Subject: [MLS] Are people open to a different approach to the cryptography?

From: Phillip Hallam-Baker <[email-masked]>
Date: Tue, 27 Feb 2018 23:53:52 -0500

I agree that perfect forward secrecy is sometimes a requirement. But it
isn't always a requirement and sometimes the requirement may be to create a
static record of a conversation.

For example, this conversation we are having now. We might well want to
make it private but have a permanent record so if we admit a new person to
the group, they can read the previous material.

For the past couple of years I have been working on multi-key approaches to
cryptography based on work by Matt Blaze and Torben Pederssen.

The approach is based on the fact that we can do math on Diffie Hellman
Keys and results.

If you add two discrete log private keys, the public key corresponding to
the result is the product of the corresponding public keys.

x + y = z
e^x . e^y = e^(x+y) = e^z

What I have designed the key agreement for my chat protocol to support is
the case in which all communication to the group is encrypted under a group
encryption key and the decryption key is split differently for each member
of the group by an administrator.

I am pretty sure I can add PFS into the agreement. But I would need to
understand the requirements a bit better first.