1 | /*
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2 | * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
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3 | *
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4 | * Licensed under the OpenSSL license (the "License"). You may not use
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5 | * this file except in compliance with the License. You can obtain a copy
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6 | * in the file LICENSE in the source distribution or at
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7 | * https://www.openssl.org/source/license.html
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8 | */
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9 |
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10 | /* Original version from Steven Schoch <schoch@sheba.arc.nasa.gov> */
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11 |
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12 | #include <stdio.h>
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13 | #include "internal/cryptlib.h"
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14 | #include <openssl/bn.h>
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15 | #include <openssl/sha.h>
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16 | #include "dsa_locl.h"
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17 | #include <openssl/asn1.h>
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18 |
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19 | static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
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20 | static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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21 | BIGNUM **rp);
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22 | static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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23 | BIGNUM **rp, const unsigned char *dgst, int dlen);
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24 | static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
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25 | DSA_SIG *sig, DSA *dsa);
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26 | static int dsa_init(DSA *dsa);
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27 | static int dsa_finish(DSA *dsa);
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28 |
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29 | static DSA_METHOD openssl_dsa_meth = {
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30 | "OpenSSL DSA method",
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31 | dsa_do_sign,
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32 | dsa_sign_setup_no_digest,
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33 | dsa_do_verify,
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34 | NULL, /* dsa_mod_exp, */
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35 | NULL, /* dsa_bn_mod_exp, */
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36 | dsa_init,
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37 | dsa_finish,
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38 | DSA_FLAG_FIPS_METHOD,
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39 | NULL,
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40 | NULL,
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41 | NULL
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42 | };
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43 |
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44 | const DSA_METHOD *DSA_OpenSSL(void)
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45 | {
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46 | return &openssl_dsa_meth;
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47 | }
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48 |
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49 | static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
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50 | {
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51 | BIGNUM *kinv = NULL;
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52 | BIGNUM *m;
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53 | BIGNUM *xr;
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54 | BN_CTX *ctx = NULL;
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55 | int reason = ERR_R_BN_LIB;
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56 | DSA_SIG *ret = NULL;
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57 | int rv = 0;
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58 |
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59 | m = BN_new();
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60 | xr = BN_new();
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61 | if (m == NULL || xr == NULL)
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62 | goto err;
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63 |
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64 | if (!dsa->p || !dsa->q || !dsa->g) {
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65 | reason = DSA_R_MISSING_PARAMETERS;
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66 | goto err;
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67 | }
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68 |
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69 | ret = DSA_SIG_new();
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70 | if (ret == NULL)
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71 | goto err;
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72 | ret->r = BN_new();
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73 | ret->s = BN_new();
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74 | if (ret->r == NULL || ret->s == NULL)
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75 | goto err;
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76 |
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77 | ctx = BN_CTX_new();
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78 | if (ctx == NULL)
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79 | goto err;
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80 | redo:
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81 | if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
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82 | goto err;
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83 |
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84 | if (dlen > BN_num_bytes(dsa->q))
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85 | /*
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86 | * if the digest length is greater than the size of q use the
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87 | * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
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88 | * 4.2
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89 | */
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90 | dlen = BN_num_bytes(dsa->q);
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91 | if (BN_bin2bn(dgst, dlen, m) == NULL)
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92 | goto err;
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93 |
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94 | /* Compute s = inv(k) (m + xr) mod q */
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95 | if (!BN_mod_mul(xr, dsa->priv_key, ret->r, dsa->q, ctx))
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96 | goto err; /* s = xr */
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97 | if (!BN_add(ret->s, xr, m))
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98 | goto err; /* s = m + xr */
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99 | if (BN_cmp(ret->s, dsa->q) > 0)
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100 | if (!BN_sub(ret->s, ret->s, dsa->q))
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101 | goto err;
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102 | if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx))
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103 | goto err;
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104 |
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105 | /*
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106 | * Redo if r or s is zero as required by FIPS 186-3: this is very
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107 | * unlikely.
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108 | */
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109 | if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
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110 | goto redo;
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111 |
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112 | rv = 1;
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113 |
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114 | err:
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115 | if (rv == 0) {
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116 | DSAerr(DSA_F_DSA_DO_SIGN, reason);
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117 | DSA_SIG_free(ret);
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118 | ret = NULL;
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119 | }
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120 | BN_CTX_free(ctx);
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121 | BN_clear_free(m);
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122 | BN_clear_free(xr);
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123 | BN_clear_free(kinv);
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124 | return ret;
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125 | }
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126 |
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127 | static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
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128 | BIGNUM **kinvp, BIGNUM **rp)
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129 | {
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130 | return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
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131 | }
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132 |
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133 | static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
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134 | BIGNUM **kinvp, BIGNUM **rp,
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135 | const unsigned char *dgst, int dlen)
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136 | {
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137 | BN_CTX *ctx = NULL;
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138 | BIGNUM *k, *kinv = NULL, *r = *rp;
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139 | int ret = 0;
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140 |
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141 | if (!dsa->p || !dsa->q || !dsa->g) {
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142 | DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
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143 | return 0;
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144 | }
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145 |
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146 | k = BN_new();
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147 | if (k == NULL)
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148 | goto err;
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149 |
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150 | if (ctx_in == NULL) {
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151 | if ((ctx = BN_CTX_new()) == NULL)
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152 | goto err;
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153 | } else
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154 | ctx = ctx_in;
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155 |
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156 | /* Get random k */
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157 | do {
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158 | if (dgst != NULL) {
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159 | /*
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160 | * We calculate k from SHA512(private_key + H(message) + random).
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161 | * This protects the private key from a weak PRNG.
