DHM refactoring: use dhm_random_below in dhm_make_common
dhm_make_common includes a piece of code that is identical to
dhm_random_below except for returning a different error code in one
case. Call dhm_random_below instead of repeating the code.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/dhm.c b/library/dhm.c
index c010d9f..4624659 100644
--- a/library/dhm.c
+++ b/library/dhm.c
@@ -180,29 +180,55 @@
return( 0 );
}
+/*
+ * Pick a random R in the range [2, M) for blinding or key generation.
+ */
+static int dhm_random_below( mbedtls_mpi *R, const mbedtls_mpi *M,
+ int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
+{
+ int ret, count;
+
+ count = 0;
+ do
+ {
+ MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( R, mbedtls_mpi_size( M ), f_rng, p_rng ) );
+
+ while( mbedtls_mpi_cmp_mpi( R, M ) >= 0 )
+ MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( R, 1 ) );
+
+ if( count++ > 10 )
+ return( MBEDTLS_ERR_MPI_NOT_ACCEPTABLE );
+ }
+ while( dhm_check_range( R, M ) != 0 );
+
+cleanup:
+ return( ret );
+}
+
static int dhm_make_common( mbedtls_dhm_context *ctx, int x_size,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
- int ret, count = 0;
+ int ret = 0;
if( mbedtls_mpi_cmp_int( &ctx->P, 0 ) == 0 )
return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA );
+ if( x_size < 0 )
+ return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA );
- /*
- * Generate X as large as possible ( < P )
- */
- do
+ if( (unsigned) x_size < mbedtls_mpi_size( &ctx->P ) )
{
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( &ctx->X, x_size, f_rng, p_rng ) );
-
- while( mbedtls_mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
- MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &ctx->X, 1 ) );
-
- if( count++ > 10 )
- return( MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED );
}
- while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
+ else
+ {
+ /* Generate X as large as possible ( <= P - 2 ) */
+ ret = dhm_random_below( &ctx->X, &ctx->P, f_rng, p_rng );
+ if( ret == MBEDTLS_ERR_MPI_NOT_ACCEPTABLE )
+ return( MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED );
+ if( ret != 0 )
+ return( ret );
+ }
/*
* Calculate GX = G^X mod P
@@ -341,31 +367,6 @@
return( ret );
}
-/*
- * Pick a random R in the range [2, M) for blinding purposes
- */
-static int dhm_random_below( mbedtls_mpi *R, const mbedtls_mpi *M,
- int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
-{
- int ret, count;
-
- count = 0;
- do
- {
- MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( R, mbedtls_mpi_size( M ), f_rng, p_rng ) );
-
- while( mbedtls_mpi_cmp_mpi( R, M ) >= 0 )
- MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( R, 1 ) );
-
- if( count++ > 10 )
- return( MBEDTLS_ERR_MPI_NOT_ACCEPTABLE );
- }
- while( dhm_check_range( R, M ) != 0 );
-
-cleanup:
- return( ret );
-}
-
/*
* Use the blinding method and optimisation suggested in section 10 of: