CENC is Optimally Secure
At FSE 2006, Iwata introduced the CENC encryption mode and proved its security up to 2 plaintext blocks processed in total. He conjectured optimal security up to a constant. In this brief note, we confirm this conjecture. Rather than proving it ourselves, we point out that the conjecture’s proof follows as a corollary of Patarin’s “Theorem Pi ⊕ Pj for any ξmax” from 2005. This connection appears to have remained unnoticed, and the sole purpose of this brief note is to make the connection explicit.