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git://git.gnupg.org/gnupg.git
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ElGamal funktioniert und ist default
This commit is contained in:
Werner Koch
parent
a51cca90b6
commit
46900fbd43
31 changed files with 1273 additions and 409 deletions
273
cipher/elgamal.c
273
cipher/elgamal.c
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@ -28,34 +28,279 @@
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#include <string.h>
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#include "util.h"
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#include "mpi.h"
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#include "cipher.h"
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#include "elgamal.h"
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/****************
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* Public key operation. Encrypt INPUT with PKEY and put result into OUTPUT.
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*
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*
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*
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* Where c is OUTPUT, m is INPUT and e,n are elements of PKEY.
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*/
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void
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elg_public(MPI output, MPI input, ELG_public_key *pkey )
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elg_free_public_key( ELG_public_key *pk )
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{
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mpi_free( pk->p ); pk->p = NULL;
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mpi_free( pk->g ); pk->g = NULL;
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mpi_free( pk->y ); pk->y = NULL;
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}
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void
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elg_free_secret_key( ELG_secret_key *sk )
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{
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mpi_free( sk->p ); sk->p = NULL;
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mpi_free( sk->g ); sk->g = NULL;
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mpi_free( sk->y ); sk->y = NULL;
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mpi_free( sk->x ); sk->x = NULL;
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}
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static void
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test_keys( ELG_public_key *pk, ELG_secret_key *sk, unsigned nbits )
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{
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MPI test = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
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MPI out1_a = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
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MPI out1_b = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
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MPI out2 = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
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mpi_set_bytes( test, nbits, get_random_byte, 0 );
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elg_encipher( out1_a, out1_b, test, pk );
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elg_decipher( out2, out1_a, out1_b, sk );
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if( mpi_cmp( test, out2 ) )
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log_fatal("ElGamal operation: encipher, decipher failed\n");
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elg_sign( out1_a, out1_b, test, sk );
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if( !elg_verify( out1_a, out1_b, test, pk ) )
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log_fatal("ElGamal operation: sign, verify failed\n");
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mpi_free( test );
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mpi_free( out1_a );
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mpi_free( out1_b );
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mpi_free( out2 );
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}
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/****************
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* generate a random secret exponent k from prime p, so
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* that k is relatively prime to p-1
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*/
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static MPI
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gen_k( MPI p )
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{
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MPI k = mpi_alloc_secure( mpi_get_nlimbs(p) );
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MPI temp = mpi_alloc( mpi_get_nlimbs(p) );
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MPI p_1 = mpi_copy(p);
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unsigned nbits = mpi_get_nbits(p);
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if( DBG_CIPHER )
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log_debug("choosing a random k ");
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mpi_sub_ui( p_1, p, 1);
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for(;;) {
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if( DBG_CIPHER )
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fputc('.', stderr);
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mpi_set_bytes( k, nbits, get_random_byte, 1 );
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mpi_set_bit( k, nbits-1 ); /* make sure it's high (needed?) */
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if( mpi_cmp( k, p_1 ) >= 0 )
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continue; /* is not smaller than (p-1) */
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if( mpi_gcd( temp, k, p_1 ) )
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break; /* okay, k is relatively prime to (p-1) */
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}
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if( DBG_CIPHER )
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fputc('\n', stderr);
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mpi_free(p_1);
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mpi_free(temp);
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return k;
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}
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/****************
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* Secret key operation. Encrypt INPUT with SKEY and put result into OUTPUT.
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*
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*
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*
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* Where m is OUTPUT, c is INPUT and d,n are elements of PKEY.
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* Generate a key pair with a key of size NBITS
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* Returns: 2 structures filles with all needed values
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*/
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void
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elg_secret(MPI output, MPI input, ELG_secret_key *skey )
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elg_generate( ELG_public_key *pk, ELG_secret_key *sk, unsigned nbits )
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{
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MPI p; /* the prime */
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MPI g;
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MPI x; /* the secret exponent */
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MPI y;
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p = generate_public_prime( nbits );
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/* FIXME: check wether we shall assert that (p-1)/2 is also prime
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* Schneier votes against it
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*/
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g = mpi_alloc_set_ui(3);
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/* select a random number */
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x = mpi_alloc_secure( nbits/BITS_PER_MPI_LIMB );
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if( DBG_CIPHER )
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log_debug("choosing a random x ");
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do {
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if( DBG_CIPHER )
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fputc('.', stderr);
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mpi_set_bytes( x, nbits, get_random_byte, 1 ); /* fixme: should be 2 */
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mpi_set_bit( x, nbits-1 ); /* make sure it's high (needed?) */
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} while( mpi_cmp( x, p ) >= 0 ); /* x must be samller than p */
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y = mpi_alloc(nbits/BITS_PER_MPI_LIMB);
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mpi_powm( y, g, x, p );
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if( DBG_CIPHER ) {
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fputc('\n', stderr);
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log_mpidump("elg p= ", p );
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log_mpidump("elg g= ", g );
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log_mpidump("elg y= ", y );
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log_mpidump("elg x= ", x );
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}
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/* copy the stuff to the key structures */
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pk->p = mpi_copy(p);
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pk->g = mpi_copy(g);
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pk->y = mpi_copy(y);
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sk->p = p;
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sk->g = g;
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sk->y = y;
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sk->x = x;
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/* now we can test our keys (this should never fail!) */
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test_keys( pk, sk, nbits - 64 );
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}
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/****************
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* Test wether the secret key is valid.
