There are no cryptographic primitives in Daml beyond sha256, see Cryptographic primitives in DAML. Generally we try to let the ledger deal with things like certificates, signing, … behind the scenes instead of exposing them in the Daml code. So there isn’t really a way to do what you are suggesting in Daml.
That said, it isn’t quite clear to me why this has to happen on ledger. Can’t you check the party ids off-ledger and use that to decide whether you agree to a proposal or similar?