partial DSA support

1 files changed, 42 insertions, 163 deletions

diff --git a/cipher/dsa.c b/cipher/dsa.c
index 07f9e707..8024ac0a 100644
--- a/cipher/dsa.c
+++ b/cipher/dsa.c
@@ -32,6 +32,7 @@ void
 dsa_free_public_key( DSA_public_key *pk )
 {
     mpi_free( pk->p ); pk->p = NULL;
+    mpi_free( pk->q ); pk->q = NULL;
     mpi_free( pk->g ); pk->g = NULL;
     mpi_free( pk->y ); pk->y = NULL;
 }
@@ -40,121 +41,13 @@ void
 dsa_free_secret_key( DSA_secret_key *sk )
 {
     mpi_free( sk->p ); sk->p = NULL;
+    mpi_free( sk->q ); sk->q = NULL;
     mpi_free( sk->g ); sk->g = NULL;
     mpi_free( sk->y ); sk->y = NULL;
     mpi_free( sk->x ); sk->x = NULL;
 }
 
 
-static void
-test_keys( DSA_public_key *pk, DSA_secret_key *sk, unsigned nbits )
-{
-    MPI test = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
-    MPI out1_a = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
-    MPI out1_b = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
-    MPI out2 = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
-
-    mpi_set_bytes( test, nbits, get_random_byte, 0 );
-
-    dsa_sign( out1_a, out1_b, test, sk );
-    if( !dsa_verify( out1_a, out1_b, test, pk ) )
-	log_fatal("DSA operation: sign, verify failed\n");
-
-    mpi_free( test );
-    mpi_free( out1_a );
-    mpi_free( out1_b );
-    mpi_free( out2 );
-}
-
-
-/****************
- * generate a random secret exponent k from prime p, so
- * that k is relatively prime to p-1
- */
-static MPI
-gen_k( MPI p )
-{
-    MPI k = mpi_alloc_secure( mpi_get_nlimbs(p) );
-    MPI temp = mpi_alloc( mpi_get_nlimbs(p) );
-    MPI p_1 = mpi_copy(p);
-    unsigned nbits = mpi_get_nbits(p);
-
-    if( DBG_CIPHER )
-	log_debug("choosing a random k ");
-    mpi_sub_ui( p_1, p, 1);
-    for(;;) {
-	if( DBG_CIPHER )
-	    fputc('.', stderr);
-	mpi_set_bytes( k, nbits, get_random_byte, 1 );
-	mpi_set_highbit( k, nbits-1 ); /* make sure it's high (really needed?) */
-	if( mpi_cmp( k, p_1 ) >= 0 )
-	    continue; /* is not smaller than (p-1) */
-	if( mpi_gcd( temp, k, p_1 ) )
-	    break;  /* okay, k is relatively prime to (p-1) */
-    }
-    if( DBG_CIPHER )
-	fputc('\n', stderr);
-    mpi_free(p_1);
-    mpi_free(temp);
-
-    return k;
-}
-
-/****************
- * Generate a key pair with a key of size NBITS
- * Returns: 2 structures filles with all needed values
- */
-void
-dsa_generate( DSA_public_key *pk, DSA_secret_key *sk, unsigned nbits )
-{
-    MPI p;    /* the prime */
-    MPI g;
-    MPI x;    /* the secret exponent */
-    MPI y;
-
-    p = generate_public_prime( nbits );
-    /* FIXME: check wether we shall assert that (p-1)/2 is also prime
-     *	      Schneier votes against it
-     */
-    g = mpi_alloc_set_ui(3);
-
-    /* select a random number */
-    x = mpi_alloc_secure( nbits/BITS_PER_MPI_LIMB );
-    if( DBG_CIPHER )
-	log_debug("choosing a random x ");
-    do {
-	if( DBG_CIPHER )
-	    fputc('.', stderr);
-	mpi_set_bytes( x, nbits, get_random_byte, 1 ); /* fixme: should be 2 */
-	mpi_set_highbit( x, nbits-1 ); /* make sure it's high (needed?) */
-    } while( mpi_cmp( x, p ) >= 0 );  /* x must be smaller than p */
-
-    y = mpi_alloc(nbits/BITS_PER_MPI_LIMB);
-    mpi_powm( y, g, x, p );
-
-    if( DBG_CIPHER ) {
-	fputc('\n', stderr);
-	log_mpidump("dsa  p= ", p );
-	log_mpidump("dsa  g= ", g );
-	log_mpidump("dsa  y= ", y );
-	log_mpidump("dsa  x= ", x );
-    }
-
-
-    /* copy the stuff to the key structures */
-    pk->p = mpi_copy(p);
-    pk->g = mpi_copy(g);
-    pk->y = mpi_copy(y);
-    sk->p = p;
-    sk->g = g;
-    sk->y = y;
-    sk->x = x;
-
-    /* now we can test our keys (this should never fail!) */
-    test_keys( pk, sk, nbits - 64 );
-}
-
-
 /****************
  * Test wether the secret key is valid.
  * Returns: if this is a valid key.
@@ -174,72 +67,58 @@ dsa_check_secret_key( DSA_secret_key *sk )
 
