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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 $ */ |
