/* * 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 #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; }