Formal Security Proof of CMAC and its Variants

EasyChair Preprint 104

Abstract

The CMAC standard, when initially proposed by Iwata and Kurosawa as OMAC1, was equipped with a complex game-based security proof. Following recent advances in formal verification for game-based security proofs, we formalize a proof of unforgeability for CMAC in EasyCrypt. A side effects of this proof are improvements of EasyCrypt libraries. This formal proof obtains security bounds very similar to Iwata and Kurosawa’s for CMAC, but also proves secure a certain number of intermediate constructions of independent interest, including ECBC, FCBC and XCBC. This work represents one more step in the direction of obtaining a reliable set of independently verifiable evidence for the security of international cryptographic standards.

Keyphrases: EasyCrypt, MAC, Security, block cipher mode, collision probability, formal proof, security proof

@booklet{EasyChair:104,
  author    = {Cécile Baritel-Ruet and François Dupressoir and Pierre-Alain Fouque and Benjamin Grégoire},
  title     = {Formal Security Proof of CMAC and its Variants},
  doi       = {10.29007/2xpx},
  howpublished = {EasyChair Preprint 104},
  year      = {EasyChair, 2018}}