New Security Proofs for the 3GPP Confidentiality and Integrity Algorithms

This paper analyses the 3GPP confidentiality and integrity schemes adopted by UniversalMobile Telecommunication System, an emerging standard for third generation wireless commu-nications. The schemes, known as f8 and f9, are based on the block cipher KASUMI. Althoughprevious works claim security proofs for f8 and f9′, where f9′ is a generalized versions of f9,it was recently shown that these proofs are incorrect. Moreover, Iwata and Kurosawa (2003)showed that it is impossible to prove f8 and f9′ secure under the standard PRP assumptionon the underlying block cipher. We address this issue here, showing that it is possible to provef8′ and f9′ secure if we make the assumption that the underlying block cipher is a securePRP-RKA against a certain class of related-key attacks; here f8′ is a generalized version of f8.Our results clarify the assumptions necessary in order for f8 and f9 to be secure and, since norelated-key attacks are known against the full eight rounds of KASUMI, lead us to believe thatthe confidentiality and integrity mechanisms used in real 3GPP applications are secure.