path: root/crypto/dsa/dsa_ossl.c

/*
 * 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
 */

/*
 * DSA 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 "crypto/bn.h"
#include <openssl/bn.h>
#include <openssl/sha.h>
#include "dsa_local.h"
#include <openssl/asn1.h>
#include "internal/deterministic_nonce.h"

#define MIN_DSA_SIGN_QBITS   128
#define MAX_DSA_SIGN_RETRIES 8

static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
                                    BIGNUM **rp);
static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
                          BIGNUM **rp, const unsigned char *dgst, int dlen,
                          unsigned int nonce_type, const char *digestname,
                          OSSL_LIB_CTX *libctx, const char *propq);
static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
                         DSA_SIG *sig, DSA *dsa);
static int dsa_init(DSA *dsa);
static int dsa_finish(DSA *dsa);
static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
                                      BN_CTX *ctx);

static DSA_METHOD openssl_dsa_meth = {
    "OpenSSL DSA method",
    dsa_do_sign,
    dsa_sign_setup_no_digest,
    dsa_do_verify,
    NULL,                       /* dsa_mod_exp, */
    NULL,                       /* dsa_bn_mod_exp, */
    dsa_init,
    dsa_finish,
    DSA_FLAG_FIPS_METHOD,
    NULL,
    NULL,
    NULL
};

static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;

#ifndef FIPS_MODULE
void DSA_set_default_method(const DSA_METHOD *meth)
{
    default_DSA_method = meth;
}
#endif /* FIPS_MODULE */

const DSA_METHOD *DSA_get_default_method(void)
{
    return default_DSA_method;
}

const DSA_METHOD *DSA_OpenSSL(void)
{
    return &openssl_dsa_meth;
}

DSA_SIG *ossl_dsa_do_sign_int(const unsigned char *dgst, int dlen, DSA *dsa,
                              unsigned int nonce_type, const char *digestname,
                              OSSL_LIB_CTX *libctx, const char *propq)
{
    BIGNUM *kinv = NULL;
    BIGNUM *m, *blind, *blindm, *tmp;
    BN_CTX *ctx = NULL;
    int reason = ERR_R_BN_LIB;
    DSA_SIG *ret = NULL;
    int rv = 0;
    int retries = 0;

    if (dsa->params.p == NULL
        || dsa->params.q == NULL
        || dsa->params.g == NULL) {
        reason = DSA_R_MISSING_PARAMETERS;
        goto err;
    }
    if (dsa->priv_key == NULL) {
        reason = DSA_R_MISSING_PRIVATE_KEY;
        goto err;
    }

    ret = DSA_SIG_new();
    if (ret == NULL)
        goto err;
    ret->r = BN_new();
    ret->s = BN_new();
    if (ret->r == NULL || ret->s == NULL)
        goto err;

    ctx = BN_CTX_new_ex(dsa->libctx);
    if (ctx == NULL)
        goto err;
    m = BN_CTX_get(ctx);
    blind = BN_CTX_get(ctx);
    blindm = BN_CTX_get(ctx);
    tmp = BN_CTX_get(ctx);
    if (tmp == NULL)
        goto err;

 redo:
    if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen,
                        nonce_type, digestname, libctx, propq))
        goto err;

    if (dlen > BN_num_bytes(dsa->params.q))
        /*
         * if the digest length is greater than the size of q use the
         * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
         * 4.2
         */
        dlen = BN_num_bytes(dsa->params.q);
    if (BN_bin2bn(dgst, dlen, m) == NULL)
        goto err;

    /*
     * The normal signature calculation is:
     *
     *   s := k^-1 * (m + r * priv_key) mod q
     *
     * We will blind this to protect against side channel attacks
     *
     *   s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
     */

    /*
     * Generate a blinding value
     * The size of q is tested in dsa_sign_setup() so there should not be an infinite loop here.
     */
    do {
        if (!BN_priv_rand_ex(blind, BN_num_bits(dsa->params.q) - 1,
                             BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, 0, ctx))
            goto err;
    } while (BN_is_zero(blind));
    BN_set_flags(blind, BN_FLG_CONSTTIME);
    BN_set_flags(blindm, BN_FLG_CONSTTIME);
    BN_set_flags(tmp, BN_FLG_CONSTTIME);

    /* tmp := blind * priv_key * r mod q */
    if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->params.q, ctx))
        goto err;
    if (!BN_mod_mul(tmp, tmp, ret->r, dsa->params.q, ctx))
        goto err;

    /* blindm := blind * m mod q */
    if (!BN_mod_mul(blindm, blind, m, dsa->params.q, ctx))
        goto err;

    /* s : = (blind * priv_key * r) + (blind * m) mod q */
    if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->params.q))
        goto err;

    /* s := s * k^-1 mod q */
    if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->params.q, ctx))
        goto err;

    /* s:= s * blind^-1 mod q */
    if (BN_mod_inverse(blind, blind, dsa->params.q, ctx) == NULL)
        goto err;
    if (!BN_mod_mul(ret->s, ret->s, blind, dsa->params.q, ctx))
        goto err;

    /*
     * Redo if r or s is zero as required by FIPS 186-4: Section 4.6
     * This is very unlikely.
     * Limit the retries so there is no possibility of an infinite
     * loop for bad domain parameter values.
     */
    if (BN_is_zero(ret->r) || BN_is_zero(ret->s)) {
        if (retries++ > MAX_DSA_SIGN_RETRIES) {
            reason = DSA_R_TOO_MANY_RETRIES;
            goto err;
        }
        goto redo;
    }
    rv = 1;
 err:
    if (rv == 0) {
        ERR_raise(ERR_LIB_DSA, reason);
        DSA_SIG_free(ret);
        ret = NULL;
    }
    BN_CTX_free(ctx);
    BN_clear_free(kinv);
    return ret;
}

static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
{
    return ossl_dsa_do_sign_int(dgst, dlen, dsa,
                                0, NULL, NULL, NULL);
}

static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
                                    BIGNUM **kinvp, BIGNUM **rp)
{
    return dsa_sign_setup