Roland Schmitz

Use of chaotic dynamical systems in cryptography

Abstract In this paper, some of the mathematical properties relevant to the use of chaotic dynamical systems in cryptography are identified and reviewed. We evaluate these properties for some of the systems proposed in the literature and explain the consequences for the level of security offered by these systems. As a conclusion, it is proposed to use only those systems that are accessible to a mathematical analysis of their chaotic properties, and some open research questions are identified.

Breaking e-banking CAPTCHAs

Many financial institutions have deployed CAPTCHAs to protect their services (e.g., e-banking) from automated attacks. In addition to CAPTCHAs for login, CAPTCHAs are also used to prevent malicious manipulation of e-banking transactions by automated Man-in-the-Middle (MitM) attackers. Despite serious financial risks, security of e-banking CAPTCHAs is largely unexplored. In this paper, we report the first comprehensive study on e-banking CAPTCHAs deployed around the world. A new set of image processing and pattern recognition techniques is proposed to break all e-banking CAPTCHA schemes that we found over the Internet, including three e-banking CAPTCHA schemes for transaction verification and 41 schemes for login. These broken e-banking CAPTCHA schemes are used by thousands of financial institutions worldwide, which are serving hundreds of millions of e-banking customers. The success rate of our proposed attacks are either equal to or close to 100%. We also discuss possible improvements to these e-banking CAPTCHA schemes and show essential difficulties of designing e-banking CAPTCHAs that are both secure and usable.

On the Security of PAS (Predicate-Based Authentication Service)

Recently a new human authentication scheme called PAS (predicate-based authentication service) was proposed, which does not require the assistance of any supplementary device. The main security claim of PAS is to resist passive adversaries who can observe the whole authentication session between the human user and the remote server. In this paper we show that PAS is insecure against both brute force attack and a probabilistic attack. In particular, we show that its security against brute force attack was strongly overestimated. Furthermore, we introduce a probabilistic attack, which can break part of the password even with a very small number of observed authentication sessions. Although the proposed attack cannot completely break the password, it can downgrade the PAS system to a much weaker system similar to common OTP (one-time password) systems.

A new approach to commutative watermarking-encryption

We propose a new approach to commutative watermarking-encryption (CWE). A permutation cipher is used to encrypt the multimedia data, which leaves the global statistics of the multimedia data intact. Therefore, any non-localized watermarking scheme that depends only on global statistics of the multimedia data can be combined with the permutation cipher to form a CWE scheme. We demonstrate this approach by giving a concrete implementation, which manipulates the global histogram to achieve watermark embedding/detection.

Breaking Randomized Linear Generation Functions Based Virtual Password System

In ICC2008 and subsequent work, Lei et al. proposed a user authentication system (virtual password system), which is claimed to be secure against identity theft attacks, including phishing, keylogging and shoulder surfing. Their authentication system is a challenge-response protocol based on a randomized linear generation function, which uses a random integer in the responses of each login session to offer security against assorted attacks. In this paper we show that their virtual password system is insecure and vulnerable to multiple attacks. We show that with high probability an attacker can recover an equivalent password with only two (or a few more) observed login sessions. We also give a brief survey of the related work and discuss the main challenges in designing user authentication methods secure against identity theft.

Towards More Robust Commutative Watermarking-Encryption of Images

Histogram-based watermarking schemes are invariant against pixel permutations and can be combined with permutation-based ciphers. However, typical histogram-based watermarking schemes based on comparison of histogram bins are prone to de-synchronization attacks, where the whole histogram is shifted by a certain amount. In this paper we investigate the possibility of avoiding this kind of attacks by synchronizing the embedding and detection processes, using the mean of the histogram as a calibration point. The resulting watermarking scheme is resistant to three common types of shifts of the histogram, while the advantages of previous histogram-based schemes, especially commutativity of watermarking and permutation-based encryption, are preserved.

Mobile Security for Internet Applications

The WebSIM is a technology for interfacing GSM SIMs with the Internet, by implementing a Web server inside a SIM. This paper discusses how this technology can be used for securing services over the Internet and describes several concrete application scenarios.

Security for the core network of third generation mobile systems

This contribution gives a survey of the present standardisation activities by 3GPP (3rd Generation Partnership Project1) in the area of security for signalling in the core network of third generation mobile systems. We give an overview of the protocols that need to be secured, present the basic principles behind the overall security architecture and describe the key management and format of secured messages, as far as they have already been finalised. In particular, we address core network security aspects of the 3GPP multimedia domain.

Towards Robust Invariant Commutative Watermarking-Encryption Based on Image Histograms

Invariant Commutative Watermarking-Encryption means to use a cipher that does not have any impact on a certain feature space, which can thus be used for embedding watermarks either before or after encryption. For example, histogram-based watermarking schemes are invariant to pixel permutations and can be combined with permutation-based ciphers to form a Commutative Watermarking-Encryption (CWE) scheme. However, typical histogram-based watermarking schemes based on comparison of histogram bins are prone to de-synchronization attacks, where the whole histogram is shifted by a certain amount. In this paper the authors investigate the possibility to avoid this kind of attacks by synchronizing the embedding and detection processes, using the mean of the histogram as a calibration point. The resulting watermarking scheme is resistant to three common types of shifts of the histogram, while the advantages of previous histogram-based schemes, especially commutativity of watermarking and permutation-based encryption, are preserved. The authors also report on the results of testing robustness of the scheme against JPEG and JPEG2000 compression.

On the Security of the UMTS System

This contribution presents an overview of the security of the 3rd generation mobile radio system UMTS as currently standardised by the 3rd Generation Partnership Project 3GPP. We discuss the underlying principles and show to which extent the security of 2nd generation systems as GSM is improved and enhanced by UMTS. The UMTS Authentication and Key Agreement protocol, the security algorithms deployed for UMTS and the interworking mechanisms between 2nd and 3rd generation systems are described in detail.