grub-savannah-mirror/grub-core/lib/libgcrypt/cipher/dsa.c

/* dsa.c - DSA signature algorithm
 * Copyright (C) 1998, 2000, 2001, 2002, 2003,
 *               2006, 2008  Free Software Foundation, Inc.
 *
 * This file is part of Libgcrypt.
 *
 * Libgcrypt is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * Libgcrypt is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "g10lib.h"
#include "mpi.h"
#include "cipher.h"

typedef struct
{
  gcry_mpi_t p;	    /* prime */
  gcry_mpi_t q;	    /* group order */
  gcry_mpi_t g;	    /* group generator */
  gcry_mpi_t y;	    /* g^x mod p */
} DSA_public_key;


typedef struct
{
  gcry_mpi_t p;	    /* prime */
  gcry_mpi_t q;	    /* group order */
  gcry_mpi_t g;	    /* group generator */
  gcry_mpi_t y;	    /* g^x mod p */
  gcry_mpi_t x;	    /* secret exponent */
} DSA_secret_key;


/* A structure used to hold domain parameters.  */
typedef struct
{
  gcry_mpi_t p;	    /* prime */
  gcry_mpi_t q;	    /* group order */
  gcry_mpi_t g;	    /* group generator */
} dsa_domain_t;


/* A sample 1024 bit DSA key used for the selftests.  */
static const char sample_secret_key[] =
"(private-key"
" (dsa"
"  (p #00AD7C0025BA1A15F775F3F2D673718391D00456978D347B33D7B49E7F32EDAB"
"      96273899DD8B2BB46CD6ECA263FAF04A28903503D59062A8865D2AE8ADFB5191"
"      CF36FFB562D0E2F5809801A1F675DAE59698A9E01EFE8D7DCFCA084F4C6F5A44"
"      44D499A06FFAEA5E8EF5E01F2FD20A7B7EF3F6968AFBA1FB8D91F1559D52D8777B#)"
"  (q #00EB7B5751D25EBBB7BD59D920315FD840E19AEBF9#)"
"  (g #1574363387FDFD1DDF38F4FBE135BB20C7EE4772FB94C337AF86EA8E49666503"
"      AE04B6BE81A2F8DD095311E0217ACA698A11E6C5D33CCDAE71498ED35D13991E"
"      B02F09AB40BD8F4C5ED8C75DA779D0AE104BC34C960B002377068AB4B5A1F984"
"      3FBA91F537F1B7CAC4D8DD6D89B0D863AF7025D549F9C765D2FC07EE208F8D15#)"
"  (y #64B11EF8871BE4AB572AA810D5D3CA11A6CDBC637A8014602C72960DB135BF46"
"      A1816A724C34F87330FC9E187C5D66897A04535CC2AC9164A7150ABFA8179827"
"      6E45831AB811EEE848EBB24D9F5F2883B6E5DDC4C659DEF944DCFD80BF4D0A20"
"      42CAA7DC289F0C5A9D155F02D3D551DB741A81695B74D4C8F477F9C7838EB0FB#)"
"  (x #11D54E4ADBD3034160F2CED4B7CD292A4EBF3EC0#)))";
/* A sample 1024 bit DSA key used for the selftests (public only).  */
static const char sample_public_key[] =
"(public-key"
" (dsa"
"  (p #00AD7C0025BA1A15F775F3F2D673718391D00456978D347B33D7B49E7F32EDAB"
"      96273899DD8B2BB46CD6ECA263FAF04A28903503D59062A8865D2AE8ADFB5191"
"      CF36FFB562D0E2F5809801A1F675DAE59698A9E01EFE8D7DCFCA084F4C6F5A44"
"      44D499A06FFAEA5E8EF5E01F2FD20A7B7EF3F6968AFBA1FB8D91F1559D52D8777B#)"
"  (q #00EB7B5751D25EBBB7BD59D920315FD840E19AEBF9#)"
"  (g #1574363387FDFD1DDF38F4FBE135BB20C7EE4772FB94C337AF86EA8E49666503"
"      AE04B6BE81A2F8DD095311E0217ACA698A11E6C5D33CCDAE71498ED35D13991E"
"      B02F09AB40BD8F4C5ED8C75DA779D0AE104BC34C960B002377068AB4B5A1F984"
"      3FBA91F537F1B7CAC4D8DD6D89B0D863AF7025D549F9C765D2FC07EE208F8D15#)"
"  (y #64B11EF8871BE4AB572AA810D5D3CA11A6CDBC637A8014602C72960DB135BF46"
"      A1816A724C34F87330FC9E187C5D66897A04535CC2AC9164A7150ABFA8179827"
"      6E45831AB811EEE848EBB24D9F5F2883B6E5DDC4C659DEF944DCFD80BF4D0A20"
"      42CAA7DC289F0C5A9D155F02D3D551DB741A81695B74D4C8F477F9C7838EB0FB#)))";




