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# Key verification flow addition: `m.key.verification.ready`
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The current key verification framework is asymmetrical in that the user who
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requests the verification is unable to select the key verification method.
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This makes it harder for more experienced users who wish to guide less
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experienced users through the verification process, especially if they are not
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verifying in-person, but are using a trusted but remote channel of verification
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(such as telephone or video conference).
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As an example, let us say that Alice is an experienced Matrix user and is
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introducing Bob to the wonders of federated communications. Alice wants to
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verify keys with Bob, so she clicks on the "Verify" button in her client on
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Bob's profile (which sends a `m.key.verification.request` message to Bob).
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Bob's device receives the verification request and prompts Bob to accept the
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verification request. At this point, under the current framework, Bob is
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responsible for choosing the verification method to use. However, with this
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proposal, Bob would be able to just accept the verification request without
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choosing a method, and allow Alice to choose the verification method.
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## Proposal
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A new event type is added to the key verification framework:
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`m.key.verification.ready`, which may be sent by the target of the
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`m.key.verification.request` message, upon receipt of the
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`m.key.verification.request` event. It has the fields:
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- `from_device`: the ID of the device that sent the `m.key.verification.ready`
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message
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- `methods`: an array of verification methods that the device supports
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It also has the usual `transaction_id` or `m.relates_to` fields for key
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verification events, depending on whether it is sent as a to-device event
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or an in-room event.
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After the `m.key.verification.ready` event is sent, either party can send an
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`m.key.verification.start` event to begin the verification. If both parties
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send an `m.key.verification.start` event, and they both specify the same
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verification method, then the event sent by the user whose user ID is the
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smallest is used, and the other `m.key.verification.start` event is ignored.
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In the case of a single user verifying two of their devices, the device ID is
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compared instead. If both parties send an `m.key.verification.start` event,
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but they specify different verification methods, the verification should be
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cancelled with a `code` of `m.unexpected_message`.
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With to-device messages, previously the sender of the
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`m.key.verification.request` message would send an `m.key.verification.cancel`
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message to the recipient's other devices when it received an
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`m.key.verification.start` event. With this new event, the sender of the
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`m.key.verification.request` message should send an `m.key.verification.cancel`
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message when it receives an `m.key.verification.ready` or
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`m.key.verification.start` message, whichever comes first.
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The `m.key.verification.ready` event is optional; the recipient of the
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`m.key.verification.request` event may respond directly with a
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`m.key.verification.start` event instead. This is for compatibility with the
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current version of the spec.
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## Potential issues
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There are now three possible ways that a key verification can be performed:
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1. A device begins a verification by sending an `m.key.verification.start`
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event. This is only possible for to-device verification.
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2. A device sends an `m.key.verification.request` event and the recipient
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replies with an `m.key.verification.start` event.
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3. A device sends an `m.key.verification.request` event and the recipient
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replies with an `m.key.verification.ready` event, and which point, either
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device can send an `m.key.verification.start` event to begin the
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verification.
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This increases the complexity of implementations.
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