Reducing the cost of authenticity with leakages: A CIML2-Secure AE scheme with one call to a strongly protected tweakable block cipher

Abstract

This paper presents CONCRETE (Commit − Encrypt − Send − the − Key) a new Authenticated Encryption mode that offers CIML2 security, that is, ciphertext integrity in the presence of nonce misuse and side-channel leakages in both encryption and decryption. CONCRETE improves on a recent line of works aiming at leveled implementations, which mix a strongly protected and energy demanding implementation of a single component, and other weakly protected and much cheaper components. Here, these components all implement a tweakable block cipher TBC. CONCRETE requires the use of the strongly protected TBC only once while supporting the leakage of the full state of the weakly protected components – it achieves CIML2 security in the so-called unbounded leakage model. All previous works need to use the strongly protected implementation at least twice. As a result, for short messages whose encryption and decryption energy costs are dominated by the strongly protected component, we halve the cost of a leakage-resilient implementation. CONCRETE additionally provides security when unverified plaintexts are released, and confidentiality in the presence of simulatable leakages in encryption and decryption.