Removed hard coding of subtitles that are embedded in a video
[pyTivo/wmcbrine/lucasnz.git] / turing.py
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1 # Turing Encryption for Python, v1.5
2 # Copyright 2013 William McBrine
3 # Based on material Copyright 2002 Qualcomm Inc., written by Greg Rose
5 # License from original C version:
6 # --------------------------------
8 # This software is free for commercial and non-commercial use subject to
9 # the following conditions:
11 # 1. Copyright remains vested in QUALCOMM Incorporated, and Copyright
12 # notices in the code are not to be removed. If this package is used in
13 # a product, QUALCOMM should be given attribution as the author of the
14 # Turing encryption algorithm. This can be in the form of a textual
15 # message at program startup or in documentation (online or textual)
16 # provided with the package.
18 # 2. Redistribution and use in source and binary forms, with or without
19 # modification, are permitted provided that the following conditions are
20 # met:
22 # a. Redistributions of source code must retain the copyright notice,
23 # this list of conditions and the following disclaimer.
25 # b. Redistributions in binary form must reproduce the above copyright
26 # notice, this list of conditions and the following disclaimer in the
27 # documentation and/or other materials provided with the
28 # distribution.
30 # c. All advertising materials mentioning features or use of this
31 # software must display the following acknowledgement: This product
32 # includes software developed by QUALCOMM Incorporated.
34 # 3. THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
35 # WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
36 # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE AND AGAINST
37 # INFRINGEMENT ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR
38 # CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
39 # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
40 # PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
41 # PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
42 # LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
43 # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
44 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
46 # 4. The license and distribution terms for any publically available
47 # version or derivative of this code cannot be changed, that is, this
48 # code cannot simply be copied and put under another distribution
49 # license including the GNU Public License.
51 # 5. The Turing family of encryption algorithms are covered by patents
52 # in the United States of America and other countries. A free and
53 # irrevocable license is hereby granted for the use of such patents to
