diff --git a/include/psa/crypto_platform.h b/include/psa/crypto_platform.h
index 50ca546fb..0f3ede891 100644
--- a/include/psa/crypto_platform.h
+++ b/include/psa/crypto_platform.h
@@ -49,4 +49,27 @@
 /* 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;
+
+/* 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 /* PSA_CRYPTO_PLATFORM_H */
diff --git a/library/psa_crypto_core.h b/library/psa_crypto_core.h
index c28968197..0f7562459 100644
--- a/library/psa_crypto_core.h
+++ b/library/psa_crypto_core.h
@@ -41,7 +41,7 @@ typedef struct
     psa_key_type_t type;
     psa_key_policy_t policy;
     psa_key_lifetime_t lifetime;
-    psa_key_id_t persistent_storage_id;
+    psa_key_file_id_t persistent_storage_id;
     unsigned allocated : 1;
     union
     {
diff --git a/library/psa_crypto_slot_management.c b/library/psa_crypto_slot_management.c
index a9458b04f..227fb5f11 100644
--- a/library/psa_crypto_slot_management.c
+++ b/library/psa_crypto_slot_management.c
@@ -189,12 +189,13 @@ exit:
  * past released version must remain valid, unless a migration path
  * is provided.
  *
- * \param key_id        The key identifier to check.
+ * \param file_id       The key identifier to check.
  *
- * \return              1 if \p key_id is acceptable, otherwise 0.
+ * \return              1 if \p file_id is acceptable, otherwise 0.
  */
-static int psa_is_key_id_valid( psa_key_id_t key_id )
+static int psa_is_key_id_valid( psa_key_file_id_t file_id )
 {
+    psa_app_key_id_t key_id = PSA_KEY_FILE_GET_KEY_ID( file_id );
     /* Reject id=0 because by general library conventions, 0 is an invalid
      * value wherever possible. */
     if( key_id == 0 )
@@ -226,7 +227,7 @@ static int psa_is_key_id_valid( psa_key_id_t key_id )
  * \retval #PSA_ERROR_STORAGE_FAILURE
  */
 static psa_status_t psa_internal_make_key_persistent( psa_key_handle_t handle,
-                                                      psa_key_id_t id )
+                                                      psa_key_file_id_t id )
 {
 #if defined(MBEDTLS_PSA_CRYPTO_STORAGE_C)
     psa_key_slot_t *slot;
@@ -253,7 +254,7 @@ static psa_status_t psa_internal_make_key_persistent( psa_key_handle_t handle,
 }
 
 static psa_status_t persistent_key_setup( psa_key_lifetime_t lifetime,
-                                          psa_key_id_t id,
+                                          psa_key_file_id_t id,
                                           psa_key_handle_t *handle,
                                           psa_status_t wanted_load_status )
 {
@@ -278,14 +279,14 @@ static psa_status_t persistent_key_setup( psa_key_lifetime_t lifetime,
 }
 
 psa_status_t psa_open_key( psa_key_lifetime_t lifetime,
-                           psa_key_id_t id,
+                           psa_key_file_id_t id,
                            psa_key_handle_t *handle )
 {
     return( persistent_key_setup( lifetime, id, handle, PSA_SUCCESS ) );
 }
 
 psa_status_t psa_create_key( psa_key_lifetime_t lifetime,
-                             psa_key_id_t id,
+                             psa_key_file_id_t id,
                              psa_key_handle_t *handle )
 {
     psa_status_t status;
diff --git a/library/psa_crypto_storage.c b/library/psa_crypto_storage.c
index b4e4076e1..42bd938de 100644
--- a/library/psa_crypto_storage.c
+++ b/library/psa_crypto_storage.c
@@ -148,7 +148,7 @@ psa_status_t psa_parse_key_data_from_storage( const uint8_t *storage_data,
     return( PSA_SUCCESS );
 }
 
-psa_status_t psa_save_persistent_key( const psa_key_id_t key,
+psa_status_t psa_save_persistent_key( const psa_key_file_id_t key,
                                       const psa_key_type_t type,
                                       const psa_key_policy_t *policy,
                                       const uint8_t *data,
@@ -186,7 +186,7 @@ void psa_free_persistent_key_data( uint8_t *key_data, size_t key_data_length )
     mbedtls_free( key_data );
 }
 