static gcry_mpi_t gen_k (gcry_mpi_t q);
static int test_keys (DSA_secret_key *sk, unsigned int qbits);
static int check_secret_key (DSA_secret_key *sk);
static gpg_err_code_t generate (DSA_secret_key *sk,
                                unsigned int nbits,
                                unsigned int qbits,
                                int transient_key,
                                dsa_domain_t *domain,
                                gcry_mpi_t **ret_factors);
static void sign (gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t input,
                  DSA_secret_key *skey);
static int verify (gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t input,
                   DSA_public_key *pkey);

static void (*progress_cb) (void *,const char *, int, int, int );
static void *progress_cb_data;


void
_gcry_register_pk_dsa_progress (void (*cb) (void *, const char *,
                                            int, int, int),
				void *cb_data)
{
  progress_cb = cb;
  progress_cb_data = cb_data;
}


static void
progress (int c)
{
  if (progress_cb)
    progress_cb (progress_cb_data, "pk_dsa", c, 0, 0);
}


/*
 * Generate a random secret exponent k less than q.
 */
static gcry_mpi_t
gen_k( gcry_mpi_t q )
{
  gcry_mpi_t k = mpi_alloc_secure( mpi_get_nlimbs(q) );
  unsigned int nbits = mpi_get_nbits(q);
  unsigned int nbytes = (nbits+7)/8;
  char *rndbuf = NULL;

  /* To learn why we don't use mpi_mod to get the requested bit size,
     read the paper: "The Insecurity of the Digital Signature
     Algorithm with Partially Known Nonces" by Nguyen and Shparlinski.
     Journal of Cryptology, New York. Vol 15, nr 3 (2003)  */

  if ( DBG_CIPHER )
    log_debug("choosing a random k ");
  for (;;)
    {
      if( DBG_CIPHER )
        progress('.');

      if ( !rndbuf || nbits < 32 )
        {
          gcry_free(rndbuf);
          rndbuf = gcry_random_bytes_secure( (nbits+7)/8, GCRY_STRONG_RANDOM );
	}
      else
        { /* Change only some of the higher bits.  We could improve
	     this by directly requesting more memory at the first call
	     to get_random_bytes() and use these extra bytes here.
	     However the required management code is more complex and
	     thus we better use this simple method.  */
          char *pp = gcry_random_bytes_secure( 4, GCRY_STRONG_RANDOM );
          memcpy( rndbuf,pp, 4 );
          gcry_free(pp);
	}
      _gcry_mpi_set_buffer( k, rndbuf, nbytes, 0 );

      /* Make sure we have the requested number of bits.  This code
         looks a bit funny but it is easy to understand if you
         consider that mpi_set_highbit clears all higher bits.  We
         don't have a clear_highbit, thus we first set the high bit
         and then clear it again.  */
      if ( mpi_test_bit( k, nbits-1 ) )
        mpi_set_highbit( k, nbits-1 );
      else
        {
          mpi_set_highbit( k, nbits-1 );
          mpi_clear_bit( k, nbits-1 );
	}

      if( !(mpi_cmp( k, q ) < 0) ) /* check: k < q */
        {
          if( DBG_CIPHER )
            progress('+');
          continue; /* no  */
        }
      if( !(mpi_cmp_ui( k, 0 ) > 0) )  /* check: k > 0 */
        {
          if( DBG_CIPHER )
            progress('-');
          continue; /* no */
        }
      break;	/* okay */
    }
  gcry_free(rndbuf);
  if( DBG_CIPHER )
    progress('\n');

  return k;
}


/* Check that a freshly generated key actually works.  Returns 0 on success. */
static int
test_keys (DSA_secret_key *sk, unsigned int qbits)
{
  int result = -1;  /* Default to failure.  */
  DSA_public_key pk;
  gcry_mpi_t data  = gcry_mpi_new (qbits);
  gcry_mpi_t sig_a = gcry_mpi_new (qbits);
  gcry_mpi_t sig_b = gcry_mpi_new (qbits);

  /* Put the relevant parameters into a public key structure.  */
  pk.p = sk->p;
  pk.q = sk->q;
  pk.g = sk->g;
  pk.y = sk->y;

  /* Create a random plaintext.  */
  gcry_mpi_randomize (data, qbits, GCRY_WEAK_RANDOM);

  /* Sign DATA using the secret key.  */
  sign (sig_a, sig_b, data, sk);

  /* Verify the signature using the public key.  */
  if ( !verify (sig_a, sig_b, data, &pk) )
    goto leave; /* Signature does not match.  */

  /* Modify the data and check that the signing fails.  */
  gcry_mpi_add_ui (data, data, 1);
  if ( verify (sig_a, sig_b, data, &pk) )
    goto leave; /* Signature matches but should not.  */

  result = 0; /* The test succeeded.  */

 leave:
  gcry_mpi_release (sig_b);
  gcry_mpi_release (sig_a);
  gcry_mpi_release (data);
  return result;
}



/*
   Generate a DSA key pair with a key of size NBITS.  If transient_key
   is true the key is generated using the standard RNG and not the
   very secure one.

