text: /* crypto/dsa/dsa_ossl.c */
  /* 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 "cryptlib.h"
  #include <openssl/bn.h>
  #include <openssl/sha.h>
  #include <openssl/dsa.h>
  #include <openssl/rand.h>
  #include <openssl/asn1.h>
  #ifdef OPENSSL_FIPS
  # include <openssl/fips.h>
  #endif
  
  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 = {
      "OpenSSL DSA method",
      dsa_do_sign,
      dsa_sign_setup,
      dsa_do_verify,
      NULL,                       /* dsa_mod_exp, */
      NULL,                       /* dsa_bn_mod_exp, */
      dsa_init,
      dsa_finish,
      DSA_FLAG_FIPS_METHOD,
      NULL,
      NULL,
      NULL
  };
  
  /*-
   * These macro wrappers replace attempts to use the dsa_mod_exp() and
   * bn_mod_exp() handlers in the DSA_METHOD structure. We avoid the problem of
   * having a the macro work as an expression by bundling an "err_instr". So;
   *
   *     if (!dsa->meth->bn_mod_exp(dsa, r,dsa->g,&k,dsa->p,ctx,
   *                 dsa->method_mont_p)) goto err;
   *
   * can be replaced by;
   *
   *     DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, &k, dsa->p, ctx,
   *                 dsa->method_mont_p);
   */
  
  #define DSA_MOD_EXP(err_instr,dsa,rr,a1,p1,a2,p2,m,ctx,in_mont) \
          do { \
          int _tmp_res53; \
          if ((dsa)->meth->dsa_mod_exp) \
                  _tmp_res53 = (dsa)->meth->dsa_mod_exp((dsa), (rr), (a1), (p1), \
                                  (a2), (p2), (m), (ctx), (in_mont)); \
          else \
                  _tmp_res53 = BN_mod_exp2_mont((rr), (a1), (p1), (a2), (p2), \
                                  (m), (ctx), (in_mont)); \
          if (!_tmp_res53) err_instr; \
          } while(0)
  #define DSA_BN_MOD_EXP(err_instr,dsa,r,a,p,m,ctx,m_ctx) \
          do { \
          int _tmp_res53; \
          if ((dsa)->meth->bn_mod_exp) \
                  _tmp_res53 = (dsa)->meth->bn_mod_exp((dsa), (r), (a), (p), \
                                  (m), (ctx), (m_ctx)); \
          else \
                  _tmp_res53 = BN_mod_exp_mont((r), (a), (p), (m), (ctx), (m_ctx)); \
          if (!_tmp_res53) err_instr; \
          } while(0)
  
  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 *kinv = NULL, *r = NULL, *s = NULL;
      BIGNUM m;
      BIGNUM xr;
      BN_CTX *ctx = NULL;
      int reason = ERR_R_BN_LIB;
      DSA_SIG *ret = NULL;
      int noredo = 0;
  
  #ifdef OPENSSL_FIPS
      if (FIPS_selftest_failed()) {
          FIPSerr(FIPS_F_DSA_DO_SIGN, FIPS_R_FIPS_SELFTEST_FAILED);
          return NULL;
      }
  
      if (FIPS_mode() && !(dsa->flags & DSA_FLAG_NON_FIPS_ALLOW)
          && (BN_num_bits(dsa->p) < OPENSSL_DSA_FIPS_MIN_MODULUS_BITS)) {
          DSAerr(DSA_F_DSA_DO_SIGN, DSA_R_KEY_SIZE_TOO_SMALL);
          return NULL;
      }
  #endif
  
      BN_init(&m);
      BN_init(&xr);
  
      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;
   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;
      }
  
      if (dlen > BN_num_bytes(dsa->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->q);
      if (BN_bin2bn(dgst, dlen, &m) == NULL)
          goto err;
  
      /* Compute  s = inv(k) (m + xr) mod q */
      if (!BN_mod_mul(&xr, dsa->priv_key, r, dsa->q, ctx))
          goto err;               /* s = xr */
      if (!BN_add(s, &xr, &m))
          goto err;               /* s = m + xr */
      if (BN_cmp(s, dsa->q) > 0)
          if (!BN_sub(s, s, dsa->q))
              goto err;
      if (!BN_mod_mul(s, s, kinv, dsa->q, ctx))
          goto err;
  
      ret = DSA_SIG_new();
      if (ret == NULL)
          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;
      }
      ret->r = r;
      ret->s = s;
  
   err:
      if (!ret) {
          DSAerr(DSA_F_DSA_DO_SIGN, reason);
          BN_free(r);
          BN_free(s);
      }
      if (ctx != NULL)
          BN_CTX_free(ctx);
      BN_clear_free(&m);
      BN_clear_free(&xr);
      if (kinv != NULL)           /* dsa->kinv is NULL now if we used it */
          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, kq, *K, *kinv = NULL, *r = NULL;
      int ret = 0;
  
      if (!dsa->p || !dsa->q || !dsa->g) {
          DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
          return 0;
      }
  
