Computer Security and Cryptography Reading Group
June 2005 List

V. Roth

URL: http://doi.acm.org/10.1145/1030083.1030116

Magnetic stripe cards are in common use for electronic payments and cash withdrawal. Reported incidents document that criminals easily pickpocket cards or skim them by swiping them through additional card readers. Personal identification numbers (PINs) are obtained by shoulder surfing, through the use of mirrors or concealed miniature cameras. Both elements, the PIN and the card, are generally sufficient to give the criminal full access to the victim's account. In this paper, we present alternative PIN entry methods to which we refer as cognitive trapdoor games. These methods make it significantly harder for a criminal to obtain PINs even if he fully observes the entire input and output of a PIN entry procedure. We also introduce the idea of probabilistic cognitive trapdoor games, which offer resilience to shoulder surfing even if the criminal records a PIN entry procedure with a camera. We studied the security as well as the usability of our methods, the results of which we also present in the paper.

URL: http://www.cs.wm.edu/~hnw/paper/usenix05.pdf

As a security mechanism at the network-layer, the IP security protocol (IPsec) has been available for years, but its usage is limited to Virtual Private Networks (VPNs). The end-to-end security services provided by IPsec have not been widely used. To bring the IPsec services into wide usage, a standard IPsec API is a potential solution. However, the realization of a user-friendly IPsec API involves many modifications on the current IPsec and Internet Key Exchange (IKE) implementations. An alternative approach is to configure application-specific IPsec policies, but the current IPsec policy system lacks the knowledge of the context of applications running at upper layers, making it infeasible to configure applicationspecific policies in practice.

In this paper, we propose an application-aware IPsec policy system on the existing IPsec/IKE infrastructure, in which a socket monitor running in the application con- text reports the socket activities to the application policy engine. In turn, the engine translates the application policies into the underlying security policies, and then writes them into the IPsec Security Policy Database (SPD) via the existing IPsec policy management interface. We im- plement a prototype in Linux (Kernel 2.6) and evaluate it in our testbed. The experimental results show that the overhead of policy translation is insignificant, and the overall system performance of the enhanced IPsec is comparable to those of security mechanisms at upper layers. Configured with the application-aware IPsec policies, both secured applications at upper layers and legacy applications can transparently obtain IP security enhancements.

E. Kirda

D. Mutz

G. Vigna

URL: http://www.cs.ucsb.edu/~vigna/pub/ 2005_kruegel_kirda_robertson_mutz_vigna_USENIX05.pdf

Intrusion detection systems that monitor sequences of system calls have recently become more sophisticated in defining legitimate application behavior. In particular, additional information, such as the value of the program counter and the configuration of the program's call stack at each system call, has been used to achieve better characterization of program behavior. While there is common agreement that this additional information complicates the task for the attacker, it is less clear to which extent an intruder is constrained.

In this paper, we present a novel technique to evade the extended detection features of state-of-the-art intrusion detection systems and reduce the task of the intruder to a traditional mimicry attack. Given a legitimate sequence of system calls, our technique allows the attacker to execute each system call in the correct execution context by obtaining and relinquishing the control of the application's execution flow through manipulation of code pointers.

We have developed a static analysis tool for Intel x86 binaries that uses symbolic execution to automatically identify instructions that can be used to redirect control flow and to compute the necessary modifications to the environment of the process. We used our tool to successfully exploit three vulnerable programs and evade detection by existing state-of-the-art system call monitors. In addition, we analyzed three real-world applications to verify the general applicability of our techniques.

C. Jackson

J. C. Mitchell

URL: http://crypto.stanford.edu/PwdHash/pwdhash.pdf

We describe a simple browser extension, PwdHash, that transparently produces a different password for each site, improving web password security and defending against password phishing and other attacks. Since the browser extension applies a cryptographic hash function to a combination of the plaintext password entered by the user, data associated with the web site, and (optionally) a private salt stored on the client machine, theft of the password received at one site will not yield a password that is useful at another site. While the scheme requires no changes on the server side, implementing this password method securely and transparently in a web browser extension turns out to be quite difficult. We describe the challenges we faced in implementing PwdHash and some techniques that may be useful to anyone facing similar security issues in a browser environment.

J. Franklin

M. Vernon

Internet sensor networks, including honeypots and log analysis centers such as the SANS Internet Storm Center, are used as a tool to detect malicious Internet traffic. For maximum effectiveness, such networks publish public reports without disclosing sensor locations, so that the Internet community can take steps to counteract the malicious traffic. Maintaining sensor anonymity is critical because if the set of sensors is known, a malicious attacker could avoid the sensors entirely or could overwhelm the sensors with errant data.

Motivated by the growing use of Internet sensors as a tool to monitor Internet traffic, we show that networks that publicly report statistics are vulnerable to intelligent probing to determine the location of sensors. In particular, we develop a new .probe response. attack technique with a number of optimizations for locating the sensors in currently deployed Internet sensor networks and illustrate the technique for a specific case study that shows how the attack would locate the sensors of the SANS Internet Storm Center using the published data from those sensors. Simulation results show that the attack can determine the identity of the sensors in this and other sensor networks in less than a week, even under a limited adversarial model. We detail critical vulnerabilities in several current anonymization schemes and demonstrate that we can quickly and efficiently discover the sensors even in the presence of sophisticated anonymity preserving methods such as prefix-preserving permutations or Bloom filters. Finally, we consider the characteristics of an Internet sensor which make it vulnerable to probe response attacks and discuss potential countermeasures.