improve description of key object in CS and include a link in Fed

api/server-server/user_keys.yaml

@@ -73,7 +73,7 @@ paths:
                   One-time keys for the queried devices. A map from user ID, to a
                   map from devices to a map from ``<algorithm>:<key_id>`` to the key object.
 
-                  See the Client-Server Key Algorithms section for more information on
+                  See the `Client-Server Key Algorithms`_ section for more information on
                   the Key Object format.
                 additionalProperties:
                   type: object

specification/modules/end_to_end_encryption.rst

@@ -83,9 +83,23 @@ Base64`_. Example:
   "JGLn/yafz74HB2AbPLYJWIVGnKAtqECOBf11yyXac2Y"
 
 The name ``signed_curve25519`` also corresponds to the Curve25519 algorithm,
-but keys using this algorithm are objects with the properties ``key`` (giving
+but a key using this algorithm is represented by an object with a the following
-the Base64-encoded 32-byte Curve25519 public key), and ``signatures`` (giving a
+properties:
-signature for the key object, as described in `Signing JSON`_). Example:
+
+``KeyObject``
+
+========== ================ =====================================================
+Parameter  Type             Description
+========== ================ =====================================================
+key        string           **Required.** The unpadded Base64-encoded 32-byte
+                            Curve25519 public key.
+signatures Signatures       **Required.** Signatures of the key object.
+
+                            The signature is calculated using the process described
+                            at `Signing JSON`_.
+========== ================ =====================================================
+
+Example:
 
 .. code:: json
 

specification/server_server_api.rst

@@ -1257,3 +1257,4 @@ issue.
 .. _`Device Management module`: ../client_server/%CLIENT_RELEASE_LABEL%.html#device-management
 .. _`End-to-End Encryption module`: ../client_server/%CLIENT_RELEASE_LABEL%.html#end-to-end-encryption
 .. _`room version specification`: ../index.html#room-versions
+.. _`Client-Server Key Algorithms`: ../client_server/%CLIENT_RELEASE_LABEL%.html#key-algorithms