54 # the extent required to utilize the Turing family of encryption
55 # algorithms for any purpose, subject to the condition that any
56 # commercial product utilising any of the Turing family of encryption
57 # algorithms should show the words "Encryption by QUALCOMM" either on
58 # the product or in the associated documentation.
60 """ Turing Encryption for Python
62 A Python implementation of Qualcomm's Turing pseudo-random number
63 generator. Loosely based on Greg Rose's TuringFast.c et al. This is
64 immensely slower than the C version, but useful for some limited
65 purposes. For Python 2.5 through 2.7.
67 """
69 __author__ = 'William McBrine <wmcbrine@gmail.com>'
70 __version__ = '1.5'
72 from itertools import izip
73 from struct import pack, unpack
75 # 8->32 _SBOX generated by Millan et. al. at Queensland University of
76 # Technology. See: E. Dawson, W. Millan, L. Burnett, G. Carter, "On the
77 # Design of 8*32 S-boxes". Unpublished report, by the Information
78 # Systems Research Centre, Queensland University of Technology, 1999.
80 _QBOX = [
81 0x1faa1887, 0x4e5e435c, 0x9165c042, 0x250e6ef4, 0x5957ee20, 0xd484fed3,
82 0xa666c502, 0x7e54e8ae, 0xd12ee9d9, 0xfc1f38d4, 0x49829b5d, 0x1b5cdf3c,
83 0x74864249, 0xda2e3963, 0x28f4429f, 0xc8432c35, 0x4af40325, 0x9fc0dd70,
84 0xd8973ded, 0x1a02dc5e, 0xcd175b42, 0xf10012bf, 0x6694d78c, 0xacaab26b,
85 0x4ec11b9a, 0x3f168146, 0xc0ea8ec5, 0xb38ac28f, 0x1fed5c0f, 0xaab4101c,
86 0xea2db082, 0x470929e1, 0xe71843de, 0x508299fc, 0xe72fbc4b, 0x2e3915dd,
87 0x9fa803fa, 0x9546b2de, 0x3c233342, 0x0fcee7c3, 0x24d607ef, 0x8f97ebab,
88 0xf37f859b, 0xcd1f2e2f, 0xc25b71da, 0x75e2269a, 0x1e39c3d1, 0xeda56b36,
89 0xf8c9def2, 0x46c9fc5f, 0x1827b3a3, 0x70a56ddf, 0x0d25b510, 0x000f85a7,
90 0xb2e82e71, 0x68cb8816, 0x8f951e2a, 0x72f5f6af, 0xe4cbc2b3, 0xd34ff55d,
91 0x2e6b6214, 0x220b83e3, 0xd39ea6f5, 0x6fe041af, 0x6b2f1f17, 0xad3b99ee,
92 0x16a65ec0, 0x757016c6, 0xba7709a4, 0xb0326e01, 0xf4b280d9, 0x4bfb1418,
93 0xd6aff227, 0xfd548203, 0xf56b9d96, 0x6717a8c0, 0x00d5bf6e, 0x10ee7888,
94 0xedfcfe64, 0x1ba193cd, 0x4b0d0184, 0x89ae4930, 0x1c014f36, 0x82a87088,
95 0x5ead6c2a, 0xef22c678, 0x31204de7, 0xc9c2e759, 0xd200248e, 0x303b446b,
96 0xb00d9fc2, 0x9914a895, 0x906cc3a1, 0x54fef170, 0x34c19155, 0xe27b8a66,
97 0x131b5e69, 0xc3a8623e, 0x27bdfa35, 0x97f068cc, 0xca3a6acd, 0x4b55e936,
98 0x86602db9, 0x51df13c1, 0x390bb16d, 0x5a80b83c, 0x22b23763, 0x39d8a911,
99 0x2cb6bc13, 0xbf5579d7, 0x6c5c2fa8, 0xa8f4196e, 0xbcdb5476, 0x6864a866,
100 0x416e16ad, 0x897fc515, 0x956feb3c, 0xf6c8a306, 0x216799d9, 0x171a9133,
101 0x6c2466dd, 0x75eb5dcd, 0xdf118f50, 0xe4afb226, 0x26b9cef3, 0xadb36189,
102 0x8a7a19b1, 0xe2c73084, 0xf77ded5c, 0x8b8bc58f, 0x06dde421, 0xb41e47fb,
