ephemeral public keys are emitted as URL-safe base64

[reivilibre]

sydent/sydent/http/servlets/store_invite_servlet.py

Line 127 in a37d60b

ephemeralPublicKeyBase64 = encode_base64(ephemeralPublicKey.encode(), True)

This is possibly a mistake, maybe this is meant to be the regular base64 alphabet.

See also: matrix-org/matrix-spec#2060

[richvdh]

According to #10, it needs to be url safe for some reason?

[richvdh]

According to #10, it needs to be url safe for some reason?

So I think the reason that the ephemeral key is url-safe encoded is that, when you send an invite to an email address, the owner of that email address receives an email with the ephemeral secret key embedded in it, in a format like:

https://app.element.io/#/room/{roomId}?
    email={emailAddress}&
    signurl=https://vector.im/_matrix/identity/api/v1/sign-ed25519?
         token={token}%26
         private_key={base64 private key}

(there is more %-encoding in the actual uri, but it is redundant)

Now, there are many levels of wrongheadedness about this (including the "email/signurl" API for Element being unspecified (matrix-org/matrix-spec#1360) and the sign-ed25519 endpoint being in a confusing place (#533)), but also:

1. There doesn't seem to be any real problem putting a non-url-safe parameter here (+ would be encoded as %2B. Or rather, %252B, since it's in a query-parameter in a query-parameter, but I digress). It's not meant to be user-visible, and there doesn't seem much scope for url-encoding foulups (unlike event ids in Room V3).
2. Even if we wanted to use url-safe encoding here, that doesn't seem to be any good reason why the public keys also need to be URL-safe encoded in the rest of the IS API and in m.room.member events.

In short, I don't really think it needs to be url-safe, but I think that's probably why @illicitonion decided it did.

[matrixbot]

For your information, this issue has been copied over to the Element fork of sydent: element-hq/sydent#593