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- mpi_exp_mod() now correctly handles negative base numbers (Closes ticket #52)

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This commit is contained in:
Paul Bakker
2012-05-16 08:02:29 +00:00
parent 5b37784f6d
commit f6198c1513
4 changed files with 47 additions and 6 deletions
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27
library/bignum.c
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@ -1387,11 +1387,28 @@ int mpi_exp_mod( mpi *X, const mpi *A, const mpi *E, const mpi *N, mpi *_RR )
size_t i, j, nblimbs;
size_t bufsize, nbits;
t_uint ei, mm, state;
mpi RR, T, W[ 2 << POLARSSL_MPI_WINDOW_SIZE ];
mpi RR, T, W[ 2 << POLARSSL_MPI_WINDOW_SIZE ], Apos;
int neg;
if( mpi_cmp_int( N, 0 ) < 0 || ( N->p[0] & 1 ) == 0 )
return( POLARSSL_ERR_MPI_BAD_INPUT_DATA );
if( mpi_cmp_int( E, 0 ) < 0 )
return( POLARSSL_ERR_MPI_BAD_INPUT_DATA );
/*
* Compensate for negative A (and correct at the end)
*/
neg = ( A->s == -1 );
mpi_init( &Apos );
if( neg )
{
MPI_CHK( mpi_copy( &Apos, A ) );
Apos.s = 1;
A = &Apos;
}
/*
* Init temps and window size
*/
@ -1547,12 +1564,18 @@ int mpi_exp_mod( mpi *X, const mpi *A, const mpi *E, const mpi *N, mpi *_RR )
*/
mpi_montred( X, N, mm, &T );
if( neg )
{
X->s = -1;
mpi_add_mpi( X, N, X );
}
cleanup:
for( i = (one << (wsize - 1)); i < (one << wsize); i++ )
mpi_free( &W[i] );
mpi_free( &W[1] ); mpi_free( &T );
mpi_free( &W[1] ); mpi_free( &T ); mpi_free( &Apos );
if( _RR == NULL )
mpi_free( &RR );