Abstract. We propose a new approach to commutative watermarkingencryption (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.
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. Based on our results we believe that currently CAPTCHAs are incapable of offering adequate security for high-value applications like e-banking.
Abstract-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.
Abstract. In this paper, we propose hPIN/hTAN, a low-cost hardware token based PIN/TAN system for protecting e-banking systems against the strong threat model where the adversary has full control over the user's computer. This threat model covers various kinds of attacks related to untrusted terminal computers, such as keyloggers, screen scrapers, session hijackers, Trojan horses and transaction generators. The core of hPIN/hTAN is a secure and easy user-computer-token interface. The security is guaranteed by the user-computer-token interface and two underlying security protocols for user/server/transaction authentication. The hPIN/hTAN system is designed as an open framework so that the underlying authentication protocols can be easily reconfigured. To minimize the costs and maximize usability, we chose two security protocols dependent on simple cryptography (a cryptographic hash function). In contrast to other hardware-based solutions, hPIN/hTAN depends on neither a second trusted channel nor a secure keypad nor external trusted center. Our prototype implementation does not involve cryptography beyond a cryptographic hash function. The minimalistic design can also help increase security because more complicated systems tend to have more security holes. As an important feature, hPIN/hTAN exploits human users' active involvement in the whole process to compensate security weaknesses caused by careless human behavior.
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