109 lines
3.7 KiB
ReStructuredText
109 lines
3.7 KiB
ReStructuredText
======================
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Third Party Identities
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======================
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A description of how email addresses, mobile phone numbers and other third
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party identifiers can be used to authenticate and discover users in Matrix.
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Overview
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========
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New users need to authenticate their account. An email or SMS text message can
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be a convenient form of authentication. Users already have email addresses
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and phone numbers for contacts in their address book. They want to communicate
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with those contacts in Matrix without manually exchanging a Matrix User ID with
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them.
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Third Party IDs
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---------------
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[[TODO(markjh): Describe the format of a 3PID]]
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Third Party ID Associations
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---------------------------
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An Associaton is a binding between a Matrix User ID and a Third Party ID (3PID).
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Each 3PID can be associated with one Matrix User ID at a time.
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[[TODO(markjh): JSON format of the association.]]
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Verification
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------------
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An Assocation must be verified by a trusted Verification Server. Email
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addresses and phone numbers can be verified by sending a token to the address
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which a client can supply to the verifier to confirm ownership.
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An email Verification Server may be capable of verifying all email 3PIDs or may
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be restricted to verifying addresses for a particular domain. A phone number
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Verification Server may be capable of verifying all phone numbers or may be
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restricted to verifying numbers for a given country or phone prefix.
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Verification Servers fulfil a similar role to Certificate Authorities in PKI so
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a similar level of vetting should be required before clients trust their
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signatures.
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A Verification Server may wish to check for existing Associations for a 3PID
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before creating a new Association.
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Discovery
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---------
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Users can discover Associations using a trusted Identity Server. Each
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Association will be signed by the Identity Server. An Identity Server may store
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the entire space of Associations or may delegate to other Identity Servers when
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looking up Associations.
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Each Association returned from an Identity Server must be signed by a
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Verification Server. Clients should check these signatures.
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Identity Servers fulfil a similar role to DNS servers.
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Privacy
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-------
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A User may publish the association between their phone number and Matrix User ID
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on the Identity Server without publishing the number in their Profile hosted on
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their homeserver.
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Identity Servers should refrain from publishing reverse mappings and should
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take steps, such as rate limiting, to prevent attackers enumerating the space of
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mappings.
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Federation
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==========
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Delegation
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----------
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Verification Servers could delegate signing to another server by issuing
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certificate to that server allowing it to verify and sign a subset of 3PID on
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its behalf. It would be necessary to provide a language for describing which
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subset of 3PIDs that server had authority to validate. Alternatively it could
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delegate the verification step to another server but sign the resulting
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association itself.
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The 3PID space will have a heirachical structure like DNS so Identity Servers
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can delegate lookups to other servers. An Identity Server should be prepared
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to host or delegate any valid association within the subset of the 3PIDs it is
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resonsible for.
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Multiple Root Verification Servers
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----------------------------------
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There can be multiple root Verification Servers and an Association could be
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signed by multiple servers if different clients trust different subsets of
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the verification servers.
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Multiple Root Identity Servers
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------------------------------
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There can be be multiple root Identity Servers. Clients will add each
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Association to all root Identity Servers.
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[[TODO(markjh): Describe how clients find the list of root Identity Servers]]
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