This seems like something we ought to be able to do electronically. I should be able to encrypt a message with recipient's pubkey and a verified timestamp from

This seems like something we ought to be able to do electronically. I should be able to encrypt a message with recipient's pubkey and a verified timestamp from NIST (for example) in addition to my digital signature, with a requirement for decryption to result in a second call to NIST from the recipient and a record available to me of when it was decrypted.