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annotate dsa_make_key.c @ 0:d7da3b1e1540 libtomcrypt

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put back the 0.95 makefile which was inadvertently merged over
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:21:40 +0000
parents
children 5d99163f7e32
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0
d7da3b1e1540 put back the 0.95 makefile which was inadvertently merged over
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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 #include "mycrypt.h"
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12
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13 #ifdef MDSA
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14
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15 int dsa_make_key(prng_state *prng, int wprng, int group_size, int modulus_size, dsa_key *key)
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16 {
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17 mp_int tmp, tmp2;
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18 int err, res;
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19 unsigned char buf[512];
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20
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21 _ARGCHK(key != NULL);
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22
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23 /* check prng */
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24 if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
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25 return err;
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26 }
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27
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28 /* check size */
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29 if (group_size >= 1024 || group_size <= 15 ||
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30 group_size >= modulus_size || (modulus_size - group_size) >= (int)sizeof(buf)) {
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31 return CRYPT_INVALID_ARG;
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32 }
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33
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34 /* init mp_ints */
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35 if ((err = mp_init_multi(&tmp, &tmp2, &key->g, &key->q, &key->p, &key->x, &key->y, NULL)) != MP_OKAY) {
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36 return mpi_to_ltc_error(err);
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37 }
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38
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39 /* make our prime q */
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40 if ((err = rand_prime(&key->q, group_size*8, prng, wprng)) != CRYPT_OK) { goto error2; }
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41
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42 /* double q */
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43 if ((err = mp_mul_2(&key->q, &tmp)) != MP_OKAY) { goto error; }
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44
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45 /* now make a random string and multply it against q */
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46 if (prng_descriptor[wprng].read(buf+1, modulus_size - group_size, prng) != (unsigned long)(modulus_size - group_size)) {
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47 err = CRYPT_ERROR_READPRNG;
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48 goto error2;
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49 }
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50
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51 /* force magnitude */
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52 buf[0] = 1;
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53
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54 /* force even */
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55 buf[modulus_size - group_size] &= ~1;
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56
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57 if ((err = mp_read_unsigned_bin(&tmp2, buf, modulus_size - group_size+1)) != MP_OKAY) { goto error; }
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58 if ((err = mp_mul(&key->q, &tmp2, &key->p)) != MP_OKAY) { goto error; }
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59 if ((err = mp_add_d(&key->p, 1, &key->p)) != MP_OKAY) { goto error; }
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60
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61 /* now loop until p is prime */
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62 for (;;) {
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63 if ((err = is_prime(&key->p, &res)) != CRYPT_OK) { goto error2; }
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64 if (res == MP_YES) break;
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65
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66 /* add 2q to p and 2 to tmp2 */
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67 if ((err = mp_add(&tmp, &key->p, &key->p)) != MP_OKAY) { goto error; }
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68 if ((err = mp_add_d(&tmp2, 2, &tmp2)) != MP_OKAY) { goto error; }
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69 }
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70
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71 /* now p = (q * tmp2) + 1 is prime, find a value g for which g^tmp2 != 1 */
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72 mp_set(&key->g, 1);
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73
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74 do {
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75 if ((err = mp_add_d(&key->g, 1, &key->g)) != MP_OKAY) { goto error; }
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76 if ((err = mp_exptmod(&key->g, &tmp2, &key->p, &tmp)) != MP_OKAY) { goto error; }
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77 } while (mp_cmp_d(&tmp, 1) == MP_EQ);
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78
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79 /* at this point tmp generates a group of order q mod p */
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80 mp_exch(&tmp, &key->g);
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81
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82 /* so now we have our DH structure, generator g, order q, modulus p
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83 Now we need a random exponent [mod q] and it's power g^x mod p
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84 */
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85 do {
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86 if (prng_descriptor[wprng].read(buf, group_size, prng) != (unsigned long)group_size) {
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87 err = CRYPT_ERROR_READPRNG;
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88 goto error2;
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89 }
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90 if ((err = mp_read_unsigned_bin(&key->x, buf, group_size)) != MP_OKAY) { goto error; }
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91 } while (mp_cmp_d(&key->x, 1) != MP_GT);
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92 if ((err = mp_exptmod(&key->g, &key->x, &key->p, &key->y)) != MP_OKAY) { goto error; }
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93
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94 key->type = PK_PRIVATE;
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95 key->qord = group_size;
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96
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97 /* shrink the ram required */
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98 if ((err = mp_shrink(&key->g)) != MP_OKAY) { goto error; }
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99 if ((err = mp_shrink(&key->p)) != MP_OKAY) { goto error; }
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100 if ((err = mp_shrink(&key->q)) != MP_OKAY) { goto error; }
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101 if ((err = mp_shrink(&key->x)) != MP_OKAY) { goto error; }
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102 if ((err = mp_shrink(&key->y)) != MP_OKAY) { goto error; }
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103
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104 err = CRYPT_OK;
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105
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106 #ifdef CLEAN_STACK
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107 zeromem(buf, sizeof(buf));
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108 #endif
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109
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110 goto done;
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111 error : err = mpi_to_ltc_error(err);
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112 error2: mp_clear_multi(&key->g, &key->q, &key->p, &key->x, &key->y, NULL);
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113 done : mp_clear_multi(&tmp, &tmp2, NULL);
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114 return err;
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115 }
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116
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117 #endif