   Returns: 2 structures filled with all needed values
 	    and an array with the n-1 factors of (p-1)
 */
static gpg_err_code_t
generate (DSA_secret_key *sk, unsigned int nbits, unsigned int qbits,
          int transient_key, dsa_domain_t *domain, gcry_mpi_t **ret_factors )
{
  gcry_mpi_t p;    /* the prime */
  gcry_mpi_t q;    /* the 160 bit prime factor */
  gcry_mpi_t g;    /* the generator */
  gcry_mpi_t y;    /* g^x mod p */
  gcry_mpi_t x;    /* the secret exponent */
  gcry_mpi_t h, e;  /* helper */
  unsigned char *rndbuf;
  gcry_random_level_t random_level;

  if (qbits)
    ; /* Caller supplied qbits.  Use this value.  */
  else if ( nbits >= 512 && nbits <= 1024 )
    qbits = 160;
  else if ( nbits == 2048 )
    qbits = 224;
  else if ( nbits == 3072 )
    qbits = 256;
  else if ( nbits == 7680 )
    qbits = 384;
  else if ( nbits == 15360 )
    qbits = 512;
  else
    return GPG_ERR_INV_VALUE;

  if (qbits < 160 || qbits > 512 || (qbits%8) )
    return GPG_ERR_INV_VALUE;
  if (nbits < 2*qbits || nbits > 15360)
    return GPG_ERR_INV_VALUE;

  if (fips_mode ())
    {
      if (nbits < 1024)
        return GPG_ERR_INV_VALUE;
      if (transient_key)
        return GPG_ERR_INV_VALUE;
    }

  if (domain->p && domain->q && domain->g)
    {
      /* Domain parameters are given; use them.  */
      p = mpi_copy (domain->p);
      q = mpi_copy (domain->q);
      g = mpi_copy (domain->g);
      gcry_assert (mpi_get_nbits (p) == nbits);
      gcry_assert (mpi_get_nbits (q) == qbits);
      h = mpi_alloc (0);
      e = NULL;
    }
  else
    {
      /* Generate new domain parameters.  */
      p = _gcry_generate_elg_prime (1, nbits, qbits, NULL, ret_factors);
      /* Get q out of factors.  */
      q = mpi_copy ((*ret_factors)[0]);
      gcry_assert (mpi_get_nbits (q) == qbits);

      /* Find a generator g (h and e are helpers).
         e = (p-1)/q */
      e = mpi_alloc (mpi_get_nlimbs (p));
      mpi_sub_ui (e, p, 1);
      mpi_fdiv_q (e, e, q);
      g = mpi_alloc (mpi_get_nlimbs (p));
      h = mpi_alloc_set_ui (1); /* (We start with 2.) */
      do
        {
          mpi_add_ui (h, h, 1);
          /* g = h^e mod p */
          gcry_mpi_powm (g, h, e, p);
        }
      while (!mpi_cmp_ui (g, 1));  /* Continue until g != 1. */
    }

  /* Select a random number X with the property:
   *	 0 < x < q-1
   * This must be a very good random number because this is the secret
   * part.  The random quality depends on the transient_key flag.  */
  random_level = transient_key ? GCRY_STRONG_RANDOM : GCRY_VERY_STRONG_RANDOM;
  if (DBG_CIPHER)
    log_debug("choosing a random x%s", transient_key? " (transient-key)":"");
  gcry_assert( qbits >= 160 );
  x = mpi_alloc_secure( mpi_get_nlimbs(q) );
  mpi_sub_ui( h, q, 1 );  /* put q-1 into h */
  rndbuf = NULL;
  do
    {
      if( DBG_CIPHER )
        progress('.');
      if( !rndbuf )
        rndbuf = gcry_random_bytes_secure ((qbits+7)/8, random_level);
      else
        { /* Change only some of the higher bits (= 2 bytes)*/
          char *r = gcry_random_bytes_secure (2, random_level);
          memcpy(rndbuf, r, 2 );
          gcry_free(r);
        }

      _gcry_mpi_set_buffer( x, rndbuf, (qbits+7)/8, 0 );
      mpi_clear_highbit( x, qbits+1 );
    }
  while ( !( mpi_cmp_ui( x, 0 )>0 && mpi_cmp( x, h )<0 ) );
  gcry_free(rndbuf);
  mpi_free( e );
  mpi_free( h );

  /* y = g^x mod p */
  y = mpi_alloc( mpi_get_nlimbs(p) );
  gcry_mpi_powm( y, g, x, p );

  if( DBG_CIPHER )
    {
      progress('\n');
      log_mpidump("dsa  p", p );
      log_mpidump("dsa  q", q );
      log_mpidump("dsa  g", g );
      log_mpidump("dsa  y", y );
      log_mpidump("dsa  x", x );
    }

  /* Copy the stuff to the key structures. */
  sk->p = p;
  sk->q = q;
  sk->g = g;
  sk->y = y;
  sk->x = x;

  /* Now we can test our keys (this should never fail!). */
  if ( test_keys (sk, qbits) )
    {
      gcry_mpi_release (sk->p); sk->p = NULL;
      gcry_mpi_release (sk->q); sk->q = NULL;
      gcry_mpi_release (sk->g); sk->g = NULL;
      gcry_mpi_release (sk->y); sk->y = NULL;
      gcry_mpi_release (sk->x); sk->x = NULL;
      fips_signal_error ("self-test after key generation failed");
      return GPG_ERR_SELFTEST_FAILED;
    }
  return 0;
}


