9.7.4. Forward Secrecy

9.7.4. Forward Secrecy

HPKE ciphertexts are not forward secret with respect to recipient compromise in any mode. This means that compromise of long-term recipient secrets allows an attacker to decrypt past ciphertexts encrypted under said secrets. This is because only long-term secrets are used on the side of the recipient.

HPKE ciphertexts are forward secret with respect to sender compromise in all modes. This is because ephemeral randomness is used on the sender's side, which is supposed to be erased directly after computation of the KEM shared secret and ciphertext.