Question on implementing separate channels

[ColonelThirtyTwo]

I'd like to use noise in a protocol that supports multiple parallel reliable streams (QUIC or enet). I'd like to avoid needing to do a handshake for each channel and just reuse the known keys from the initiating channel instead. I believe I have a solution, but I'm no cryptography expert and I'd like a second opinion.

Section 11.4 about out-of-order messsages says that it's possible to decrypt messages out-of-order simply by providing the nonce that the message was encrypted with. That seems to me that the only changing state in the connection, barring re-keys, is the nonce.

Therefore, I think I can support multiple streams by generating and keeping track of separate nonces for each channel, and setting the appropriate nonce in the reader before en/decrypting the channel's message.

The library I am using (snow, for rust) seems to just use a 64-bit counter for the nonce. I believe I should be able to partition that as 32 bits for the channel ID and 32 bits for the counter. They shouldn't overlap as long as I make sure the counter does not overflow.

Is this sound? Are there any security flaws that I have overlooked?

[mimoo]

You could derive a per-stream symmetric key based on the result of the handshake and the stream ID

BTW check out nQUIC