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diff --git a/docs/MSC1711_certificates_FAQ.md b/docs/MSC1711_certificates_FAQ.md new file mode 100644 index 0000000000..8eb22656db --- /dev/null +++ b/docs/MSC1711_certificates_FAQ.md @@ -0,0 +1,338 @@ +# MSC1711 Certificates FAQ + +The goal of Synapse 0.99.0 is to act as a stepping stone to Synapse 1.0.0. It +supports the r0.1 release of the server to server specification, but is +compatible with both the legacy Matrix federation behaviour (pre-r0.1) as well +as post-r0.1 behaviour, in order to allow for a smooth upgrade across the +federation. + +The most important thing to know is that Synapse 1.0.0 will require a valid TLS +certificate on federation endpoints. Self signed certificates will not be +sufficient. + +Synapse 0.99.0 makes it easy to configure TLS certificates and will +interoperate with both >= 1.0.0 servers as well as existing servers yet to +upgrade. + +**It is critical that all admins upgrade to 0.99.0 and configure a valid TLS +certificate.** Admins will have 1 month to do so, after which 1.0.0 will be +released and those servers without a valid certificate will not longer be able +to federate with >= 1.0.0 servers. + +Full details on how to carry out this configuration change is given +[below](#configuring-certificates-for-compatibility-with-synapse-100). A +timeline and some frequently asked questions are also given below. + +For more details and context on the release of the r0.1 Server/Server API and +imminent Matrix 1.0 release, you can also see our +[main talk from FOSDEM 2019](https://matrix.org/blog/2019/02/04/matrix-at-fosdem-2019/). + +## Contents +* Timeline +* Configuring certificates for compatibility with Synapse 1.0 +* FAQ + * Synapse 0.99.0 has just been released, what do I need to do right now? + * How do I upgrade? + * What will happen if I do not set up a valid federation certificate + immediately? + * What will happen if I do nothing at all? + * When do I need a SRV record or .well-known URI? + * Can I still use an SRV record? + * I have created a .well-known URI. Do I still need an SRV record? + * It used to work just fine, why are you breaking everything? + * Can I manage my own certificates rather than having Synapse renew + certificates itself? + * Do you still recommend against using a reverse proxy on the federation port? + * Do I still need to give my TLS certificates to Synapse if I am using a + reverse proxy? + * Do I need the same certificate for the client and federation port? + * How do I tell Synapse to reload my keys/certificates after I replace them? + +## Timeline + +**5th Feb 2019 - Synapse 0.99.0 is released.** + +All server admins are encouraged to upgrade. + +0.99.0: + +- provides support for ACME to make setting up Let's Encrypt certs easy, as + well as .well-known support. + +- does not enforce that a valid CA cert is present on the federation API, but + rather makes it easy to set one up. + +- provides support for .well-known + +Admins should upgrade and configure a valid CA cert. Homeservers that require a +.well-known entry (see below), should retain their SRV record and use it +alongside their .well-known record. + +**>= 5th March 2019 - Synapse 1.0.0 is released** + +1.0.0 will land no sooner than 1 month after 0.99.0, leaving server admins one +month after 5th February to upgrade to 0.99.0 and deploy their certificates. In +accordance with the the [S2S spec](https://matrix.org/docs/spec/server_server/r0.1.0.html) +1.0.0 will enforce certificate validity. This means that any homeserver without a +valid certificate after this point will no longer be able to federate with +1.0.0 servers. + + +## Configuring certificates for compatibility with Synapse 1.0.0 + +### If you do not currently have an SRV record + +In this case, your `server_name` points to the host where your Synapse is +running. There is no need to create a `.well-known` URI or an SRV record, but +you will need to give Synapse a valid, signed, certificate. + +The easiest way to do that is with Synapse's built-in ACME (Let's Encrypt) +support. Full details are in [ACME.md](./ACME.md) but, in a nutshell: + + 1. Allow Synapse to listen on port 80 with `authbind`, or forward it from a + reverse proxy. + 2. Enable acme support in `homeserver.yaml`. + 3. Move your old certificates out of the way. + 4. Restart Synapse. + +### If you do have an SRV record currently + +If you are using an SRV record, your matrix domain (`server_name`) may not +point to the same host that your Synapse is running on (the 'target +domain'). (If it does, you can follow the recommendation above; otherwise, read +on.) + +Let's assume that your `server_name` is `example.com`, and your Synapse is +hosted at a target domain of `customer.example.net`. Currently you should have +an SRV record which looks like: + +``` +_matrix._tcp.example.com. IN SRV 10 5 8000 customer.example.net. +``` + +In this situation, you have three choices for how to proceed: + +#### Option 1: give Synapse a certificate for your matrix domain + +Synapse 1.0 will expect your server to present a TLS certificate for your +`server_name` (`example.com` in the above example). You can achieve this by +doing