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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: idea.c,v 1.4 2000/07/15 17:47:58 mdw Exp $ |
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4 | * |
5 | * Implementation of the IDEA cipher |
6 | * |
7 | * (c) 1999 Straylight/Edgeware |
8 | */ |
9 | |
10 | /*----- Licensing notice --------------------------------------------------* |
11 | * |
12 | * This file is part of Catacomb. |
13 | * |
14 | * Catacomb is free software; you can redistribute it and/or modify |
15 | * it under the terms of the GNU Library General Public License as |
16 | * published by the Free Software Foundation; either version 2 of the |
17 | * License, or (at your option) any later version. |
18 | * |
19 | * Catacomb is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
22 | * GNU Library General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU Library General Public |
25 | * License along with Catacomb; if not, write to the Free |
26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
27 | * MA 02111-1307, USA. |
28 | */ |
29 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: idea.c,v $ |
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33 | * Revision 1.4 2000/07/15 17:47:58 mdw |
34 | * Fix bug in decryption key scheduling. |
35 | * |
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36 | * Revision 1.3 2000/07/02 18:24:39 mdw |
37 | * Use a new multiplication function from an Ascom white paper to resist |
38 | * timing attacks. |
39 | * |
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40 | * Revision 1.2 2000/06/17 11:24:08 mdw |
41 | * New key size interface. |
42 | * |
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43 | * Revision 1.1 1999/09/03 08:41:12 mdw |
44 | * Initial import. |
45 | * |
46 | */ |
47 | |
48 | /*----- Header files ------------------------------------------------------*/ |
49 | |
50 | #include <assert.h> |
51 | #include <stdio.h> |
52 | #include <stdlib.h> |
53 | #include <string.h> |
54 | |
55 | #include <mLib/bits.h> |
56 | |
57 | #include "blkc.h" |
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58 | #include "gcipher.h" |
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59 | #include "idea.h" |
60 | |
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61 | /*----- Global variables --------------------------------------------------*/ |
62 | |
63 | const octet idea_keysz[] = { KSZ_SET, IDEA_KEYSZ }; |
64 | |
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65 | /*----- Main code ---------------------------------------------------------*/ |
66 | |
67 | /* --- @inv@ --- * |
68 | * |
69 | * Arguments: @uint16 n@ = number to invert |
70 | * |
71 | * Returns: Multiplicative inverse of @n@ %$\pmod{2^{16} + 1}$%. |
72 | * |
73 | * Use: Computes multiplicative inverses. This is handy for the |
74 | * decryption key scheduling. |
75 | */ |
76 | |
77 | static uint16 inv(uint16 n) |
78 | { |
79 | uint32 m = 0x10001; |
80 | uint32 a = 1, b = 0; |
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81 | uint32 nn = n; |
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82 | |
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83 | if (!nn) |
84 | nn = 0x10000; |
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85 | for (;;) { |
86 | uint32 q, r, t; |
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87 | if (!(r = m % nn)) |
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88 | break; |
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89 | q = m / nn; |
90 | m = nn; nn = r; |
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91 | t = a; a = b - q * a; b = t; |
92 | } |
93 | if (a > MASK16) |
94 | a += 1; |
95 | return (U16(a)); |
96 | } |
97 | |
98 | /* --- @MUL@ --- * |
99 | * |
100 | * Arguments @x@ and @y@ are two 32-bit values to multiply. On exit, @x@ is |
101 | * the product of the two arguments. The result is not normalized back to 16 |
102 | * bits; the arguments are not expected to be normalized. |
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103 | * |
104 | * This code is from `Side Channel Attack Hardening of the IDEA Cipher', |
105 | * published by Ascom Tech. |
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106 | */ |
107 | |
108 | #define MUL(x, y) do { \ |
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109 | unsigned _t; \ |
110 | uint32 _tt; \ |
111 | \ |
112 | x = U16(x - 1); \ |
113 | _t = U16(y - 1); \ |
114 | _tt = (uint32)x * (uint32)_t + (uint32)x + (uint32)_t + 1; \ |
115 | x = U16(_tt); \ |
116 | _t = U16(_tt >> 16); \ |
117 | x = x - _t + (x <= _t); \ |
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118 | } while (0) |
119 | |
120 | /* --- @idea_init@ --- * |
121 | * |
122 | * Arguments: @idea_ctx *k@ = pointer to key block |
123 | * @const void *buf@ = pointer to key buffer |
124 | * @size_t sz@ = size of key material |
125 | * |
126 | * Returns: --- |
127 | * |
128 | * Use: Initializes an IDEA key buffer. The buffer must be exactly |
129 | * 16 bytes in size, because IDEA is only defined with a key |
