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The system we propose offers substantial benefits for both producers and consumers of RSS data. The chief incentive for content providers is the lower cost associ- ated with publishing micronews: large Web sites with many readers may offer large volumes of timely content to FeedTree clients without fear of saturating their net- work links, and a smaller Web site need not fear sudden popularity when publishing a FeedTree feed. FeedTree also offers publishers an opportunity to provide differen- tiated RSS services, perhaps by publishing simple (low- bandwidth) headlines in a conventional RSS feed, while delivering full HTML stories in FeedTree. End users will receive even better news service with FeedTree than is currently. | Security Analysis of a Cryptographically-Enabled RFID Device Stephen C. Bono Matthew Green Aviel D. Rubin Adam Stubblefield Michael Szydlo Ari Juels Abstract We describe our success in defeating the security of an RFID device known as a Digital Signature Transponder DST . Manufactured by Texas Instruments DST and variant devices help secure millions of SpeedPass payment transponders and automobile ignition keys. Our analysis of the DST involved three phases 1. Reverse engineering Starting from a rough published schematic we determined the complete functional details of the cipher underpinning the challenge-response protocol in the DST. We accomplished this with only oracle or black-box access to an ordinary DST that is by experimental observation of responses output by the device. 2. Key cracking The key length for the DST is only 40 bits. With an array of of sixteen FPGAs operating in parallel we can recover a DST key in under an hour using two responses to arbitrary challenges. 3. Simulation Given the key and serial number of a DST we are able to simulate its RF output so as to spoof a reader. As validation of our results we purchased gasoline at a service station and started an automobile using simulated DST devices. We accomplished all of these steps using inexpensive off-the-shelf equipment and with minimal RF expertise. This suggests that an attacker with modest resources can emulate a target DST after brief short-range scanning or long-range eavesdropping across several authentication sessions. We conclude that the cryptographic protection afforded by the DST device is relatively weak. Key words Digital Signature Transponder DST immobilizer Hellman time-space tradeoff RFID Department of Computer Science The Johns Hopkins University 3400 N. Charles Street Baltimore MD 21218 USA. Email sbono mgreen astubble rubin @cs.jhu.edu. tRSA Laboratories 174 Middlesex Turnpike MA 01739 USA. Email ajuels mszydlo @rsasecurity.com. 1 Introduction Radio-Frequency .