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June 2008
March 2008
Cold Boot Attacks on Encryption Keys - Center for information technology policy
by rike_
Contrary to popular assumption, DRAMs used in most modern computers retain their contents for seconds to minutes after power is lost, even at operating temperatures and even if removed from a motherboard. Although DRAMs become less reliable when they are not refreshed, they are not immediately erased, and their contents persist sufficiently for malicious (or forensic) acquisition of usable full-system memory images. We show that this phenomenon limits the ability of an operating system to protect cryptographic key material from an attacker with physical access. We use cold reboots to mount attacks on popular disk encryption systems — BitLocker, FileVault, dm-crypt, and TrueCrypt — using no special devices or materials. We experimentally characterize the extent and predictability of memory remanence and report that remanence times can be increased dramatically with simple techniques. We offer new algorithms for finding cryptographic keys in memory images and for correcting errors caused by bit decay. Though we discuss several strategies for partially mitigating these risks, we know of no simple remedy that would eliminate them.
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February 2008
November 2007
Birthday problem / Birthday paradox
by wabaus
A great description of the concept/math behind the Birthday problem. Basically, if you have 23 people in a room, odds are better than 50-50 that 2 folks will share the same birthday. [With a group of 7, odds are better than 50-50 that two folks have a birthday within a week of each other.]
Also the basis for the "Birthday attack" hacking vector. Given a hashing (1-way encryption) algorithm of fixed length output, multiple inputs can result in the same hash. It is very difficult to guess an alternate input that will hash into a match of a single given result. But given a large known set of results (e.g., a user account database table) it become more likely that an alternate input might result in a match of at least one existing hash.
Thinking on such things keeps the mind sharp :)
