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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 { |
143
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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; |
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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 */ |
143
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29 if (group_size >= MDSA_MAX_GROUP || group_size <= 15 || |
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30 group_size >= modulus_size || (modulus_size - group_size) >= MDSA_DELTA) { |
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31 return CRYPT_INVALID_ARG; |
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32 } |
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33 |
143
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34 /* allocate ram */ |
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35 buf = XMALLOC(MDSA_DELTA); |
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36 if (buf == NULL) { |
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37 return CRYPT_MEM; |
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38 } |
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39 |
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40 /* init mp_ints */ |
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41 if ((err = mp_init_multi(&tmp, &tmp2, &key->g, &key->q, &key->p, &key->x, &key->y, NULL)) != MP_OKAY) { |
143
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42 err = mpi_to_ltc_error(err); |
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43 goto __ERR; |
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44 } |
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45 |
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46 /* make our prime q */ |
143
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47 if ((err = rand_prime(&key->q, group_size*8, prng, wprng)) != CRYPT_OK) { goto __ERR; } |
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48 |
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49 /* double q */ |
143
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50 if ((err = mp_mul_2(&key->q, &tmp)) != MP_OKAY) { goto error; } |
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51 |
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52 /* now make a random string and multply it against q */ |
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53 if (prng_descriptor[wprng].read(buf+1, modulus_size - group_size, prng) != (unsigned long)(modulus_size - group_size)) { |
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54 err = CRYPT_ERROR_READPRNG; |
143
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55 goto __ERR; |
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56 } |
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57 |
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58 /* force magnitude */ |
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59 buf[0] = 1; |
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60 |
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61 /* force even */ |
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62 buf[modulus_size - group_size] &= ~1; |
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63 |
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64 if ((err = mp_read_unsigned_bin(&tmp2, buf, modulus_size - group_size+1)) != MP_OKAY) { goto error; } |
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65 if ((err = mp_mul(&key->q, &tmp2, &key->p)) != MP_OKAY) { goto error; } |
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66 if ((err = mp_add_d(&key->p, 1, &key->p)) != MP_OKAY) { goto error; } |
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67 |
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68 /* now loop until p is prime */ |
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69 for (;;) { |
143
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70 if ((err = is_prime(&key->p, &res)) != CRYPT_OK) { goto __ERR; } |
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71 if (res == MP_YES) break; |
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72 |
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73 /* add 2q to p and 2 to tmp2 */ |
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74 if ((err = mp_add(&tmp, &key->p, &key->p)) != MP_OKAY) { goto error; } |
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75 if ((err = mp_add_d(&tmp2, 2, &tmp2)) != MP_OKAY) { goto error; } |
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76 } |
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77 |
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78 /* now p = (q * tmp2) + 1 is prime, find a value g for which g^tmp2 != 1 */ |
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79 mp_set(&key->g, 1); |
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80 |
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81 do { |
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82 if ((err = mp_add_d(&key->g, 1, &key->g)) != MP_OKAY) { goto error; } |
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83 if ((err = mp_exptmod(&key->g, &tmp2, &key->p, &tmp)) != MP_OKAY) { goto error; } |
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84 } while (mp_cmp_d(&tmp, 1) == MP_EQ); |
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85 |
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86 /* at this point tmp generates a group of order q mod p */ |
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87 mp_exch(&tmp, &key->g); |
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88 |
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89 /* so now we have our DH structure, generator g, order q, modulus p |
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90 Now we need a random exponent [mod q] and it's power g^x mod p |
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91 */ |
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92 do { |
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93 if (prng_descriptor[wprng].read(buf, group_size, prng) != (unsigned long)group_size) { |
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94 err = CRYPT_ERROR_READPRNG; |
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95 goto __ERR; |
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96 } |
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97 if ((err = mp_read_unsigned_bin(&key->x, buf, group_size)) != MP_OKAY) { goto error; } |
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98 } while (mp_cmp_d(&key->x, 1) != MP_GT); |
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99 if ((err = mp_exptmod(&key->g, &key->x, &key->p, &key->y)) != MP_OKAY) { goto error; } |
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100 |
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101 key->type = PK_PRIVATE; |
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102 key->qord = group_size; |
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103 |
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104 /* shrink the ram required */ |
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105 if ((err = mp_shrink(&key->g)) != MP_OKAY) { goto error; } |
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106 if ((err = mp_shrink(&key->p)) != MP_OKAY) { goto error; } |
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107 if ((err = mp_shrink(&key->q)) != MP_OKAY) { goto error; } |
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108 if ((err = mp_shrink(&key->x)) != MP_OKAY) { goto error; } |
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109 if ((err = mp_shrink(&key->y)) != MP_OKAY) { goto error; } |
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110 |
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111 #ifdef CLEAN_STACK |
143
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112 zeromem(buf, MDSA_DELTA); |
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113 #endif |
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114 |
143
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115 err = CRYPT_OK; |
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116 goto done; |
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117 error: |
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118 err = mpi_to_ltc_error(err); |
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119 __ERR: |
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120 mp_clear_multi(&key->g, &key->q, &key->p, &key->x, &key->y, NULL); |
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121 done: |
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122 mp_clear_multi(&tmp, &tmp2, NULL); |
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123 |
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124 XFREE(buf); |
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125 return err; |
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126 } |
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127 |
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128 #endif |