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New function mbedtls_dhm_get_value to copy a field of a DHM context

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Reduce the need to break the DHM abstraction by accessing the context directly.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-05-27 22:50:53 +02:00
parent 487bbf6805
commit 71acc6e8d9
5 changed files with 99 additions and 4 deletions
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2
ChangeLog.d/dhm-fields.txt
View file

@ -1,6 +1,8 @@
Features
* The new functions mbedtls_dhm_get_len() and mbedtls_dhm_get_bitlen()
query the size of the modulus in a Diffie-Hellman context.
* The new function mbedtls_dhm_get_value() copy a field out of a
Diffie-Hellman context.
API changes
* Instead of accessing the len field of a DHM context, which is no longer

27
include/mbedtls/dhm.h
View file

@ -85,6 +85,17 @@
#define MBEDTLS_ERR_DHM_FILE_IO_ERROR -0x3480 /**< Read or write of file failed. */
#define MBEDTLS_ERR_DHM_SET_GROUP_FAILED -0x3580 /**< Setting the modulus and generator failed. */
/** Which parameter to access in mbedtls_dhm_get_value(). */
typedef enum
{
MBEDTLS_DHM_PARAM_P, /*!< The prime modulus. */
MBEDTLS_DHM_PARAM_G, /*!< The generator. */
MBEDTLS_DHM_PARAM_X, /*!< Our secret value. */
MBEDTLS_DHM_PARAM_GX, /*!< Our public key = \c G^X mod \c P. */
MBEDTLS_DHM_PARAM_GY, /*!< The public key of the peer = \c G^Y mod \c P. */
MBEDTLS_DHM_PARAM_K, /*!< The shared secret = \c G^(XY) mod \c P. */
} mbedtls_dhm_parameter;
#ifdef __cplusplus
extern "C" {
#endif
@ -301,6 +312,22 @@ size_t mbedtls_dhm_get_bitlen( const mbedtls_dhm_context *ctx );
*/
size_t mbedtls_dhm_get_len( const mbedtls_dhm_context *ctx );
/**
* \brief This function copies a parameter of a DHM key.
*
* \param dest The MPI object to copy the value into. It must be
* initialized.
* \param ctx The DHM context to query.
* \param param The parameter to copy.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_DHM_BAD_INPUT_DATA if \p field is invalid.
* \return An \c MBEDTLS_ERR_MPI_XXX error code if the copy fails.
*/
int mbedtls_dhm_get_value( mbedtls_mpi *dest,
const mbedtls_dhm_context *ctx,
mbedtls_dhm_parameter param );
/**
* \brief This function frees and clears the components
* of a DHM context.

31
library/dhm.c
View file

@ -134,6 +134,37 @@ size_t mbedtls_dhm_get_len( const mbedtls_dhm_context *ctx )
return( mbedtls_mpi_size( &ctx->P ) );
}
int mbedtls_dhm_get_value( mbedtls_mpi *dest,
const mbedtls_dhm_context *ctx,
mbedtls_dhm_parameter param )
{
const mbedtls_mpi *src = NULL;
switch( param )
{
case MBEDTLS_DHM_PARAM_P:
src = &ctx->P;
break;
case MBEDTLS_DHM_PARAM_G:
src = &ctx->G;
break;
case MBEDTLS_DHM_PARAM_X:
src = &ctx->X;
break;
case MBEDTLS_DHM_PARAM_GX:
src = &ctx->GX;
break;
case MBEDTLS_DHM_PARAM_GY:
src = &ctx->GY;
break;
case MBEDTLS_DHM_PARAM_K:
src = &ctx->K;
break;
default:
return( MBEDTLS_ERR_DHM_BAD_INPUT_DATA );
}
return( mbedtls_mpi_copy( dest, src ) );
}
/*
* Parse the ServerKeyExchange parameters
*/

6
library/ssl_tls.c
View file

@ -3871,8 +3871,10 @@ int mbedtls_ssl_conf_dh_param_ctx( mbedtls_ssl_config *conf, mbedtls_dhm_context
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
if( ( ret = mbedtls_mpi_copy( &conf->dhm_P, &dhm_ctx->P ) ) != 0 ||
( ret = mbedtls_mpi_copy( &conf->dhm_G, &dhm_ctx->G ) ) != 0 )
if( ( ret = mbedtls_dhm_get_value( &conf->dhm_P, dhm_ctx,
MBEDTLS_DHM_PARAM_P ) ) != 0 ||
( ret = mbedtls_dhm_get_value( &conf->dhm_G, dhm_ctx,
MBEDTLS_DHM_PARAM_G ) ) != 0 )
{
mbedtls_mpi_free( &conf->dhm_P );
mbedtls_mpi_free( &conf->dhm_G );

