Git initHEAD2.0_alphamaster2.0alpha1.0_post

1 files changed, 510 insertions, 0 deletions

diff --git a/cipher/elgamal.c b/cipher/elgamal.c
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+/* elgamal.c  -  elgamal Public Key encryption
+ * Copyright (C) 1998, 2000, 2001, 2003,
+ *               2004 Free Software Foundation, Inc.
+ *
+ * For a description of the algorithm, see:
+ *   Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
+ *   ISBN 0-471-11709-9. Pages 476 ff.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+ * USA.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "util.h"
+#include "mpi.h"
+#include "cipher.h"
+#include "elgamal.h"
+
+typedef struct {
+    MPI p;	    /* prime */
+    MPI g;	    /* group generator */
+    MPI y;	    /* g^x mod p */
+} ELG_public_key;
+
+
+typedef struct {
+    MPI p;	    /* prime */
+    MPI g;	    /* group generator */
+    MPI y;	    /* g^x mod p */
+    MPI x;	    /* secret exponent */
+} ELG_secret_key;
+
+
+static void test_keys( ELG_secret_key *sk, unsigned nbits );
+static MPI gen_k( MPI p, int small_k );
+static void generate( ELG_secret_key *sk, unsigned nbits, MPI **factors );
+static int  check_secret_key( ELG_secret_key *sk );
+static void do_encrypt(MPI a, MPI b, MPI input, ELG_public_key *pkey );
+static void decrypt(MPI output, MPI a, MPI b, ELG_secret_key *skey );
+
+
+static void (*progress_cb) ( void *, int );
+static void *progress_cb_data;
+
+void
+register_pk_elg_progress ( void (*cb)( void *, 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, c );
+    else
+	fputc( c, stderr );
+}
+
+
+/****************
+ * Michael Wiener's table about subgroup sizes to match field sizes
+ * (floating around somewhere - Fixme: need a reference)
+ */
+static unsigned int
+wiener_map( unsigned int n )
+{
+    static struct { unsigned int p_n, q_n; } t[] =
+    {	/*   p	  q	 attack cost */
+	{  512, 119 },	/* 9 x 10^17 */
+	{  768, 145 },	/* 6 x 10^21 */
+	{ 1024, 165 },	/* 7 x 10^24 */
+	{ 1280, 183 },	/* 3 x 10^27 */
+	{ 1536, 198 },	/* 7 x 10^29 */
+	{ 1792, 212 },	/* 9 x 10^31 */
+	{ 2048, 225 },	/* 8 x 10^33 */
+	{ 2304, 237 },	/* 5 x 10^35 */
+	{ 2560, 249 },	/* 3 x 10^37 */
+	{ 2816, 259 },	/* 1 x 10^39 */
+	{ 3072, 269 },	/* 3 x 10^40 */
+	{ 3328, 279 },	/* 8 x 10^41 */
+	{ 3584, 288 },	/* 2 x 10^43 */
+	{ 3840, 296 },	/* 4 x 10^44 */
+	{ 4096, 305 },	/* 7 x 10^45 */
+	{ 4352, 313 },	/* 1 x 10^47 */
+	{ 4608, 320 },	/* 2 x 10^48 */
+	{ 4864, 328 },	/* 2 x 10^49 */
+	{ 5120, 335 },	/* 3 x 10^50 */
+	{ 0, 0 }
+    };
+    int i;
+
+    for(i=0; t[i].p_n; i++ )  {
+	if( n <= t[i].p_n )
+	    return t[i].q_n;
+    }
+    /* not in table - use some arbitrary high number ;-) */
+    return  n / 8 + 200;
+}
+
+static void
+test_keys( ELG_secret_key *sk, unsigned nbits )
+{
+    ELG_public_key pk;
+    MPI test = mpi_alloc( 0 );
+    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 );
+
+    pk.p = sk->p;
+    pk.g = sk->g;
+    pk.y = sk->y;
+
+    /*mpi_set_bytes( test, nbits, get_random_byte, 0 );*/
+    {	char *p = get_random_bits( nbits, 0, 0 );
+	mpi_set_buffer( test, p, (nbits+7)/8, 0 );
+	xfree(p);
+    }
+
+    do_encrypt( out1_a, out1_b, test, &pk );
+    decrypt( out2, out1_a, out1_b, sk );
+    if( mpi_cmp( test, out2 ) )
+	log_fatal("Elgamal operation: encrypt, decrypt 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.  With SMALL_K set, k will be selected for
+ * better encryption performance - this must never bee used signing!
