rijndael.py 10.7 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
"""
A pure python (slow) implementation of rijndael with a decent interface

To include -

from rijndael import rijndael

To do a key setup -

r = rijndael(key, block_size = 16)

key must be a string of length 16, 24, or 32
blocksize must be 16, 24, or 32. Default is 16

To use -

ciphertext = r.encrypt(plaintext)
plaintext = r.decrypt(ciphertext)

If any strings are of the wrong length a ValueError is thrown
"""

# ported from the Java reference code by Bram Cohen, April 2001
# this code is public domain, unless someone makes 
# an intellectual property claim against the reference 
# code, in which case it can be made public domain by 
# deleting all the comments and renaming all the variables

import copy
import string

shifts = [[[0, 0], [1, 3], [2, 2], [3, 1]],
          [[0, 0], [1, 5], [2, 4], [3, 3]],
          [[0, 0], [1, 7], [3, 5], [4, 4]]]

# [keysize][block_size]
num_rounds = {16: {16: 10, 24: 12, 32: 14}, 24: {16: 12, 24: 12, 32: 14}, 32: {16: 14, 24: 14, 32: 14}}

A = [[1, 1, 1, 1, 1, 0, 0, 0],
     [0, 1, 1, 1, 1, 1, 0, 0],
     [0, 0, 1, 1, 1, 1, 1, 0],
     [0, 0, 0, 1, 1, 1, 1, 1],
     [1, 0, 0, 0, 1, 1, 1, 1],
     [1, 1, 0, 0, 0, 1, 1, 1],
     [1, 1, 1, 0, 0, 0, 1, 1],
     [1, 1, 1, 1, 0, 0, 0, 1]]

# produce log and alog tables, needed for multiplying in the
# field GF(2^m) (generator = 3)
alog = [1]
for i in xrange(255):
    j = (alog[-1] << 1) ^ alog[-1]
    if j & 0x100 != 0:
        j ^= 0x11B
    alog.append(j)

log = [0] * 256
for i in xrange(1, 255):
    log[alog[i]] = i

# multiply two elements of GF(2^m)
def mul(a, b):
    if a == 0 or b == 0:
        return 0
    return alog[(log[a & 0xFF] + log[b & 0xFF]) % 255]

# substitution box based on F^{-1}(x)
box = [[0] * 8 for i in xrange(256)]
box[1][7] = 1
for i in xrange(2, 256):
    j = alog[255 - log[i]]
    for t in xrange(8):
        box[i][t] = (j >> (7 - t)) & 0x01

B = [0, 1, 1, 0, 0, 0, 1, 1]

# affine transform:  box[i] <- B + A*box[i]
cox = [[0] * 8 for i in xrange(256)]
for i in xrange(256):
    for t in xrange(8):
        cox[i][t] = B[t]
        for j in xrange(8):
            cox[i][t] ^= A[t][j] * box[i][j]

# S-boxes and inverse S-boxes
S =  [0] * 256
Si = [0] * 256
for i in xrange(256):
    S[i] = cox[i][0] << 7
    for t in xrange(1, 8):
        S[i] ^= cox[i][t] << (7-t)
    Si[S[i] & 0xFF] = i

# T-boxes
G = [[2, 1, 1, 3],
    [3, 2, 1, 1],
    [1, 3, 2, 1],
    [1, 1, 3, 2]]

AA = [[0] * 8 for i in xrange(4)]

for i in xrange(4):
    for j in xrange(4):
        AA[i][j] = G[i][j]
        AA[i][i+4] = 1

for i in xrange(4):
    pivot = AA[i][i]
    if pivot == 0:
        t = i + 1
        while AA[t][i] == 0 and t < 4:
            t += 1
            assert t != 4, 'G matrix must be invertible'
            for j in xrange(8):
                AA[i][j], AA[t][j] = AA[t][j], AA[i][j]
            pivot = AA[i][i]
    for j in xrange(8):
        if AA[i][j] != 0:
            AA[i][j] = alog[(255 + log[AA[i][j] & 0xFF] - log[pivot & 0xFF]) % 255]
    for t in xrange(4):
        if i != t:
            for j in xrange(i+1, 8):
                AA[t][j] ^= mul(AA[i][j], AA[t][i])
            AA[t][i] = 0

iG = [[0] * 4 for i in xrange(4)]

for i in xrange(4):
    for j in xrange(4):
        iG[i][j] = AA[i][j + 4]

def mul4(a, bs):
    if a == 0:
        return 0
    r = 0
    for b in bs:
        r <<= 8
        if b != 0:
            r = r | mul(a, b)
    return r

