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New internal function mbedtls_mpi_resize_clear

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The idiom "resize an mpi to a given size" appeared 4 times. Unify it
in a single function. Guarantee that the value is set to 0, which is
required by some of the callers and not a significant expense where
not required.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-06-02 22:17:52 +02:00
parent ceefe5d269
commit ed32b576a4
1 changed files with 27 additions and 31 deletions
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58
library/bignum.c
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@ -181,6 +181,27 @@ int mbedtls_mpi_shrink( mbedtls_mpi *X, size_t nblimbs )
return( 0 );
}
/* Resize X to have exactly n limbs and set it to 0. */
static int mbedtls_mpi_resize_clear( mbedtls_mpi *X, size_t limbs )
{
if( limbs == 0 )
{
mbedtls_mpi_free( X );
return( 0 );
}
else if( X->n == limbs )
{
memset( X->p, 0, limbs * ciL );
X->s = 1;
return( 0 );
}
else
{
mbedtls_mpi_free( X );
return( mbedtls_mpi_grow( X, limbs ) );
}
}
/*
* Copy the contents of Y into X
*/
@ -838,14 +859,7 @@ int mbedtls_mpi_read_binary_le( mbedtls_mpi *X,
size_t const limbs = CHARS_TO_LIMBS( buflen );
/* Ensure that target MPI has exactly the necessary number of limbs */
if( X->n != limbs )
{
mbedtls_mpi_free( X );
mbedtls_mpi_init( X );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, limbs ) );
}
MBEDTLS_MPI_CHK( mbedtls_mpi_lset( X, 0 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_resize_clear( X, limbs ) );
for( i = 0; i < buflen; i++ )
X->p[i / ciL] |= ((mbedtls_mpi_uint) buf[i]) << ((i % ciL) << 3);
@ -874,17 +888,11 @@ int mbedtls_mpi_read_binary( mbedtls_mpi *X, const unsigned char *buf, size_t bu
MPI_VALIDATE_RET( buflen == 0 || buf != NULL );
/* Ensure that target MPI has exactly the necessary number of limbs */
if( X->n != limbs )
{
mbedtls_mpi_free( X );
mbedtls_mpi_init( X );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, limbs ) );
}
MBEDTLS_MPI_CHK( mbedtls_mpi_lset( X, 0 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_resize_clear( X, limbs ) );
/* Avoid calling `memcpy` with NULL source argument,
/* Avoid calling `memcpy` with NULL source or destination argument,
* even if buflen is 0. */
if( buf != NULL )
if( buflen != 0 )
{
Xp = (unsigned char*) X->p;
memcpy( Xp + overhead, buf, buflen );
@ -2438,13 +2446,7 @@ int mbedtls_mpi_fill_random( mbedtls_mpi *X, size_t size,
MPI_VALIDATE_RET( f_rng != NULL );
/* Ensure that target MPI has exactly the necessary number of limbs */
if( X->n != limbs )
{
mbedtls_mpi_free( X );
mbedtls_mpi_init( X );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, limbs ) );
}
X->s = 1;
MBEDTLS_MPI_CHK( mbedtls_mpi_resize_clear( X, limbs ) );
if( size == 0 )
return( 0 );
@ -2493,13 +2495,7 @@ int mbedtls_mpi_random( mbedtls_mpi *X,
/* Ensure that target MPI has exactly the same number of limbs
* as the upper bound, even if the upper bound has leading zeros.
* This is necessary for the mbedtls_mpi_lt_mpi_ct() check. */
if( X->n != N->n )
{
mbedtls_mpi_free( X );
mbedtls_mpi_init( X );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, N->n ) );
}
X->s = 1;
MBEDTLS_MPI_CHK( mbedtls_mpi_resize_clear( X, N->n ) );
/*
* Match the procedure given in RFC 6979 §3.3 (deterministic ECDSA)