-psa_status_t psa_load_persistent_key( psa_key_id_t key,
+psa_status_t psa_load_persistent_key( psa_key_file_id_t key,
                                       psa_key_type_t *type,
                                       psa_key_policy_t *policy,
                                       uint8_t **data,
diff --git a/library/psa_crypto_storage.h b/library/psa_crypto_storage.h
index 74f9e230d..7e5aae9f9 100644
--- a/library/psa_crypto_storage.h
+++ b/library/psa_crypto_storage.h
@@ -86,7 +86,7 @@ extern "C" {
  * \retval PSA_ERROR_STORAGE_FAILURE
  * \retval PSA_ERROR_ALREADY_EXISTS
  */
-psa_status_t psa_save_persistent_key( const psa_key_id_t key,
+psa_status_t psa_save_persistent_key( const psa_key_file_id_t key,
                                       const psa_key_type_t type,
                                       const psa_key_policy_t *policy,
                                       const uint8_t *data,
@@ -117,7 +117,7 @@ psa_status_t psa_save_persistent_key( const psa_key_id_t key,
  * \retval PSA_ERROR_STORAGE_FAILURE
  * \retval PSA_ERROR_DOES_NOT_EXIST
  */
-psa_status_t psa_load_persistent_key( psa_key_id_t key,
+psa_status_t psa_load_persistent_key( psa_key_file_id_t key,
                                       psa_key_type_t *type,
                                       psa_key_policy_t *policy,
                                       uint8_t **data,
@@ -134,7 +134,7 @@ psa_status_t psa_load_persistent_key( psa_key_id_t key,
  *         or the key did not exist.
  * \retval PSA_ERROR_STORAGE_FAILURE
  */
-psa_status_t psa_destroy_persistent_key( const psa_key_id_t key );
+psa_status_t psa_destroy_persistent_key( const psa_key_file_id_t key );
 
 /**
  * \brief Free the temporary buffer allocated by psa_load_persistent_key().
diff --git a/library/psa_crypto_storage_backend.h b/library/psa_crypto_storage_backend.h
index 83bd2f359..dd534d2ff 100644
--- a/library/psa_crypto_storage_backend.h
+++ b/library/psa_crypto_storage_backend.h
@@ -56,7 +56,7 @@ extern "C" {
  * \retval PSA_ERROR_STORAGE_FAILURE
  * \retval PSA_ERROR_DOES_NOT_EXIST
  */
-psa_status_t psa_crypto_storage_load( const psa_key_id_t key, uint8_t *data,
+psa_status_t psa_crypto_storage_load( const psa_key_file_id_t key, uint8_t *data,
                                       size_t data_size );
 
 /**
@@ -75,7 +75,7 @@ psa_status_t psa_crypto_storage_load( const psa_key_id_t key, uint8_t *data,
  * \retval PSA_ERROR_STORAGE_FAILURE
  * \retval PSA_ERROR_ALREADY_EXISTS
  */
-psa_status_t psa_crypto_storage_store( const psa_key_id_t key,
+psa_status_t psa_crypto_storage_store( const psa_key_file_id_t key,
                                        const uint8_t *data,
                                        size_t data_length );
 
@@ -92,7 +92,7 @@ psa_status_t psa_crypto_storage_store( const psa_key_id_t key,
  * \retval 1
  *         Persistent data present for slot number
  */
-int psa_is_key_present_in_storage( const psa_key_id_t key );
+int psa_is_key_present_in_storage( const psa_key_file_id_t key );
 
 /**
  * \brief Get data length for given key slot number.
@@ -104,7 +104,7 @@ int psa_is_key_present_in_storage( const psa_key_id_t key );
  * \retval PSA_SUCCESS
  * \retval PSA_ERROR_STORAGE_FAILURE
  */
-psa_status_t psa_crypto_storage_get_data_length( const psa_key_id_t key,
+psa_status_t psa_crypto_storage_get_data_length( const psa_key_file_id_t key,
                                                  size_t *data_length );
 
 
diff --git a/library/psa_crypto_storage_file.c b/library/psa_crypto_storage_file.c
index c7ff1be01..c4a534fe3 100644
--- a/library/psa_crypto_storage_file.c
+++ b/library/psa_crypto_storage_file.c
@@ -49,7 +49,7 @@
 
 enum { MAX_LOCATION_LEN = sizeof(CRYPTO_STORAGE_FILE_LOCATION) + 40 };
 