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* Returns: if this is a valid key.
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*/
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int
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elg_check_secret_key( ELG_secret_key *sk )
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{
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int rc;
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MPI y = mpi_alloc( mpi_get_nlimbs(sk->y) );
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mpi_powm( y, sk->g, sk->x, sk->p );
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rc = !mpi_cmp( y, sk->y );
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mpi_free( y );
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return rc;
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}
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void
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elg_encipher(MPI a, MPI b, MPI input, ELG_public_key *pkey )
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{
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MPI k;
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k = gen_k( pkey->p );
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mpi_powm( a, pkey->g, k, pkey->p );
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/* b = (y^k * input) mod p
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* = ((y^k mod p) * (input mod p)) mod p
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* and because input is < p (FIXME: check this!)
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* = ((y^k mod p) * input) mod p
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*/
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mpi_powm( b, pkey->y, k, pkey->p );
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mpi_mulm( b, b, input, pkey->p );
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#if 0
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if( DBG_CIPHER ) {
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log_mpidump("elg encipher y= ", pkey->y);
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log_mpidump("elg encipher p= ", pkey->p);
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log_mpidump("elg encipher k= ", k);
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log_mpidump("elg encipher M= ", input);
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log_mpidump("elg encipher a= ", a);
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log_mpidump("elg encipher b= ", b);
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}
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#endif
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mpi_free(k);
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}
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void
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elg_decipher(MPI output, MPI a, MPI b, ELG_secret_key *skey )
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{
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MPI t1 = mpi_alloc_secure( mpi_get_nlimbs( skey->p ) );
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/* output = b/(a^x) mod p */
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mpi_powm( t1, a, skey->x, skey->p );
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mpi_invm( t1, t1, skey->p );
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mpi_mulm( output, b, t1, skey->p );
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#if 0
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if( DBG_CIPHER ) {
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log_mpidump("elg decipher x= ", skey->x);
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log_mpidump("elg decipher p= ", skey->p);
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log_mpidump("elg decipher a= ", a);
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log_mpidump("elg decipher b= ", b);
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log_mpidump("elg decipher M= ", output);
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}
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#endif
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mpi_free(t1);
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}
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/****************
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* Make an Elgamal signature out of INPUT
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*/
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void
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elg_sign(MPI a, MPI b, MPI input, ELG_secret_key *skey )
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{
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MPI k;
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MPI t = mpi_alloc( mpi_get_nlimbs(a) );
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MPI inv = mpi_alloc( mpi_get_nlimbs(a) );
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MPI p_1 = mpi_copy(skey->p);
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/*
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* b = (t * inv) mod (p-1)
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* b = (t * inv(k,(p-1),(p-1)) mod (p-1)
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* b = (((M-x*a) mod (p-1)) * inv(k,(p-1),(p-1))) mod (p-1)
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*
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*/
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mpi_sub_ui(p_1, p_1, 1);
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k = gen_k( skey->p );
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mpi_powm( a, skey->g, k, skey->p );
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mpi_mul(t, skey->x, a );
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mpi_subm(t, input, t, p_1 );
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while( mpi_is_neg(t) )
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mpi_add(t, t, p_1);
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mpi_invm(inv, k, p_1 );
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mpi_mulm(b, t, inv, p_1 );
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#if 0
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if( DBG_CIPHER ) {
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log_mpidump("elg sign p= ", skey->p);
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log_mpidump("elg sign g= ", skey->g);
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log_mpidump("elg sign y= ", skey->y);
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log_mpidump("elg sign x= ", skey->x);
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log_mpidump("elg sign k= ", k);
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log_mpidump("elg sign M= ", input);
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log_mpidump("elg sign a= ", a);
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log_mpidump("elg sign b= ", b);
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}
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#endif
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mpi_free(k);
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mpi_free(t);
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mpi_free(inv);
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mpi_free(p_1);
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}
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/****************
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* Returns true if the signature composed from A and B is valid.
