yuezonghe | 824eb0c | 2024-06-27 02:32:26 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved. |
| 3 | * |
| 4 | * Licensed under the OpenSSL license (the "License"). You may not use |
| 5 | * this file except in compliance with the License. You can obtain a copy |
| 6 | * in the file LICENSE in the source distribution or at |
| 7 | * https://www.openssl.org/source/license.html |
| 8 | */ |
| 9 | |
| 10 | #include <stdio.h> |
| 11 | #include "internal/cryptlib.h" |
| 12 | #include "dh_local.h" |
| 13 | #include "crypto/bn.h" |
| 14 | |
| 15 | static int generate_key(DH *dh); |
| 16 | static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh); |
| 17 | static int dh_bn_mod_exp(const DH *dh, BIGNUM *r, |
| 18 | const BIGNUM *a, const BIGNUM *p, |
| 19 | const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx); |
| 20 | static int dh_init(DH *dh); |
| 21 | static int dh_finish(DH *dh); |
| 22 | |
| 23 | int DH_generate_key(DH *dh) |
| 24 | { |
| 25 | return dh->meth->generate_key(dh); |
| 26 | } |
| 27 | |
| 28 | /*- |
| 29 | * NB: This function is inherently not constant time due to the |
| 30 | * RFC 5246 (8.1.2) padding style that strips leading zero bytes. |
| 31 | */ |
| 32 | int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh) |
| 33 | { |
| 34 | int ret = 0, i; |
| 35 | volatile size_t npad = 0, mask = 1; |
| 36 | |
| 37 | /* compute the key; ret is constant unless compute_key is external */ |
| 38 | if ((ret = dh->meth->compute_key(key, pub_key, dh)) <= 0) |
| 39 | return ret; |
| 40 | |
| 41 | /* count leading zero bytes, yet still touch all bytes */ |
| 42 | for (i = 0; i < ret; i++) { |
| 43 | mask &= !key[i]; |
| 44 | npad += mask; |
| 45 | } |
| 46 | |
| 47 | /* unpad key */ |
| 48 | ret -= npad; |
| 49 | /* key-dependent memory access, potentially leaking npad / ret */ |
| 50 | memmove(key, key + npad, ret); |
| 51 | /* key-dependent memory access, potentially leaking npad / ret */ |
| 52 | memset(key + ret, 0, npad); |
| 53 | |
| 54 | return ret; |
| 55 | } |
| 56 | |
| 57 | int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh) |
| 58 | { |
| 59 | int rv, pad; |
| 60 | |
| 61 | /* rv is constant unless compute_key is external */ |
| 62 | rv = dh->meth->compute_key(key, pub_key, dh); |
| 63 | if (rv <= 0) |
| 64 | return rv; |
| 65 | pad = BN_num_bytes(dh->p) - rv; |
| 66 | /* pad is constant (zero) unless compute_key is external */ |
| 67 | if (pad > 0) { |
| 68 | memmove(key + pad, key, rv); |
| 69 | memset(key, 0, pad); |
| 70 | } |
| 71 | return rv + pad; |
| 72 | } |
| 73 | |
| 74 | static DH_METHOD dh_ossl = { |
| 75 | "OpenSSL DH Method", |
| 76 | generate_key, |
| 77 | compute_key, |
| 78 | dh_bn_mod_exp, |
| 79 | dh_init, |
| 80 | dh_finish, |
| 81 | DH_FLAG_FIPS_METHOD, |
| 82 | NULL, |
| 83 | NULL |
| 84 | }; |
| 85 | |
| 86 | static const DH_METHOD *default_DH_method = &dh_ossl; |
| 87 | |
| 88 | const DH_METHOD *DH_OpenSSL(void) |
| 89 | { |
| 90 | return &dh_ossl; |
| 91 | } |
| 92 | |
| 93 | void DH_set_default_method(const DH_METHOD *meth) |
| 94 | { |
| 95 | default_DH_method = meth; |
| 96 | } |
| 97 | |
| 98 | const DH_METHOD *DH_get_default_method(void) |
| 99 | { |
| 100 | return default_DH_method; |
| 101 | } |
| 102 | |
| 103 | static int generate_key(DH *dh) |
| 104 | { |
| 105 | int ok = 0; |
| 106 | int generate_new_key = 0; |
| 107 | unsigned l; |
| 108 | BN_CTX *ctx = NULL; |
| 109 | BN_MONT_CTX *mont = NULL; |
| 110 | BIGNUM *pub_key = NULL, *priv_key = NULL; |
| 111 | |
| 112 | if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) { |
| 113 | DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_LARGE); |
| 114 | return 0; |
| 115 | } |
| 116 | |
| 117 | ctx = BN_CTX_new(); |
| 118 | if (ctx == NULL) |
| 119 | goto err; |
| 120 | |
| 121 | if (dh->priv_key == NULL) { |
| 122 | priv_key = BN_secure_new(); |
| 123 | if (priv_key == NULL) |
| 124 | goto err; |
| 125 | generate_new_key = 1; |
| 126 | } else |
| 127 | priv_key = dh->priv_key; |
| 128 | |
| 129 | if (dh->pub_key == NULL) { |
| 130 | pub_key = BN_new(); |
| 131 | if (pub_key == NULL) |
