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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: idea.c,v 1.3 2000/07/02 18:24:39 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 1.3 2000/07/02 18:24:39 mdw |
34 | * Use a new multiplication function from an Ascom white paper to resist |
35 | * timing attacks. |
36 | * |
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37 | * Revision 1.2 2000/06/17 11:24:08 mdw |
38 | * New key size interface. |
39 | * |
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40 | * Revision 1.1 1999/09/03 08:41:12 mdw |
41 | * Initial import. |
42 | * |
43 | */ |
44 | |
45 | /*----- Header files ------------------------------------------------------*/ |
46 | |
47 | #include <assert.h> |
48 | #include <stdio.h> |
49 | #include <stdlib.h> |
50 | #include <string.h> |
51 | |
52 | #include <mLib/bits.h> |
53 | |
54 | #include "blkc.h" |
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55 | #include "gcipher.h" |
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56 | #include "idea.h" |
57 | |
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58 | /*----- Global variables --------------------------------------------------*/ |
59 | |
60 | const octet idea_keysz[] = { KSZ_SET, IDEA_KEYSZ }; |
61 | |
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62 | /*----- Main code ---------------------------------------------------------*/ |
63 | |
64 | /* --- @inv@ --- * |
65 | * |
66 | * Arguments: @uint16 n@ = number to invert |
67 | * |
68 | * Returns: Multiplicative inverse of @n@ %$\pmod{2^{16} + 1}$%. |
69 | * |
70 | * Use: Computes multiplicative inverses. This is handy for the |
71 | * decryption key scheduling. |
72 | */ |
73 | |
74 | static uint16 inv(uint16 n) |
75 | { |
76 | uint32 m = 0x10001; |
77 | uint32 a = 1, b = 0; |
78 | |
79 | for (;;) { |
80 | uint32 q, r, t; |
81 | if (!(r = m % n)) |
82 | break; |
83 | q = m / n; |
84 | m = n; n = r; |
85 | t = a; a = b - q * a; b = t; |
86 | } |
87 | if (a > MASK16) |
88 | a += 1; |
89 | return (U16(a)); |
90 | } |
91 | |
92 | /* --- @MUL@ --- * |
93 | * |
94 | * Arguments @x@ and @y@ are two 32-bit values to multiply. On exit, @x@ is |
95 | * the product of the two arguments. The result is not normalized back to 16 |
96 | * bits; the arguments are not expected to be normalized. |
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97 | * |
98 | * This code is from `Side Channel Attack Hardening of the IDEA Cipher', |
99 | * published by Ascom Tech. |
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100 | */ |
101 | |
102 | #define MUL(x, y) do { \ |
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103 | unsigned _t; \ |
104 | uint32 _tt; \ |
105 | \ |
106 | x = U16(x - 1); \ |
107 | _t = U16(y - 1); \ |
108 | _tt = (uint32)x * (uint32)_t + (uint32)x + (uint32)_t + 1; \ |
109 | x = U16(_tt); \ |
110 | _t = U16(_tt >> 16); \ |
111 | x = x - _t + (x <= _t); \ |
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112 | } while (0) |
113 | |
114 | /* --- @idea_init@ --- * |
115 | * |
116 | * Arguments: @idea_ctx *k@ = pointer to key block |
117 | * @const void *buf@ = pointer to key buffer |
118 | * @size_t sz@ = size of key material |
119 | * |
120 | * Returns: --- |
121 | * |
122 | * Use: Initializes an IDEA key buffer. The buffer must be exactly |
123 | * 16 bytes in size, because IDEA is only defined with a key |
124 | * size of 128 bits. |
125 | */ |
126 | |
127 | void idea_init(idea_ctx *k, const void *buf, size_t sz) |
128 | { |
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129 | KSZ_ASSERT(idea, sz); |
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130 | |
131 | /* --- Unpack the encryption key --- */ |
132 | |
133 | { |
134 | const octet *p = buf; |
135 | uint16 *q = k->e; |
136 | uint32 a = LOAD32(p + 0); |
137 | uint32 b = LOAD32(p + 4); |
138 | uint32 c = LOAD32(p + 8); |
139 | uint32 d = LOAD32(p + 12); |
140 | int i; |
141 | |
142 | /* --- Main unpacking loop --- */ |
143 | |
144 | for (i = 0; i < 6; i++) { |
145 | |
146 | /* --- Spit out the next 8 subkeys --- */ |
147 | |
148 | q[0] = U16(a >> 16); |
149 | q[1] = U16(a >> 0); |
150 | q[2] = U16(b >> 16); |
151 | q[3] = U16(b >> 0); |
