after getting an answer to Security over multi-streaming such as SCTP i have found that i do not have the capacity to give a public key or certificate to the other end securely (to be sure MitM cannot substitute one and that no-one can see it). i do have the capacity to send a 256-bit key securely. both ends are under the same admin but there is no opportunity to set up a key or cert on either end besides the mentioned limited capacity (because it is a cloud image launched when needed). "shared secret" seems to be the wrong terminology as all uses i see for this refer to sharing between different parties (the "sharing" is just between these two ends). this is also a symmetric connection once established ... such as a VPN (it will be used as a VPN and it will use SCTP). my question is: how can i be sure this is secure? security is hard.
i have used openssl before in this script and am looking to use its C-layer API for this project.