ECDH: not restartable unless explicitly enabled

This is mainly for the benefit of SSL modules, which only supports restart in
a limited number of cases. In the other cases (ECDHE_PSK) it would currently
return ERR_ECP_IN_PROGRESS and the user would thus call ssl_handshake() again,
but the SSL code wouldn't handle state properly and things would go wrong in
possibly unexpected ways.  This is undesirable, so it should be possible for
the SSL module to choose if ECDHE should behave the old or the new way.

Not that it also brings ECDHE more in line with the other modules which
already have that choice available (by passing a NULL or valid restart
context).
This commit is contained in:
Manuel Pégourié-Gonnard 2017-05-18 12:35:37 +02:00
parent 1f1f2a1ca6
commit 23e416261c
5 changed files with 68 additions and 12 deletions

View File

@ -53,6 +53,7 @@ typedef struct
mbedtls_ecp_point Vf; /*!< un-blinding value (for later) */
mbedtls_mpi _d; /*!< previous d (for later) */
#if defined(MBEDTLS_ECP_RESTARTABLE)
int restart_enabled; /*!< enable restartalbe EC computations? */
mbedtls_ecp_restart_ctx rs; /*!< restart context for EC computations */
#endif
}
@ -220,6 +221,22 @@ int mbedtls_ecdh_calc_secret( mbedtls_ecdh_context *ctx, size_t *olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
#if defined(MBEDTLS_ECP_RESTARTABLE)
/**
* \brief Enable restartable EC computations for this context.
* (Default: disabled.)
*
* \sa \c mbedtls_ecp_set_max_ops()
*
* \note It is not possible to safely disable restartable
* computations once enabled, except by free-ing the context,
* which cancels possible in-progress operations.
*
* \param ctx ECDH context
*/
void mbedtls_ecdh_enable_restart( mbedtls_ecdh_context *ctx );
#endif /* MBEDTLS_ECP_RESTARTABLE */
#ifdef __cplusplus
}
#endif

View File

@ -155,6 +155,16 @@ void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx )
#endif
}
#if defined(MBEDTLS_ECP_RESTARTABLE)
/*
* Enable restartable operations for context
*/
void mbedtls_ecdh_enable_restart( mbedtls_ecdh_context *ctx )
{
ctx->restart_enabled = 1;
}
#endif
/*
* Setup and write the ServerKeyExhange parameters (RFC 4492)
* struct {
@ -175,7 +185,8 @@ int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen,
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
#if defined(MBEDTLS_ECP_RESTARTABLE)
rs_ctx = &ctx->rs;
if( ctx->restart_enabled )
rs_ctx = &ctx->rs;
#endif
if( ( ret = ecdh_gen_public_restartable( &ctx->grp, &ctx->d, &ctx->Q,
@ -260,7 +271,8 @@ int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen,
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
#if defined(MBEDTLS_ECP_RESTARTABLE)
rs_ctx = &ctx->rs;
if( ctx->restart_enabled )
rs_ctx = &ctx->rs;
#endif
if( ( ret = ecdh_gen_public_restartable( &ctx->grp, &ctx->d, &ctx->Q,
@ -307,7 +319,8 @@ int mbedtls_ecdh_calc_secret( mbedtls_ecdh_context *ctx, size_t *olen,
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
#if defined(MBEDTLS_ECP_RESTARTABLE)
rs_ctx = &ctx->rs;
if( ctx->restart_enabled )
rs_ctx = &ctx->rs;
#endif
if( ( ret = ecdh_compute_shared_restartable( &ctx->grp,

View File

@ -2902,6 +2902,9 @@ static int ssl_write_client_key_exchange( mbedtls_ssl_context *ssl )
i = 4;
#if defined(MBEDTLS_SSL__ECP_RESTARTABLE)
if( ssl->handshake->ec_restart_enabled)
mbedtls_ecdh_enable_restart( &ssl->handshake->ecdh_ctx );
if( ssl->handshake->ecrs_state == ssl_ecrs_ecdh_public_done )
goto ecdh_calc_secret;
#endif

View File

@ -38,18 +38,34 @@ ECDH exchange #2
depends_on:MBEDTLS_ECP_DP_SECP521R1_ENABLED
ecdh_exchange:MBEDTLS_ECP_DP_SECP521R1
ECDH restartable rfc 5903 p256 restart disabled
ECDH restartable rfc 5903 p256 restart enabled max_ops=0
depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":0:0:0
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":1:0:0:0
ECDH restartable rfc 5903 p256 restart max_ops=1
ECDH restartable rfc 5903 p256 restart enabled max_ops=1
depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":1:1:10000
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":1:1:1:10000
ECDH restartable rfc 5903 p256 restart max_ops=10000
ECDH restartable rfc 5903 p256 restart enabled max_ops=10000
depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":10000:0:0
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":1:10000:0:0
ECDH restartable rfc 5903 p256 restart max_ops=250
ECDH restartable rfc 5903 p256 restart enabled max_ops=250
depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":250:2:32
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":1:250:2:32
ECDH restartable rfc 5903 p256 restart disabled max_ops=0
depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":0:0:0:0
ECDH restartable rfc 5903 p256 restart disabled max_ops=1
depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":0:1:0:0
ECDH restartable rfc 5903 p256 restart disabled max_ops=10000
depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":0:10000:0:0
ECDH restartable rfc 5903 p256 restart disabled max_ops=250
depends_on:MBEDTLS_ECP_DP_SECP256R1_ENABLED
ecdh_restart:MBEDTLS_ECP_DP_SECP256R1:"C88F01F510D9AC3F70A292DAA2316DE544E9AAB8AFE84049C62A9C57862D1433":"C6EF9C5D78AE012A011164ACB397CE2088685D8F06BF9BE0B283AB46476BEE53":"D6840F6B42F6EDAFD13116E0E12565202FEF8E9ECE7DCE03812464D04B9442DE":0:250:0:0

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@ -161,7 +161,7 @@ exit:
/* BEGIN_CASE depends_on:MBEDTLS_ECP_RESTARTABLE */
void ecdh_restart( int id, char *dA_str, char *dB_str, char *z_str,
int max_ops, int min_restart, int max_restart )
int enable, int max_ops, int min_restart, int max_restart )
{
int ret;
mbedtls_ecdh_context srv, cli;
@ -192,8 +192,15 @@ void ecdh_restart( int id, char *dA_str, char *dB_str, char *z_str,
* as in ecdh_primitive_test_vec */
TEST_ASSERT( srv.grp.nbits % 8 == 0 );
/* set up restart parameters */
mbedtls_ecp_set_max_ops( max_ops );
if( enable)
{
mbedtls_ecdh_enable_restart( &srv );
mbedtls_ecdh_enable_restart( &cli );
}
/* server writes its paramaters */
memset( buf, 0x00, sizeof( buf ) );
len = 0;