2 * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the Apache License 2.0 (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
11 * DH low level APIs are deprecated for public use, but still ok for
14 #include "internal/deprecated.h"
17 #include "internal/cryptlib.h"
19 #include "crypto/bn.h"
20 #include "crypto/dh.h"
21 #include "crypto/security_bits.h"
24 # define MIN_STRENGTH 112
26 # define MIN_STRENGTH 80
29 static int generate_key(DH *dh);
30 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
31 const BIGNUM *a, const BIGNUM *p,
32 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
33 static int dh_init(DH *dh);
34 static int dh_finish(DH *dh);
36 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
39 BN_MONT_CTX *mont = NULL;
46 if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) {
47 ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE);
51 if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
52 ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL);
56 ctx = BN_CTX_new_ex(dh->libctx);
60 tmp = BN_CTX_get(ctx);
64 if (dh->priv_key == NULL) {
65 ERR_raise(ERR_LIB_DH, DH_R_NO_PRIVATE_VALUE);
69 if (dh->flags & DH_FLAG_CACHE_MONT_P) {
70 mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
71 dh->lock, dh->params.p, ctx);
72 BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
76 /* TODO(3.0) : Solve in a PR related to Key validation for DH */
78 if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
79 ERR_raise(ERR_LIB_DH, DH_R_INVALID_PUBKEY);
83 if (!dh->meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->params.p, ctx,
85 ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB);
89 /* return the padded key, i.e. same number of bytes as the modulus */
90 ret = BN_bn2binpad(tmp, key, BN_num_bytes(dh->params.p));
98 * NB: This function is inherently not constant time due to the
99 * RFC 5246 (8.1.2) padding style that strips leading zero bytes.
101 int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
104 volatile size_t npad = 0, mask = 1;
106 /* compute the key; ret is constant unless compute_key is external */
108 ret = compute_key(key, pub_key, dh);
110 ret = dh->meth->compute_key(key, pub_key, dh);
115 /* count leading zero bytes, yet still touch all bytes */
116 for (i = 0; i < ret; i++) {
123 /* key-dependent memory access, potentially leaking npad / ret */
124 memmove(key, key + npad, ret);
125 /* key-dependent memory access, potentially leaking npad / ret */
126 memset(key + ret, 0, npad);
131 int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
135 /* rv is constant unless compute_key is external */
137 rv = compute_key(key, pub_key, dh);
139 rv = dh->meth->compute_key(key, pub_key, dh);
143 pad = BN_num_bytes(dh->params.p) - rv;
144 /* pad is constant (zero) unless compute_key is external */
146 memmove(key + pad, key, rv);
152 static DH_METHOD dh_ossl = {
164 static const DH_METHOD *default_DH_method = &dh_ossl;
166 const DH_METHOD *DH_OpenSSL(void)
171 const DH_METHOD *DH_get_default_method(void)
173 return default_DH_method;
176 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
177 const BIGNUM *a, const BIGNUM *p,
178 const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
180 return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
183 static int dh_init(DH *dh)
185 dh->flags |= DH_FLAG_CACHE_MONT_P;
186 ossl_ffc_params_init(&dh->params);
191 static int dh_finish(DH *dh)
193 BN_MONT_CTX_free(dh->method_mont_p);
198 void DH_set_default_method(const DH_METHOD *meth)
200 default_DH_method = meth;
202 #endif /* FIPS_MODULE */
204 int DH_generate_key(DH *dh)
207 return generate_key(dh);
209 return dh->meth->generate_key(dh);
213 int ossl_dh_generate_public_key(BN_CTX *ctx, const DH *dh,
214 const BIGNUM *priv_key, BIGNUM *pub_key)
217 BIGNUM *prk = BN_new();
218 BN_MONT_CTX *mont = NULL;
223 if (dh->flags & DH_FLAG_CACHE_MONT_P) {
225 * We take the input DH as const, but we lie, because in some cases we
226 * want to get a hold of its Montgomery context.
