annotate libtomcrypt/src/math/rand_prime.c @ 533:805ae74ec024

Encrypt in-place, avoid an extra malloc
author Matt Johnston <matt@ucc.asn.au>
date Sun, 01 Mar 2009 14:38:25 +0000
parents 0cbe8f6dbf9e
children f849a5ca2efc
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382
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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.com
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10 */
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11 #include "tomcrypt.h"
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12
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13 /**
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14 @file rand_prime.c
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15 Generate a random prime, Tom St Denis
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16 */
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17
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18 #define USE_BBS 1
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19
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20 int rand_prime(void *N, long len, prng_state *prng, int wprng)
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21 {
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22 int err, res, type;
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23 unsigned char *buf;
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24
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25 LTC_ARGCHK(N != NULL);
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26
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27 /* get type */
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28 if (len < 0) {
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29 type = USE_BBS;
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30 len = -len;
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31 } else {
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32 type = 0;
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33 }
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34
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35 /* allow sizes between 2 and 512 bytes for a prime size */
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36 if (len < 2 || len > 512) {
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37 return CRYPT_INVALID_PRIME_SIZE;
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38 }
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39
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40 /* valid PRNG? Better be! */
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41 if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
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42 return err;
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43 }
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44
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45 /* allocate buffer to work with */
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46 buf = XCALLOC(1, len);
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47 if (buf == NULL) {
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48 return CRYPT_MEM;
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49 }
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50
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51 do {
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52 /* generate value */
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53 if (prng_descriptor[wprng].read(buf, len, prng) != (unsigned long)len) {
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54 XFREE(buf);
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55 return CRYPT_ERROR_READPRNG;
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56 }
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57
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58 /* munge bits */
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59 buf[0] |= 0x80 | 0x40;
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60 buf[len-1] |= 0x01 | ((type & USE_BBS) ? 0x02 : 0x00);
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61
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62 /* load value */
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63 if ((err = mp_read_unsigned_bin(N, buf, len)) != CRYPT_OK) {
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64 XFREE(buf);
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65 return err;
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66 }
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67
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68 /* test */
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69 if ((err = mp_prime_is_prime(N, 8, &res)) != CRYPT_OK) {
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70 XFREE(buf);
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71 return err;
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72 }
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73 } while (res == LTC_MP_NO);
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74
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75 #ifdef LTC_CLEAN_STACK
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76 zeromem(buf, len);
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77 #endif
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78
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79 XFREE(buf);
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80 return CRYPT_OK;
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81 }
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82
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83
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84
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85 /* $Source: /cvs/libtom/libtomcrypt/src/math/rand_prime.c,v $ */
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86 /* $Revision: 1.6 $ */
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87 /* $Date: 2006/03/31 14:15:35 $ */