Open AccessOptimal PRFs from Blockcipher Designs
Author(s) -
Bart Mennink,
Samuel Neves
Publication year - 2017
Publication title -
iacr transaction on symmetric cryptology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.715
H-Index - 10
ISSN - 2519-173X
DOI - 10.46586/tosc.v2017.i3.228-252
Subject(s) - gcm transcription factors , permutation (music) , computer science , heuristic , pseudorandom function family , state (computer science) , cryptography , function (biology) , theoretical computer science , mode (computer interface) , algorithm , general circulation model , physics , artificial intelligence , operating system , ecology , climate change , evolutionary biology , acoustics , biology
Cryptographic modes built on top of a blockcipher usually rely on the assumption that this primitive behaves like a pseudorandom permutation (PRP). For many of these modes, including counter mode and GCM, stronger security guarantees could be derived if they were based on a PRF design. We propose a heuristic method of transforming a dedicated blockcipher design into a dedicated PRF design. Intuitively, the method consists of evaluating the blockcipher once, with one or more intermediate state values fed-forward. It shows strong resemblance with the optimally secure EDMD construction by Mennink and Neves (CRYPTO 2017), but the use of internal state values make their security analysis formally inapplicable. In support of its security, we give the rationale of relying on the EDMD function (as opposed to alternatives), and present analysis of simplified versions of our conversion method applied to the AES. We conjecture that our main proposal AES-PRF, AES with a feed-forward of the middle state, achieves close to optimal security. We apply the design to GCM and GCM-SIV, and demonstrate how it entails significant security improvements. We furthermore demonstrate how the technique extends to tweakable blockciphers and allows for security improvements in, for instance, PMAC1.