Merge pull request #3130 from gbryant-arm/generic-psk
Clarify and simplify PSK
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 1c98a5e..7fec65e 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -2682,6 +2682,9 @@
* \note This is mainly useful for clients. Servers will usually
* want to use \c mbedtls_ssl_conf_psk_cb() instead.
*
+ * \note A PSK set by \c mbedtls_ssl_set_hs_psk() in the PSK callback
+ * takes precedence over a PSK configured by this function.
+ *
* \warning Currently, clients can only register a single pre-shared key.
* Calling this function or mbedtls_ssl_conf_psk_opaque() more
* than once will overwrite values configured in previous calls.
@@ -2715,6 +2718,10 @@
* \note This is mainly useful for clients. Servers will usually
* want to use \c mbedtls_ssl_conf_psk_cb() instead.
*
+ * \note An opaque PSK set by \c mbedtls_ssl_set_hs_psk_opaque() in
+ * the PSK callback takes precedence over an opaque PSK
+ * configured by this function.
+ *
* \warning Currently, clients can only register a single pre-shared key.
* Calling this function or mbedtls_ssl_conf_psk() more than
* once will overwrite values configured in previous calls.
@@ -2752,6 +2759,9 @@
* \note This should only be called inside the PSK callback,
* i.e. the function passed to \c mbedtls_ssl_conf_psk_cb().
*
+ * \note A PSK set by this function takes precedence over a PSK
+ * configured by \c mbedtls_ssl_conf_psk().
+ *
* \param ssl The SSL context to configure a PSK for.
* \param psk The pointer to the pre-shared key.
* \param psk_len The length of the pre-shared key in bytes.
@@ -2769,6 +2779,9 @@
* \note This should only be called inside the PSK callback,
* i.e. the function passed to \c mbedtls_ssl_conf_psk_cb().
*
+ * \note An opaque PSK set by this function takes precedence over an
+ * opaque PSK configured by \c mbedtls_ssl_conf_psk_opaque().
+ *
* \param ssl The SSL context to configure a PSK for.
* \param psk The identifier of the key slot holding the PSK.
* For the duration of the current handshake, the key slot
@@ -2807,9 +2820,14 @@
* on the SSL context to set the correct PSK and return \c 0.
* Any other return value will result in a denied PSK identity.
*
- * \note If you set a PSK callback using this function, then you
- * don't need to set a PSK key and identity using
- * \c mbedtls_ssl_conf_psk().
+ * \note A dynamic PSK (i.e. set by the PSK callback) takes
+ * precedence over a static PSK (i.e. set by
+ * \c mbedtls_ssl_conf_psk() or
+ * \c mbedtls_ssl_conf_psk_opaque()).
+ * This means that if you set a PSK callback using this
+ * function, you don't need to set a PSK using
+ * \c mbedtls_ssl_conf_psk() or
+ * \c mbedtls_ssl_conf_psk_opaque()).
*
* \param conf The SSL configuration to register the callback with.
* \param f_psk The callback for selecting and setting the PSK based
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index f83d014..e92381c 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -921,7 +921,60 @@
#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
int mbedtls_ssl_psk_derive_premaster( mbedtls_ssl_context *ssl, mbedtls_key_exchange_type_t key_ex );
-#endif
+
+/**
+ * Get the first defined PSK by order of precedence:
+ * 1. handshake PSK set by \c mbedtls_ssl_set_hs_psk() in the PSK callback
+ * 2. static PSK configured by \c mbedtls_ssl_conf_psk()
+ * Return a code and update the pair (PSK, PSK length) passed to this function
+ */
+static inline int mbedtls_ssl_get_psk( const mbedtls_ssl_context *ssl,
+ const unsigned char **psk, size_t *psk_len )
+{
+ if( ssl->handshake->psk != NULL && ssl->handshake->psk_len > 0 )
+ {
+ *psk = ssl->handshake->psk;
+ *psk_len = ssl->handshake->psk_len;
+ }
+
+ else if( ssl->conf->psk != NULL && ssl->conf->psk_len > 0 )
+ {
+ *psk = ssl->conf->psk;
+ *psk_len = ssl->conf->psk_len;
+ }
+
+ else
+ {
+ *psk = NULL;
+ *psk_len = 0;
+ return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
+ }
+
+ return( 0 );
+}
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+/**
+ * Get the first defined opaque PSK by order of precedence:
+ * 1. handshake PSK set by \c mbedtls_ssl_set_hs_psk_opaque() in the PSK
+ * callback
+ * 2. static PSK configured by \c mbedtls_ssl_conf_psk_opaque()
+ * Return an opaque PSK
+ */
+static inline psa_key_handle_t mbedtls_ssl_get_opaque_psk(
+ const mbedtls_ssl_context *ssl )
+{
+ if( ssl->handshake->psk_opaque != 0 )
+ return( ssl->handshake->psk_opaque );
+
+ if( ssl->conf->psk_opaque != 0 )
+ return( ssl->conf->psk_opaque );
+
+ return( 0 );
+}
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
#if defined(MBEDTLS_PK_C)
unsigned char mbedtls_ssl_sig_from_pk( mbedtls_pk_context *pk );
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index d0adfd9..dbc5a3e 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1514,9 +1514,7 @@
MBEDTLS_SSL_DEBUG_MSG( 2, ( "perform PSA-based PSK-to-MS expansion" ) );
- psk = ssl->conf->psk_opaque;
- if( handshake->psk_opaque != 0 )
- psk = handshake->psk_opaque;
+ psk = mbedtls_ssl_get_opaque_psk( ssl );
if( hash_alg == MBEDTLS_MD_SHA384 )
alg = PSA_ALG_TLS12_PSK_TO_MS(PSA_ALG_SHA_384);
@@ -1850,14 +1848,18 @@
{
unsigned char *p = ssl->handshake->premaster;
unsigned char *end = p + sizeof( ssl->handshake->premaster );
- const unsigned char *psk = ssl->conf->psk;
- size_t psk_len = ssl->conf->psk_len;
+ const unsigned char *psk = NULL;
+ size_t psk_len = 0;
- /* If the psk callback was called, use its result */
- if( ssl->handshake->psk != NULL )
+ if( mbedtls_ssl_get_psk( ssl, &psk, &psk_len )
+ == MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED )
{
- psk = ssl->handshake->psk;
- psk_len = ssl->handshake->psk_len;
+ /*
+ * This should never happen because the existence of a PSK is always
+ * checked before calling this function
+ */
+ MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+ return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
/*
