Improve the server key exchange portion of the s2s specification

Most of the text has been shuffled into the swagger definitions to bring it closer to where it matters. This also attempts to clarify what is out in the wild. Most importantly, the first version of the key exchange is outright removed from the specification. Other research points/questions are: * What is a "Key ID"? * https://github.com/matrix-org/synapse/blob/1241156c82644d5609f45659607a356af5d8fe08/synapse/rest/key/v2/local_key_resource.py#L81-L83 * https://github.com/matrix-org/synapse/blob/1241156c82644d5609f45659607a356af5d8fe08/synapse/rest/key/v2/local_key_resource.py#L88-L91 * Returning a cached response if the server throws a 400, 500, or otherwise not-offline status code * https://github.com/matrix-org/synapse/blob/1241156c82644d5609f45659607a356af5d8fe08/synapse/rest/key/v2/remote_key_resource.py#L227-L229 * `minimum_valid_until_ts` default * This branch of the ladder: https://github.com/matrix-org/synapse/blob/1241156c82644d5609f45659607a356af5d8fe08/synapse/rest/key/v2/remote_key_resource.py#L192 * Returning empty arrays when querying offline/no servers * Queried by hand against matrix.org as a notary server with a fake domain name to query * Returning all keys even when querying for specific keys * Queried by hand using matrix.org as a notary server against a server publishing multiple keys. The examples and descriptions were also improved as part of this commit.
matrix-org · Jul 18, 2018 · 5fb786b · 5fb786b
1 parent 2cfbd6e
commit 5fb786b
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diff --git a/api/server-server/definitions/keys.yaml b/api/server-server/definitions/keys.yaml
@@ -20,50 +20,60 @@ properties:
   server_name:
     type: string
     description: DNS name of the homeserver.
-    required: true # TODO: Verify
+    required: true
     example: "example.org"
   verify_keys:
     type: object
-    description: Public keys of the homeserver for verifying digital signatures.
-    required: true # TODO: Verify
+    description: |-
+      Public keys of the homeserver for verifying digital signatures. 
+      
+      The object's key is the algorithm and version combined (``ed25519`` being the 
+      algorithm and ``abc123`` being the version in the example below). Together,
+      this forms the Key ID.
+    required: true
     additionalProperties:
       type: object
       title: Verify Key
       example: {
-        "ed25519:auto2": {
-          "key": "Base+64+Encoded+Signature+Verification+Key"
+        "ed25519:abc123": {
+          "key": "VGhpcyBzaG91bGQgYmUgYSByZWFsIGVkMjU1MTkgcGF5bG9hZA=="
         }
       }
       properties:
         key:
           type: string
-          description: The key
+          description: The `Unpadded Base64`_ encoded key.
           required: true
-          example: "Base+64+Encoded+Signature+Verification+Key"
+          example: "VGhpcyBzaG91bGQgYmUgYSByZWFsIGVkMjU1MTkgcGF5bG9hZA=="
   old_verify_keys:
     type: object
-    description: The public keys that the server used to use and when it stopped using them.
+    description: |-
+      The public keys that the server used to use and when it stopped using them. 
+      
+      The object's key is the algorithm and version combined (``ed25519`` being the 
+      algorithm and ``0ldK3y`` being the version in the example below). Together,
+      this forms the Key ID.
     additionalProperties:
       type: object
       title: Old Verify Key
       example: {
-        "ed25519:auto1": {
+        "ed25519:0ldK3y": {
           "expired_ts": 922834800000,
-          "key": "Base+64+Encoded+Signature+Verification+Key"
+          "key": "VGhpcyBzaG91bGQgYmUgeW91ciBvbGQga2V5J3MgZWQyNTUxOSBwYXlsb2FkLg=="
         }
       }
       properties:
         expired_ts:
           type: integer
           format: int64
-          description: The expiration time.
+          description: POSIX timestamp for when this key expired.
           required: true
           example: 922834800000
         key:
           type: string
-          description: The key.
+          description: The `Unpadded Base64`_ encoded key.
           required: true
-          example: "Base+64+Encoded+Signature+Verification+Key"
+          example: "VGhpcyBzaG91bGQgYmUgeW91ciBvbGQga2V5J3MgZWQyNTUxOSBwYXlsb2FkLg=="
   signatures:
     type: object
     description: Digital signatures for this object signed using the ``verify_keys``.
