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/*
* Copyright 1995-2023 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)
{
#ifdef S390X_MOD_EXP
return s390x_mod_exp(r, a, p, m, ctx, m_ctx);
#else
return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
#endif
}
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(
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