152 | q[4] = U16(c >> 16); |
153 | q[5] = U16(c >> 0); |
154 | q[6] = U16(d >> 16); |
155 | q[7] = U16(d >> 0); |
156 | q += 8; |
157 | |
158 | /* --- Rotate and permute the subkeys --- */ |
159 | |
160 | { |
161 | uint32 t = a; |
162 | a = U32((a << 25) | (b >> 7)); |
163 | b = U32((b << 25) | (c >> 7)); |
164 | c = U32((c << 25) | (d >> 7)); |
165 | d = U32((d << 25) | (t >> 7)); |
166 | } |
167 | } |
168 | |
169 | /* --- Write out the tail-enders --- */ |
170 | |
171 | q[0] = U16(a >> 16); |
172 | q[1] = U16(a >> 0); |
173 | q[2] = U16(b >> 16); |
174 | q[3] = U16(b >> 0); |
175 | } |
176 | |
177 | /* --- Convert this into the decryption key --- */ |
178 | |
179 | { |
180 | uint16 *p = k->e + 52; |
181 | uint16 *q = k->d; |
182 | int i; |
183 | |
184 | /* --- Translate the main round keys --- */ |
185 | |
186 | for (i = 0; i < 8; i++) { |
187 | p -= 6; |
188 | q[4] = p[0]; |
189 | q[5] = p[1]; |
190 | q[0] = inv(p[2]); |
191 | q[3] = inv(p[5]); |
192 | if (i) { |
193 | q[1] = 0x10000 - p[4]; |
194 | q[2] = 0x10000 - p[3]; |
195 | } else { |
196 | q[1] = 0x10000 - p[3]; |
197 | q[2] = 0x10000 - p[4]; |
198 | } |
199 | q += 6; |
200 | } |
201 | |
202 | /* --- Translate the tail-enders --- */ |
203 | |
204 | p -= 4; |
205 | q[0] = inv(p[0]); |
206 | q[1] = 0x10000 - p[1]; |
207 | q[2] = 0x10000 - p[2]; |
208 | q[3] = inv(p[3]); |
209 | } |
210 | } |
211 | |
212 | /* --- @ROUND@ --- */ |
213 | |
214 | #define MIX(k, a, b, c, d) do { \ |
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215 | MUL(a, k[0]); \ |
216 | b += k[1]; \ |
217 | c += k[2]; \ |
218 | MUL(d, k[3]); \ |
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219 | } while (0) |
220 | |
221 | #define MA(k, a, b, c, d) do { \ |
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222 | unsigned _u = a ^ c; \ |
223 | unsigned _v = b ^ d; \ |
224 | MUL(_u, k[4]); \ |
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225 | _v += _u; \ |
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226 | MUL(_v, k[5]); \ |
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227 | _u += _v; \ |
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228 | a ^= _v; \ |
229 | b ^= _u; \ |
230 | c ^= _v; \ |
231 | d ^= _u; \ |
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232 | } while (0); |
233 | |
234 | #define ROUND(k, a, b, c, d) do { \ |
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235 | MIX(k, a, b, c, d); \ |
236 | MA(k, a, b, c, d); \ |
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237 | (k) += 6; \ |
238 | } while (0) |
239 | |
240 | /* --- Encryption --- */ |
241 | |
242 | #define EBLK(k, a, b, c, d) do { \ |
243 | unsigned _a = U16(a >> 16); \ |
244 | unsigned _b = U16(a >> 0); \ |
245 | unsigned _c = U16(b >> 16); \ |
246 | unsigned _d = U16(b >> 0); \ |
247 | const uint16 *_k = (k); \ |
248 | \ |
249 | ROUND(_k, _a, _b, _c, _d); \ |
250 | ROUND(_k, _a, _c, _b, _d); \ |
251 | ROUND(_k, _a, _b, _c, _d); \ |
252 | ROUND(_k, _a, _c, _b, _d); \ |
253 | ROUND(_k, _a, _b, _c, _d); \ |
254 | ROUND(_k, _a, _c, _b, _d); \ |
255 | ROUND(_k, _a, _b, _c, _d); \ |
256 | ROUND(_k, _a, _c, _b, _d); \ |
257 | MIX (_k, _a, _c, _b, _d); \ |
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258 | c = (U16(_a) << 16) | U16(_c); \ |
259 | d = (U16(_b) << 16) | U16(_d); \ |
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260 | } while (0) |
261 | |
262 | #define DBLK(k, a, b) EBLK((k), (a), (b)) |
263 | |
264 | /* --- @idea_eblk@, @idea_dblk@ --- * |
265 | * |
266 | * Arguments: @const idea_ctx *k@ = pointer to a key block |
267 | * @const uint32 s[2]@ = pointer to source block |
268 | * @uint32 d[2]@ = pointer to destination block |
269 | * |
270 | * Returns: --- |
271 | * |
272 | * Use: Low-level block encryption and decryption. |
273 | */ |
274 | |
275 | void idea_eblk(const idea_ctx *k, const uint32 *s, uint32 *d) |
276 | { |
277 | EBLK(k->e, s[0], s[1], d[0], d[1]); |
278 | } |
279 | |
280 | void idea_dblk(const idea_ctx *k, const uint32 *s, uint32 *d) |
281 | { |
282 | EBLK(k->d, s[0], s[1], d[0], d[1]); |
283 | } |
284 | |
285 | BLKC_TEST(IDEA, idea) |
286 | |
287 | /*----- That's all, folks -------------------------------------------------*/ |