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