Merge pull request #59 from gilles-peskine-arm/psa-its-64_bit_internal_key_id

Support key file IDs encoding the key owner

include/mbedtls/config.h

@@ -1156,6 +1156,21 @@
  */
 //#define MBEDTLS_PSA_HAS_ITS_IO
 
+/* MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER
+ *
+ * In PSA key storage, encode the owner of the key.
+ *
+ * This is only meaningful when building the library as part of a
+ * multi-client service. When you activate this option, you must provide
+ * an implementation of the type psa_key_owner_id_t and a translation
+ * from psa_key_file_id_t to file name in all the storage backends that
+ * you wish to support.
+ *
+ * Note that this option is meant for internal use only and may be removed
+ * without notice.
+ */
+//#define MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER
+
 /**
  * \def MBEDTLS_MEMORY_DEBUG
  *

include/psa/crypto_platform.h

@@ -49,4 +49,53 @@
 /* Integral type representing a key handle. */
 typedef uint16_t psa_key_handle_t;
 
+/* This implementation distinguishes *application key identifiers*, which
+ * are the key identifiers specified by the application, from
+ * *key file identifiers*, which are the key identifiers that the library
+ * sees internally. The two types can be different if there is a remote
+ * call layer between the application and the library which supports
+ * multiple client applications that do not have access to each others'
+ * keys. The point of having different types is that the key file
+ * identifier may encode not only the key identifier specified by the
+ * application, but also the the identity of the application.
+ *
+ * Note that this is an internal concept of the library and the remote
+ * call layer. The application itself never sees anything other than
+ * #psa_app_key_id_t with its standard definition.
+ */
+
+/* The application key identifier is always what the application sees as
+ * #psa_key_id_t. */
+typedef uint32_t psa_app_key_id_t;
+
+#if defined(MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER)
+
+#if defined(PSA_CRYPTO_SECURE)
+/* Building for the PSA Crypto service on a PSA platform. */
+/* A key owner is a PSA partition identifier. */
+typedef int32_t psa_key_owner_id_t;
+#endif
+
+typedef struct
+{
+    uint32_t key_id;
+    psa_key_owner_id_t owner;
+} psa_key_file_id_t;
+#define PSA_KEY_FILE_GET_KEY_ID( file_id ) ( ( file_id ).key_id )
+
+/* Since crypto.h is used as part of the PSA Cryptography API specification,
+ * it must use standard types for things like the argument of psa_open_key().
+ * If it wasn't for that constraint, psa_open_key() would take a
+ * `psa_key_file_id_t` argument. As a workaround, make `psa_key_id_t` an
+ * alias for `psa_key_file_id_t` when building for a multi-client service. */
+typedef psa_key_file_id_t psa_key_id_t;
+
+#else /* !MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER */
+
+/* By default, a key file identifier is just the application key identifier. */
+typedef psa_app_key_id_t psa_key_file_id_t;
+#define PSA_KEY_FILE_GET_KEY_ID( id ) ( id )
+
+#endif /* !MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER */
+
 #endif /* PSA_CRYPTO_PLATFORM_H */

include/psa/crypto_types.h

@@ -90,7 +90,14 @@ typedef uint32_t psa_key_lifetime_t;
 
 /** Encoding of identifiers of persistent keys.
  */
+/* Implementation-specific quirk: The Mbed Crypto library can be built as
+ * part of a multi-client service that exposes the PSA Crypto API in each
+ * client and encodes the client identity in the key id argument of functions
+ * such as psa_open_key(). In this build configuration, we define
+ * psa_key_id_t in crypto_platform.h instead of here. */
+#if !defined(MBEDTLS_PSA_CRYPTO_KEY_FILE_ID_ENCODES_OWNER)
 typedef uint32_t psa_key_id_t;
+#endif
 
 /**@}*/