/* $OpenBSD: dsa_ossl.c,v 1.44 2022/02/24 08:35:45 tb Exp $ */

/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)

 * All rights reserved.

 *

 * This package is an SSL implementation written

 * by Eric Young (eay@cryptsoft.com).

 * The implementation was written so as to conform with Netscapes SSL.

 * 

 * This library is free for commercial and non-commercial use as long as

 * the following conditions are aheared to.  The following conditions

 * apply to all code found in this distribution, be it the RC4, RSA,

 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation

 * included with this distribution is covered by the same copyright terms

 * except that the holder is Tim Hudson (tjh@cryptsoft.com).

 * 

 * Copyright remains Eric Young's, and as such any Copyright notices in

 * the code are not to be removed.

 * If this package is used in a product, Eric Young should be given attribution

 * as the author of the parts of the library used.

 * This can be in the form of a textual message at program startup or

 * in documentation (online or textual) provided with the package.

 * 

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. All advertising materials mentioning features or use of this software

 *    must display the following acknowledgement:

 *    "This product includes cryptographic software written by

 *     Eric Young (eay@cryptsoft.com)"

 *    The word 'cryptographic' can be left out if the rouines from the library

 *    being used are not cryptographic related :-).

 * 4. If you include any Windows specific code (or a derivative thereof) from 

 *    the apps directory (application code) you must include an acknowledgement:

 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"

 * 

 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 * 

 * The licence and distribution terms for any publically available version or

 * derivative of this code cannot be changed.  i.e. this code cannot simply be

 * copied and put under another distribution licence

 * [including the GNU Public Licence.]

 */

/* Original version from Steven Schoch <schoch@sheba.arc.nasa.gov> */

#include <stdio.h>

#include <openssl/asn1.h>

#include <openssl/bn.h>

#include <openssl/dsa.h>

#include <openssl/err.h>

#include <openssl/sha.h>

#include "bn_lcl.h"

#include "dsa_locl.h"

static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);

static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,

    BIGNUM **rp);

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 DSA_METHOD openssl_dsa_meth = {

  .name = "OpenSSL DSA method",

  .dsa_do_sign = dsa_do_sign,

  .dsa_sign_setup = dsa_sign_setup,

  .dsa_do_verify = dsa_do_verify,

  .init = dsa_init,

  .finish = dsa_finish,

};

const DSA_METHOD *

DSA_OpenSSL(void)

{

  return &openssl_dsa_meth;

}

static DSA_SIG *

dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)

{

  BIGNUM b, bm, bxr, binv, m, *kinv = NULL, *r = NULL, *s = NULL;

  BN_CTX *ctx = NULL;

  int reason = ERR_R_BN_LIB;

  DSA_SIG *ret = NULL;

  int noredo = 0;

  BN_init(&b);

  BN_init(&binv);

  BN_init(&bm);

  BN_init(&bxr);

  BN_init(&m);

  if (!dsa->p || !dsa->q || !dsa->g) {

    reason = DSA_R_MISSING_PARAMETERS;

    goto err;

  }

  s = BN_new();

  if (s == NULL)

    goto err;

  ctx = BN_CTX_new();

  if (ctx == NULL)

    goto err;

  /*

   * If the digest length is greater than N (the bit length of q), the

   * leftmost N bits of the digest shall be used, see FIPS 186-3, 4.2.

   * In this case the digest length is given in bytes.

   */

  if (dlen > BN_num_bytes(dsa->q))

    dlen = BN_num_bytes(dsa->q);

  if (BN_bin2bn(dgst, dlen, &m) == NULL)

    goto err;

 redo:

  if (dsa->kinv == NULL || dsa->r == NULL) {

    if (!DSA_sign_setup(dsa, ctx, &kinv, &r))

      goto err;

  } else {

    kinv = dsa->kinv;

    dsa->kinv = NULL;

    r = dsa->r;

    dsa->r = NULL;

    noredo = 1;

  }

  /*

   * Compute:

   *

   *  s = inv(k)(m + xr) mod q

   *

   * In order to reduce the possibility of a side-channel attack, the

   * following is calculated using a blinding value:

   *

   *  s = inv(b)(bm + bxr)inv(k) mod q

   *

   * Where b is a random value in the range [1, q).