+ */
+static MPI
+gen_k( MPI p, int small_k )
+{
+    MPI k = mpi_alloc_secure( 0 );
+    MPI temp = mpi_alloc( mpi_get_nlimbs(p) );
+    MPI p_1 = mpi_copy(p);
+    unsigned int orig_nbits = mpi_get_nbits(p);
+    unsigned int nbits;
+    unsigned int nbytes;
+    char *rndbuf = NULL;
+
+    if (small_k)
+      {
+        /* Using a k much lesser than p is sufficient for encryption and
+         * it greatly improves the encryption performance.  We use
+         * Wiener's table and add a large safety margin.
+         */
+        nbits = wiener_map( orig_nbits ) * 3 / 2;
+        if( nbits >= orig_nbits )
+          BUG();
+      }
+    else
+      nbits = orig_nbits;
+
+    nbytes = (nbits+7)/8;
+    if( DBG_CIPHER )
+	log_debug("choosing a random k of %u bits", nbits);
+    mpi_sub_ui( p_1, p, 1);
+    for(;;) {
+	if( !rndbuf || nbits < 32 ) {
+	    xfree(rndbuf);
+	    rndbuf = get_random_bits( nbits, 1, 1 );
+	}
+	else { /* Change only some of the higher bits. */
+	    /* We could impprove this by directly requesting more memory
+	     * at the first call to get_random_bits() and use this the here
+	     * maybe it is easier to do this directly in random.c
+	     * Anyway, it is highly inlikely that we will ever reach this code
+	     */
+	    char *pp = get_random_bits( 32, 1, 1 );
+	    memcpy( rndbuf,pp, 4 );
+	    xfree(pp);
+	}
+	mpi_set_buffer( k, rndbuf, nbytes, 0 );
+
+	for(;;) {
+	    if( !(mpi_cmp( k, p_1 ) < 0) ) {  /* check: k < (p-1) */
+		if( DBG_CIPHER )
+		    progress('+');
+		break; /* no  */
+	    }
+	    if( !(mpi_cmp_ui( k, 0 ) > 0) ) { /* check: k > 0 */
+		if( DBG_CIPHER )
+		    progress('-');
+		break; /* no */
+	    }
+	    if( mpi_gcd( temp, k, p_1 ) )
+		goto found;  /* okay, k is relatively prime to (p-1) */
+	    mpi_add_ui( k, k, 1 );
+	    if( DBG_CIPHER )
+		progress('.');
+	}
+    }
+  found:
+    xfree(rndbuf);
+    if( DBG_CIPHER )
+	progress('\n');
+    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
+ *	    and an array with n-1 factors of (p-1)
+ */
+static void
+generate(  ELG_secret_key *sk, unsigned int nbits, MPI **ret_factors )
+{
+    MPI p;    /* the prime */
+    MPI p_min1;
+    MPI g;
+    MPI x;    /* the secret exponent */
+    MPI y;
+    MPI temp;
+    unsigned int qbits;
+    unsigned int xbits;
+    byte *rndbuf;
+
+    p_min1 = mpi_alloc( (nbits+BITS_PER_MPI_LIMB-1)/BITS_PER_MPI_LIMB );
+    temp   = mpi_alloc( (nbits+BITS_PER_MPI_LIMB-1)/BITS_PER_MPI_LIMB );
+    qbits = wiener_map( nbits );
+    if( qbits & 1 ) /* better have a even one */
+	qbits++;
+    g = mpi_alloc(1);
+    p = generate_elg_prime( 0, nbits, qbits, g, ret_factors );
+    mpi_sub_ui(p_min1, p, 1);
+
+
+    /* select a random number which has these properties:
+     *	 0 < x < p-1
+     * This must be a very good random number because this is the
+     * secret part.  The prime is public and may be shared anyway,
+     * so a random generator level of 1 is used for the prime.