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162 | */
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163 | if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
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164 | dlen, ctx))
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165 | goto err;
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166 | } else if (!BN_rand_range(k, dsa->q))
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167 | goto err;
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168 | } while (BN_is_zero(k));
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169 |
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170 | BN_set_flags(k, BN_FLG_CONSTTIME);
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171 |
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172 | if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
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173 | if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
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174 | dsa->lock, dsa->p, ctx))
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175 | goto err;
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176 | }
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177 |
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178 | /* Compute r = (g^k mod p) mod q */
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179 |
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180 | /*
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181 | * We do not want timing information to leak the length of k, so we
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182 | * compute g^k using an equivalent exponent of fixed length. (This
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183 | * is a kludge that we need because the BN_mod_exp_mont() does not
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184 | * let us specify the desired timing behaviour.)
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185 | */
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186 |
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187 | if (!BN_add(k, k, dsa->q))
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188 | goto err;
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189 | if (BN_num_bits(k) <= BN_num_bits(dsa->q)) {
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190 | if (!BN_add(k, k, dsa->q))
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191 | goto err;
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192 | }
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193 |
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194 | if ((dsa)->meth->bn_mod_exp != NULL) {
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195 | if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx,
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196 | dsa->method_mont_p))
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197 | goto err;
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198 | } else {
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199 | if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
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200 | goto err;
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201 | }
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202 |
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203 | if (!BN_mod(r, r, dsa->q, ctx))
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204 | goto err;
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205 |
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206 | /* Compute part of 's = inv(k) (m + xr) mod q' */
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207 | if ((kinv = BN_mod_inverse(NULL, k, dsa->q, ctx)) == NULL)
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208 | goto err;
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209 |
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210 | BN_clear_free(*kinvp);
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211 | *kinvp = kinv;
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212 | kinv = NULL;
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213 | ret = 1;
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214 | err:
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215 | if (!ret)
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216 | DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
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217 | if (ctx != ctx_in)
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218 | BN_CTX_free(ctx);
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219 | BN_clear_free(k);
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220 | return ret;
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221 | }
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222 |
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223 | static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
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224 | DSA_SIG *sig, DSA *dsa)
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225 | {
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226 | BN_CTX *ctx;
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227 | BIGNUM *u1, *u2, *t1;
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228 | BN_MONT_CTX *mont = NULL;
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229 | const BIGNUM *r, *s;
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230 | int ret = -1, i;
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231 | if (!dsa->p || !dsa->q || !dsa->g) {
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232 | DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
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233 | return -1;
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234 | }
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235 |
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236 | i = BN_num_bits(dsa->q);
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237 | /* fips 186-3 allows only different sizes for q */
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238 | if (i != 160 && i != 224 && i != 256) {
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239 | DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
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240 | return -1;
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241 | }
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242 |
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243 | if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
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244 | DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
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245 | return -1;
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246 | }
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247 | u1 = BN_new();
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248 | u2 = BN_new();
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249 | t1 = BN_new();
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250 | ctx = BN_CTX_new();
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251 | if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
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252 | goto err;
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253 |
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254 | DSA_SIG_get0(sig, &r, &s);
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255 |
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256 | if (BN_is_zero(r) || BN_is_negative(r) ||
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257 | BN_ucmp(r, dsa->q) >= 0) {
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258 | ret = 0;
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259 | goto err;
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260 | }
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261 | if (BN_is_zero(s) || BN_is_negative(s) ||
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262 | BN_ucmp(s, dsa->q) >= 0) {
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263 | ret = 0;
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264 | goto err;
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265 | }
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266 |
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267 | /*
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268 | * Calculate W = inv(S) mod Q save W in u2
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269 | */
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270 | if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
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271 | goto err;
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272 |
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273 | /* save M in u1 */
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274 | if (dgst_len > (i >> 3))
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275 | /*
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276 | * if the digest length is greater than the size of q use the
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277 | * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
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278 | * 4.2
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279 | */
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280 | dgst_len = (i >> 3);
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281 | if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
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282 | goto err;
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283 |
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284 | /* u1 = M * w mod q */
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285 | if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx))
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286 | goto err;
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287 |
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288 | /* u2 = r * w mod q */
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289 | if (!BN_mod_mul(u2, r, u2, dsa->q, ctx))
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290 | goto err;
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291 |
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292 | if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
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293 | mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
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294 | dsa->lock, dsa->p, ctx);
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295 | if (!mont)
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296 | goto err;
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297 | }
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298 |
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299 | if (dsa->meth->dsa_mod_exp != NULL) {
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300 | if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2,
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301 | dsa->p, ctx, mont))
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302 | goto err;
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303 | } else {
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304 | if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
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305 | mont))
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306 | goto err;
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307 | }
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308 |
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309 | /* let u1 = u1 mod q */
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310 | if (!BN_mod(u1, t1, dsa->q, ctx))
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311 | goto err;
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312 |
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313 | /*
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314 | * V is now in u1. If the signature is correct, it will be equal to R.
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315 | */
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316 | ret = (BN_ucmp(u1, r) == 0);
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317 |
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318 | err:
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319 | if (ret < 0)
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320 | DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
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321 | BN_CTX_free(ctx);
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322 | BN_free(u1);
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323 | BN_free(u2);
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324 | BN_free(t1);
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325 | return (ret);
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326 | }
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327 |
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328 | static int dsa_init(DSA *dsa)
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329 | {
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330 | dsa->flags |= DSA_FLAG_CACHE_MONT_P;
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331 | return (1);
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332 | }
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333 |
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334 | static int dsa_finish(DSA *dsa)
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335 | {
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336 | BN_MONT_CTX_free(dsa->method_mont_p);
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337 | return (1);
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338 | }
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