Persistent Symmetric Keys in OpenPGP

This document defines a new packet and algorithm for the OpenPGP standard (RFC 9580) to support persistent symmetric keys, for message encryption using authenticated encryption with additional data (AEAD) and for message authentication using AEAD authentication tags. This enables the use of symmetric cryptography for data storage (and other contexts that do not require asymmetric cryptography), for improved performance, smaller keys, and improved resistance to quantum computing.