Ross J. Anderson

Information hiding-a survey

Information-hiding techniques have recently become important in a number of application areas. Digital audio, video, and pictures are increasingly furnished with distinguishing but imperceptible marks, which may contain a hidden copyright notice or serial number or even help to prevent unauthorized copying directly. Military communications systems make increasing use of traffic security techniques which, rather than merely concealing the content of a message using encryption, seek to conceal its sender, its receiver, or its very existence. Similar techniques are used in some mobile phone systems and schemes proposed for digital elections. Criminals try to use whatever traffic security properties are provided intentionally or otherwise in the available communications systems, and police forces try to restrict their use. However, many of the techniques proposed in this young and rapidly evolving field can trace their history back to antiquity, and many of them are surprisingly easy to circumvent. In this article, we try to give an overview of the field, of what we know, what works, what does not, and what are the interesting topics for research.

On the limits of steganography

In this paper, we clarify what steganography is and what it can do. We contrast it with the related disciplines of cryptography and traffic security, present a unified terminology agreed at the first international workshop on the subject, and outline a number of approaches-many of them developed to hide encrypted copyright marks or serial numbers in digital audio or video. We then present a number of attacks, some new, on such information hiding schemes. This leads to a discussion of the formidable obstacles that lie in the way of a general theory of information hiding systems (in the sense that Shannon gave us a general theory of secrecy systems). However, theoretical considerations lead to ideas of practical value, such as the use of parity checks to amplify covertness and provide public key steganography. Finally, we show that public key information hiding systems exist, and are not necessarily constrained to the case where the warden is passive.

Attacks on Copyright Marking Systems

In the last few years, a large number of schemes have been proposed for hiding copyright marks and other information in digital pictures, video, audio and other multimedia objects. We describe some contenders that have appeared in the research literature and in the field; we then present a number of attacks that enable the information hidden by them to be removed or otherwise rendered unusable.

Low Cost Attacks on Tamper Resistant Devices

There has been considerable recent interest in the level of tamper resistance that can be provided by low cost devices such as smart-cards. It is known that such devices can be reverse engineered using chip testing equipment, but a state of the art semiconductor laboratory costs millions of dollars. In this paper, we describe a number of attacks that can be mounted by opponents with much shallower pockets.

Why information security is hard - an economic perspective

According to one common view, information security comes down to technical measures. Given better access control policy models, formal proofs of cryptographic protocols, approved firewalls, better ways of detecting intrusions and malicious code, and better tools for system evaluation and assurance, the problems can be solved. The author puts forward a contrary view: information insecurity is at least as much due to perverse incentives. Many of the problems can be explained more clearly and convincingly using the language of microeconomics: network externalities, asymmetric information, moral hazard, adverse selection, liability dumping and the tragedy of the commons.

Optical Fault Induction Attacks

We describe a new class of attacks on secure microcontrollers and smartcards. Illumination of a target transistor causes it to conduct, thereby inducing a transient fault. Such attacks are practical; they do not even require expensive laser equipment. We have carried them out using a flashgun bought second-hand from a camera store for

Password memorability and security: empirical results

30 and with an

Combining Crypto with Biometrics Effectively

8 laser pointer. As an illustration of the power of this attack, we developed techniques to set or reset any individual bit of SRAM in a microcontroller. Unless suitable countermeasures are taken, optical probing may also be used to induce errors in cryptographic computations or protocols, and to disrupt the processors control flow. It thus provides a powerful extension of existing glitching and fault analysis techniques. This vulnerability may pose a big problem for the industry, similar to those resulting from probing attacks in the mid-1990s and power analysis attacks in the late 1990s.We have therefore developed a technology to block these attacks. We use self-timed dual-rail circuit design techniques whereby a logical 1 or 0 is not encoded by a high or low voltage on a single line, but by (HL) or (LH) on a pair of lines. The combination (HH) signals an alarm, which will typically reset the processor. Circuits can be designed so that single-transistor failures do not lead to security failure. This technology may also make power analysis attacks very much harder too.

Why cryptosystems fail

Users rarely choose passwords that are both hard to guess and easy to remember. To determine how to help users choose good passwords, the authors performed a controlled trial of the effects of giving users different kinds of advice. Some of their results challenge the established wisdom.

A security policy model for clinical information systems

We propose the first practical and secure way to integrate the iris biometric into cryptographic applications. A repeatable binary string, which we call a biometric key, is generated reliably from genuine iris codes. A well-known difficulty has been how to cope with the 10 to 20 percent of error bits within an iris code and derive an error-free key. To solve this problem, we carefully studied the error patterns within iris codes and devised a two-layer error correction technique that combines Hadamard and Reed-Solomon codes. The key is generated from a subjects iris image with the aid of auxiliary error-correction data, which do not reveal the key and can be saved in a tamper-resistant token, such as a smart card. The reproduction of the key depends on two factors: the iris biometric and the token. The attacker has to procure both of them to compromise the key. We evaluated our technique using iris samples from 70 different eyes, with 10 samples from each eye. We found that an error-free key can be reproduced reliably from genuine iris codes with a 99.5 percent success rate. We can generate up to 140 bits of biometric key, more than enough for 128-bit AES. The extraction of a repeatable binary string from biometrics opens new possible applications, where a strong binding is required between a person and cryptographic operations. For example, it is possible to identify individuals without maintaining a central database of biometric templates, to which privacy objections-might be raised