      BN_init(&k);
      BN_init(&kq);
  
      if (ctx_in == NULL) {
          if ((ctx = BN_CTX_new()) == NULL)
              goto err;
      } else
          ctx = ctx_in;
  
      if ((r = BN_new()) == NULL)
          goto err;
  
      /* Get random k */
      do
          if (!BN_rand_range(&k, dsa->q))
              goto err;
      while (BN_is_zero(&k)) ;
      if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {
          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 */
  
      if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {
          if (!BN_copy(&kq, &k))
              goto err;
  
          /*
           * We do not want timing information to leak the length of k, so we
           * compute g^k using an equivalent exponent of fixed length. (This
           * is a kludge that we need because the BN_mod_exp_mont() does not
           * let us specify the desired timing behaviour.)
           */
  
          if (!BN_add(&kq, &kq, dsa->q))
              goto err;
          if (BN_num_bits(&kq) <= BN_num_bits(dsa->q)) {
              if (!BN_add(&kq, &kq, dsa->q))
                  goto err;
          }
  
          K = &kq;
      } else {
          K = &k;
      }
      DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, K, dsa->p, ctx,
                     dsa->method_mont_p);
      if (!BN_mod(r, r, dsa->q, ctx))
          goto err;
  
      /* Compute  part of 's = inv(k) (m + xr) mod q' */
      if ((kinv = BN_mod_inverse(NULL, &k, dsa->q, ctx)) == NULL)
          goto err;
  
      if (*kinvp != NULL)
          BN_clear_free(*kinvp);
      *kinvp = kinv;
      kinv = NULL;
      if (*rp != NULL)
          BN_clear_free(*rp);
      *rp = r;
      ret = 1;
   err:
      if (!ret) {
          DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
          if (r != NULL)
              BN_clear_free(r);
      }
      if (ctx_in == NULL)
          BN_CTX_free(ctx);
      BN_clear_free(&k);
      BN_clear_free(&kq);
      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 ret = -1, i;
      if (!dsa->p || !dsa->q || !dsa->g) {
          DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
          return -1;
      }
  
      i = BN_num_bits(dsa->q);
      /* fips 186-3 allows only different sizes for q */
      if (i != 160 && i != 224 && i != 256) {
          DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
          return -1;
      }
  #ifdef OPENSSL_FIPS
      if (FIPS_selftest_failed()) {
          FIPSerr(FIPS_F_DSA_DO_VERIFY, FIPS_R_FIPS_SELFTEST_FAILED);
          return -1;
      }
  
      if (FIPS_mode() && !(dsa->flags & DSA_FLAG_NON_FIPS_ALLOW)
          && (BN_num_bits(dsa->p) < OPENSSL_DSA_FIPS_MIN_MODULUS_BITS)) {
          DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_KEY_SIZE_TOO_SMALL);
          return -1;
      }
  #endif
  
      if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
          DSAerr(DSA_F_DSA_DO_VERIFY, 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 save W in u2
       */
      if ((BN_mod_inverse(&u2, sig->s, dsa->q, ctx)) == NULL)
          goto err;
  
      /* save M in u1 */
      if (dgst_len > (i >> 3))
          /*
           * 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
           */
          dgst_len = (i >> 3);
      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;
      }
  
      DSA_MOD_EXP(goto err, dsa, &t1, dsa->g, &u1, dsa->pub_key, &u2, dsa->p,
                  ctx, mont);
      /* BN_copy(&u1,&t1); */
      /* let u1 = u1 mod q */
      if (!BN_mod(&u1, &t1, dsa->q, ctx))
          goto err;
  
      /*
       * V is now in u1.  If the signature is correct, it will be equal to R.
       */
      ret = (BN_ucmp(&u1, sig->r) == 0);
  
   err:
      if (ret < 0)
          DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
      if (ctx != NULL)
          BN_CTX_free(ctx);
      BN_free(&u1);
      BN_free(&u2);
      BN_free(&t1);
      return (ret);
  }
  
  static int dsa_init(DSA *dsa)
  {
  #ifdef OPENSSL_FIPS
      FIPS_selftest_check();
  #endif
      dsa->flags |= DSA_FLAG_CACHE_MONT_P;
      return (1);
  }
  
  static int dsa_finish(DSA *dsa)
  {
      if (dsa->method_mont_p)
          BN_MONT_CTX_free(dsa->method_mont_p);
      return (1);
  }
  