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Add warnings regarding the use of DHM in general

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Hanno Becker 2017-09-28 10:33:29 +01:00
parent e764324d96
commit a2f6b72cbb
2 changed files with 44 additions and 0 deletions
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21
include/mbedtls/config.h
View file

@ -618,6 +618,13 @@
* MBEDTLS_TLS_DHE_PSK_WITH_CAMELLIA_128_CBC_SHA256 * MBEDTLS_TLS_DHE_PSK_WITH_CAMELLIA_128_CBC_SHA256
* MBEDTLS_TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA * MBEDTLS_TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA
* MBEDTLS_TLS_DHE_PSK_WITH_RC4_128_SHA * MBEDTLS_TLS_DHE_PSK_WITH_RC4_128_SHA
*
* \warning The possibility for the use of custom groups
* in the use of DHM in TLS constitutes a security
* risk. If possible, it is recommended to use
* EC-based key exchanges instead. See the documentation
* at the top of dhm.h for more information.
*
*/ */
#define MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED #define MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED
@ -717,6 +724,13 @@
* MBEDTLS_TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA256 * MBEDTLS_TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA256
* MBEDTLS_TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA * MBEDTLS_TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA
* MBEDTLS_TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA * MBEDTLS_TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA
*
* \warning The possibility for the use of custom groups
* in the use of DHM in TLS constitutes a security
* risk. If possible, it is recommended to use
* EC-based key exchanges instead. See the documentation
* at the top of dhm.h for more information.
*
*/ */
#define MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED #define MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED
@ -1835,6 +1849,13 @@
* *
* This module is used by the following key exchanges: * This module is used by the following key exchanges:
* DHE-RSA, DHE-PSK * DHE-RSA, DHE-PSK
*
* \warning The possibility for the use of custom groups
* in the use of DHM in TLS constitutes a security
* risk. If possible, it is recommended to use
* EC-based key exchanges instead. See the documentation
* at the top of dhm.h for more information.
*
*/ */
#define MBEDTLS_DHM_C #define MBEDTLS_DHM_C

23
include/mbedtls/dhm.h
View file

@ -19,6 +19,29 @@
* limitations under the License. * limitations under the License.
* *
* This file is part of mbed TLS (https://tls.mbed.org) * This file is part of mbed TLS (https://tls.mbed.org)
*
* \warning The security of the DHM key exchange relies on the proper choice
* of prime modulus - optimally, it should be a safe prime. The usage
* of non-safe primes both decreases the difficulty of the underlying
* discrete logarithm problem and can lead to small subgroup attacks
* leaking private exponent bits when invalid public keys are used
* and not detected. This is especially relevant if the same DHM parameters
* are reused for multiple key exchanges as in static DHM, while the
* criticality of small-subgroup attacks is lower for ephemeral DHM.
*
* For performance reasons, the code does neither perform primality
* nor safe primality tests, nor the expensive checks for invalid
* subgroups.
*
* The possibility for the use of custom, non-safe primes in DHM
* is a deficiency in the TLS protocol that has been adressed only
* recently through the addition of the named group extension from
* RFC 7919, which however is not yet implemented in Mbed TLS.
*
* If possible, we recommend to use elliptic curve based key
* exchanges instead of DHM-based ones, because the former only
* accepts standardized groups.
*
*/ */
#ifndef MBEDTLS_DHM_H #ifndef MBEDTLS_DHM_H
#define MBEDTLS_DHM_H #define MBEDTLS_DHM_H