103 0xb1cc715e, 0x68c0ff99, 0x5d122f0f, 0xa4d25184, 0x097a5e6c, 0x0cbf18bc,
104 0xc2d7c6e0, 0x8bb7e420, 0xa11f523f, 0x35d9b8a2, 0x03da1a6b, 0x06888c02,
105 0x7dd1e354, 0x6bba7d79, 0x32cc7753, 0xe52d9655, 0xa9829da1, 0x301590a7,
106 0x9bc1c149, 0x13537f1c, 0xd3779b69, 0x2d71f2b7, 0x183c58fa, 0xacdc4418,
107 0x8d8c8c76, 0x2620d9f0, 0x71a80d4d, 0x7a74c473, 0x449410e9, 0xa20e4211,
108 0xf9c8082b, 0x0a6b334a, 0xb5f68ed2, 0x8243cc1b, 0x453c0ff3, 0x9be564a0,
109 0x4ff55a4f, 0x8740f8e7, 0xcca7f15f, 0xe300fe21, 0x786d37d6, 0xdfd506f1,
110 0x8ee00973, 0x17bbde36, 0x7a670fa8, 0x5c31ab9e, 0xd4dab618, 0xcc1f52f5,
111 0xe358eb4f, 0x19b9e343, 0x3a8d77dd, 0xcdb93da6, 0x140fd52d, 0x395412f8,
112 0x2ba63360, 0x37e53ad0, 0x80700f1c, 0x7624ed0b, 0x703dc1ec, 0xb7366795,
113 0xd6549d15, 0x66ce46d7, 0xd17abe76, 0xa448e0a0, 0x28f07c02, 0xc31249b7,
114 0x6e9ed6ba, 0xeaa47f78, 0xbbcfffbd, 0xc507ca84, 0xe965f4da, 0x8e9f35da,
115 0x6ad2aa44, 0x577452ac, 0xb5d674a7, 0x5461a46a, 0x6763152a, 0x9c12b7aa,
116 0x12615927, 0x7b4fb118, 0xc351758d, 0x7e81687b, 0x5f52f0b3, 0x2d4254ed,
117 0xd4c77271, 0x0431acab, 0xbef94aec, 0xfee994cd, 0x9c4d9e81, 0xed623730,
118 0xcf8a21e8, 0x51917f0b, 0xa7a9b5d6, 0xb297adf8, 0xeed30431, 0x68cac921,
119 0xf1b35d46, 0x7a430a36, 0x51194022, 0x9abca65e, 0x85ec70ba, 0x39aea8cc,
120 0x737bae8b, 0x582924d5, 0x03098a5a, 0x92396b81, 0x18de2522, 0x745c1cb8,
121 0xa1b8fe1d, 0x5db3c697, 0x29164f83, 0x97c16376, 0x8419224c, 0x21203b35,
122 0x833ac0fe, 0xd966a19a, 0xaaf0b24f, 0x40fda998, 0xe7d52d71, 0x390896a8,
123 0xcee6053f, 0xd0b0d300, 0xff99cbcc, 0x065e3d40
126 # Multiplication table for Turing using 0xd02b4367
128 _MULTAB = [
129 0x00000000, 0xd02b4367, 0xed5686ce, 0x3d7dc5a9, 0x97ac41d1, 0x478702b6,
130 0x7afac71f, 0xaad18478, 0x631582ef, 0xb33ec188, 0x8e430421, 0x5e684746,
131 0xf4b9c33e, 0x24928059, 0x19ef45f0, 0xc9c40697, 0xc62a4993, 0x16010af4,
132 0x2b7ccf5d, 0xfb578c3a, 0x51860842, 0x81ad4b25, 0xbcd08e8c, 0x6cfbcdeb,
133 0xa53fcb7c, 0x7514881b, 0x48694db2, 0x98420ed5, 0x32938aad, 0xe2b8c9ca,
134 0xdfc50c63, 0x0fee4f04, 0xc154926b, 0x117fd10c, 0x2c0214a5, 0xfc2957c2,
135 0x56f8d3ba, 0x86d390dd, 0xbbae5574, 0x6b851613, 0xa2411084, 0x726a53e3,
136 0x4f17964a, 0x9f3cd52d, 0x35ed5155, 0xe5c61232, 0xd8bbd79b, 0x089094fc,
137 0x077edbf8, 0xd755989f, 0xea285d36, 0x3a031e51, 0x90d29a29, 0x40f9d94e,
138 0x7d841ce7, 0xadaf5f80, 0x646b5917, 0xb4401a70, 0x893ddfd9, 0x59169cbe,
139 0xf3c718c6, 0x23ec5ba1, 0x1e919e08, 0xcebadd6f, 0xcfa869d6, 0x1f832ab1,
140 0x22feef18, 0xf2d5ac7f, 0x58042807, 0x882f6b60, 0xb552aec9, 0x6579edae,
141 0xacbdeb39, 0x7c96a85e, 0x41eb6df7, 0x91c02e90, 0x3b11aae8, 0xeb3ae98f,
142 0xd6472c26, 0x066c6f41, 0x09822045, 0xd9a96322, 0xe4d4a68b, 0x34ffe5ec,