/* Generate a DSA key pair with a key of size NBITS using the
   algorithm given in FIPS-186-3.  If USE_FIPS186_2 is true,
   FIPS-186-2 is used and thus the length is restricted to 1024/160.
   If DERIVEPARMS is not NULL it may contain a seed value.  If domain
   parameters are specified in DOMAIN, DERIVEPARMS may not be given
   and NBITS and QBITS must match the specified domain parameters.  */
static gpg_err_code_t
generate_fips186 (DSA_secret_key *sk, unsigned int nbits, unsigned int qbits,
                  gcry_sexp_t deriveparms, int use_fips186_2,
                  dsa_domain_t *domain,
                  int *r_counter, void **r_seed, size_t *r_seedlen,
                  gcry_mpi_t *r_h)
{
  gpg_err_code_t ec;
  struct {
    gcry_sexp_t sexp;
    const void *seed;
    size_t seedlen;
  } initial_seed = { NULL, NULL, 0 };
  gcry_mpi_t prime_q = NULL;
  gcry_mpi_t prime_p = NULL;
  gcry_mpi_t value_g = NULL; /* The generator. */
  gcry_mpi_t value_y = NULL; /* g^x mod p */
  gcry_mpi_t value_x = NULL; /* The secret exponent. */
  gcry_mpi_t value_h = NULL; /* Helper.  */
  gcry_mpi_t value_e = NULL; /* Helper.  */

  /* Preset return values.  */
  *r_counter = 0;
  *r_seed = NULL;
  *r_seedlen = 0;
  *r_h = NULL;

  /* Derive QBITS from NBITS if requested  */
  if (!qbits)
    {
      if (nbits == 1024)
        qbits = 160;
      else if (nbits == 2048)
        qbits = 224;
      else if (nbits == 3072)
        qbits = 256;
    }

  /* Check that QBITS and NBITS match the standard.  Note that FIPS
     186-3 uses N for QBITS and L for NBITS.  */
  if (nbits == 1024 && qbits == 160)
    ;
  else if (nbits == 2048 && qbits == 224)
    ;
  else if (nbits == 2048 && qbits == 256)
    ;
  else if (nbits == 3072 && qbits == 256)
    ;
  else
    return GPG_ERR_INV_VALUE;

  if (domain->p && domain->q && domain->g)
    {
      /* Domain parameters are given; use them.  */
      prime_p = mpi_copy (domain->p);
      prime_q = mpi_copy (domain->q);
      value_g = mpi_copy (domain->g);
      gcry_assert (mpi_get_nbits (prime_p) == nbits);
      gcry_assert (mpi_get_nbits (prime_q) == qbits);
      gcry_assert (!deriveparms);
      ec = 0;
    }
  else
    {
      /* Generate new domain parameters.  */

      /* Get an initial seed value.  */
      if (deriveparms)
        {
          initial_seed.sexp = gcry_sexp_find_token (deriveparms, "seed", 0);
          if (initial_seed.sexp)
            initial_seed.seed = gcry_sexp_nth_data (initial_seed.sexp, 1,
                                                    &initial_seed.seedlen);
        }

      /* Fixme: Enable 186-3 after it has been approved and after fixing
         the generation function.  */
      /*   if (use_fips186_2) */
      (void)use_fips186_2;
      ec = _gcry_generate_fips186_2_prime (nbits, qbits,
                                           initial_seed.seed,
                                           initial_seed.seedlen,
                                           &prime_q, &prime_p,
                                           r_counter,
                                           r_seed, r_seedlen);
      /*   else */
      /*     ec = _gcry_generate_fips186_3_prime (nbits, qbits, NULL, 0, */
      /*                                          &prime_q, &prime_p, */
      /*                                          r_counter, */
      /*                                          r_seed, r_seedlen, NULL); */
      gcry_sexp_release (initial_seed.sexp);
      if (ec)
        goto leave;

      /* Find a generator g (h and e are helpers).
         e = (p-1)/q */
      value_e = mpi_alloc_like (prime_p);
      mpi_sub_ui (value_e, prime_p, 1);
      mpi_fdiv_q (value_e, value_e, prime_q );
      value_g = mpi_alloc_like (prime_p);
      value_h = mpi_alloc_set_ui (1);
      do
        {
          mpi_add_ui (value_h, value_h, 1);
          /* g = h^e mod p */
          mpi_powm (value_g, value_h, value_e, prime_p);
        }
      while (!mpi_cmp_ui (value_g, 1));  /* Continue until g != 1.  */
    }


  /* Select a random number x with:  0 < x < q  */
  value_x = gcry_mpi_snew (qbits);
  do
    {
      if( DBG_CIPHER )
        progress('.');
      gcry_mpi_randomize (value_x, qbits, GCRY_VERY_STRONG_RANDOM);
      mpi_clear_highbit (value_x, qbits+1);
    }
  while (!(mpi_cmp_ui (value_x, 0) > 0 && mpi_cmp (value_x, prime_q) < 0));

