We study authenticated encryption (AE) modes dedicated to very short messages, which are crucial for Internet-of-things applications. Since the existing general-purpose AE modes need at least three block cipher calls for non-empty messages, we explore the design space for AE modes that use at most two calls. We proposed a family of AE modes, dubbed Manx, that work when the total input length is less than $2n$ bits, using an $n$-bit block cipher. Notably, the second construction of Manx can encrypt almost n-bit plaintext and saves one or two block cipher calls from the standard modes, such as GCM or OCB, keeping the comparable provable security. We also present benchmarks on popular 8/32-bit microprocessors using AES. Our results show the clear advantage of Manx over the previous modes for such short messages.

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Author Of this post: Alexandre Adomnicai

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