Fix information leak in ecp_gen_keypair_base
The function mbedtls_ecp_gen_keypair_base did not wipe the stack buffer used to
hold the private exponent before returning. This commit fixes this by not using
a stack buffer in the first place but instead calling mpi_fill_random directly
to acquire the necessary random MPI.
@@ -1953,7 +1953,6 @@ int mbedtls_ecp_gen_keypair_base( mbedtls_ecp_group *grp,
{
/* SEC1 3.2.1: Generate d such that 1 <= n < N */
int count = 0;
- unsigned char rnd[MBEDTLS_ECP_MAX_BYTES];
/*
* Match the procedure given in RFC 6979 (deterministic ECDSA):
@@ -1964,8 +1963,7 @@ int mbedtls_ecp_gen_keypair_base( mbedtls_ecp_group *grp,
*/
do
{
- MBEDTLS_MPI_CHK( f_rng( p_rng, rnd, n_size ) );
- MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( d, rnd, n_size ) );
+ MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( d, n_size, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( d, 8 * n_size - grp->nbits ) );
/*
