Our crypto libraries have:
- DSA (4096, 512)
- DH (4096)
- AES (256)
- SHA (512)
Let us say these are implemented directly in hardware so that trying to pull the pieces out is not possible, and the CPU isn't really fast enough to implement crypto itself.
Can we develop a protocol that permits us to exchange public keys, and at some later date send messages by courier or some means that does not assume live communication. That is, DH won't work directly because message round-trip time is intolerably long.
This question is far more interesting on a theoretical basis than any practical means by which I might have gotten here.