T1 = []
T2 = []
T3 = []
T4 = []
T5 = []
T6 = []
T7 = []
T8 = []
U1 = []
U2 = []
U3 = []
U4 = []

for t in xrange(256):
    s = S[t]
    T1.append(mul4(s, G[0]))
    T2.append(mul4(s, G[1]))
    T3.append(mul4(s, G[2]))
    T4.append(mul4(s, G[3]))

    s = Si[t]
    T5.append(mul4(s, iG[0]))
    T6.append(mul4(s, iG[1]))
    T7.append(mul4(s, iG[2]))
    T8.append(mul4(s, iG[3]))

    U1.append(mul4(t, iG[0]))
    U2.append(mul4(t, iG[1]))
    U3.append(mul4(t, iG[2]))
    U4.append(mul4(t, iG[3]))

# round constants
rcon = [1]
r = 1
for t in xrange(1, 30):
    r = mul(2, r)
    rcon.append(r)

del A
del AA
del pivot
del B
del G
del box
del log
del alog
del i
del j
del r
del s
del t
del mul
del mul4
del cox
del iG

class rijndael:
    def __init__(self, key, block_size = 16):
        if block_size != 16 and block_size != 24 and block_size != 32:
            raise ValueError('Invalid block size: ' + str(block_size))
        if len(key) != 16 and len(key) != 24 and len(key) != 32:
            raise ValueError('Invalid key size: ' + str(len(key)))
        self.block_size = block_size

        ROUNDS = num_rounds[len(key)][block_size]
        BC = block_size / 4
        # encryption round keys
        Ke = [[0] * BC for i in xrange(ROUNDS + 1)]
        # decryption round keys
        Kd = [[0] * BC for i in xrange(ROUNDS + 1)]
        ROUND_KEY_COUNT = (ROUNDS + 1) * BC
        KC = len(key) / 4

        # copy user material bytes into temporary ints
        tk = []
        for i in xrange(0, KC):
            tk.append((ord(key[i * 4]) << 24) | (ord(key[i * 4 + 1]) << 16) |
                (ord(key[i * 4 + 2]) << 8) | ord(key[i * 4 + 3]))

        # copy values into round key arrays
        t = 0
        j = 0
        while j < KC and t < ROUND_KEY_COUNT:
            Ke[t / BC][t % BC] = tk[j]
            Kd[ROUNDS - (t / BC)][t % BC] = tk[j]
            j += 1
            t += 1
        tt = 0
        rconpointer = 0
        while t < ROUND_KEY_COUNT:
            # extrapolate using phi (the round key evolution function)
            tt = tk[KC - 1]
            tk[0] ^= (S[(tt >> 16) & 0xFF] & 0xFF) << 24 ^  \
                     (S[(tt >>  8) & 0xFF] & 0xFF) << 16 ^  \
                     (S[ tt        & 0xFF] & 0xFF) <<  8 ^  \
                     (S[(tt >> 24) & 0xFF] & 0xFF)       ^  \
                     (rcon[rconpointer]    & 0xFF) << 24
            rconpointer += 1
            if KC != 8:
                for i in xrange(1, KC):
                    tk[i] ^= tk[i-1]
            else:
                for i in xrange(1, KC / 2):
                    tk[i] ^= tk[i-1]
                tt = tk[KC / 2 - 1]
                tk[KC / 2] ^= (S[ tt        & 0xFF] & 0xFF)       ^ \
                              (S[(tt >>  8) & 0xFF] & 0xFF) <<  8 ^ \
                              (S[(tt >> 16) & 0xFF] & 0xFF) << 16 ^ \
                              (S[(tt >> 24) & 0xFF] & 0xFF) << 24
                for i in xrange(KC / 2 + 1, KC):
                    tk[i] ^= tk[i-1]
            # copy values into round key arrays
            j = 0
            while j < KC and t < ROUND_KEY_COUNT:
                Ke[t / BC][t % BC] = tk[j]
                Kd[ROUNDS - (t / BC)][t % BC] = tk[j]
                j += 1
                t += 1
        # inverse MixColumn where needed
        for r in xrange(1, ROUNDS):
            for j in xrange(BC):
                tt = Kd[r][j]
                Kd[r][j] = U1[(tt >> 24) & 0xFF] ^ \
                           U2[(tt >> 16) & 0xFF] ^ \
                           U3[(tt >>  8) & 0xFF] ^ \
                           U4[ tt        & 0xFF]
        self.Ke = Ke
        self.Kd = Kd

    def encrypt(self, plaintext):
        if len(plaintext) != self.block_size:
            raise ValueError('wrong block length, expected ' + str(self.block_size) + ' got ' + str(len(plaintext)))
        Ke = self.Ke

