Difference between revisions of "XEP-Remarks/XEP-0373: OpenPGP for XMPP"

XEP-Remarks/XEP-0373: OpenPGP for XMPP (view source)

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+=== Multi-User-Chat / Group Chat ===
+There are different ways of tackling multi user-chat.
+The naive way would be to simply gather all the keys of all recipients and encrypt outgoing messages to all recipient keys.
+Another possibility (experimental, not sure if there is support for this in libraries/the OpenPGP spec yet) would be to use Proxy-Reencryption using ECC/PQC keys. This would require server-side support:
+* There is a group chat key per group chat.
+* (For ECC keys) For each member of the chat, the point on the curve gets multiplied by a unique scalar. The result is a new recipient key.
+* The server distributes recipient keys to the recipients
+* When sending a message, the user uses the group chat's encryption key
+* The server "reencrypts" the message for each recipient and delivers it
+* The users can decrypt the message
+This methodology prevents the server from learning about message contents, but simplifies key management. Unfortunately this would require server-side support and support in OpenPGP spec/tooling, so this is very future-work-ish.
+See https://www.researchgate.net/publication/299487198_Elliptic_Curve_Based_Proxy_Re-Encryption
+See "Automatic Forwarding" section in https://cryptpad.fr/pad/#/2/pad/view/9IyR9CkooqMQHOiUQ2a7UE88FAMklY1XF2vqnkCY6xg/
 = Issues =