Stream Confidentiality: it appears you are using an RSA public key encryption scheme which is deterministic and thus

Question

not CPA-secure?  Can an attacker ever obtain the sender's public keys or because the sender is from a channel with integrity (a private blockchain with known actors) the risk is nullified? are you possibly using some form of the more efficient and CPA-secure hybrid encryption techniques by encrypting the senders public key?

Answer 1

I assume you're referring to this guide here:

https://www.multichain.com/developers/stream-confidentiality/

If so this is just an example of how to implement this and MultiChain doesn't require you to use RSA or any other specific encryption scheme for the distribution of the keys that grant access to specific stream items. You're welcome to replace RSA with any other asymmetric cryptography algorithm of choice.