  /* y = g^x mod p */
  value_y = mpi_alloc_like (prime_p);
  gcry_mpi_powm (value_y, value_g, value_x, prime_p);

  if (DBG_CIPHER)
    {
      progress('\n');
      log_mpidump("dsa  p", prime_p );
      log_mpidump("dsa  q", prime_q );
      log_mpidump("dsa  g", value_g );
      log_mpidump("dsa  y", value_y );
      log_mpidump("dsa  x", value_x );
      log_mpidump("dsa  h", value_h );
    }

  /* Copy the stuff to the key structures. */
  sk->p = prime_p; prime_p = NULL;
  sk->q = prime_q; prime_q = NULL;
  sk->g = value_g; value_g = NULL;
  sk->y = value_y; value_y = NULL;
  sk->x = value_x; value_x = NULL;
  *r_h = value_h; value_h = NULL;

 leave:
  gcry_mpi_release (prime_p);
  gcry_mpi_release (prime_q);
  gcry_mpi_release (value_g);
  gcry_mpi_release (value_y);
  gcry_mpi_release (value_x);
  gcry_mpi_release (value_h);
  gcry_mpi_release (value_e);

  /* As a last step test this keys (this should never fail of course). */
  if (!ec && test_keys (sk, qbits) )
    {
      gcry_mpi_release (sk->p); sk->p = NULL;
      gcry_mpi_release (sk->q); sk->q = NULL;
      gcry_mpi_release (sk->g); sk->g = NULL;
      gcry_mpi_release (sk->y); sk->y = NULL;
      gcry_mpi_release (sk->x); sk->x = NULL;
      fips_signal_error ("self-test after key generation failed");
      ec = GPG_ERR_SELFTEST_FAILED;
    }

  if (ec)
    {
      *r_counter = 0;
      gcry_free (*r_seed); *r_seed = NULL;
      *r_seedlen = 0;
      gcry_mpi_release (*r_h); *r_h = NULL;
    }

  return ec;
}



/*
   Test whether the secret key is valid.
   Returns: if this is a valid key.
 */
static int
check_secret_key( DSA_secret_key *sk )
{
  int rc;
  gcry_mpi_t y = mpi_alloc( mpi_get_nlimbs(sk->y) );

  gcry_mpi_powm( y, sk->g, sk->x, sk->p );
  rc = !mpi_cmp( y, sk->y );
  mpi_free( y );
  return rc;
}



/*
   Make a DSA signature from HASH and put it into r and s.
 */
static void
sign(gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t hash, DSA_secret_key *skey )
{
  gcry_mpi_t k;
  gcry_mpi_t kinv;
  gcry_mpi_t tmp;

  /* Select a random k with 0 < k < q */
  k = gen_k( skey->q );

  /* r = (a^k mod p) mod q */
  gcry_mpi_powm( r, skey->g, k, skey->p );
  mpi_fdiv_r( r, r, skey->q );

  /* kinv = k^(-1) mod q */
  kinv = mpi_alloc( mpi_get_nlimbs(k) );
  mpi_invm(kinv, k, skey->q );

  /* s = (kinv * ( hash + x * r)) mod q */
  tmp = mpi_alloc( mpi_get_nlimbs(skey->p) );
  mpi_mul( tmp, skey->x, r );
  mpi_add( tmp, tmp, hash );
  mpi_mulm( s , kinv, tmp, skey->q );

  mpi_free(k);
  mpi_free(kinv);
  mpi_free(tmp);
}


/*
   Returns true if the signature composed from R and S is valid.
 */
static int
verify (gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t hash, DSA_public_key *pkey )
{
  int rc;
  gcry_mpi_t w, u1, u2, v;
  gcry_mpi_t base[3];
  gcry_mpi_t ex[3];

  if( !(mpi_cmp_ui( r, 0 ) > 0 && mpi_cmp( r, pkey->q ) < 0) )
    return 0; /* assertion	0 < r < q  failed */
  if( !(mpi_cmp_ui( s, 0 ) > 0 && mpi_cmp( s, pkey->q ) < 0) )
    return 0; /* assertion	0 < s < q  failed */

  w  = mpi_alloc( mpi_get_nlimbs(pkey->q) );
  u1 = mpi_alloc( mpi_get_nlimbs(pkey->q) );
  u2 = mpi_alloc( mpi_get_nlimbs(pkey->q) );
  v  = mpi_alloc( mpi_get_nlimbs(pkey->p) );

  /* w = s^(-1) mod q */
  mpi_invm( w, s, pkey->q );

  /* u1 = (hash * w) mod q */
  mpi_mulm( u1, hash, w, pkey->q );

  /* u2 = r * w mod q  */
  mpi_mulm( u2, r, w, pkey->q );

