Shaking up authenticated encryption

Authenticated encryption (AE) is a cryptographic mechanism that allows communicating parties to protect the confidentiality and integrity of messages exchanged over a public channel, provided they share a secret key. In this work, we present new AE schemes leveraging the SHA- 3 standard functions SHAKE128 and SHAKE256, offering 128 and 256 bits of security strength, respectively, and their “Turbo” counterparts. They support session-based communication, where a ciphertext authenticates the sequence of messages since the start of the session. The chaining in the session allows decryption in segments, avoiding the need to buffer the entire deciphered cryptogram between decryption and validation. And, thanks to the collision resistance of (Turbo)SHAKE, they provide so-called CMT-4 committing security, meaning that they provide strong guarantees that a ciphertext uniquely binds to the key, plaintext and associated data. The AE schemes we propose have a unique combination of advantages. The most important are that 1) their security is based on the security claim of SHAKE, that has received a large amount of public scrutiny, that 2) they make use of the standard KECCAK-p permutation that not only receives more and more dedicated hardware support, but also allows competitive software-only implementations thanks to the TurboSHAKE instances, and that 3) they do not suffer from a 64-bit birthday bound like most AES-based schemes. Of independent interest, we introduce the deck cipher as the stateful counterpart of the deck function and the duplex cipher generalizing keyed duplex and harmonize their security notions. Finally, we provide an elegant solution for multi-layer domain separation.