Analysing the IOBC Authenticated Encryption Mode

Abstract. The idea of combining a very simple form of added plaintext redundancy with a special mode of data encryption to provide data in-tegrity is an old one; however, despite its wide deployment in protocols such as Kerberos, it has largely been superseded by provably secure au-thenticated encryption techniques. In this paper we cryptanalyse a block cipher mode of operation called IOBC, possibly the only remaining en-cryption mode designed for such use that has not previously been ana-lyzed. We show that IOBC is subject to known-plaintext-based forgery attacks with a complexity of around 2n=3, where n is the block cipher block length.

Integrity-protecting block cipher modes - Untangling a tangled web

This paper re-examines the security of three related block cipher modes of operation designed toprovide authenticated encryption. These modes, known as PES-PCBC, IOBC and EPBC, were all proposed in the mid-1990s. However, analyses of security of the latter two modes were published more recently. In each case one or more papers describing security issues with the schemes were eventually published, although a flaw in one of these analyses (of EPBC) was subsequently discovered - this means that until now EPBC had no known major issues. This paper establishes that, despite this, all three schemes possess defects which should prevent their use - especially as there are a number of efficient alternative schemes possessing proofs of security

Breaking Into the KeyStore: A Practical Forgery Attack Against Android KeyStore

We analyze the security of Android KeyStore, a system service whose purpose is to shield users credentials and cryptographic keys. The KeyStore protects the integrity and the confidentiality of keys by using a particular encryption scheme. Our main results are twofold. First, we formally prove that the used encryption scheme does not provide integrity, which means that an attacker is able to undetectably modify the stored keys. Second, we exploit this flaw to define a forgery attack breaching the security guaranteed by the KeyStore. In particular, our attack allows a malicious application to make mobile apps to unwittingly perform secure protocols using weak keys. The threat is concrete: the attacker goes undetected while compromising the security of users. Our findings highlight an important fact: intuition often goes wrong when security is concerned. Unfortunately, system designers still tend to choose cryptographic schemes not for their proved security but for their apparent simplicity. We show, once again, that this is not a good choice, since it usually results in severe consequences for the whole underlying system