| /* |
| * Copyright 1995-2022 The OpenSSL Project Authors. All Rights Reserved. |
| * |
| * Licensed under the Apache License 2.0 (the "License"). You may not use |
| * this file except in compliance with the License. You can obtain a copy |
| * in the file LICENSE in the source distribution or at |
| * https://www.openssl.org/source/license.html |
| */ |
| |
| /* |
| * DH low level APIs are deprecated for public use, but still ok for |
| * internal use. |
| */ |
| #include "internal/deprecated.h" |
| |
| #include <stdio.h> |
| #include "internal/cryptlib.h" |
| #include "dh_local.h" |
| #include "crypto/bn.h" |
| #include "crypto/dh.h" |
| #include "crypto/security_bits.h" |
| |
| #ifdef FIPS_MODULE |
| # define MIN_STRENGTH 112 |
| #else |
| # define MIN_STRENGTH 80 |
| #endif |
| |
| static int generate_key(DH *dh); |
| static int dh_bn_mod_exp(const DH *dh, BIGNUM *r, |
| const BIGNUM *a, const BIGNUM *p, |
| const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx); |
| static int dh_init(DH *dh); |
| static int dh_finish(DH *dh); |
| |
| /* |
| * See SP800-56Ar3 Section 5.7.1.1 |
| * Finite Field Cryptography Diffie-Hellman (FFC DH) Primitive |
| */ |
| int ossl_dh_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh) |
| { |
| BN_CTX *ctx = NULL; |
| BN_MONT_CTX *mont = NULL; |
| BIGNUM *z = NULL, *pminus1; |
| int ret = -1; |
| |
| if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) { |
| ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE); |
| goto err; |
| } |
| |
| if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) { |
| ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL); |
| return 0; |
| } |
| |
| ctx = BN_CTX_new_ex(dh->libctx); |
| if (ctx == NULL) |
| goto err; |
| BN_CTX_start(ctx); |
| pminus1 = BN_CTX_get(ctx); |
| z = BN_CTX_get(ctx); |
| if (z == NULL) |
| goto err; |
| |
| if (dh->priv_key == NULL) { |
| ERR_raise(ERR_LIB_DH, DH_R_NO_PRIVATE_VALUE); |
| goto err; |
| } |
| |
| if (dh->flags & DH_FLAG_CACHE_MONT_P) { |
| mont = BN_MONT_CTX_set_locked(&dh->method_mont_p, |
| dh->lock, dh->params.p, ctx); |
| BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME); |
| if (!mont) |
| goto err; |
| } |
| |
| /* (Step 1) Z = pub_key^priv_key mod p */ |
| if (!dh->meth->bn_mod_exp(dh, z, pub_key, dh->priv_key, dh->params.p, ctx, |
| mont)) { |
| ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB); |
| goto err; |
| } |
| |
| /* (Step 2) Error if z <= 1 or z = p - 1 */ |
| if (BN_copy(pminus1, dh->params.p) == NULL |
| || !BN_sub_word(pminus1, 1) |
| || BN_cmp(z, BN_value_one()) <= 0 |
| || BN_cmp(z, pminus1) == 0) { |
| ERR_raise(ERR_LIB_DH, DH_R_INVALID_SECRET); |
| goto err; |
| } |
| |
| /* return the padded key, i.e. same number of bytes as the modulus */ |
| ret = BN_bn2binpad(z, key, BN_num_bytes(dh->params.p)); |
| err: |
| BN_clear(z); /* (Step 2) destroy intermediate values */ |
| BN_CTX_end(ctx); |
| BN_CTX_free(ctx); |
| return ret; |
| } |
| |
| /*- |
| * NB: This function is inherently not constant time due to the |
| * RFC 5246 (8.1.2) padding style that strips leading zero bytes. |
| */ |
| int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh) |
| { |
| int ret = 0, i; |
| volatile size_t npad = 0, mask = 1; |
| |
| /* compute the key; ret is constant unless compute_key is external */ |
| #ifdef FIPS_MODULE |
| ret = ossl_dh_compute_key(key, pub_key, dh); |
| #else |
| ret = dh->meth->compute_key(key, pub_key, dh); |
| #endif |
| if (ret <= 0) |
| return ret; |
| |
| /* count leading zero bytes, yet still touch all bytes */ |
| for (i = 0; i < ret; i++) { |
| mask &= !key[i]; |
| npad += mask; |
| } |
| |
| /* unpad key */ |
| ret -= npad; |
| /* key-dependent memory access, potentially leaking npad / ret */ |
| memmove(key, key + npad, ret); |
| /* key-dependent memory access, potentially leaking npad / ret */ |
