# Oddly Shaped Pegs

An inquiry into the Nature and Causes of Stuff

## FOCS ’09 crypto accepts

The FOCS 2009 accepted papers are posted, with abstracts. See the chair’s comments here, and other topic-specific discussions here, here and here. Despite some excellent submissions not making it in, there are still some (few!) crypto papers, all of which look interesting. In no particular order:

• Steven Myers and abhi shelat. One bit encryption is complete
• Yi Deng, Vipul Goyal and Amit Sahai. Resolving the Simultaneous Resettability Conjecture and a New Non-Black-Box Simulation Strategy
• Yuval Ishai, Eyal Kushilevitz, Rafail Ostrovsky and Amit Sahai. Extracting Correlations
• Yael Tauman Kalai, Xin Li and Anup Rao. 2-Source Extractors Under Computational Assumptions and Cryptography with Defective Randomness

Quantum crypto papers:

Not exactly crypto, but highly relevant:

• Iftach Haitner. A Parallel Repetition Theorem for Any Interactive Argument
• Falk Unger. A Probabilistic Inequality with Applications to Threshold Direct Product Theorems

Scanning over the FOCS abstracts is hard because of information overload. I will try to read all of the papers on the list above (maybe I’ll even attend the conference) but for now two stand out because they resolve problems I have thought about:

First, Steve and abhi’s surprising paper (not yet available online), which gives a black-box construction of many-bit CCA-secure encryption from 1-bit CCA-secure encryption. This question is tied to very basic notions of authenticity and secrecy in cryptography. For CPA-secure encryption (that is, encryption secure against passive attacks), increasing the message length is straightforward: Goldwasser and Micali showed that encrypting each bit separately works (a classic example of a “hybrid” argument). However, for schemes that must resist active attacks, such as chosen-ciphertext attacks (CCA), bit-by-bit encryption fails miserably. Prior to this paper, there existed (limited) impossibility results, but no evidence that a black-box construction was possible.

Second, André and Iordanis’ paper on optimal strong quantum coin flipping. Information-theoretically secure quantum coin flipping was proved to be impossible in the late 90’s by Mayers and Lo and Chau, using the same techniques that rule out information-theoretically secure oblivious transfer and bit commitment. That result only rules out protocols that produce a very good biased coin (with bias 1/2+o(1)). However, protocols were constantly being proposed (and occasionally broken) which  produced weakly biased coins. This new paper gives a protocol matching Kitaev’s lower bound of $1/\sqrt{2}\approx 0.707$ on the minimal bias. This is not of critical importance in practice, but it does elucidate one of the key phenomena which distinguish quantum from classical cryptographic protocols.