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annotate omac_init.c @ 18:712dd6dfb0eb libtomcrypt

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makefile
author Matt Johnston <matt@ucc.asn.au>
date Tue, 15 Jun 2004 14:34:07 +0000
parents d7da3b1e1540
children 5d99163f7e32
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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 memcpy(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