Robust authenticated-encryption: AEZ and the problem that it solves
Viet Tung Hoang, Ted Krovetz · 2014
Abstract. With a scheme for robust authenticated-encryption a user can select an arbitrary value λ ≥ 0 and then encrypt a plaintext of any length into a ciphertext that’s λ characters longer. The scheme must provide all the privacy and authenticity possible for the requested λ. We formalize and investigate this idea, and construct a well-optimized solution, AEZ, from the AES round function. Our scheme encrypts strings at almost the same rate as OCB-AES or CTR-AES (on Haswell, AEZ has a peak speed of about 0.7 cpb). To accomplish this we employ an approach we call accelerated provable security: the scheme is designed and proven secure in the provable-security tradition, but, to improve speed, one instantiates by scaling down most instances of the underlying primitive. Keywords:AEZ, arbitrary-input blockciphers, authenticated encryption, robust AE, misuse resistance,