  /* v =  g^u1 * y^u2 mod p mod q */
  base[0] = pkey->g; ex[0] = u1;
  base[1] = pkey->y; ex[1] = u2;
  base[2] = NULL;    ex[2] = NULL;
  mpi_mulpowm( v, base, ex, pkey->p );
  mpi_fdiv_r( v, v, pkey->q );

  rc = !mpi_cmp( v, r );

  mpi_free(w);
  mpi_free(u1);
  mpi_free(u2);
  mpi_free(v);

  return rc;
}


/*********************************************
 **************  interface  ******************
 *********************************************/

static gcry_err_code_t
dsa_generate_ext (int algo, unsigned int nbits, unsigned long evalue,
                  const gcry_sexp_t genparms,
                  gcry_mpi_t *skey, gcry_mpi_t **retfactors,
                  gcry_sexp_t *r_extrainfo)
{
  gpg_err_code_t ec;
  DSA_secret_key sk;
  gcry_sexp_t l1;
  unsigned int qbits = 0;
  gcry_sexp_t deriveparms = NULL;
  gcry_sexp_t seedinfo = NULL;
  int transient_key = 0;
  int use_fips186_2 = 0;
  int use_fips186 = 0;
  dsa_domain_t domain;

  (void)algo;    /* No need to check it.  */
  (void)evalue;  /* Not required for DSA. */

  memset (&domain, 0, sizeof domain);

  if (genparms)
    {
      gcry_sexp_t domainsexp;

      /* Parse the optional qbits element.  */
      l1 = gcry_sexp_find_token (genparms, "qbits", 0);
      if (l1)
        {
          char buf[50];
          const char *s;
          size_t n;

          s = gcry_sexp_nth_data (l1, 1, &n);
          if (!s || n >= DIM (buf) - 1 )
            {
              gcry_sexp_release (l1);
              return GPG_ERR_INV_OBJ; /* No value or value too large.  */
            }
          memcpy (buf, s, n);
          buf[n] = 0;
          qbits = (unsigned int)strtoul (buf, NULL, 0);
          gcry_sexp_release (l1);
        }

      /* Parse the optional transient-key flag.  */
      l1 = gcry_sexp_find_token (genparms, "transient-key", 0);
      if (l1)
        {
          transient_key = 1;
          gcry_sexp_release (l1);
        }

      /* Get the optional derive parameters.  */
      deriveparms = gcry_sexp_find_token (genparms, "derive-parms", 0);

      /* Parse the optional "use-fips186" flags.  */
      l1 = gcry_sexp_find_token (genparms, "use-fips186", 0);
      if (l1)
        {
          use_fips186 = 1;
          gcry_sexp_release (l1);
        }
      l1 = gcry_sexp_find_token (genparms, "use-fips186-2", 0);
      if (l1)
        {
          use_fips186_2 = 1;
          gcry_sexp_release (l1);
        }

      /* Check whether domain parameters are given.  */
      domainsexp = gcry_sexp_find_token (genparms, "domain", 0);
      if (domainsexp)
        {
          /* DERIVEPARMS can't be used together with domain
             parameters.  NBITS abnd QBITS may not be specified
             because there values are derived from the domain
             parameters.  */
          if (deriveparms || qbits || nbits)
            {
              gcry_sexp_release (domainsexp);
              gcry_sexp_release (deriveparms);
              return GPG_ERR_INV_VALUE;
            }

          /* Put all domain parameters into the domain object.  */
          l1 = gcry_sexp_find_token (domainsexp, "p", 0);
          domain.p = gcry_sexp_nth_mpi (l1, 1, GCRYMPI_FMT_USG);
          gcry_sexp_release (l1);
          l1 = gcry_sexp_find_token (domainsexp, "q", 0);
          domain.q = gcry_sexp_nth_mpi (l1, 1, GCRYMPI_FMT_USG);
          gcry_sexp_release (l1);
          l1 = gcry_sexp_find_token (domainsexp, "g", 0);
          domain.g = gcry_sexp_nth_mpi (l1, 1, GCRYMPI_FMT_USG);
          gcry_sexp_release (l1);
          gcry_sexp_release (domainsexp);

          /* Check that all domain parameters are available.  */
          if (!domain.p || !domain.q || !domain.g)
            {
              gcry_mpi_release (domain.p);
              gcry_mpi_release (domain.q);
              gcry_mpi_release (domain.g);
              gcry_sexp_release (deriveparms);
              return GPG_ERR_MISSING_VALUE;
            }

          /* Get NBITS and QBITS from the domain parameters.  */
          nbits = mpi_get_nbits (domain.p);
          qbits = mpi_get_nbits (domain.q);
        }
    }

  if (deriveparms || use_fips186 || use_fips186_2 || fips_mode ())
    {
      int counter;
      void *seed;
      size_t seedlen;
      gcry_mpi_t h_value;

