Embed TLS with Authentication of Cryptographic Attestation

[tumberger]

All of the KMS documentation in AWS seems just like a pretty big distraction. TLS with mutual authentication should be sufficient to encrypt private payloads into the enclave. The key point here is that 1) no transactions/bundles are sent before verifying that the communication partner is the enclave itself (can be done by requesting the attestation document), 2) verifying that the correct code is run (can be done by verifying the attestation document and comparing PCR hashes which ensures that the expected docker image is run).

ToDo in the dumme nitro enclave repo to enable this:

• Embed TLS into the gRPC exchange
• Ensure that the communication partner is the actual enclave by requesting and verifying the attestation document with the embedded public key, and leveraging a fresh nonce