| memset(key + ret, 0, npad); |
| |
| return ret; |
| } |
| |
| int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh) |
| { |
| int rv, pad; |
| |
| /* rv is constant unless compute_key is external */ |
| #ifdef FIPS_MODULE |
| rv = ossl_dh_compute_key(key, pub_key, dh); |
| #else |
| rv = dh->meth->compute_key(key, pub_key, dh); |
| #endif |
| if (rv <= 0) |
| return rv; |
| pad = BN_num_bytes(dh->params.p) - rv; |
| /* pad is constant (zero) unless compute_key is external */ |
| if (pad > 0) { |
| memmove(key + pad, key, rv); |
| memset(key, 0, pad); |
| } |
| return rv + pad; |
| } |
| |
| static DH_METHOD dh_ossl = { |
| "OpenSSL DH Method", |
| generate_key, |
| ossl_dh_compute_key, |
| dh_bn_mod_exp, |
| dh_init, |
| dh_finish, |
| DH_FLAG_FIPS_METHOD, |
| NULL, |
| NULL |
| }; |
| |
| static const DH_METHOD *default_DH_method = &dh_ossl; |
| |
| const DH_METHOD *DH_OpenSSL(void) |
| { |
| return &dh_ossl; |
| } |
| |
| const DH_METHOD *DH_get_default_method(void) |
| { |
| return default_DH_method; |
| } |
| |
| static int dh_bn_mod_exp(const DH *dh, BIGNUM *r, |
| const BIGNUM *a, const BIGNUM *p, |
| const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx) |
| { |
| return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx); |
| } |
| |
| static int dh_init(DH *dh) |
| { |
| dh->flags |= DH_FLAG_CACHE_MONT_P; |
| ossl_ffc_params_init(&dh->params); |
| dh->dirty_cnt++; |
| return 1; |
| } |
| |
| static int dh_finish(DH *dh) |
| { |
| BN_MONT_CTX_free(dh->method_mont_p); |
| return 1; |
| } |
| |
| #ifndef FIPS_MODULE |
| void DH_set_default_method(const DH_METHOD *meth) |
| { |
| default_DH_method = meth; |
| } |
| #endif /* FIPS_MODULE */ |
| |
| int DH_generate_key(DH *dh) |
| { |
| #ifdef FIPS_MODULE |
| return generate_key(dh); |
| #else |
| return dh->meth->generate_key(dh); |
| #endif |
| } |
| |
| int ossl_dh_generate_public_key(BN_CTX *ctx, const DH *dh, |
| const BIGNUM *priv_key, BIGNUM *pub_key) |
| { |
| int ret = 0; |
| BIGNUM *prk = BN_new(); |
| BN_MONT_CTX *mont = NULL; |
| |
| if (prk == NULL) |
| return 0; |
| |
| if (dh->flags & DH_FLAG_CACHE_MONT_P) { |
| /* |
| * We take the input DH as const, but we lie, because in some cases we |
| * want to get a hold of its Montgomery context. |
| * |
| * We cast to remove the const qualifier in this case, it should be |
| * fine... |
| */ |
| BN_MONT_CTX **pmont = (BN_MONT_CTX **)&dh->method_mont_p; |
| |
| mont = BN_MONT_CTX_set_locked(pmont, dh->lock, dh->params.p, ctx); |
| if (mont == NULL) |
| goto err; |
| } |
| BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME); |
| |
| /* pub_key = g^priv_key mod p */ |
| if (!dh->meth->bn_mod_exp(dh, pub_key, dh->params.g, prk, dh->params.p, |
| ctx, mont)) |
| goto err; |
| ret = 1; |
| err: |
| BN_clear_free(prk); |
| return ret; |
| } |
| |
| static int generate_key(DH *dh) |
| { |
| int ok = 0; |
| int generate_new_key = 0; |
| #ifndef FIPS_MODULE |
| unsigned l; |
| #endif |
| BN_CTX *ctx = NULL; |
| BIGNUM *pub_key = NULL, *priv_key = NULL; |
| |
| if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) { |
| ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE); |
| return 0; |
| } |
| |
| if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) { |
| ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL); |
| return 0; |
| } |
| |
| ctx = BN_CTX_new_ex(dh->libctx); |
| if (ctx == NULL) |
| goto err; |
| |
| if (dh->priv_key == NULL) { |
| priv_key = BN_secure_new(); |
| if (priv_key == NULL) |
| goto err; |
| generate_new_key = 1; |
| } else { |
| priv_key = dh->priv_key; |
| } |
| |
| if (dh->pub_key == NULL) { |
| pub_key = BN_new(); |
| if (pub_key == NULL) |
| goto err; |
| } else { |
| pub_key = dh->pub_key; |
| } |
| if (generate_new_key) { |
| /* Is it an approved safe prime ?*/ |
