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mpi_fill_random_internal: remove spurious grow() call

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Since the internal function mpi_fill_random_internal() assumes that X
has the right size, there is no need to call grow().

To further simplify the function, set the sign outside, and zero out
the non-randomized part directly.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-04-13 21:55:35 +02:00
parent 3d60ece16c
commit a16001e2d9
1 changed files with 5 additions and 2 deletions
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7
library/bignum.c
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@ -2397,6 +2397,7 @@ cleanup:
/* Fill X with n_bytes random bytes. /* Fill X with n_bytes random bytes.
* X must already have room for those bytes. * X must already have room for those bytes.
* The size and sign of X are unchanged.
* n_bytes must not be 0. * n_bytes must not be 0.
*/ */
static int mpi_fill_random_internal( static int mpi_fill_random_internal(
@ -2409,9 +2410,9 @@ static int mpi_fill_random_internal(
if( X->n < limbs ) if( X->n < limbs )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA ); return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
MBEDTLS_MPI_CHK( mbedtls_mpi_lset( X, 0 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, limbs ) );
memset( X->p, 0, overhead );
memset( (unsigned char *) X->p + limbs * ciL, 0, ( X->n - limbs ) * ciL );
MBEDTLS_MPI_CHK( f_rng( p_rng, (unsigned char *) X->p + overhead, n_bytes ) ); MBEDTLS_MPI_CHK( f_rng( p_rng, (unsigned char *) X->p + overhead, n_bytes ) );
mpi_bigendian_to_host( X->p, limbs ); mpi_bigendian_to_host( X->p, limbs );
@ -2443,6 +2444,7 @@ int mbedtls_mpi_fill_random( mbedtls_mpi *X, size_t size,
mbedtls_mpi_init( X ); mbedtls_mpi_init( X );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, limbs ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, limbs ) );
} }
X->s = 1;
if( size == 0 ) if( size == 0 )
return( 0 ); return( 0 );
@ -2501,6 +2503,7 @@ int mbedtls_mpi_random( mbedtls_mpi *X,
mbedtls_mpi_init( X ); mbedtls_mpi_init( X );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, N->n ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, N->n ) );
} }
X->s = 1;
/* /*
* Match the procedure given in RFC 6979 §3.3 (deterministic ECDSA) * Match the procedure given in RFC 6979 §3.3 (deterministic ECDSA)