[messaging] Signal Protocol Licensing/Intellectual Property Status

[Nadim Kobeissi]

Hello,
I am wondering regarding the "Signal Protocol" (the four-way Diffie-Hellman AKE + the double ratchet)'s licensing/intellectual property status.

To be precise, I am wondering specifically about the protocol and algorithms, and NOT any implementation or code.

Are the protocols and algorithms all in public domain, or is there an imposed license, intellectual property claim, or patent of some kind? I think this is especially pertinent given their increasingly wide adoption.

Thanks,
Nadim