@@ -72,7 +82,7 @@ properties:
       title: Signed Server
       example: {
         "example.org": {
-          "ad25519:auto2": "Base+64+Encoded+Signature+Verification+Key"
+          "ad25519:abc123": "VGhpcyBzaG91bGQgYWN0dWFsbHkgYmUgYSBzaWduYXR1cmU="
         }
       }
       additionalProperties:
@@ -87,10 +97,12 @@ properties:
       properties:
         sha256:
           type: string
-          description: The encoded fingerprint.
-          example: Base+64+Encoded+SHA-256-Fingerprint
+          description: The `Unpadded Base64`_ encoded fingerprint
+          example: "VGhpcyBpcyBoYXNoIHdoaWNoIHNob3VsZCBiZSBieXRlcw=="
   valid_until_ts:
     type: integer
     format: int64
-    description: POSIX timestamp when the list of valid keys should be refreshed.
+    description: |-
+      POSIX timestamp when the list of valid keys should be refreshed. Keys used beyond this
+      timestamp are no longer valid.
     example: 1052262000000
diff --git a/api/server-server/definitions/keys_query_response.yaml b/api/server-server/definitions/keys_query_response.yaml
@@ -15,13 +15,13 @@ type: object
 description: Server keys
 example: {
   "server_keys": [{
-    $ref: "../examples/server_key.json"
+    $ref: "../examples/server_key_notary_signed.json"
   }]
 }
 properties:
   server_keys:
     type: array
     title: Server Keys
-    description: The server keys.
+    description: The queried server's keys, signed by the notary server.
     items:
       $ref: "keys.yaml"
diff --git a/api/server-server/examples/server_key.json b/api/server-server/examples/server_key.json
@@ -1,23 +1,23 @@
 {
     "server_name": "example.org",
     "verify_keys": {
-        "ed25519:auto2": {
-        "key": "Base+64+Encoded+Signature+Verification+Key"
+        "ed25519:abc123": {
+            "key": "VGhpcyBzaG91bGQgYmUgYSByZWFsIGVkMjU1MTkgcGF5bG9hZA=="
         }
     },
     "old_verify_keys": {
-        "ed25519:auto1": {
+        "ed25519:0ldk3y": {
         "expired_ts": 922834800000,
-            "key": "Base+64+Encoded+Old+Verify+Key"
+            "key": "VGhpcyBzaG91bGQgYmUgeW91ciBvbGQga2V5J3MgZWQyNTUxOSBwYXlsb2FkLg=="
         }
     },
     "signatures": {
         "example.org": {
-        "ed25519:auto2": "Base+64+Encoded+Signature"
+            "ed25519:auto2": "VGhpcyBzaG91bGQgYWN0dWFsbHkgYmUgYSBzaWduYXR1cmU="
         }
     },
     "tls_fingerprints": [{
-        "sha256": "Base+64+Encoded+SHA-256-Fingerprint"
+        "sha256": "VGhpcyBpcyBoYXNoIHdoaWNoIHNob3VsZCBiZSBieXRlcw=="
     }],
     "valid_until_ts": 1052262000000
 }
diff --git a/api/server-server/examples/server_key_notary_signed.json b/api/server-server/examples/server_key_notary_signed.json
@@ -0,0 +1,11 @@
+{
+    "$ref": "server_key.json",
+    "signatures": {
+        "example.org": {
+            "ed25519:abc123": "VGhpcyBzaG91bGQgYWN0dWFsbHkgYmUgYSBzaWduYXR1cmU="
+        },
+        "notary.server.com": {
+            "ed25519:010203": "VGhpcyBpcyBhbm90aGVyIHNpZ25hdHVyZQ=="
+        }
+    }
+}
diff --git a/api/server-server/keys_query.yaml b/api/server-server/keys_query.yaml
@@ -25,49 +25,60 @@ produces:
 paths:
   "/query/{serverName}/{keyId}":
     get:
-      summary: Retrieve a server key.
-      description: Retrieve a server key.
-      operationId: perspectivesKeyQuery
+      summary: Query for another server's keys
+      description: |-
+        Query for another server's keys. The receiving (notary) server must
+        sign the keys returned by the queried server.
+      operationId: getQueryKeys
       parameters:
         - in: path
           name: serverName
           type: string
-          description: Server name.
+          description: The server's DNS name to query
           required: true
           x-example: matrix.org
         - in: path
           name: keyId
           type: string
-          description: Key ID.
-          required: true
-          x-example: TODO # No examples in spec so far
+          description: |-
+            The key ID to look up. If omitted or empty, all the server's keys
+            are to be queried for.
