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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
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2 * |
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3 * LibTomCrypt is a library that provides various cryptographic |
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4 * algorithms in a highly modular and flexible manner. |
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5 * |
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6 * The library is free for all purposes without any express |
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7 * guarantee it works. |
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8 * |
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9 * Tom St Denis, [email protected], http://libtomcrypt.org |
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10 */ |
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11 /* OMAC1 Support by Tom St Denis (for 64 and 128 bit block ciphers only) */ |
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12 #include "mycrypt.h" |
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13 |
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14 #ifdef OMAC |
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15 |
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16 int omac_init(omac_state *omac, int cipher, const unsigned char *key, unsigned long keylen) |
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17 { |
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18 int err, x, y, mask, msb, len; |
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19 |
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20 _ARGCHK(omac != NULL); |
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21 _ARGCHK(key != NULL); |
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22 |
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23 /* schedule the key */ |
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24 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) { |
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25 return err; |
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26 } |
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27 |
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28 /* now setup the system */ |
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29 switch (cipher_descriptor[cipher].block_length) { |
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30 case 8: mask = 0x1B; |
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31 len = 8; |
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32 break; |
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33 case 16: mask = 0x87; |
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34 len = 16; |
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35 break; |
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36 default: return CRYPT_INVALID_ARG; |
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37 } |
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38 |
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39 if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &omac->key)) != CRYPT_OK) { |
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40 return err; |
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41 } |
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42 |
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43 /* ok now we need Lu and Lu^2 [calc one from the other] */ |
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44 |
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45 /* first calc L which is Ek(0) */ |
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46 zeromem(omac->Lu[0], cipher_descriptor[cipher].block_length); |
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47 cipher_descriptor[cipher].ecb_encrypt(omac->Lu[0], omac->Lu[0], &omac->key); |
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48 |
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49 /* now do the mults, whoopy! */ |
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50 for (x = 0; x < 2; x++) { |
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51 /* if msb(L * u^(x+1)) = 0 then just shift, otherwise shift and xor constant mask */ |
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52 msb = omac->Lu[x][0] >> 7; |
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53 |
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54 /* shift left */ |
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55 for (y = 0; y < (len - 1); y++) { |
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56 omac->Lu[x][y] = ((omac->Lu[x][y] << 1) | (omac->Lu[x][y+1] >> 7)) & 255; |
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57 } |
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58 omac->Lu[x][len - 1] = ((omac->Lu[x][len - 1] << 1) ^ (msb ? mask : 0)) & 255; |
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59 |
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60 /* copy up as require */ |
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61 if (x == 0) { |
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62 XMEMCPY(omac->Lu[1], omac->Lu[0], sizeof(omac->Lu[0])); |
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63 } |
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64 } |
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65 |
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66 /* setup state */ |
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67 omac->cipher_idx = cipher; |
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68 omac->buflen = 0; |
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69 omac->blklen = len; |
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70 zeromem(omac->prev, sizeof(omac->prev)); |
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71 zeromem(omac->block, sizeof(omac->block)); |
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72 |
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73 return CRYPT_OK; |
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74 } |
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75 |
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76 #endif |