143 0x9e2e6194, 0x4e0522f3, 0x7378e75a, 0xa353a43d, 0x6a97a2aa, 0xbabce1cd,
144 0x87c12464, 0x57ea6703, 0xfd3be37b, 0x2d10a01c, 0x106d65b5, 0xc04626d2,
145 0x0efcfbbd, 0xded7b8da, 0xe3aa7d73, 0x33813e14, 0x9950ba6c, 0x497bf90b,
146 0x74063ca2, 0xa42d7fc5, 0x6de97952, 0xbdc23a35, 0x80bfff9c, 0x5094bcfb,
147 0xfa453883, 0x2a6e7be4, 0x1713be4d, 0xc738fd2a, 0xc8d6b22e, 0x18fdf149,
148 0x258034e0, 0xf5ab7787, 0x5f7af3ff, 0x8f51b098, 0xb22c7531, 0x62073656,
149 0xabc330c1, 0x7be873a6, 0x4695b60f, 0x96bef568, 0x3c6f7110, 0xec443277,
150 0xd139f7de, 0x0112b4b9, 0xd31dd2e1, 0x03369186, 0x3e4b542f, 0xee601748,
151 0x44b19330, 0x949ad057, 0xa9e715fe, 0x79cc5699, 0xb008500e, 0x60231369,
152 0x5d5ed6c0, 0x8d7595a7, 0x27a411df, 0xf78f52b8, 0xcaf29711, 0x1ad9d476,
153 0x15379b72, 0xc51cd815, 0xf8611dbc, 0x284a5edb, 0x829bdaa3, 0x52b099c4,
154 0x6fcd5c6d, 0xbfe61f0a, 0x7622199d, 0xa6095afa, 0x9b749f53, 0x4b5fdc34,
155 0xe18e584c, 0x31a51b2b, 0x0cd8de82, 0xdcf39de5, 0x1249408a, 0xc26203ed,
156 0xff1fc644, 0x2f348523, 0x85e5015b, 0x55ce423c, 0x68b38795, 0xb898c4f2,
157 0x715cc265, 0xa1778102, 0x9c0a44ab, 0x4c2107cc, 0xe6f083b4, 0x36dbc0d3,
158 0x0ba6057a, 0xdb8d461d, 0xd4630919, 0x04484a7e, 0x39358fd7, 0xe91eccb0,
159 0x43cf48c8, 0x93e40baf, 0xae99ce06, 0x7eb28d61, 0xb7768bf6, 0x675dc891,
160 0x5a200d38, 0x8a0b4e5f, 0x20daca27, 0xf0f18940, 0xcd8c4ce9, 0x1da70f8e,
161 0x1cb5bb37, 0xcc9ef850, 0xf1e33df9, 0x21c87e9e, 0x8b19fae6, 0x5b32b981,
162 0x664f7c28, 0xb6643f4f, 0x7fa039d8, 0xaf8b7abf, 0x92f6bf16, 0x42ddfc71,
163 0xe80c7809, 0x38273b6e, 0x055afec7, 0xd571bda0, 0xda9ff2a4, 0x0ab4b1c3,
164 0x37c9746a, 0xe7e2370d, 0x4d33b375, 0x9d18f012, 0xa06535bb, 0x704e76dc,
165 0xb98a704b, 0x69a1332c, 0x54dcf685, 0x84f7b5e2, 0x2e26319a, 0xfe0d72fd,
166 0xc370b754, 0x135bf433, 0xdde1295c, 0x0dca6a3b, 0x30b7af92, 0xe09cecf5,
167 0x4a4d688d, 0x9a662bea, 0xa71bee43, 0x7730ad24, 0xbef4abb3, 0x6edfe8d4,
168 0x53a22d7d, 0x83896e1a, 0x2958ea62, 0xf973a905, 0xc40e6cac, 0x14252fcb,
169 0x1bcb60cf, 0xcbe023a8, 0xf69de601, 0x26b6a566, 0x8c67211e, 0x5c4c6279,
170 0x6131a7d0, 0xb11ae4b7, 0x78dee220, 0xa8f5a147, 0x958864ee, 0x45a32789,
171 0xef72a3f1, 0x3f59e096, 0x0224253f, 0xd20f6658
174 # Basic _SBOX for Turing.
176 # This was generated by keying RC4 with the 11-character string "Alan
177 # Turing", and then ignoring 256 generated bytes. Then the current
178 # permutation was tested for nonlinearity, another byte generated, etc.,
179 # until a total of 10000 bytes had been generated. The best observed min
180 # nonlinearity was 104, which first occurred after 736 bytes had been
181 # generated. The corresponding state table is used in Turing. By happy
182 # coincidence it also has no fixed points (ie. _SBOX[x] != x for all x).