      ec = generate_fips186 (&sk, nbits, qbits, deriveparms, use_fips186_2,
                             &domain,
                             &counter, &seed, &seedlen, &h_value);
      gcry_sexp_release (deriveparms);
      if (!ec && h_value)
        {
          /* Format the seed-values unless domain parameters are used
             for which a H_VALUE of NULL is an indication.  */
          ec = gpg_err_code (gcry_sexp_build
                             (&seedinfo, NULL,
                              "(seed-values(counter %d)(seed %b)(h %m))",
                              counter, (int)seedlen, seed, h_value));
          if (ec)
            {
              gcry_mpi_release (sk.p); sk.p = NULL;
              gcry_mpi_release (sk.q); sk.q = NULL;
              gcry_mpi_release (sk.g); sk.g = NULL;
              gcry_mpi_release (sk.y); sk.y = NULL;
              gcry_mpi_release (sk.x); sk.x = NULL;
            }
          gcry_free (seed);
          gcry_mpi_release (h_value);
        }
    }
  else
    {
      ec = generate (&sk, nbits, qbits, transient_key, &domain, retfactors);
    }

  gcry_mpi_release (domain.p);
  gcry_mpi_release (domain.q);
  gcry_mpi_release (domain.g);

  if (!ec)
    {
      skey[0] = sk.p;
      skey[1] = sk.q;
      skey[2] = sk.g;
      skey[3] = sk.y;
      skey[4] = sk.x;

      if (!r_extrainfo)
        {
          /* Old style interface - return the factors - if any - at
             retfactors.  */
        }
      else if (!*retfactors && !seedinfo)
        {
          /* No factors and no seedinfo, thus there is nothing to return.  */
          *r_extrainfo = NULL;
        }
      else
        {
          /* Put the factors into extrainfo and set retfactors to NULL
             to make use of the new interface.  Note that the factors
             are not confidential thus we can store them in standard
             memory.  */
          int nfactors, i, j;
          char *p;
          char *format = NULL;
          void **arg_list = NULL;

          for (nfactors=0; *retfactors && (*retfactors)[nfactors]; nfactors++)
            ;
          /* Allocate space for the format string:
               "(misc-key-info%S(pm1-factors%m))"
             with one "%m" for each factor and construct it.  */
          format = gcry_malloc (50 + 2*nfactors);
          if (!format)
            ec = gpg_err_code_from_syserror ();
          else
            {
              p = stpcpy (format, "(misc-key-info");
              if (seedinfo)
                p = stpcpy (p, "%S");
              if (nfactors)
                {
                  p = stpcpy (p, "(pm1-factors");
                  for (i=0; i < nfactors; i++)
                    p = stpcpy (p, "%m");
                  p = stpcpy (p, ")");
                }
              p = stpcpy (p, ")");

              /* Allocate space for the list of factors plus one for
                 an S-expression plus an extra NULL entry for safety
                 and fill it with the factors.  */
              arg_list = gcry_calloc (nfactors+1+1, sizeof *arg_list);
              if (!arg_list)
                ec = gpg_err_code_from_syserror ();
              else
                {
                  i = 0;
                  if (seedinfo)
                    arg_list[i++] = &seedinfo;
                  for (j=0; j < nfactors; j++)
                    arg_list[i++] = (*retfactors) + j;
                  arg_list[i] = NULL;

                  ec = gpg_err_code (gcry_sexp_build_array
                                     (r_extrainfo, NULL, format, arg_list));
                }
            }

          gcry_free (arg_list);
          gcry_free (format);
          for (i=0; i < nfactors; i++)
            {
              gcry_mpi_release ((*retfactors)[i]);
              (*retfactors)[i] = NULL;
            }
          gcry_free (*retfactors);
          *retfactors = NULL;
          if (ec)
            {
              for (i=0; i < 5; i++)
                {
                  gcry_mpi_release (skey[i]);
                  skey[i] = NULL;
                }
            }
        }
    }

  gcry_sexp_release (seedinfo);
  return ec;
}


static gcry_err_code_t
dsa_generate (int algo, unsigned int nbits, unsigned long evalue,
              gcry_mpi_t *skey, gcry_mpi_t **retfactors)
{
  (void)evalue;
  return dsa_generate_ext (algo, nbits, 0, NULL, skey, retfactors, NULL);
}



static gcry_err_code_t
dsa_check_secret_key (int algo, gcry_mpi_t *skey)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  DSA_secret_key sk;

  (void)algo;

  if ((! skey[0]) || (! skey[1]) || (! skey[2]) || (! skey[3]) || (! skey[4]))
    err = GPG_ERR_BAD_MPI;
  else
    {
      sk.p = skey[0];
      sk.q = skey[1];
      sk.g = skey[2];
      sk.y = skey[3];
      sk.x = skey[4];
      if (! check_secret_key (&sk))
	err = GPG_ERR_BAD_SECKEY;
    }

  return err;
}


static gcry_err_code_t
dsa_sign (int algo, gcry_mpi_t *resarr, gcry_mpi_t data, gcry_mpi_t *skey)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  DSA_secret_key sk;

  (void)algo;

  if ((! data)
      || (! skey[0]) || (! skey[1]) || (! skey[2])
      || (! skey[3]) || (! skey[4]))
    err = GPG_ERR_BAD_MPI;
  else
    {
      sk.p = skey[0];
      sk.q = skey[1];
      sk.g = skey[2];
      sk.y = skey[3];
      sk.x = skey[4];
      resarr[0] = mpi_alloc (mpi_get_nlimbs (sk.p));
      resarr[1] = mpi_alloc (mpi_get_nlimbs (sk.p));
      sign (resarr[0], resarr[1], data, &sk);
    }
  return err;
}

static gcry_err_code_t
dsa_verify (int algo, gcry_mpi_t hash, gcry_mpi_t *data, gcry_mpi_t *pkey,
            int (*cmp) (void *, gcry_mpi_t), void *opaquev)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  DSA_public_key pk;