+     *
+     * I don't see a reason to have a x of about the same size as the
+     * p.  It should be sufficient to have one about the size of q or
+     * the later used k plus a large safety margin. Decryption will be
+     * much faster with such an x.  Note that this is not optimal for
+     * signing keys becuase it makes an attack using accidential small
+     * K values even easier.  Well, one should not use ElGamal signing
+     * anyway.
+     */
+    xbits = qbits * 3 / 2;
+    if( xbits >= nbits )
+	BUG();
+    x = mpi_alloc_secure( xbits/BITS_PER_MPI_LIMB );
+    if( DBG_CIPHER )
+	log_debug("choosing a random x of size %u", xbits );
+    rndbuf = NULL;
+    do {
+	if( DBG_CIPHER )
+	    progress('.');
+	if( rndbuf ) { /* change only some of the higher bits */
+	    if( xbits < 16 ) {/* should never happen ... */
+		xfree(rndbuf);
+		rndbuf = get_random_bits( xbits, 2, 1 );
+	    }
+	    else {
+		char *r = get_random_bits( 16, 2, 1 );
+		memcpy(rndbuf, r, 16/8 );
+		xfree(r);
+	    }
+	}
+	else
+	    rndbuf = get_random_bits( xbits, 2, 1 );
+	mpi_set_buffer( x, rndbuf, (xbits+7)/8, 0 );
+	mpi_clear_highbit( x, xbits+1 );
+    } while( !( mpi_cmp_ui( x, 0 )>0 && mpi_cmp( x, p_min1 )<0 ) );
+    xfree(rndbuf);
+
+    y = mpi_alloc(nbits/BITS_PER_MPI_LIMB);
+    mpi_powm( y, g, x, p );
+
+    if( DBG_CIPHER ) {
+	progress('\n');
+	log_mpidump("elg  p= ", p );
+	log_mpidump("elg  g= ", g );
+	log_mpidump("elg  y= ", y );
+	log_mpidump("elg  x= ", x );
+    }
+
+    /* copy the stuff to the key structures */
+    sk->p = p;
+    sk->g = g;
+    sk->y = y;
+    sk->x = x;
+
+    /* now we can test our keys (this should never fail!) */
+    test_keys( sk, nbits - 64 );
+
+    mpi_free( p_min1 );
+    mpi_free( temp   );
+}
+
+
+/****************
+ * Test whether the secret key is valid.
+ * Returns: if this is a valid key.
+ */
+static int
+check_secret_key( ELG_secret_key *sk )
+{
+    int rc;
+    MPI y = mpi_alloc( mpi_get_nlimbs(sk->y) );
+
+    mpi_powm( y, sk->g, sk->x, sk->p );
+    rc = !mpi_cmp( y, sk->y );
+    mpi_free( y );
+    return rc;
+}
+
+
+static void
+do_encrypt(MPI a, MPI b, MPI input, ELG_public_key *pkey )
+{
+    MPI k;
+
+    /* Note: maybe we should change the interface, so that it
+     * is possible to check that input is < p and return an
+     * error code.