37
tests/suites/test_suite_dhm.function
View file

@ -1,6 +1,23 @@
/* BEGIN_HEADER */
#include "mbedtls/dhm.h"
int check_get_value( const mbedtls_dhm_context *ctx,
mbedtls_dhm_parameter param,
const mbedtls_mpi *expected )
{
mbedtls_mpi actual;
int ok = 0;
mbedtls_mpi_init( &actual );
TEST_ASSERT( mbedtls_dhm_get_value( &actual, ctx, param ) == 0 );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &actual, expected ) == 0 );
ok = 1;
exit:
mbedtls_mpi_free( &actual );
return( ok );
}
/* Sanity checks on a Diffie-Hellman parameter: check the length-value
* syntax and check that the value is the expected one (taken from the
* DHM context by the caller). */
@ -102,6 +119,8 @@ void dhm_do_dhm( int radix_P, char *input_P, int x_size,
TEST_ASSERT( mbedtls_mpi_read_string( &ctx_srv.P, radix_P, input_P ) == 0 );
TEST_ASSERT( mbedtls_mpi_read_string( &ctx_srv.G, radix_G, input_G ) == 0 );
pub_cli_len = mbedtls_mpi_size( &ctx_srv.P );
TEST_ASSERT( check_get_value( &ctx_srv, MBEDTLS_DHM_PARAM_P, &ctx_srv.P ) );
TEST_ASSERT( check_get_value( &ctx_srv, MBEDTLS_DHM_PARAM_G, &ctx_srv.G ) );
/*
* First key exchange
@ -118,6 +137,9 @@ void dhm_do_dhm( int radix_P, char *input_P, int x_size,
ske[ske_len++] = 0;
ske[ske_len++] = 0;
TEST_ASSERT( mbedtls_dhm_read_params( &ctx_cli, &p, ske + ske_len ) == 0 );
/* The domain parameters must be the same on both side. */
TEST_ASSERT( check_get_value( &ctx_cli, MBEDTLS_DHM_PARAM_P, &ctx_srv.P ) );
TEST_ASSERT( check_get_value( &ctx_cli, MBEDTLS_DHM_PARAM_G, &ctx_srv.G ) );
TEST_ASSERT( mbedtls_dhm_make_public( &ctx_cli, x_size, pub_cli, pub_cli_len,
&mbedtls_test_rnd_pseudo_rand,
@ -134,6 +156,17 @@ void dhm_do_dhm( int radix_P, char *input_P, int x_size,
TEST_ASSERT( sec_srv_len != 0 );
TEST_ASSERT( memcmp( sec_srv, sec_cli, sec_srv_len ) == 0 );
/* Internal value checks */
TEST_ASSERT( check_get_value( &ctx_cli, MBEDTLS_DHM_PARAM_X, &ctx_cli.X ) );
TEST_ASSERT( check_get_value( &ctx_srv, MBEDTLS_DHM_PARAM_X, &ctx_srv.X ) );
/* Cross-checks */
TEST_ASSERT( check_get_value( &ctx_cli, MBEDTLS_DHM_PARAM_GX, &ctx_srv.GY ) );
TEST_ASSERT( check_get_value( &ctx_cli, MBEDTLS_DHM_PARAM_GY, &ctx_srv.GX ) );
TEST_ASSERT( check_get_value( &ctx_cli, MBEDTLS_DHM_PARAM_K, &ctx_srv.K ) );
TEST_ASSERT( check_get_value( &ctx_srv, MBEDTLS_DHM_PARAM_GX, &ctx_cli.GY ) );
TEST_ASSERT( check_get_value( &ctx_srv, MBEDTLS_DHM_PARAM_GY, &ctx_cli.GX ) );
TEST_ASSERT( check_get_value( &ctx_srv, MBEDTLS_DHM_PARAM_K, &ctx_cli.K ) );
/* Re-do calc_secret on server a few times to test update of blinding values */
for( i = 0; i < 3; i++ )
{
@ -231,8 +264,8 @@ void dhm_file( char * filename, char * p, char * g, int len )
TEST_EQUAL( mbedtls_dhm_get_len( &ctx ), (size_t) len );
TEST_EQUAL( mbedtls_dhm_get_bitlen( &ctx ), mbedtls_mpi_bitlen( &P ) );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &ctx.P, &P ) == 0 );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &ctx.G, &G ) == 0 );
TEST_ASSERT( check_get_value( &ctx, MBEDTLS_DHM_PARAM_P, &P ) );
TEST_ASSERT( check_get_value( &ctx, MBEDTLS_DHM_PARAM_G, &G ) );
exit:
mbedtls_mpi_free( &P ); mbedtls_mpi_free( &G );