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*/
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int
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elg_verify(MPI a, MPI b, MPI input, ELG_public_key *pkey )
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{
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int rc;
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MPI t1 = mpi_alloc( mpi_get_nlimbs(a) );
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MPI t2 = mpi_alloc( mpi_get_nlimbs(a) );
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mpi_powm( t1, pkey->y, a, pkey->p );
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mpi_powm( t2, a, b, pkey->p );
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mpi_mulm( t1, t1, t2, pkey->p );
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mpi_powm( t2, pkey->g, input, pkey->p );
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rc = !mpi_cmp( t1, t2 );
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mpi_free(t1);
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mpi_free(t2);
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return rc;
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}
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@ -23,23 +23,27 @@
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#include "mpi.h"
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typedef struct {
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MPI e; /* exponent */
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MPI n; /* modulus */
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MPI p; /* prime */
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MPI g; /* group generator */
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MPI y; /* g^x mod p */
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} ELG_public_key;
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typedef struct {
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MPI e; /* public exponent */
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MPI n; /* public modulus */
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MPI p; /* prime p. */
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MPI q; /* prime q. */
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MPI d; /* exponent */
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MPI u; /* inverse of p mod q. */
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MPI p; /* prime */
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MPI g; /* group generator */
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MPI y; /* g^x mod p */
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MPI x; /* secret exponent */
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} ELG_secret_key;
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void elg_public(MPI output, MPI input, ELG_public_key *skey );
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void elg_secret(MPI output, MPI input, ELG_secret_key *skey );
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void elg_free_public_key( ELG_public_key *pk );
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void elg_free_secret_key( ELG_secret_key *sk );
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void elg_generate( ELG_public_key *pk, ELG_secret_key *sk, unsigned nbits );
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int elg_check_secret_key( ELG_secret_key *sk );
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void elg_encipher(MPI a, MPI b, MPI input, ELG_public_key *pkey );
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void elg_decipher(MPI output, MPI a, MPI b, ELG_secret_key *skey );
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void elg_sign(MPI a, MPI b, MPI input, ELG_secret_key *skey);
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int elg_verify(MPI a, MPI b, MPI input, ELG_public_key *pkey);
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#endif /*G10_ELGAMAL_H*/
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@ -29,13 +29,26 @@
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static int no_of_small_prime_numbers;
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static int rabin_miller( MPI n );
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static MPI gen_prime( unsigned nbits, int mode );
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/****************
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* Generate a prime number (stored in secure memory)
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*/
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MPI
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generate_random_prime( unsigned nbits )
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generate_secret_prime( unsigned nbits )
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{
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return gen_prime( nbits, 1 );
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}
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MPI
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generate_public_prime( unsigned nbits )
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{
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return gen_prime( nbits, 0 );
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}
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static MPI
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gen_prime( unsigned nbits, int secret )
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{
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unsigned nlimbs;
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@ -61,7 +74,7 @@ generate_random_prime( unsigned nbits )
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val_3 = mpi_alloc( nlimbs );
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mpi_set_ui(val_3, 3);
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result = mpi_alloc( nlimbs );
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prime = mpi_alloc_secure( nlimbs );
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prime = secret? mpi_alloc_secure( nlimbs ): mpi_alloc( nlimbs );
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count1 = count2 = 0;
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/* enter (endless) loop */
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for(;;) {
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@ -95,8 +95,8 @@ rsa_generate( RSA_public_key *pk, RSA_secret_key *sk, unsigned nbits )
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MPI f;
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/* select two (very secret) primes */
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p = generate_random_prime( nbits / 2 );
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q = generate_random_prime( nbits / 2 );
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p = generate_secret_prime( nbits / 2 );
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q = generate_secret_prime( nbits / 2 );
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if( mpi_cmp( p, q ) > 0 ) /* p shall be smaller than q (for calc of u)*/
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mpi_swap(p,q);
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/* calculate Euler totient: phi = (p-1)(q-1) */
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@ -120,10 +120,10 @@ rsa_generate( RSA_public_key *pk, RSA_secret_key *sk, unsigned nbits )
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mpi_add_ui( e, e, 2);
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/* calculate the secret key d = e^1 mod phi */
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d = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
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mpi_inv_mod(d, e, f );
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mpi_invm(d, e, f );
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/* calculate the inverse of p and q (used for chinese remainder theorem)*/
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u = mpi_alloc( nbits / BITS_PER_MPI_LIMB );
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mpi_inv_mod(u, p, q );
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mpi_invm(u, p, q );
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if( DBG_CIPHER ) {
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log_mpidump(" p= ", p );
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