+     */
+
+    k = gen_k( pkey->p, 1 );
+    mpi_powm( a, pkey->g, k, pkey->p );
+    /* b = (y^k * input) mod p
+     *	 = ((y^k mod p) * (input mod p)) mod p
+     * and because input is < p
+     *	 = ((y^k mod p) * input) mod p
+     */
+    mpi_powm( b, pkey->y, k, pkey->p );
+    mpi_mulm( b, b, input, pkey->p );
+#if 0
+    if( DBG_CIPHER ) {
+	log_mpidump("elg encrypted y= ", pkey->y);
+	log_mpidump("elg encrypted p= ", pkey->p);
+	log_mpidump("elg encrypted k= ", k);
+	log_mpidump("elg encrypted M= ", input);
+	log_mpidump("elg encrypted a= ", a);
+	log_mpidump("elg encrypted b= ", b);
+    }
+#endif
+    mpi_free(k);
+}
+
+
+static void
+decrypt(MPI output, MPI a, MPI b, ELG_secret_key *skey )
+{
+    MPI t1 = mpi_alloc_secure( mpi_get_nlimbs( skey->p ) );
+
+    /* output = b/(a^x) mod p */
+    mpi_powm( t1, a, skey->x, skey->p );
+    mpi_invm( t1, t1, skey->p );
+    mpi_mulm( output, b, t1, skey->p );
+#if 0
+    if( DBG_CIPHER ) {
+	log_mpidump("elg decrypted x= ", skey->x);
+	log_mpidump("elg decrypted p= ", skey->p);
+	log_mpidump("elg decrypted a= ", a);
+	log_mpidump("elg decrypted b= ", b);
+	log_mpidump("elg decrypted M= ", output);
+    }
+#endif
+    mpi_free(t1);
+}
+
+
+/*********************************************
+ **************  interface  ******************
+ *********************************************/
+
+int
+elg_generate( int algo, unsigned nbits, MPI *skey, MPI **retfactors )
+{
+    ELG_secret_key sk;
+
+    if( !is_ELGAMAL(algo) )
+	return G10ERR_PUBKEY_ALGO;
+
+    generate( &sk, nbits, retfactors );
+    skey[0] = sk.p;
+    skey[1] = sk.g;
+    skey[2] = sk.y;
+    skey[3] = sk.x;
+    return 0;
+}
+
+
+int
+elg_check_secret_key( int algo, MPI *skey )
+{
+    ELG_secret_key sk;
+
+    if( !is_ELGAMAL(algo) )
+	return G10ERR_PUBKEY_ALGO;
+    if( !skey[0] || !skey[1] || !skey[2] || !skey[3] )
+	return G10ERR_BAD_MPI;
+
+    sk.p = skey[0];
+    sk.g = skey[1];
+    sk.y = skey[2];
+    sk.x = skey[3];
+    if( !check_secret_key( &sk ) )
+	return G10ERR_BAD_SECKEY;
+
+    return 0;
+}
+
+
+int
+elg_encrypt( int algo, MPI *resarr, MPI data, MPI *pkey )
+{
+    ELG_public_key pk;
+
+    if( !is_ELGAMAL(algo) )
+	return G10ERR_PUBKEY_ALGO;
+    if( !data || !pkey[0] || !pkey[1] || !pkey[2] )
+	return G10ERR_BAD_MPI;
+
+    pk.p = pkey[0];
+    pk.g = pkey[1];
+    pk.y = pkey[2];
+    resarr[0] = mpi_alloc( mpi_get_nlimbs( pk.p ) );
+    resarr[1] = mpi_alloc( mpi_get_nlimbs( pk.p ) );
+    do_encrypt( resarr[0], resarr[1], data, &pk );
+    return 0;
+}
+
+int
+elg_decrypt( int algo, MPI *result, MPI *data, MPI *skey )
+{
+    ELG_secret_key sk;
+
+    if( !is_ELGAMAL(algo) )
+	return G10ERR_PUBKEY_ALGO;
+    if( !data[0] || !data[1]
+	|| !skey[0] || !skey[1] || !skey[2] || !skey[3] )
+	return G10ERR_BAD_MPI;
+
+    sk.p = skey[0];
+    sk.g = skey[1];
+    sk.y = skey[2];
+    sk.x = skey[3];
+    *result = mpi_alloc_secure( mpi_get_nlimbs( sk.p ) );
+    decrypt( *result, data[0], data[1], &sk );
+    return 0;
+}
+
+
+unsigned int
+elg_get_nbits( int algo, MPI *pkey )
+{
+    if( !is_ELGAMAL(algo) )
+	return 0;
+    return mpi_get_nbits( pkey[0] );
+}
+
+
+/****************
+ * Return some information about the algorithm.  We need algo here to
+ * distinguish different flavors of the algorithm.
+ * Returns: A pointer to string describing the algorithm or NULL if
+ *	    the ALGO is invalid.
+ * Usage: Bit 0 set : allows signing
+ *	      1 set : allows encryption
+ */
+const char *
+elg_get_info( int algo, int *npkey, int *nskey, int *nenc, int *nsig,
+							 int *use )
+{
+    *npkey = 3;
+    *nskey = 4;
+    *nenc = 2;
+    *nsig = 2;
+
+    switch( algo ) {
+      case PUBKEY_ALGO_ELGAMAL_E:
+	*use = PUBKEY_USAGE_ENC;
+	return "ELG-E";
+      default: *use = 0; return NULL;
+    }
+}