   */

  if (!bn_rand_interval(&b, BN_value_one(), dsa->q))

    goto err;

  if (BN_mod_inverse_ct(&binv, &b, dsa->q, ctx) == NULL)

    goto err;

  if (!BN_mod_mul(&bxr, &b, dsa->priv_key, dsa->q, ctx)) /* bx */

    goto err;

  if (!BN_mod_mul(&bxr, &bxr, r, dsa->q, ctx)) /* bxr */

    goto err;

  if (!BN_mod_mul(&bm, &b, &m, dsa->q, ctx)) /* bm */

    goto err;

  if (!BN_mod_add(s, &bxr, &bm, dsa->q, ctx)) /* s = bm + bxr */

    goto err;

  if (!BN_mod_mul(s, s, kinv, dsa->q, ctx)) /* s = b(m + xr)k^-1 */

    goto err;

  if (!BN_mod_mul(s, s, &binv, dsa->q, ctx)) /* s = (m + xr)k^-1 */

    goto err;

  /*

   * Redo if r or s is zero as required by FIPS 186-3: this is very

   * unlikely.

   */

  if (BN_is_zero(r) || BN_is_zero(s)) {

    if (noredo) {

      reason = DSA_R_NEED_NEW_SETUP_VALUES;

      goto err;

    }

    goto redo;

  }

  if ((ret = DSA_SIG_new()) == NULL) {

    reason = ERR_R_MALLOC_FAILURE;

    goto err;

  }

  ret->r = r;

  ret->s = s;

 err:

  if (!ret) {

    DSAerror(reason);

    BN_free(r);

    BN_free(s);

  }

  BN_CTX_free(ctx);

  BN_clear_free(&b);

  BN_clear_free(&bm);

  BN_clear_free(&bxr);

  BN_clear_free(&binv);

  BN_clear_free(&m);

  BN_clear_free(kinv);

  return ret;

}

static int

dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)

{

  BN_CTX *ctx;

  BIGNUM k, l, m, *kinv = NULL, *r = NULL;

  int q_bits, ret = 0;

  if (!dsa->p || !dsa->q || !dsa->g) {

    DSAerror(DSA_R_MISSING_PARAMETERS);

    return 0;

  }

  BN_init(&k);

  BN_init(&l);

  BN_init(&m);

  if (ctx_in == NULL) {

    if ((ctx = BN_CTX_new()) == NULL)

      goto err;

  } else

    ctx = ctx_in;

  if ((r = BN_new()) == NULL)

    goto err;

  /* Preallocate space */

  q_bits = BN_num_bits(dsa->q);

  if (!BN_set_bit(&k, q_bits) ||

      !BN_set_bit(&l, q_bits) ||

      !BN_set_bit(&m, q_bits))

    goto err;

  if (!bn_rand_interval(&k, BN_value_one(), dsa->q))

    goto err;

  BN_set_flags(&k, BN_FLG_CONSTTIME);

  if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {

    if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,

        CRYPTO_LOCK_DSA, dsa->p, ctx))

      goto err;

  }

  /* Compute r = (g^k mod p) mod q */

  /*

   * We do not want timing information to leak the length of k,

   * so we compute G^k using an equivalent exponent of fixed

   * bit-length.

   *

   * We unconditionally perform both of these additions to prevent a

   * small timing information leakage.  We then choose the sum that is

   * one bit longer than the modulus.

   *

   * TODO: revisit the BN_copy aiming for a memory access agnostic

   * conditional copy.

