(i),)) for i in xrange(1000)]
n = 0
t1 = time.time()
while True:
for test_string in test_strings:
cipher.encryptCTR(test_string)
n += 1000
t2 = time.time()
if t2 – t1 >= 5.0:
break
print "%(count)i encryptions in %(time)0.1f seconds: %(throughput)0.1f enc/s" % {
‘count’: n,
‘time’: t2 – t1,
‘throughput’: n / (t2 – t1),
}
[/python]

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