@ -106,15 +106,17 @@ Server implementation
Retrieving Server Keys
~~~~~~~~~~~~~~~~~~~~~~
Version 2
+++++++++
.. NOTE ::
There was once a "version 1" of the key exchange. It has been removed from the
specification due to lack of significance. It may be reviewed `here
<https://github.com/matrix-org/matrix-doc/blob/51faf8ed2e4a63d4cfd6d23183698ed169956cc0/specification/server_server_api.rst#232version-1>`_.
Each homeserver publishes its public keys under `` /_matrix/key/v2/server/ `` .
Homeservers query for keys by either getting `` /_matrix/key/v2/server/ ``
Each homeserver publishes its public keys under `` /_matrix/key/v2/server/ {keyId}
Homeservers query for keys by either getting `` /_matrix/key/v2/server/ {keyId} ``
directly or by querying an intermediate notary server using a
`` /_matrix/key/v2/query `` API. Intermediate notary servers query the
`` /_matrix/key/v2/server/ `` API on behalf of another server and sign the
response with their own key. A server may query multiple notary servers to
`` /_matrix/key/v2/query /{serverName}/{keyId} `` API. Intermediate notary servers
query the `` /_matrix/key/v2/server/ {keyId} `` API on behalf of another server and
sign the response with their own key. A server may query multiple notary servers to
ensure that they all report the same public keys.
This approach is borrowed from the `Perspectives Project`_ , but modified to
@ -126,113 +128,33 @@ server by querying other servers.
.. _Perspectives Project: https://web.archive.org/web/20170702024706/https://perspectives-project.org/
Publishing Keys
^^^^^^^^^^^^^^^
+++++++++++++++
Homeservers publish the allowed TLS fingerprints and signing keys in a JSON
object at `` /_matrix/key/v2/server/{key_id} `` . The response contains a list of
`` verify_keys `` that are valid for signing federation requests made by the
server and for signing events. It contains a list of `` old_verify_keys `` which
home server and for signing events. It contains a list of `` old_verify_keys `` which
are only valid for signing events. Finally the response contains a list of TLS
certificate fingerprints to validate any connection made to the server.
A server may have multiple keys active at a given time. A server may have any
number of old keys. It is recommended that servers return a single JSON
response listing all of its keys whenever any `` key_id `` is requested to reduce
the number of round trips needed to discover the relevant keys for a server.
However a server may return different responses for a different `` key_id `` .
The `` tls_certificates `` field contains a list of hashes of the X.509 TLS
certificates currently used by the server. The list must include SHA-256 hashes
for every certificate currently in use by the server. These fingerprints are
valid until the millisecond POSIX timestamp in `` valid_until_ts `` .
The `` verify_keys `` can be used to sign requests and events made by the server
until the millisecond POSIX timestamp in `` valid_until_ts `` . If a homeserver
receives an event with a `` origin_server_ts `` after the `` valid_until_ts `` then
it should request that `` key_id `` for the originating server to check whether
the key has expired.
The `` old_verify_keys `` can be used to sign events with an `` origin_server_ts ``
before the `` expired_ts `` . The `` expired_ts `` is a millisecond POSIX timestamp
of when the originating server stopped using that key.
Intermediate notary servers should cache a response for half of its remaining
lifetime to avoid serving a stale response. Originating servers should avoid
returning responses that expire in less than an hour to avoid repeated requests
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 a server goes offline intermediate notary servers should continue to return
the last response they received from that server so that the signatures of old
events sent by that server can still be checked.
certificate fingerprints to validate any connection made to the homeserver.
{{keys_server_ss_http_api}}
Querying Keys Through Another Server
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Servers may offer a query API `` /_matrix/key/v2/query/ `` for getting the keys
for another server. This API can be used to GET a list of JSON objects for a
given server or to POST a bulk query for a number of keys from a number of
servers. Either way the response is a list of JSON objects containing the
JSON published by the server under `` /_matrix/key/v2/server/ `` signed by
both the originating server and by this server.
The `` minimum_valid_until_ts `` is a millisecond POSIX timestamp indicating
when the returned certificate will need to be valid until to be useful to the
requesting server. This can be set using the maximum `` origin_server_ts `` of
a batch of events that a requesting server is trying to validate. This allows
an intermediate notary server to give a prompt cached response even if the
originating server is offline.
This API can return keys for servers that are offline by using cached responses
taken from when the server was online. Keys can be queried from multiple
servers to mitigate against DNS spoofing.
{{keys_query_ss_http_api}}
Version 1
+++++++++
.. WARNING ::
Version 1 of key distribution is obsolete.
++++++++++++++++++++++++++++++++++++
Servers may query another server's keys through a notary server. The notary
server may be another homeserver. The notary server will retrieve keys from
the queried servers through use of the `` /_matrix/key/v2/server/{keyId} ``
API. The notary server will additionally sign the response from the queried
server before returning the results.
Homeservers publish their TLS certificates and signing keys in a JSON object
at `` /_matrix/key/v1 `` .
==================== =================== ======================================
Key Type Description
==================== =================== ======================================
`` server_name `` String DNS name of the homeserver.
`` verify_keys `` Object Public keys of the homeserver for
verifying digital signatures.
`` signatures `` Object Digital signatures for this object
signed using the `` verify_keys `` .
`` tls_certificate `` String The X.509 TLS certificate used by this
this server encoded as `Unpadded Base64`_ .
==================== =================== ======================================
.. code :: json
Notary servers can return keys for servers that are offline or having issues
serving their own keys by using cached responses. Keys can be queried from
multiple servers to mitigate against DNS spoofing.
{
"server_name": "example.org",
"signatures": {
"example.org": {
"ed25519:auto": "Base+64+Encoded+Signature"
}
},
"tls_certificate": "Base+64+Encoded+DER+Encoded+X509+TLS+Certificate",
"verify_keys": {
"ed25519:auto": "Base+64+Encoded+Signature+Verification+Key"
}
}
{{keys_query_ss_http_api}}
When fetching the keys for a server the client should check that the TLS
certificate in the JSON matches the TLS server certificate for the connection
and should check that the JSON signatures are correct for the supplied
`` verify_keys `` .
Transactions
------------
Travis Ralston
6 years ago