 
 /****************
- * Make an Elgamal signature out of INPUT
+ * Make a DSA signature out of INPUT
  */
 
 void
-dsa_sign(MPI a, MPI b, MPI input, DSA_secret_key *skey )
+dsa_sign(MPI r, MPI s, MPI input, DSA_secret_key *skey )
 {
-    MPI k;
-    MPI t   = mpi_alloc( mpi_get_nlimbs(a) );
-    MPI inv = mpi_alloc( mpi_get_nlimbs(a) );
-    MPI p_1 = mpi_copy(skey->p);
-
-   /*
-    * b = (t * inv) mod (p-1)
-    * b = (t * inv(k,(p-1),(p-1)) mod (p-1)
-    * b = (((M-x*a) mod (p-1)) * inv(k,(p-1),(p-1))) mod (p-1)
-    *
-    */
-    mpi_sub_ui(p_1, p_1, 1);
-    k = gen_k( skey->p );
-    mpi_powm( a, skey->g, k, skey->p );
-    mpi_mul(t, skey->x, a );
-    mpi_subm(t, input, t, p_1 );
-    while( mpi_is_neg(t) )
-	mpi_add(t, t, p_1);
-    mpi_invm(inv, k, p_1 );
-    mpi_mulm(b, t, inv, p_1 );
-
-  #if 0
-    if( DBG_CIPHER ) {
-	log_mpidump("dsa sign p= ", skey->p);
-	log_mpidump("dsa sign g= ", skey->g);
-	log_mpidump("dsa sign y= ", skey->y);
-	log_mpidump("dsa sign x= ", skey->x);
-	log_mpidump("dsa sign k= ", k);
-	log_mpidump("dsa sign M= ", input);
-	log_mpidump("dsa sign a= ", a);
-	log_mpidump("dsa sign b= ", b);
-    }
-  #endif
-    mpi_free(k);
-    mpi_free(t);
-    mpi_free(inv);
-    mpi_free(p_1);
 }
 
 
 /****************
- * Returns true if the signature composed from A and B is valid.
+ * Returns true if the signature composed from R and S is valid.
  */
 int
-dsa_verify(MPI a, MPI b, MPI input, DSA_public_key *pkey )
+dsa_verify(MPI r, MPI s, MPI input, DSA_public_key *pkey )
 {
     int rc;
-    MPI t1 = mpi_alloc( mpi_get_nlimbs(a) );
-    MPI t2 = mpi_alloc( mpi_get_nlimbs(a) );
-
-    mpi_powm( t1, pkey->y, a, pkey->p );
-    mpi_powm( t2, a, b, pkey->p );
-    mpi_mulm( t1, t1, t2, pkey->p );
-
-    mpi_powm( t2, pkey->g, input, pkey->p );
-
-    rc = !mpi_cmp( t1, t2 );
-
-    mpi_free(t1);
-    mpi_free(t2);
+    MPI w, u1, u2, v;
+    MPI base[3];
+    MPI exp[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 = (input * w) mod q */
+    mpi_mulm( u1, input, 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; exp[0] = u1;
+    base[1] = pkey->y; exp[1] = u2;
+    base[2] = NULL;    exp[2] = NULL;
+    mpi_mulpowm( v, base, exp, 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;
 }