Paper 2013/269

CMCC: Misuse Resistant Authenticated Encryption with Minimal Ciphertext Expansion

Jonathan Trostle

Abstract

In some wireless environments, minimizing the size of messages is paramount due to the resulting significant energy savings. We present CMCC, an authenticated encryption scheme with associated data (AEAD) that is also nonce misuse resistant. The main focus for this work is minimizing ciphertext expansion, especially for short messages including plaintext lengths less than the underlying block cipher length (e.g., 16 bytes). For many existing AEAD schemes, a successful forgery leads directly to a loss of confidentiality. For CMCC, changes to the ciphertext randomize the resulting plaintext, thus forgeries do not necessarily result in a loss of confidentiality which allows us to reduce the length of the authentication tag. For protocols that send short messages, our scheme is similar to Counter with CBC-MAC (CCM) for computational overhead but has much smaller expansion. We prove both a misuse resistant authenticated encryption (MRAE) security bound and an authenticated encryption (AE) security bound for CMCC. We also present a variation of CMCC, CWM, which provides a further strengthening of the security bounds. Our contributions include both stateless and stateful versions which enable minimal sized message numbers using different network related trade-offs.

Note: Revised version.