static gcry_mpi_t
gen_prime (unsigned int nbits, int secret, int randomlevel,
int (*extra_check)(void *, gcry_mpi_t), void *extra_check_arg)
{
gcry_mpi_t prime, ptest, pminus1, val_2, val_3, result;
int i;
unsigned int x, step;
unsigned int count1, count2;
int *mods;
/* if ( DBG_CIPHER ) */
/* log_debug ("generate a prime of %u bits ", nbits ); */
if (nbits < 16)
log_fatal ("can't generate a prime with less than %d bits\n", 16);
mods = gcry_xmalloc( no_of_small_prime_numbers * sizeof *mods );
/* Make nbits fit into gcry_mpi_t implementation. */
val_2 = mpi_alloc_set_ui( 2 );
val_3 = mpi_alloc_set_ui( 3);
prime = secret? gcry_mpi_snew ( nbits ): gcry_mpi_new ( nbits );
result = mpi_alloc_like( prime );
pminus1= mpi_alloc_like( prime );
ptest = mpi_alloc_like( prime );
count1 = count2 = 0;
for (;;)
{ /* try forvever */
int dotcount=0;
/* generate a random number */
gcry_mpi_randomize( prime, nbits, randomlevel );
/* Set high order bit to 1, set low order bit to 1. If we are
generating a secret prime we are most probably doing that
for RSA, to make sure that the modulus does have the
requested key size we set the 2 high order bits. */
mpi_set_highbit (prime, nbits-1);
if (secret)
mpi_set_bit (prime, nbits-2);
mpi_set_bit(prime, 0);
/* Calculate all remainders. */
for (i=0; (x = small_prime_numbers[i]); i++ )
mods[i] = mpi_fdiv_r_ui(NULL, prime, x);
/* Now try some primes starting with prime. */
for(step=0; step < 20000; step += 2 )
{
/* Check against all the small primes we have in mods. */
count1++;
for (i=0; (x = small_prime_numbers[i]); i++ )
{
while ( mods[i] + step >= x )
mods[i] -= x;
if ( !(mods[i] + step) )
break;
}
if ( x )
continue; /* Found a multiple of an already known prime. */
mpi_add_ui( ptest, prime, step );
/* Do a fast Fermat test now. */
count2++;
mpi_sub_ui( pminus1, ptest, 1);
gcry_mpi_powm( result, val_2, pminus1, ptest );
if ( !mpi_cmp_ui( result, 1 ) )
{
/* Not composite, perform stronger tests */
if (is_prime(ptest, 5, &count2 ))
{
if (!mpi_test_bit( ptest, nbits-1-secret ))
{
progress('\n');
log_debug ("overflow in prime generation\n");
break; /* Stop loop, continue with a new prime. */
}
if (extra_check && extra_check (extra_check_arg, ptest))
{
/* The extra check told us that this prime is
not of the caller's taste. */
progress ('/');
}
else
{
/* Got it. */
mpi_free(val_2);
mpi_free(val_3);
mpi_free(result);
mpi_free(pminus1);
mpi_free(prime);
gcry_free(mods);
return ptest;
}
}
}
if (++dotcount == 10 )
{
progress('.');
dotcount = 0;
}
}
progress(':'); /* restart with a new random value */
}
}
static MPI
gen_prime( unsigned nbits, int secret, int randomlevel )
{
unsigned nlimbs;
MPI prime, ptest, pminus1, val_2, val_3, result;
int i;
unsigned x, step;
unsigned count1, count2;
int *mods;
if( 0 && DBG_CIPHER )
log_debug("generate a prime of %u bits ", nbits );
if( !no_of_small_prime_numbers ) {
for(i=0; small_prime_numbers[i]; i++ )
no_of_small_prime_numbers++;
}
mods = m_alloc( no_of_small_prime_numbers * sizeof *mods );
/* make nbits fit into MPI implementation */
nlimbs = (nbits + BITS_PER_MPI_LIMB - 1) / BITS_PER_MPI_LIMB;
val_2 = mpi_alloc_set_ui( 2 );
val_3 = mpi_alloc_set_ui( 3);
prime = secret? mpi_alloc_secure( nlimbs ): mpi_alloc( nlimbs );
result = mpi_alloc_like( prime );
pminus1= mpi_alloc_like( prime );
ptest = mpi_alloc_like( prime );
count1 = count2 = 0;
for(;;) { /* try forvever */
int dotcount=0;
/* generate a random number */
{ char *p = get_random_bits( nbits, randomlevel, secret );
mpi_set_buffer( prime, p, (nbits+7)/8, 0 );
m_free(p);
}
/* set high order bit to 1, set low order bit to 1 */
mpi_set_highbit( prime, nbits-1 );
mpi_set_bit( prime, 0 );
/* calculate all remainders */
for(i=0; (x = small_prime_numbers[i]); i++ )
mods[i] = mpi_fdiv_r_ui(NULL, prime, x);
/* now try some primes starting with prime */
for(step=0; step < 20000; step += 2 ) {
/* check against all the small primes we have in mods */
count1++;
for(i=0; (x = small_prime_numbers[i]); i++ ) {
while( mods[i] + step >= x )
mods[i] -= x;
if( !(mods[i] + step) )
break;
}
if( x )
continue; /* found a multiple of an already known prime */
mpi_add_ui( ptest, prime, step );
/* do a faster Fermat test */
count2++;
mpi_sub_ui( pminus1, ptest, 1);
mpi_powm( result, val_2, pminus1, ptest );
if( !mpi_cmp_ui( result, 1 ) ) { /* not composite */
/* perform stronger tests */
if( is_prime(ptest, 5, &count2 ) ) {
if( !mpi_test_bit( ptest, nbits-1 ) ) {
progress('\n');
log_debug("overflow in prime generation\n");
break; /* step loop, continue with a new prime */
}
mpi_free(val_2);
mpi_free(val_3);
mpi_free(result);
mpi_free(pminus1);
mpi_free(prime);
m_free(mods);
return ptest;
}
}
if( ++dotcount == 10 ) {
progress('.');
dotcount = 0;
}
}
progress(':'); /* restart with a new random value */
}
}