| 132 | goto err; |
| 133 | } else |
| 134 | pub_key = dh->pub_key; |
| 135 | |
| 136 | if (dh->flags & DH_FLAG_CACHE_MONT_P) { |
| 137 | mont = BN_MONT_CTX_set_locked(&dh->method_mont_p, |
| 138 | dh->lock, dh->p, ctx); |
| 139 | if (!mont) |
| 140 | goto err; |
| 141 | } |
| 142 | |
| 143 | if (generate_new_key) { |
| 144 | if (dh->q) { |
| 145 | do { |
| 146 | if (!BN_priv_rand_range(priv_key, dh->q)) |
| 147 | goto err; |
| 148 | } |
| 149 | while (BN_is_zero(priv_key) || BN_is_one(priv_key)); |
| 150 | } else { |
| 151 | /* secret exponent length */ |
| 152 | l = dh->length ? dh->length : BN_num_bits(dh->p) - 1; |
| 153 | if (!BN_priv_rand(priv_key, l, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY)) |
| 154 | goto err; |
| 155 | /* |
| 156 | * We handle just one known case where g is a quadratic non-residue: |
| 157 | * for g = 2: p % 8 == 3 |
| 158 | */ |
| 159 | if (BN_is_word(dh->g, DH_GENERATOR_2) && !BN_is_bit_set(dh->p, 2)) { |
| 160 | /* clear bit 0, since it won't be a secret anyway */ |
| 161 | if (!BN_clear_bit(priv_key, 0)) |
| 162 | goto err; |
| 163 | } |
| 164 | } |
| 165 | } |
| 166 | |
| 167 | { |
| 168 | BIGNUM *prk = BN_new(); |
| 169 | |
| 170 | if (prk == NULL) |
| 171 | goto err; |
| 172 | BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME); |
| 173 | |
| 174 | if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) { |
| 175 | BN_clear_free(prk); |
| 176 | goto err; |
| 177 | } |
| 178 | /* We MUST free prk before any further use of priv_key */ |
| 179 | BN_clear_free(prk); |
| 180 | } |
| 181 | |
| 182 | dh->pub_key = pub_key; |
| 183 | dh->priv_key = priv_key; |
| 184 | ok = 1; |
| 185 | err: |
| 186 | if (ok != 1) |
| 187 | DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB); |
| 188 | |
| 189 | if (pub_key != dh->pub_key) |
| 190 | BN_free(pub_key); |
| 191 | if (priv_key != dh->priv_key) |
| 192 | BN_free(priv_key); |
| 193 | BN_CTX_free(ctx); |
| 194 | return ok; |
| 195 | } |
| 196 | |
| 197 | static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh) |
| 198 | { |
| 199 | BN_CTX *ctx = NULL; |
| 200 | BN_MONT_CTX *mont = NULL; |
| 201 | BIGNUM *tmp; |
| 202 | int ret = -1; |
| 203 | int check_result; |
| 204 | |
| 205 | if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) { |
| 206 | DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE); |
| 207 | goto err; |
| 208 | } |
| 209 | |
| 210 | ctx = BN_CTX_new(); |
| 211 | if (ctx == NULL) |
| 212 | goto err; |
| 213 | BN_CTX_start(ctx); |
| 214 | tmp = BN_CTX_get(ctx); |
| 215 | if (tmp == NULL) |
| 216 | goto err; |
| 217 | |
| 218 | if (dh->priv_key == NULL) { |
| 219 | DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE); |
| 220 | goto err; |
| 221 | } |
| 222 | |
| 223 | if (dh->flags & DH_FLAG_CACHE_MONT_P) { |
| 224 | mont = BN_MONT_CTX_set_locked(&dh->method_mont_p, |
| 225 | dh->lock, dh->p, ctx); |
| 226 | BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME); |
| 227 | if (!mont) |
| 228 | goto err; |
| 229 | } |
| 230 | |
| 231 | if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) { |
| 232 | DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY); |
| 233 | goto err; |
| 234 | } |
| 235 | |
| 236 | if (!dh-> |
| 237 | meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) { |
| 238 | DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB); |
| 239 | goto err; |
| 240 | } |
| 241 | |
| 242 | ret = BN_bn2binpad(tmp, key, BN_num_bytes(dh->p)); |
| 243 | err: |
| 244 | BN_CTX_end(ctx); |
| 245 | BN_CTX_free(ctx); |
| 246 | return ret; |
| 247 | } |
| 248 | |
| 249 | static int dh_bn_mod_exp(const DH *dh, BIGNUM *r, |
| 250 | const BIGNUM *a, const BIGNUM *p, |
| 251 | const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx) |
| 252 | { |
| 253 | return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx); |
| 254 | } |
| 255 | |
| 256 | static int dh_init(DH *dh) |
| 257 | { |
| 258 | dh->flags |= DH_FLAG_CACHE_MONT_P; |
| 259 | return 1; |
| 260 | } |
| 261 | |
| 262 | static int dh_finish(DH *dh) |
| 263 | { |
| 264 | BN_MONT_CTX_free(dh->method_mont_p); |
| 265 | return 1; |
| 266 | } |