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DHM: use mbedtls_mpi_random for blinding and key generation

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Instead of generating blinding values and keys in a not-quite-uniform way
(https://github.com/ARMmbed/mbedtls/issues/4245) with copy-pasted code,
use mbedtls_mpi_random().

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-03-31 23:04:50 +02:00
parent 58df4c9098
commit 16e3668d14
2 changed files with 5 additions and 15 deletions
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18
library/dhm.c
View File

@ -150,25 +150,15 @@ int mbedtls_dhm_read_params( mbedtls_dhm_context *ctx,
}
/*
* Pick a random R in the range [2, M) for blinding or key generation.
* Pick a random R in the range [2, M-2] 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;
int ret;
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 );
MBEDTLS_MPI_CHK( mbedtls_mpi_random( R, 3, M, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( R, R, 1 ) );
cleanup:
return( ret );

2
tests/suites/test_suite_dhm.data
View File

@ -74,7 +74,7 @@ Diffie-Hellman trivial subgroup #2
dhm_do_dhm:10:"23":1:10:"-1":MBEDTLS_ERR_DHM_BAD_INPUT_DATA
Diffie-Hellman small modulus
dhm_do_dhm:10:"3":1:10:"5":MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED
dhm_do_dhm:10:"3":1:10:"5":MBEDTLS_ERR_DHM_MAKE_PARAMS_FAILED+MBEDTLS_ERR_MPI_BAD_INPUT_DATA
Diffie-Hellman zero modulus
dhm_do_dhm:10:"0":1:10:"5":MBEDTLS_ERR_DHM_BAD_INPUT_DATA