        BC = self.block_size / 4
        ROUNDS = len(Ke) - 1
        if BC == 4:
            SC = 0
        elif BC == 6:
            SC = 1
        else:
            SC = 2
        s1 = shifts[SC][1][0]
        s2 = shifts[SC][2][0]
        s3 = shifts[SC][3][0]
        a = [0] * BC
        # temporary work array
        t = []
        # plaintext to ints + key
        for i in xrange(BC):
            t.append((ord(plaintext[i * 4    ]) << 24 |
                      ord(plaintext[i * 4 + 1]) << 16 |
                      ord(plaintext[i * 4 + 2]) <<  8 |
                      ord(plaintext[i * 4 + 3])        ) ^ Ke[0][i])
        # apply round transforms
        for r in xrange(1, ROUNDS):
            for i in xrange(BC):
                a[i] = (T1[(t[ i           ] >> 24) & 0xFF] ^
                        T2[(t[(i + s1) % BC] >> 16) & 0xFF] ^
                        T3[(t[(i + s2) % BC] >>  8) & 0xFF] ^
                        T4[ t[(i + s3) % BC]        & 0xFF]  ) ^ Ke[r][i]
            t = copy.copy(a)
        # last round is special
        result = []
        for i in xrange(BC):
            tt = Ke[ROUNDS][i]
            result.append((S[(t[ i           ] >> 24) & 0xFF] ^ (tt >> 24)) & 0xFF)
            result.append((S[(t[(i + s1) % BC] >> 16) & 0xFF] ^ (tt >> 16)) & 0xFF)
            result.append((S[(t[(i + s2) % BC] >>  8) & 0xFF] ^ (tt >>  8)) & 0xFF)
            result.append((S[ t[(i + s3) % BC]        & 0xFF] ^  tt       ) & 0xFF)
        return string.join(map(chr, result), '')

    def decrypt(self, ciphertext):
        if len(ciphertext) != self.block_size:
            raise ValueError('wrong block length, expected ' + str(self.block_size) + ' got ' + str(len(ciphertext)))
        Kd = self.Kd

        BC = self.block_size / 4
        ROUNDS = len(Kd) - 1
        if BC == 4:
            SC = 0
        elif BC == 6:
            SC = 1
        else:
            SC = 2
        s1 = shifts[SC][1][1]
        s2 = shifts[SC][2][1]
        s3 = shifts[SC][3][1]
        a = [0] * BC
        # temporary work array
        t = [0] * BC
        # ciphertext to ints + key
        for i in xrange(BC):
            t[i] = (ord(ciphertext[i * 4    ]) << 24 |
                    ord(ciphertext[i * 4 + 1]) << 16 |
                    ord(ciphertext[i * 4 + 2]) <<  8 |
                    ord(ciphertext[i * 4 + 3])        ) ^ Kd[0][i]
        # apply round transforms
        for r in xrange(1, ROUNDS):
            for i in xrange(BC):
                a[i] = (T5[(t[ i           ] >> 24) & 0xFF] ^
                        T6[(t[(i + s1) % BC] >> 16) & 0xFF] ^
                        T7[(t[(i + s2) % BC] >>  8) & 0xFF] ^
                        T8[ t[(i + s3) % BC]        & 0xFF]  ) ^ Kd[r][i]
            t = copy.copy(a)
        # last round is special
        result = []
        for i in xrange(BC):
            tt = Kd[ROUNDS][i]
            result.append((Si[(t[ i           ] >> 24) & 0xFF] ^ (tt >> 24)) & 0xFF)
            result.append((Si[(t[(i + s1) % BC] >> 16) & 0xFF] ^ (tt >> 16)) & 0xFF)
            result.append((Si[(t[(i + s2) % BC] >>  8) & 0xFF] ^ (tt >>  8)) & 0xFF)
            result.append((Si[ t[(i + s3) % BC]        & 0xFF] ^  tt       ) & 0xFF)
        return string.join(map(chr, result), '')

def encrypt(key, block):
    return rijndael(key, len(block)).encrypt(block)

def decrypt(key, block):
    return rijndael(key, len(block)).decrypt(block)

def test():
    def t(kl, bl):
        b = 'b' * bl
        r = rijndael('a' * kl, bl)
        assert r.decrypt(r.encrypt(b)) == b
    t(16, 16)
    t(16, 24)
    t(16, 32)
    t(24, 16)
    t(24, 24)
    t(24, 32)
    t(32, 16)
    t(32, 24)
    t(32, 32)