130 | * size of 128 bits. |
131 | */ |
132 | |
133 | void idea_init(idea_ctx *k, const void *buf, size_t sz) |
134 | { |
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135 | KSZ_ASSERT(idea, sz); |
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136 | |
137 | /* --- Unpack the encryption key --- */ |
138 | |
139 | { |
140 | const octet *p = buf; |
141 | uint16 *q = k->e; |
142 | uint32 a = LOAD32(p + 0); |
143 | uint32 b = LOAD32(p + 4); |
144 | uint32 c = LOAD32(p + 8); |
145 | uint32 d = LOAD32(p + 12); |
146 | int i; |
147 | |
148 | /* --- Main unpacking loop --- */ |
149 | |
150 | for (i = 0; i < 6; i++) { |
151 | |
152 | /* --- Spit out the next 8 subkeys --- */ |
153 | |
154 | q[0] = U16(a >> 16); |
155 | q[1] = U16(a >> 0); |
156 | q[2] = U16(b >> 16); |
157 | q[3] = U16(b >> 0); |
158 | q[4] = U16(c >> 16); |
159 | q[5] = U16(c >> 0); |
160 | q[6] = U16(d >> 16); |
161 | q[7] = U16(d >> 0); |
162 | q += 8; |
163 | |
164 | /* --- Rotate and permute the subkeys --- */ |
165 | |
166 | { |
167 | uint32 t = a; |
168 | a = U32((a << 25) | (b >> 7)); |
169 | b = U32((b << 25) | (c >> 7)); |
170 | c = U32((c << 25) | (d >> 7)); |
171 | d = U32((d << 25) | (t >> 7)); |
172 | } |
173 | } |
174 | |
175 | /* --- Write out the tail-enders --- */ |
176 | |
177 | q[0] = U16(a >> 16); |
178 | q[1] = U16(a >> 0); |
179 | q[2] = U16(b >> 16); |
180 | q[3] = U16(b >> 0); |
181 | } |
182 | |
183 | /* --- Convert this into the decryption key --- */ |
184 | |
185 | { |
186 | uint16 *p = k->e + 52; |
187 | uint16 *q = k->d; |
188 | int i; |
189 | |
190 | /* --- Translate the main round keys --- */ |
191 | |
192 | for (i = 0; i < 8; i++) { |
193 | p -= 6; |
194 | q[4] = p[0]; |
195 | q[5] = p[1]; |
196 | q[0] = inv(p[2]); |
197 | q[3] = inv(p[5]); |
198 | if (i) { |
199 | q[1] = 0x10000 - p[4]; |
200 | q[2] = 0x10000 - p[3]; |
201 | } else { |
202 | q[1] = 0x10000 - p[3]; |
203 | q[2] = 0x10000 - p[4]; |
204 | } |
205 | q += 6; |
206 | } |
207 | |
208 | /* --- Translate the tail-enders --- */ |
209 | |
210 | p -= 4; |
211 | q[0] = inv(p[0]); |
212 | q[1] = 0x10000 - p[1]; |
213 | q[2] = 0x10000 - p[2]; |
214 | q[3] = inv(p[3]); |
215 | } |
216 | } |
217 | |
218 | /* --- @ROUND@ --- */ |
219 | |
220 | #define MIX(k, a, b, c, d) do { \ |
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221 | MUL(a, k[0]); \ |
222 | b += k[1]; \ |
223 | c += k[2]; \ |
224 | MUL(d, k[3]); \ |
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225 | } while (0) |
226 | |
227 | #define MA(k, a, b, c, d) do { \ |
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228 | unsigned _u = a ^ c; \ |
229 | unsigned _v = b ^ d; \ |
230 | MUL(_u, k[4]); \ |
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231 | _v += _u; \ |
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232 | MUL(_v, k[5]); \ |
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233 | _u += _v; \ |
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234 | a ^= _v; \ |
235 | b ^= _u; \ |
236 | c ^= _v; \ |
237 | d ^= _u; \ |
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238 | } while (0); |
239 | |
240 | #define ROUND(k, a, b, c, d) do { \ |
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241 | MIX(k, a, b, c, d); \ |
242 | MA(k, a, b, c, d); \ |
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243 | (k) += 6; \ |
244 | } while (0) |
245 | |
246 | /* --- Encryption --- */ |
247 | |
248 | #define EBLK(k, a, b, c, d) do { \ |
249 | unsigned _a = U16(a >> 16); \ |
250 | unsigned _b = U16(a >> 0); \ |
251 | unsigned _c = U16(b >> 16); \ |
252 | unsigned _d = U16(b >> 0); \ |
253 | const uint16 *_k = (k); \ |
254 | \ |
255 | ROUND(_k, _a, _b, _c, _d); \ |
256 | ROUND(_k, _a, _c, _b, _d); \ |
257 | ROUND(_k, _a, _b, _c, _d); \ |
258 | ROUND(_k, _a, _c, _b, _d); \ |
259 | ROUND(_k, _a, _b, _c, _d); \ |
260 | ROUND(_k, _a, _c, _b, _d); \ |
261 | ROUND(_k, _a, _b, _c, _d); \ |
262 | ROUND(_k, _a, _c, _b, _d); \ |
263 | MIX (_k, _a, _c, _b, _d); \ |
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264 | c = ((uint32)U16(_a) << 16) | (uint32)U16(_c); \ |
265 | d = ((uint32)U16(_b) << 16) | (uint32)U16(_d); \ |
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266 | } while (0) |
267 | |
268 | #define DBLK(k, a, b) EBLK((k), (a), (b)) |
269 | |
270 | /* --- @idea_eblk@, @idea_dblk@ --- * |
271 | * |
272 | * Arguments: @const idea_ctx *k@ = pointer to a key block |
273 | * @const uint32 s[2]@ = pointer to source block |
274 | * @uint32 d[2]@ = pointer to destination block |
275 | * |
276 | * Returns: --- |
277 | * |
278 | * Use: Low-level block encryption and decryption. |
279 | */ |
280 | |
281 | void idea_eblk(const idea_ctx *k, const uint32 *s, uint32 *d) |
282 | { |
283 | EBLK(k->e, s[0], s[1], d[0], d[1]); |
284 | } |
285 | |
286 | void idea_dblk(const idea_ctx *k, const uint32 *s, uint32 *d) |
287 | { |
288 | EBLK(k->d, s[0], s[1], d[0], d[1]); |
289 | } |
290 | |
291 | BLKC_TEST(IDEA, idea) |
292 | |
293 | /*----- That's all, folks -------------------------------------------------*/ |