one of the following: + + * Acquire a certificate for the `server_name` yourself (for example, using + `certbot`), and give it and the key to Synapse via `tls_certificate_path` + and `tls_private_key_path`, or: + + * Use Synapse's [ACME support](./ACME.md), and forward port 80 on the + `server_name` domain to your Synapse instance. + +#### Option 2: run Synapse behind a reverse proxy + +If you have an existing reverse proxy set up with correct TLS certificates for +your domain, you can simply route all traffic through the reverse proxy by +updating the SRV record appropriately (or removing it, if the proxy listens on +8448). + +See [reverse_proxy.rst](reverse_proxy.rst) for information on setting up a +reverse proxy. + +#### Option 3: add a .well-known file to delegate your matrix traffic + +This will allow you to keep Synapse on a separate domain, without having to +give it a certificate for the matrix domain. + +You can do this with a `.well-known` file as follows: + + 1. Keep the SRV record in place - it is needed for backwards compatibility + with Synapse 0.34 and earlier. + + 2. Give synapse a certificate corresponding to the target domain + (`customer.example.net` in the above example). Currently Synapse's ACME + support [does not support + this](https://github.com/matrix-org/synapse/issues/4552), so you will have + to acquire a certificate yourself and give it to Synapse via + `tls_certificate_path` and `tls_private_key_path`. + + 3. Restart Synapse to ensure the new certificate is loaded. + + 4. Arrange for a `.well-known` file at + `https://<server_name>/.well-known/matrix/server` with contents: + + ```json + {"m.server": "<target server name>"} + ``` + + where the target server name is resolved as usual (i.e. SRV lookup, falling + back to talking to port 8448). + + In the above example, where synapse is listening on port 8000, + `https://example.com/.well-known/matrix/server` should have `m.server` set to one of: + + 1. `customer.example.net` ─ with a SRV record on + `_matrix._tcp.customer.example.com` pointing to port 8000, or: + + 2. `customer.example.net` ─ updating synapse to listen on the default port + 8448, or: + + 3. `customer.example.net:8000` ─ ensuring that if there is a reverse proxy + on `customer.example.net:8000` it correctly handles HTTP requests with + Host header set to `customer.example.net:8000`. + + +## FAQ + +### Synapse 0.99.0 has just been released, what do I need to do right now? + +Upgrade as soon as you can in preparation for Synapse 1.0.0, and update your +TLS certificates as [above](#configuring-certificates-for-compatibility-with-synapse-100). + +### What will happen if I do not set up a valid federation certificate immediately? + +Nothing initially, but once 1.0.0 is in the wild it will not be possible to +federate with 1.0.0 servers. + +### What will happen if I do nothing at all? + +If the admin takes no action at all, and remains on a Synapse < 0.99.0 then the +homeserver will be unable to federate with those who have implemented +.well-known. Then, as above, once the month upgrade window has expired the +homeserver will not be able to federate with any Synapse >= 1.0.0 + +### When do I need a SRV record or .well-known URI? + +If your homeserver listens on the default federation port (8448), and your +`server_name` points to the host that your homeserver runs on, you do not need an +SRV record or `.well-known/matrix/server` URI. + +For instance, if you registered `example.com` and pointed its DNS A record at a +fresh Upcloud VPS or similar, you could install Synapse 0.99 on that host, +giving it a server_name of `example.com`, and it would automatically generate a +valid TLS certificate for you via Let's Encrypt and no SRV record or +`.well-known` URI would be needed. + +This is the common case, although you can add an SRV record or +`.well-known/matrix/server` URI for completeness if you wish. + +**However**, if your server does not listen on port 8448, or if your `server_name` +does not point to the host that your homeserver runs on, you will need to let +other servers know how to find it. + +In this case, you should see ["If you do have an SRV record +currently"](#if-you-do-have-an-srv-record-currently) above. + +### Can I still use an SRV record? + +Firstly, if you didn't need an SRV record before (because your server is +listening on port 8448 of your server_name), you certainly don't need one now: +the defaults are still the same. + +If you previously had an SRV record, you can keep using it provided you are +able to give Synapse a TLS certificate corresponding to your server name. For +example, suppose you had the following SRV record, which directs matrix traffic +for example.com to matrix.example.com:443: + +``` +_matrix._tcp.example.com. IN SRV 10 5 443 matrix.example.com +``` + +In this case, Synapse must be given a certificate for example.com - or be +configured to acquire one from Let's Encrypt. + +If you are unable to give Synapse a certificate for your server_name, you will +also need to use a .well-known URI instead. However, see also "I have created a +.well-known URI. Do I still need an SRV record?". + +### I have created a .well-known URI. Do I still need