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Abstract. Attacks are presented on the IBM 4758 CCA and the Visa Security Module. Two new attack principles are demonstrated. Related key attacks use known or chosen differences between two cryptographic keys. Data protected with one key can then be abused by manipulation using the other key. Meet in the middle attacks work by generating a large number of unknown keys of the same type, thus reducing the key space that must be searched to discover the value of one of the keys in the type. Design heuristics are presented to avoid these attacks and other common errors.

A whole new family of attacks has recently been discovered on the application programming interfaces (APIs) used by security processors. These extend and generalise a number of attacks already known on authentication protocols. The basic idea is that by presenting valid commands to the security processor, but in an unexpected sequence, it is possible to obtain results that break the security policy envisioned by its designer. Such attacks are economically important, as security processors are used to support a wide range of services, from automatic teller machines through pay-TV to prepayment utility metering. Designing APIs that resist such attacks is difficult, as a typical security processor needs a substantial command set with several dozen commands that allow it to service a number of external and internal protocols. The attacks are also scientifically interesting; preventing them may become an important new application area for formal methods and design verification tools generally.

Abstract-EMV, also known as "Chip and PIN", is the leading system for card payments worldwide. It is used throughout Europe and much of Asia, and is starting to be introduced in North America too. Payment cards contain a chip so they can execute an authentication protocol. This protocol requires point-of-sale (POS) terminals or ATMs to generate a nonce, called the unpredictable number, for each transaction to ensure it is fresh. We have discovered two serious problems: a widespread implementation flaw and a deeper, more difficult to fix flaw with the EMV protocol itself. The first flaw is that some EMV implementers have merely used counters, timestamps or home-grown algorithms to supply this nonce. This exposes them to a "pre-play" attack which is indistinguishable from card cloning from the standpoint of the logs available to the card-issuing bank, and can be carried out even if it is impossible to clone a card physically. Card cloning is the very type of fraud that EMV was supposed to prevent. We describe how we detected the vulnerability, a survey methodology we developed to chart the scope of the weakness, evidence from ATM and terminal experiments in the field, and our implementation of proof-of-concept attacks. We found flaws in widely-used ATMs from the largest manufacturers. We can now explain at least some of the increasing number of frauds in which victims are refused refunds by banks which claim that EMV cards cannot be cloned and that a customer involved in a dispute must therefore be mistaken or complicit. The second problem was exposed by the above work. Independent of the random number quality, there is a protocol failure: the actual random number generated by the terminal can simply be replaced by one the attacker used earlier when capturing an authentication code from the card. This variant of the pre-play attack may be carried out by malware in an ATM or POS terminal, or by a man-in-the-middle between the terminal and the acquirer. We explore the design and implementation mistakes that enabled these flaws to evade detection until now: shortcomings of the EMV specification, of the EMV kernel certification process, of implementation testing, formal analysis, and monitoring customer complaints. Finally we discuss countermeasures. More than a year after our initial responsible disclosure of these flaws to the banks, action has only been taken to mitigate the first of them, while we have seen a likely case of the second in the wild, and the spread of ATM and POS malware is making it ever more of a threat.