228 * We cast to remove the const qualifier in this case, it should be
231 BN_MONT_CTX **pmont = (BN_MONT_CTX **)&dh->method_mont_p;
233 mont = BN_MONT_CTX_set_locked(pmont, dh->lock, dh->params.p, ctx);
237 BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
239 /* pub_key = g^priv_key mod p */
240 if (!dh->meth->bn_mod_exp(dh, pub_key, dh->params.g, prk, dh->params.p,
249 static int generate_key(DH *dh)
252 int generate_new_key = 0;
257 BIGNUM *pub_key = NULL, *priv_key = NULL;
259 if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) {
260 ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE);
264 if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
265 ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL);
269 ctx = BN_CTX_new_ex(dh->libctx);
273 if (dh->priv_key == NULL) {
274 priv_key = BN_secure_new();
275 if (priv_key == NULL)
277 generate_new_key = 1;
279 priv_key = dh->priv_key;
282 if (dh->pub_key == NULL) {
287 pub_key = dh->pub_key;
289 if (generate_new_key) {
290 /* Is it an approved safe prime ?*/
291 if (DH_get_nid(dh) != NID_undef) {
293 ossl_ifc_ffc_compute_security_bits(BN_num_bits(dh->params.p));
295 if (dh->params.q == NULL
296 || dh->length > BN_num_bits(dh->params.q))
298 /* dh->length = maximum bit length of generated private key */
299 if (!ossl_ffc_generate_private_key(ctx, &dh->params, dh->length,
300 max_strength, priv_key))
304 if (dh->params.q == NULL)
307 if (dh->params.q == NULL) {
308 /* secret exponent length, must satisfy 2^(l-1) <= p */
310 && dh->length >= BN_num_bits(dh->params.p))
312 l = dh->length ? dh->length : BN_num_bits(dh->params.p) - 1;
313 if (!BN_priv_rand_ex(priv_key, l, BN_RAND_TOP_ONE,
314 BN_RAND_BOTTOM_ANY, ctx))
317 * We handle just one known case where g is a quadratic non-residue:
318 * for g = 2: p % 8 == 3
320 if (BN_is_word(dh->params.g, DH_GENERATOR_2)
321 && !BN_is_bit_set(dh->params.p, 2)) {
322 /* clear bit 0, since it won't be a secret anyway */
323 if (!BN_clear_bit(priv_key, 0))
329 /* Do a partial check for invalid p, q, g */
330 if (!ossl_ffc_params_simple_validate(dh->libctx, &dh->params,
331 FFC_PARAM_TYPE_DH, NULL))
334 * For FFC FIPS 186-4 keygen
335 * security strength s = 112,
336 * Max Private key size N = len(q)
338 if (!ossl_ffc_generate_private_key(ctx, &dh->params,
339 BN_num_bits(dh->params.q),
347 if (!ossl_dh_generate_public_key(ctx, dh, priv_key, pub_key))
350 dh->pub_key = pub_key;
351 dh->priv_key = priv_key;
356 ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB);
358 if (pub_key != dh->pub_key)
360 if (priv_key != dh->priv_key)
366 int ossl_dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
368 int err_reason = DH_R_BN_ERROR;
369 BIGNUM *pubkey = NULL;
373 if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
375 DH_get0_pqg(dh, &p, NULL, NULL);
376 if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
377 err_reason = DH_R_NO_PARAMETERS_SET;
381 * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
382 * public key is of size not equal to size of p
384 if (BN_is_zero(pubkey) || p_size != len) {
385 err_reason = DH_R_INVALID_PUBKEY;
388 if (DH_set0_key(dh, pubkey, NULL) != 1)
392 ERR_raise(ERR_LIB_DH, err_reason);
397 size_t ossl_dh_key2buf(const DH *dh, unsigned char **pbuf_out, size_t size,
400 const BIGNUM *pubkey;
401 unsigned char *pbuf = NULL;
405 DH_get0_pqg(dh, &p, NULL, NULL);
406 DH_get0_key(dh, &pubkey, NULL);
407 if (p == NULL || pubkey == NULL
408 || (p_size = BN_num_bytes(p)) == 0
409 || BN_num_bytes(pubkey) == 0) {
410 ERR_raise(ERR_LIB_DH, DH_R_INVALID_PUBKEY);
413 if (pbuf_out != NULL && (alloc || *pbuf_out != NULL)) {
415 if (size >= (size_t)p_size)
418 pbuf = OPENSSL_malloc(p_size);
422 ERR_raise(ERR_LIB_DH, ERR_R_MALLOC_FAILURE);
426 * As per Section 4.2.8.1 of RFC 8446 left pad public
427 * key with zeros to the size of p
429 if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) {
432 ERR_raise(ERR_LIB_DH, DH_R_BN_ERROR);