184 _SBOX = [
185 0x61, 0x51, 0xeb, 0x19, 0xb9, 0x5d, 0x60, 0x38, 0x7c, 0xb2, 0x06, 0x12,
186 0xc4, 0x5b, 0x16, 0x3b, 0x2b, 0x18, 0x83, 0xb0, 0x7f, 0x75, 0xfa, 0xa0,
187 0xe9, 0xdd, 0x6d, 0x7a, 0x6b, 0x68, 0x2d, 0x49, 0xb5, 0x1c, 0x90, 0xf7,
188 0xed, 0x9f, 0xe8, 0xce, 0xae, 0x77, 0xc2, 0x13, 0xfd, 0xcd, 0x3e, 0xcf,
189 0x37, 0x6a, 0xd4, 0xdb, 0x8e, 0x65, 0x1f, 0x1a, 0x87, 0xcb, 0x40, 0x15,
190 0x88, 0x0d, 0x35, 0xb3, 0x11, 0x0f, 0xd0, 0x30, 0x48, 0xf9, 0xa8, 0xac,
191 0x85, 0x27, 0x0e, 0x8a, 0xe0, 0x50, 0x64, 0xa7, 0xcc, 0xe4, 0xf1, 0x98,
192 0xff, 0xa1, 0x04, 0xda, 0xd5, 0xbc, 0x1b, 0xbb, 0xd1, 0xfe, 0x31, 0xca,
193 0xba, 0xd9, 0x2e, 0xf3, 0x1d, 0x47, 0x4a, 0x3d, 0x71, 0x4c, 0xab, 0x7d,
194 0x8d, 0xc7, 0x59, 0xb8, 0xc1, 0x96, 0x1e, 0xfc, 0x44, 0xc8, 0x7b, 0xdc,
195 0x5c, 0x78, 0x2a, 0x9d, 0xa5, 0xf0, 0x73, 0x22, 0x89, 0x05, 0xf4, 0x07,
196 0x21, 0x52, 0xa6, 0x28, 0x9a, 0x92, 0x69, 0x8f, 0xc5, 0xc3, 0xf5, 0xe1,
197 0xde, 0xec, 0x09, 0xf2, 0xd3, 0xaf, 0x34, 0x23, 0xaa, 0xdf, 0x7e, 0x82,
198 0x29, 0xc0, 0x24, 0x14, 0x03, 0x32, 0x4e, 0x39, 0x6f, 0xc6, 0xb1, 0x9b,
199 0xea, 0x72, 0x79, 0x41, 0xd8, 0x26, 0x6c, 0x5e, 0x2c, 0xb4, 0xa2, 0x53,
200 0x57, 0xe2, 0x9c, 0x86, 0x54, 0x95, 0xb6, 0x80, 0x8c, 0x36, 0x67, 0xbd,
201 0x08, 0x93, 0x2f, 0x99, 0x5a, 0xf8, 0x3a, 0xd7, 0x56, 0x84, 0xd2, 0x01,
202 0xf6, 0x66, 0x4d, 0x55, 0x8b, 0x0c, 0x0b, 0x46, 0xb7, 0x3c, 0x45, 0x91,
203 0xa4, 0xe3, 0x70, 0xd6, 0xfb, 0xe6, 0x10, 0xa9, 0xc9, 0x00, 0x9e, 0xe7,
204 0x4f, 0x76, 0x25, 0x3f, 0x5f, 0xa3, 0x33, 0x20, 0x02, 0xef, 0x62, 0x74,
205 0xee, 0x17, 0x81, 0x42, 0x58, 0x0a, 0x4b, 0x63, 0xe5, 0xbe, 0x6e, 0xad,
206 0xbf, 0x43, 0x94, 0x97
209 _MAXKEY = 32 # bytes
210 _MAXKIV = 48 # bytes
211 _LFSRLEN = 17 # words
213 def _rotl(w, x):
214 """ Rotate w left x bits """
215 return (w << x) | (w >> (32 - x))
217 def _fixed_strans(w):
218 """ Reversible transformation of a word, based on the S-boxes """
219 b = _SBOX[w >> 24]
220 w = ((w ^ _QBOX[b]) & 0x00ffffff) | (b << 24)
221 b = _SBOX[(w >> 16) & 0xff]
222 w = ((w ^ _rotl(_QBOX[b], 8)) & 0xff00ffff) | (b << 16)
223 b = _SBOX[(w >> 8) & 0xff]
224 w = ((w ^ _rotl(_QBOX[b], 16)) & 0xffff00ff) | (b << 8)
225 b = _SBOX[w & 0xff]
226 w = ((w ^ _rotl(_QBOX[b], 24)) & 0xffffff00) | b
227 return w
229 def _mixwords(w):
230 """ Pseudo-Hadamard Transform """
231 total = sum(w)
232 return [(i + total) & 0xffffffff for i in w[:-1] + [0]]
234 class KeyLengthError(Exception):
235 pass
237 class IVLengthError(Exception):
238 pass
240 class Turing(object):
241 def __init__(self, key=None, iv=None):
242 self.sbox = [[], [], [], []] # precalculated S-boxes
244 if key:
245 self.setkey(key)
246 if iv:
247 self.loadiv(iv)
249 def _strans(self, w, b):
250 """ Push a word through the keyed S-boxes """
251 n = (w >> 24, (w >> 16) & 0xff, (w >> 8) & 0xff, w & 0xff)
252 if b:
253 n = n[b:] + n[:b]
254 s = self.sbox
255 return s[0][n[0]] ^ s[1][n[1]] ^ s[2][n[2]] ^ s[3][n[3]]
257 def setkey(self, key):
258 """ Key the cipher.