+          required: false
+          x-example: "ed25519:abc123"
         - in: query
           name: minimum_valid_until_ts
           type: integer
           format: int64
-          description: Minimum Valid Until Milliseconds.
-          required: true # TODO: Verify 
+          description: |-
+            A millisecond POSIX timestamp indicating when the returned certificates
+            will need to be valid until to be useful to the requesting server.
+
+            If not supplied, the current time as determined by the notary server is used.
+          required: false
           x-example: 1234567890
       responses:
         200:
-          description: The keys for the server
+          description: |-
+            The keys for the server, or an empty array if the server could not be reached
+            and no cached keys were available.
           schema:
             $ref: "definitions/keys_query_response.yaml"
   "/query":
     post:
-      summary: Retrieve a server key
-      description: Retrieve a server key.
-      operationId: bulkPerspectivesKeyQuery
+      summary: Query for several server's keys
+      description: |-
+        Query for keys from multiple servers in a batch format. The receiving (notary)
+        server must sign the keys returned by the queried servers.
+      operationId: postQueryKeys
       parameters:
         - in: body
           name: body
           schema:
             type: object
-            # TODO: Improve example
             example: {
               "server_keys": {
-                "{server_name}": {
-                  "{key_id}": {
+                "example.org": {
+                  "ed25519:abc123": {
                     "minimum_valid_until_ts": 1234567890
                   }
                 }
@@ -76,24 +87,42 @@ paths:
             properties:
               server_keys:
                 type: object
-                description: The query criteria.
+                description: |-
+                  The query criteria. The outer ``string`` key on the object is the
+                  server name (eg: ``matrix.org``). The inner ``string`` key is the
+                  Key ID to query for the particular server. If no key IDs are given
+                  to be queried, the notary server should query for all keys. If no
+                  servers are given, the notary server must return an empty ``server_keys``
+                  array in the response.
+
+                  The notary server may return multiple keys regardless of the Key IDs
+                  given.
                 additionalProperties:
                   type: object
                   name: ServerName
                   description: The server names to query.
                   additionalProperties:
                     type: object
                     title: Query Criteria
-                    description: The server keys to query.
+                    description: The server key IDs to query.
                     properties:
                       minimum_valid_until_ts:
                         type: integer
                         format: int64
-                        description: Minimum Valid Until MS.
+                        description: |-
+                          A millisecond POSIX timestamp indicating when the returned 
+                          certificates will need to be valid until to be useful to the 
+                          requesting server.
+
+                          If not supplied, the current time as determined by the notary
+                          server is used.
                         example: 1234567890
             required: ['server_keys']
       responses:
         200:
-          description: The keys for the server.
+          description: |-
+            The keys for the queried servers, signed by the notary server. Servers which
+            are offline and have no cached keys will not be included in the result. This
+            may result in an empty array.
           schema:
             $ref: "definitions/keys_query_response.yaml"
diff --git a/api/server-server/keys_server.yaml b/api/server-server/keys_server.yaml
@@ -25,18 +25,38 @@ produces:
 paths:
   "/server/{keyId}":
     get:
-      summary: Get the server's key
-      description: Get the server's key.
+      summary: Get the homeserver's public key(s)
+      description: |-
+        Gets the homeserver's published TLS fingerprints and signing keys.
+        The homeserver may have any number of active keys and may have a
+        number of old keys. Homeservers SHOULD return a single JSON object
+        listing all of its keys, regardless of the ``keyId`` path argument.
+        This is to reduce the number of round trips needed to discover the
+        relevant keys for a homeserver.
+
+        Intermediate notary servers should cache a response for half of its
+        lifetime to avoid serving a stale response. Originating servers should
+        avoid returning responses that expire in less than an hour to avoid
+        repeated reqests for a certificate that is about to expire. Requesting
+        servers should limit how frequently they query for certificates to
+        avoid flooding a server with requests.
+
+        If the server fails to respond to this request, intermediate notary
+        servers should continue to return the last response they received
+        from the server so that the signatures of old events can still be
+        checked.
       operationId: getServerKey
       parameters:
         - in: path
           name: keyId
           type: string
-          description: Key ID
+          description: |-
+            The key ID to look up. If omitted or empty, all server keys are
+            to be returned.
           required: false
-          x-example: TODO # No examples in the spec so far
+          x-example: "ed25519:abc123"
       responses:
         200:
-          description: The server's keys.
+          description: The homeserver's keys
           schema:
             $ref: "definitions/keys.yaml"