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Do not require UIA when first uploading cross-signing keys #1828

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Jun 6, 2024
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Do not require UIA when first uploading cross-signing keys #1828

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Do not require UIA when first uploading cross-signing keys
zecakeh May 27, 2024
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zecakeh May 27, 2024
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zecakeh May 29, 2024
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zecakeh May 29, 2024
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1 change: 1 addition & 0 deletions changelogs/client_server/newsfragments/1828.feature
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@@ -0,0 +1 @@
Do not require UIA when first uploading cross-signing keys, as per [MSC3967](https://github.com/matrix-org/matrix-spec-proposals/pull/3967).
15 changes: 15 additions & 0 deletions data/api/client-server/cross_signing.yaml
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Expand Up @@ -19,11 +19,26 @@ paths:
/keys/device_signing/upload:
post:
x-addedInMatrixVersion: "1.1"
x-changedInMatrixVersion:
"1.11": UIA is not always required for this endpoint.
summary: Upload cross-signing keys.
description: |-
Publishes cross-signing keys for the user.

This API endpoint uses the [User-Interactive Authentication API](/client-server-api/#user-interactive-authentication-api).

User-Interactive Authentication MUST be performed, except in these cases:
- there is no existing cross-signing master key uploaded to the homeserver, OR
- there is an existing cross-signing master key and it exactly matches the
cross-signing master key provided in the request body. If there are any additional
keys provided in the request (self-signing key, user-signing key) they MUST also
match the existing keys stored on the server. In other words, the request contains
no new keys.
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I copied this section from the MSC, but it seems to ignore the case where a client uploads the master key and the other keys (self-signing and user-signing) separately.

My understanding according to the paragraph below is that setting the other keys if they were not set before, or re-uploading the same keys, should not require UIA, even if the master key is not part of the request (i.e. it was already uploaded before).

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The MSC (and this wording in particular) seems to imply that you have to upload the MSK on each request, otherwise you have to do UIA. I'm not sure that's what was intended, but it's probably ok, and we can't really just change it without another MSC.


This allows clients to freely upload one set of keys, but not modify/overwrite keys if
they already exist. Allowing clients to upload the same set of keys more than once
makes this endpoint idempotent in the case where the response is lost over the network,
which would otherwise cause a UIA challenge upon retry.
operationId: uploadCrossSigningKeys
security:
- accessTokenQuery: []
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