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add DSA key generation

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This commit is contained in:
Werner Koch 1998-05-05 20:34:20 +00:00
parent 42b03f6ebd
commit 69cf10ffab
17 changed files with 324 additions and 29 deletions
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118
cipher/dsa.c
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@ -22,6 +22,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "util.h"
#include "mpi.h"
#include "cipher.h"
@ -74,6 +75,123 @@ dsa_free_secret_key( DSA_secret_key *sk )
}
static void
test_keys( DSA_public_key *pk, DSA_secret_key *sk, unsigned qbits )
{
MPI test = mpi_alloc( qbits / BITS_PER_MPI_LIMB );
MPI out1_a = mpi_alloc( qbits / BITS_PER_MPI_LIMB );
MPI out1_b = mpi_alloc( qbits / BITS_PER_MPI_LIMB );
mpi_set_bytes( test, qbits, get_random_byte, 0 );
dsa_sign( out1_a, out1_b, test, sk );
if( !dsa_verify( out1_a, out1_b, test, pk ) )
log_fatal("DSA:: sign, verify failed\n");
mpi_free( test );
mpi_free( out1_a );
mpi_free( out1_b );
}
/****************
* Generate a DSA key pair with a key of size NBITS
* Returns: 2 structures filled with all needed values
* and an array with the n-1 factors of (p-1)
*/
void
dsa_generate( DSA_public_key *pk, DSA_secret_key *sk,
unsigned nbits, MPI **ret_factors )
{
MPI p; /* the prime */
MPI q; /* the 160 bit prime factor */
MPI g; /* the generator */
MPI y; /* g^x mod p */
MPI x; /* the secret exponent */
MPI h, e; /* helper */
unsigned qbits;
byte *rndbuf;
assert( nbits >= 512 && nbits <= 1024 );
qbits = 160;
p = generate_elg_prime( 1, nbits, qbits, NULL, ret_factors );
/* get q out of factors */
q = mpi_copy((*ret_factors)[0]);
if( mpi_get_nbits(q) != qbits )
BUG();
/* 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 */
mpi_powm( g, h, e, p );
} while( !mpi_cmp_ui( g, 1 ) ); /* continue until g != 1 */
/* select a random number which has these properties:
* 0 < x < q-1
* This must be a very good random number because this
* is the secret part. */
if( DBG_CIPHER )
log_debug("choosing a random x ");
assert( qbits >= 16 );
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 )
fputc('.', stderr);
if( !rndbuf )
rndbuf = get_random_bits( qbits, 2, 1 );
else { /* change only some of the higher bits (= 2 bytes)*/
char *r = get_random_bits( 16, 2, 1 );
memcpy(rndbuf, r, 16/8 );
m_free(r);
}
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 ) );
m_free(rndbuf);
mpi_free( e );
mpi_free( h );
/* y = g^x mod p */
y = mpi_alloc( mpi_get_nlimbs(p) );
mpi_powm( y, g, x, p );
if( DBG_CIPHER ) {
fputc('\n', stderr);
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 */
pk->p = mpi_copy(p);
pk->q = mpi_copy(q);
pk->g = mpi_copy(g);
pk->y = mpi_copy(y);
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!) */
test_keys( pk, sk, qbits );
}
/****************
* Test whether the secret key is valid.
* Returns: if this is a valid key.