  (void)algo;
  (void)cmp;
  (void)opaquev;

  if ((! data[0]) || (! data[1]) || (! hash)
      || (! pkey[0]) || (! pkey[1]) || (! pkey[2]) || (! pkey[3]))
    err = GPG_ERR_BAD_MPI;
  else
    {
      pk.p = pkey[0];
      pk.q = pkey[1];
      pk.g = pkey[2];
      pk.y = pkey[3];
      if (! verify (data[0], data[1], hash, &pk))
	err = GPG_ERR_BAD_SIGNATURE;
    }
  return err;
}


static unsigned int
dsa_get_nbits (int algo, gcry_mpi_t *pkey)
{
  (void)algo;

  return mpi_get_nbits (pkey[0]);
}



/*
     Self-test section.
 */

static const char *
selftest_sign_1024 (gcry_sexp_t pkey, gcry_sexp_t skey)
{
  static const char sample_data[] =
    "(data (flags raw)"
    " (value #a0b1c2d3e4f500102030405060708090a1b2c3d4#))";
  static const char sample_data_bad[] =
    "(data (flags raw)"
    " (value #a0b1c2d3e4f510102030405060708090a1b2c3d4#))";

  const char *errtxt = NULL;
  gcry_error_t err;
  gcry_sexp_t data = NULL;
  gcry_sexp_t data_bad = NULL;
  gcry_sexp_t sig = NULL;

  err = gcry_sexp_sscan (&data, NULL,
                         sample_data, strlen (sample_data));
  if (!err)
    err = gcry_sexp_sscan (&data_bad, NULL,
                           sample_data_bad, strlen (sample_data_bad));
  if (err)
    {
      errtxt = "converting data failed";
      goto leave;
    }

  err = gcry_pk_sign (&sig, data, skey);
  if (err)
    {
      errtxt = "signing failed";
      goto leave;
    }
  err = gcry_pk_verify (sig, data, pkey);
  if (err)
    {
      errtxt = "verify failed";
      goto leave;
    }
  err = gcry_pk_verify (sig, data_bad, pkey);
  if (gcry_err_code (err) != GPG_ERR_BAD_SIGNATURE)
    {
      errtxt = "bad signature not detected";
      goto leave;
    }


 leave:
  gcry_sexp_release (sig);
  gcry_sexp_release (data_bad);
  gcry_sexp_release (data);
  return errtxt;
}


static gpg_err_code_t
selftests_dsa (selftest_report_func_t report)
{
  const char *what;
  const char *errtxt;
  gcry_error_t err;
  gcry_sexp_t skey = NULL;
  gcry_sexp_t pkey = NULL;

  /* Convert the S-expressions into the internal representation.  */
  what = "convert";
  err = gcry_sexp_sscan (&skey, NULL,
                         sample_secret_key, strlen (sample_secret_key));
  if (!err)
    err = gcry_sexp_sscan (&pkey, NULL,
                           sample_public_key, strlen (sample_public_key));
  if (err)
    {
      errtxt = gcry_strerror (err);
      goto failed;
    }

  what = "key consistency";
  err = gcry_pk_testkey (skey);
  if (err)
    {
      errtxt = gcry_strerror (err);
      goto failed;
    }

  what = "sign";
  errtxt = selftest_sign_1024 (pkey, skey);
  if (errtxt)
    goto failed;

  gcry_sexp_release (pkey);
  gcry_sexp_release (skey);
  return 0; /* Succeeded. */

 failed:
  gcry_sexp_release (pkey);
  gcry_sexp_release (skey);
  if (report)
    report ("pubkey", GCRY_PK_DSA, what, errtxt);
  return GPG_ERR_SELFTEST_FAILED;
}


/* Run a full self-test for ALGO and return 0 on success.  */
static gpg_err_code_t
run_selftests (int algo, int extended, selftest_report_func_t report)
{
  gpg_err_code_t ec;

  (void)extended;

  switch (algo)
    {
    case GCRY_PK_DSA:
      ec = selftests_dsa (report);
      break;
    default:
      ec = GPG_ERR_PUBKEY_ALGO;
      break;

    }
  return ec;
}




static const char *dsa_names[] =
  {
    "dsa",
    "openpgp-dsa",
    NULL,
  };

gcry_pk_spec_t _gcry_pubkey_spec_dsa =
  {
    "DSA", dsa_names,
    "pqgy", "pqgyx", "", "rs", "pqgy",
    GCRY_PK_USAGE_SIGN,
    dsa_generate,
    dsa_check_secret_key,
    NULL,
    NULL,
    dsa_sign,
    dsa_verify,
    dsa_get_nbits
  };
pk_extra_spec_t _gcry_pubkey_extraspec_dsa =
  {
    run_selftests,
    dsa_generate_ext
  };