an SRV record? + +As of Synapse 0.99, Synapse will first check for the existence of a `.well-known` +URI and follow any delegation it suggests. It will only then check for the +existence of an SRV record. + +That means that the SRV record will often be redundant. However, you should +remember that there may still be older versions of Synapse in the federation +which do not understand `.well-known` URIs, so if you removed your SRV record you +would no longer be able to federate with them. + +It is therefore best to leave the SRV record in place for now. Synapse 0.34 and +earlier will follow the SRV record (and not care about the invalid +certificate). Synapse 0.99 and later will follow the .well-known URI, with the +correct certificate chain. + +### It used to work just fine, why are you breaking everything? + +We have always wanted Matrix servers to be as easy to set up as possible, and +so back when we started federation in 2014 we didn't want admins to have to go +through the cumbersome process of buying a valid TLS certificate to run a +server. This was before Let's Encrypt came along and made getting a free and +valid TLS certificate straightforward. So instead, we adopted a system based on +[Perspectives](https://en.wikipedia.org/wiki/Convergence_(SSL)): an approach +where you check a set of "notary servers" (in practice, homeservers) to vouch +for the validity of a certificate rather than having it signed by a CA. As long +as enough different notaries agree on the certificate's validity, then it is +trusted. + +However, in practice this has never worked properly. Most people only use the +default notary server (matrix.org), leading to inadvertent centralisation which +we want to eliminate. Meanwhile, we never implemented the full consensus +algorithm to query the servers participating in a room to determine consensus +on whether a given certificate is valid. This is fiddly to get right +(especially in face of sybil attacks), and we found ourselves questioning +whether it was worth the effort to finish the work and commit to maintaining a +secure certificate validation system as opposed to focusing on core Matrix +development. + +Meanwhile, Let's Encrypt came along in 2016, and put the final nail in the +coffin of the Perspectives project (which was already pretty dead). So, the +Spec Core Team decided that a better approach would be to mandate valid TLS +certificates for federation alongside the rest of the Web. More details can be +found in +[MSC1711](https://github.com/matrix-org/matrix-doc/blob/master/proposals/1711-x509-for-federation.md#background-the-failure-of-the-perspectives-approach). + +This results in a breaking change, which is disruptive, but absolutely critical +for the security model. However, the existence of Let's Encrypt as a trivial +way to replace the old self-signed certificates with valid CA-signed ones helps +smooth things over massively, especially as Synapse can now automate Let's +Encrypt certificate generation if needed. + +### Can I manage my own certificates rather than having Synapse renew certificates itself? + +Yes, you are welcome to manage your certificates yourself. Synapse will only +attempt to obtain certificates from Let's Encrypt if you configure it to do +so.The only requirement is that there is a valid TLS cert present for +federation end points. + +### Do you still recommend against using a reverse proxy on the federation port? + +We no longer actively recommend against using a reverse proxy. Many admins will +find it easier to direct federation traffic to a reverse proxy and manage their +own TLS certificates, and this is a supported configuration. + +See [reverse_proxy.rst](reverse_proxy.rst) for information on setting up a +reverse proxy. + +### Do I still need to give my TLS certificates to Synapse if I am using a reverse proxy? + +Practically speaking, this is no longer necessary. + +If you are using a reverse proxy for all of your TLS traffic, then you can set +`no_tls: True`. In that case, the only reason Synapse needs the certificate is +to populate a legacy 'tls_fingerprints' field in the federation API. This is +ignored by Synapse 0.99.0 and later, and the only time pre-0.99 Synapses will +check it is when attempting to fetch the server keys - and generally this is +delegated via `matrix.org`, which is on 0.99.0. + +However, there is a bug in Synapse 0.99.0 +[4554](<https://github.com/matrix-org/synapse/issues/4554>) which prevents +Synapse from starting if you do not give it a TLS certificate. To work around +this, you can give it any TLS certificate at all. This will be fixed soon. + +### Do I need the same certificate for the client and federation port? + +No. There is nothing stopping you from using different certificates, +particularly if you are using a reverse proxy. However, Synapse will use the +same certificate on any ports where TLS is configured. + +### How do I tell Synapse to reload my keys/certificates after I replace them? + +Synapse will reload the keys and certificates when it receives a SIGHUP - for +example `kill -HUP $(cat homeserver.pid)`. Alternatively, simply restart +Synapse, though this will result in downtime while it restarts. |