diff options
Diffstat (limited to '')
| -rw-r--r-- | cipher/dsa.c | 45 |
1 files changed, 32 insertions, 13 deletions
diff --git a/cipher/dsa.c b/cipher/dsa.c index cbd90ac5f..9154f49d6 100644 --- a/cipher/dsa.c +++ b/cipher/dsa.c @@ -66,30 +66,49 @@ static MPI gen_k( MPI q ) { MPI k = mpi_alloc_secure( mpi_get_nlimbs(q) ); - unsigned nbits = mpi_get_nbits(q); + unsigned int nbits = mpi_get_nbits(q); + unsigned int nbytes = (nbits+7)/8; + char *rndbuf = NULL; if( DBG_CIPHER ) log_debug("choosing a random k "); for(;;) { if( DBG_CIPHER ) progress('.'); - { char *p = get_random_bits( nbits, 1, 1 ); - mpi_set_buffer( k, p, (nbits+7)/8, 0 ); - m_free(p); - /* make sure that the number is of the exact lenght */ - if( mpi_test_bit( k, nbits-1 ) ) - mpi_set_highbit( k, nbits-1 ); - else { - mpi_set_highbit( k, nbits-1 ); - mpi_clear_bit( k, nbits-1 ); - } + + if( !rndbuf || nbits < 32 ) { + m_free(rndbuf); + rndbuf = get_random_bits( nbits, 1, 1 ); + } + else { /* change only some of the higher bits */ + /* we could imporove 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 */ + char *pp = get_random_bits( 32, 1, 1 ); + memcpy( rndbuf,pp, 4 ); + m_free(pp); } - if( !(mpi_cmp( k, q ) < 0) ) /* check: k < q */ + mpi_set_buffer( k, rndbuf, nbytes, 0 ); + if( mpi_test_bit( k, nbits-1 ) ) + mpi_set_highbit( k, nbits-1 ); + else { + mpi_set_highbit( k, nbits-1 ); + mpi_clear_bit( k, nbits-1 ); + } + + if( !(mpi_cmp( k, q ) < 0) ) { /* check: k < q */ + if( DBG_CIPHER ) + progress('+'); continue; /* no */ - if( !(mpi_cmp_ui( k, 0 ) > 0) ) /* check: k > 0 */ + } + if( !(mpi_cmp_ui( k, 0 ) > 0) ) { /* check: k > 0 */ + if( DBG_CIPHER ) + progress('-'); continue; /* no */ + } break; /* okay */ } + m_free(rndbuf); if( DBG_CIPHER ) progress('\n'); |