| if (DH_get_nid(dh) != NID_undef) { |
| int max_strength = |
| ossl_ifc_ffc_compute_security_bits(BN_num_bits(dh->params.p)); |
| |
| if (dh->params.q == NULL |
| || dh->length > BN_num_bits(dh->params.q)) |
| goto err; |
| /* dh->length = maximum bit length of generated private key */ |
| if (!ossl_ffc_generate_private_key(ctx, &dh->params, dh->length, |
| max_strength, priv_key)) |
| goto err; |
| } else { |
| #ifdef FIPS_MODULE |
| if (dh->params.q == NULL) |
| goto err; |
| #else |
| if (dh->params.q == NULL) { |
| /* secret exponent length, must satisfy 2^(l-1) <= p */ |
| if (dh->length != 0 |
| && dh->length >= BN_num_bits(dh->params.p)) |
| goto err; |
| l = dh->length ? dh->length : BN_num_bits(dh->params.p) - 1; |
| if (!BN_priv_rand_ex(priv_key, l, BN_RAND_TOP_ONE, |
| BN_RAND_BOTTOM_ANY, 0, ctx)) |
| goto err; |
| /* |
| * We handle just one known case where g is a quadratic non-residue: |
| * for g = 2: p % 8 == 3 |
| */ |
| if (BN_is_word(dh->params.g, DH_GENERATOR_2) |
| && !BN_is_bit_set(dh->params.p, 2)) { |
| /* clear bit 0, since it won't be a secret anyway */ |
| if (!BN_clear_bit(priv_key, 0)) |
| goto err; |
| } |
| } else |
| #endif |
| { |
| /* Do a partial check for invalid p, q, g */ |
| if (!ossl_ffc_params_simple_validate(dh->libctx, &dh->params, |
| FFC_PARAM_TYPE_DH, NULL)) |
| goto err; |
| /* |
| * For FFC FIPS 186-4 keygen |
| * security strength s = 112, |
| * Max Private key size N = len(q) |
| */ |
| if (!ossl_ffc_generate_private_key(ctx, &dh->params, |
| BN_num_bits(dh->params.q), |
| MIN_STRENGTH, |
| priv_key)) |
| goto err; |
| } |
| } |
| } |
| |
| if (!ossl_dh_generate_public_key(ctx, dh, priv_key, pub_key)) |
| goto err; |
| |
| dh->pub_key = pub_key; |
| dh->priv_key = priv_key; |
| dh->dirty_cnt++; |
| ok = 1; |
| err: |
| if (ok != 1) |
| ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB); |
| |
| if (pub_key != dh->pub_key) |
| BN_free(pub_key); |
| if (priv_key != dh->priv_key) |
| BN_free(priv_key); |
| BN_CTX_free(ctx); |
| return ok; |
| } |
| |
| int ossl_dh_buf2key(DH *dh, const unsigned char *buf, size_t len) |
| { |
| int err_reason = DH_R_BN_ERROR; |
| BIGNUM *pubkey = NULL; |
| const BIGNUM *p; |
| int ret; |
| |
| if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL) |
| goto err; |
| DH_get0_pqg(dh, &p, NULL, NULL); |
| if (p == NULL || BN_num_bytes(p) == 0) { |
| err_reason = DH_R_NO_PARAMETERS_SET; |
| goto err; |
| } |
| /* Prevent small subgroup attacks per RFC 8446 Section 4.2.8.1 */ |
| if (!ossl_dh_check_pub_key_partial(dh, pubkey, &ret)) { |
| err_reason = DH_R_INVALID_PUBKEY; |
| goto err; |
| } |
| if (DH_set0_key(dh, pubkey, NULL) != 1) |
| goto err; |
| return 1; |
| err: |
| ERR_raise(ERR_LIB_DH, err_reason); |
| BN_free(pubkey); |
| return 0; |
| } |
| |
| size_t ossl_dh_key2buf(const DH *dh, unsigned char **pbuf_out, size_t size, |
| int alloc) |
| { |
| const BIGNUM *pubkey; |
| unsigned char *pbuf = NULL; |
| const BIGNUM *p; |
| int p_size; |
| |
| DH_get0_pqg(dh, &p, NULL, NULL); |
| DH_get0_key(dh, &pubkey, NULL); |
| if (p == NULL || pubkey == NULL |
| || (p_size = BN_num_bytes(p)) == 0 |
| || BN_num_bytes(pubkey) == 0) { |
| ERR_raise(ERR_LIB_DH, DH_R_INVALID_PUBKEY); |
| return 0; |
| } |
| if (pbuf_out != NULL && (alloc || *pbuf_out != NULL)) { |
| if (!alloc) { |
| if (size >= (size_t)p_size) |
| pbuf = *pbuf_out; |
| } else { |
| pbuf = OPENSSL_malloc(p_size); |
| } |
| |
| if (pbuf == NULL) { |
| ERR_raise(ERR_LIB_DH, ERR_R_MALLOC_FAILURE); |
| return 0; |
| } |
| /* |
| * As per Section 4.2.8.1 of RFC 8446 left pad public |
| * key with zeros to the size of p |
| */ |
| if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) { |
| if (alloc) |
| OPENSSL_free(pbuf); |
| ERR_raise(ERR_LIB_DH, DH_R_BN_ERROR); |
| return 0; |
| } |
| *pbuf_out = pbuf; |
| } |
| return p_size; |
| } |