259 Table version; gathers words, mixes them, saves them.
260 Then compiles lookup tables for the keyed S-boxes.
263 keylength = len(key)
264 if keylength & 3 or keylength > _MAXKEY:
265 raise KeyLengthError
266 fmt = '>%dL' % (keylength / 4)
267 mkey = _mixwords([_fixed_strans(n) for n in unpack(fmt, key)])
269 # build S-box lookup tables
270 for l, m in enumerate(self.sbox):
271 sh1 = 8 * l
272 sh2 = 24 - sh1
273 mask = (0xff << sh2) ^ 0xffffffff
274 for j in xrange(256):
275 w = 0
276 k = j
277 for i, key in enumerate(mkey):
278 k = _SBOX[((key >> sh2) & 0xff) ^ k]
279 w ^= _rotl(_QBOX[k], i + sh1)
280 m.append( (w & mask) | (k << sh2) )
282 self.mkey = mkey
284 def loadiv(self, iv):
285 """ Load the Initialization Vector.
286 Actually, this fills the LFSR, with IV, key, length, and
287 more. IV goes through the fixed S-box, key is premixed, the
288 rest go through the keyed S-boxes.
291 ivlength, klength = len(iv), len(self.mkey)
292 # check args
293 if ivlength & 3 or (ivlength + 4 * klength) > _MAXKIV:
294 raise IVLengthError
295 # first copy in the IV, mixing as we go
296 fmt = '>%dL' % (ivlength / 4)
297 lfsr = [_fixed_strans(n) for n in unpack(fmt, iv)]
298 # now continue with the premixed key
299 lfsr.extend(self.mkey)
300 # now the length-dependent word
301 lfsr.append( (klength << 4) | (ivlength >> 2) | 0x01020300 )
302 # ... and fill the rest of the register
303 j = 0
304 while len(lfsr) < _LFSRLEN:
305 lfsr.append(self._strans((lfsr[j] + lfsr[-1]) & 0xffffffff, 0))
306 j += 1
307 # finally mix all the words
308 self.lfsr = _mixwords(lfsr)
310 def _step(self, n=1):
311 """ Step the LFSR """
312 lfsr = self.lfsr
313 while n:
314 oldw = lfsr.pop(0)
315 neww = (lfsr[14] ^ lfsr[3] ^
316 ((oldw & 0xffffff) << 8) ^ _MULTAB[oldw >> 24])
317 lfsr.append(neww)
318 n -= 1
320 def _round(self):
321 """ A single round """
322 self._step()
323 things = _mixwords([self.lfsr[n] for n in (16, 13, 6, 1, 0)])
324 things = _mixwords([self._strans(i, n)
325 for i, n in izip(things, (0, 1, 2, 3, 0))])
326 self._step(3)
327 things = [(i + self.lfsr[n]) & 0xffffffff
328 for i, n in izip(things, (14, 12, 8, 1, 0))]
329 self._step()
330 return pack('>5L', *things)
332 def gen(self, skip, length):
333 """ Generate length characters of output, skipping the first
334 skip characters.
337 while skip > 20:
338 self._step(5)
339 skip -= 20
340 buf = ''
341 while len(buf) < length + skip:
342 buf += self._round()
343 return buf[skip:length + skip]
345 def crypt(self, source, skip=0):
346 """ Return a transformed (encrypted or decrypted) version of the
347 source string, skipping the first skip bytes of the Turing
348 data.
351 xor_data = self.gen(skip, len(source))
352 fmt = '%dB' % len(source)
353 d2 = unpack(fmt, source)
354 x2 = unpack(fmt, xor_data)
355 return pack(fmt, *(a ^ b for a, b in izip(d2, x2)))