-static void key_id_to_location( const psa_key_id_t key,
+static void key_id_to_location( const psa_key_file_id_t key,
                                 char *location,
                                 size_t location_size )
 {
@@ -58,7 +58,7 @@ static void key_id_to_location( const psa_key_id_t key,
                       (unsigned long) key );
 }
 
-psa_status_t psa_crypto_storage_load( const psa_key_id_t key, uint8_t *data,
+psa_status_t psa_crypto_storage_load( const psa_key_file_id_t key, uint8_t *data,
                                       size_t data_size )
 {
     psa_status_t status = PSA_SUCCESS;
@@ -83,7 +83,7 @@ exit:
     return( status );
 }
 
-int psa_is_key_present_in_storage( const psa_key_id_t key )
+int psa_is_key_present_in_storage( const psa_key_file_id_t key )
 {
     char slot_location[MAX_LOCATION_LEN];
     FILE *file;
@@ -101,7 +101,7 @@ int psa_is_key_present_in_storage( const psa_key_id_t key )
     return( 1 );
 }
 
-psa_status_t psa_crypto_storage_store( const psa_key_id_t key,
+psa_status_t psa_crypto_storage_store( const psa_key_file_id_t key,
                                        const uint8_t *data,
                                        size_t data_length )
 {
@@ -156,7 +156,7 @@ exit:
     return( status );
 }
 
-psa_status_t psa_destroy_persistent_key( const psa_key_id_t key )
+psa_status_t psa_destroy_persistent_key( const psa_key_file_id_t key )
 {
     FILE *file;
     char slot_location[MAX_LOCATION_LEN];
@@ -175,7 +175,7 @@ psa_status_t psa_destroy_persistent_key( const psa_key_id_t key )
     return( PSA_SUCCESS );
 }
 
-psa_status_t psa_crypto_storage_get_data_length( const psa_key_id_t key,
+psa_status_t psa_crypto_storage_get_data_length( const psa_key_file_id_t key,
                                                  size_t *data_length )
 {
     psa_status_t status = PSA_SUCCESS;
diff --git a/library/psa_crypto_storage_its.c b/library/psa_crypto_storage_its.c
index bb0d0cdf1..a60a8f3ab 100644
--- a/library/psa_crypto_storage_its.c
+++ b/library/psa_crypto_storage_its.c
@@ -36,12 +36,12 @@
 #include "mbedtls/platform.h"
 #endif
 
-static psa_storage_uid_t psa_its_identifier_of_slot( psa_key_id_t key )
+static psa_storage_uid_t psa_its_identifier_of_slot( psa_key_file_id_t key )
 {
     return( key );
 }
 
-psa_status_t psa_crypto_storage_load( const psa_key_id_t key, uint8_t *data,
+psa_status_t psa_crypto_storage_load( const psa_key_file_id_t key, uint8_t *data,
                                       size_t data_size )
 {
     psa_status_t status;
@@ -57,7 +57,7 @@ psa_status_t psa_crypto_storage_load( const psa_key_id_t key, uint8_t *data,
     return( status );
 }
 
-int psa_is_key_present_in_storage( const psa_key_id_t key )
+int psa_is_key_present_in_storage( const psa_key_file_id_t key )
 {
     psa_status_t ret;
     psa_storage_uid_t data_identifier = psa_its_identifier_of_slot( key );
@@ -70,7 +70,7 @@ int psa_is_key_present_in_storage( const psa_key_id_t key )
     return( 1 );
 }
 
-psa_status_t psa_crypto_storage_store( const psa_key_id_t key,
+psa_status_t psa_crypto_storage_store( const psa_key_file_id_t key,
                                        const uint8_t *data,
                                        size_t data_length )
 {
@@ -105,7 +105,7 @@ exit:
     return( status );
 }
 
-psa_status_t psa_destroy_persistent_key( const psa_key_id_t key )
+psa_status_t psa_destroy_persistent_key( const psa_key_file_id_t key )
 {
     psa_status_t ret;
     psa_storage_uid_t data_identifier = psa_its_identifier_of_slot( key );
@@ -125,7 +125,7 @@ psa_status_t psa_destroy_persistent_key( const psa_key_id_t key )
     return( PSA_SUCCESS );
 }
 
-psa_status_t psa_crypto_storage_get_data_length( const psa_key_id_t key,
+psa_status_t psa_crypto_storage_get_data_length( const psa_key_file_id_t key,
                                                  size_t *data_length )
 {
     psa_status_t status;