   */

  if (!BN_add(&l, &k, dsa->q) ||

      !BN_add(&m, &l, dsa->q) ||

      !BN_copy(&k, BN_num_bits(&l) > q_bits ? &l : &m))

    goto err;

  if (dsa->meth->bn_mod_exp != NULL) {

    if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, &k, dsa->p, ctx,

        dsa->method_mont_p))

      goto err;

  } else {

    if (!BN_mod_exp_mont_ct(r, dsa->g, &k, dsa->p, ctx,

        dsa->method_mont_p))

      goto err;

  }

  if (!BN_mod_ct(r, r, dsa->q, ctx))

    goto err;

  /* Compute  part of 's = inv(k) (m + xr) mod q' */

  if ((kinv = BN_mod_inverse_ct(NULL, &k, dsa->q, ctx)) == NULL)

    goto err;

  BN_clear_free(*kinvp);

  *kinvp = kinv;

  kinv = NULL;

  BN_clear_free(*rp);

  *rp = r;

  ret = 1;

 err:

  if (!ret) {

    DSAerror(ERR_R_BN_LIB);

    BN_clear_free(r);

  }

  if (ctx_in == NULL)

    BN_CTX_free(ctx);

  BN_clear_free(&k);

  BN_clear_free(&l);

  BN_clear_free(&m);

  return ret;

}

static int

dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, DSA *dsa)

{

  BN_CTX *ctx;

  BIGNUM u1, u2, t1;

  BN_MONT_CTX *mont = NULL;

  int qbits;

  int ret = -1;

  if (!dsa->p || !dsa->q || !dsa->g) {

    DSAerror(DSA_R_MISSING_PARAMETERS);

    return -1;

  }

  /* FIPS 186-3 allows only three different sizes for q. */

  qbits = BN_num_bits(dsa->q);

  if (qbits != 160 && qbits != 224 && qbits != 256) {

    DSAerror(DSA_R_BAD_Q_VALUE);

    return -1;

  }

  if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {

    DSAerror(DSA_R_MODULUS_TOO_LARGE);

    return -1;

  }

  BN_init(&u1);

  BN_init(&u2);

  BN_init(&t1);

  if ((ctx = BN_CTX_new()) == NULL)

    goto err;

  if (BN_is_zero(sig->r) || BN_is_negative(sig->r) ||

      BN_ucmp(sig->r, dsa->q) >= 0) {

    ret = 0;

    goto err;

  }

  if (BN_is_zero(sig->s) || BN_is_negative(sig->s) ||

      BN_ucmp(sig->s, dsa->q) >= 0) {

    ret = 0;

    goto err;

  }

  /* Calculate w = inv(s) mod q, saving w in u2. */

  if ((BN_mod_inverse_ct(&u2, sig->s, dsa->q, ctx)) == NULL)

    goto err;

  /*

   * 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.

   */

  if (dgst_len > (qbits >> 3))

    dgst_len = (qbits >> 3);

  /* Save m in u1. */

  if (BN_bin2bn(dgst, dgst_len, &u1) == NULL)

    goto err;

  /* u1 = m * w mod q */

  if (!BN_mod_mul(&u1, &u1, &u2, dsa->q, ctx))

    goto err;

  /* u2 = r * w mod q */

  if (!BN_mod_mul(&u2, sig->r, &u2, dsa->q, ctx))

    goto err;

  if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {

    mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,

        CRYPTO_LOCK_DSA, dsa->p, ctx);

    if (!mont)

      goto err;

  }

  if (dsa->meth->dsa_mod_exp != NULL) {

    if (!dsa->meth->dsa_mod_exp(dsa, &t1, dsa->g, &u1, dsa->pub_key,

        &u2, dsa->p, ctx, mont))

      goto err;

  } else {

    if (!BN_mod_exp2_mont(&t1, dsa->g, &u1, dsa->pub_key, &u2,

        dsa->p, ctx, mont))

      goto err;

  }

  /* BN_copy(&u1,&t1); */

  /* let u1 = u1 mod q */

  if (!BN_mod_ct(&u1, &t1, dsa->q, ctx))

    goto err;

  /* v is in u1 - if the signature is correct, it will be equal to r. */

  ret = BN_ucmp(&u1, sig->r) == 0;

 err:

  if (ret < 0)

    DSAerror(ERR_R_BN_LIB);

  BN_CTX_free(ctx);

  BN_free(&u1);

  BN_free(&u2);

  BN_free(&t1);

  return ret;

}

static int

dsa_init(DSA *dsa)

{

  dsa->flags |= DSA_FLAG_CACHE_MONT_P;

  return 1;

}

static int

dsa_finish(DSA *dsa)

{

  BN_MONT_CTX_free(dsa->method_mont_p);

  return 1;

}