> If I have your key, I can send you an encrypted GPG message, without you needing to know who am, or for any kind of message from you back to me. HMACs require

> If I have your key, I can send you an encrypted GPG message, without you needing to know who am, or for any kind of message from you back to me. HMACs require a shared secret. No, they don't. I described a naive RSA+AES hybrid cryptosystem here that includes HMAC authentication without a pre-shared key: https://paragonie.com/blog/2018/04/protecting-rsa-based-protocols-against-adaptive-chosen-ciphertext-attacks https://paragonie.com/blog/2018/04/protecting-rsa-based-prot...