Cryptographic authentication of validators' session keys in network

[rphmeier]

Using an additional signature using validator session keys on a derived value from the underlying DH shared secret of the network connection.

cc @burdges and @tomaka

[rphmeier]

for libp2p we would want a function of some kind like connection.derive_from_shared_secret("constant string") -> H256 which does a cryptographic hash of the shared secret and concatenation of the constant string.

[burdges]

s/and concatenation of/concatenated with/

It's unclear if there is a reasonable way to extract session key information from libp2p, but even if we do so it makes auditing hard because the security of validators binding to sessions now reduces to the transport security.

I think GNUNet addresses this with its CADET layer that maintains connection state between nodes independent from the underlying transport layer. We could do a much simpler things, but we should asses if adding a CADET like layer to libp2p would solve a wider array of problems.

[rphmeier]

yes, relying purely on the transport is also not as agnostic as I'd like. The overhead of doing another DH agreement or similar on top will not be prohibitive, as we need a handshake message for other reasons anyway.

Collators will also need to do this authentication with validators.

[burdges]

We should consider if this layer should do more complex things, like the forwarding that CADET does.

[burdges]

There is a vaguely similar layer already but afaik they do not use it much:
https://github.com/libp2p/specs/tree/master/relay
https://github.com/libp2p/rust-libp2p/tree/master/relay

[rphmeier]

Authentication of session keys should also be limited only to when they change.

[burdges]

In principle, some relay circuit might straddle multiple lower level connections, thanks to doing its own encryption. I'm doubtful if that's worth the engineering work, but it's possible and CADET does that, which improves its forward security properties thanks to ratcheting. I doubt the forward security properties matter so much to us, but maybe for other libp2p users.

[gavofyork]

@rphmeier is this required for this milestone?

[rphmeier]

AFAIK only for Polkadot, and not for Substrate