## Cryptology ePrint Archive: Report 2016/514

Cryptography with Auxiliary Input and Trapdoor from Constant-Noise LPN

Yu Yu and Jiang Zhang

Abstract: Dodis, Kalai and Lovett (STOC 2009) initiated the study of the Learning Parity with Noise (LPN) problem with (static) exponentially hard-to-invert auxiliary input. In particular, they showed that under a new assumption (called Learning Subspace with Noise) the above is quasi-polynomially hard in the high (polynomially close to uniform) noise regime.

Inspired by the sampling from subspace'' technique by Yu (eprint 2009 / 467) and Goldwasser et al. (ITCS 2010), we show that standard LPN can work in a mode (reducible to itself) where the constant-noise LPN (by sampling its matrix from a random subspace) is robust against sub-exponentially hard-to-invert auxiliary input with comparable security to the underlying LPN. Plugging this into the framework of [DKL09], we obtain the same applications as considered in [DKL09] (i.e., CPA/CCA secure symmetric encryption schemes, average-case obfuscators, reusable and robust extractors) with resilience to a more general class of leakages, improved efficiency and better security under standard assumptions.

As a main contribution, under constant-noise LPN with certain sub-exponential hardness (i.e., $2^{\omega(n^{1/2})}$ for secret size $n$) we obtain a variant of the LPN with security on poly-logarithmic entropy sources, which in turn implies CPA/CCA secure public-key encryption (PKE) schemes and oblivious transfer (OT) protocols. Prior to this, basing PKE and OT on constant-noise LPN had been an open problem since Alekhnovich's work (FOCS 2003).

Category / Keywords: foundations / Cryptography with Auxiliary Input, Learning Parity with Noise, Post-quantum Cryptography, Public-Key Encryption

Original Publication (with minor differences): IACR-CRYPTO-2016

Date: received 25 May 2016, last revised 29 May 2016

Contact author: yuyuathk at gmail com

Available format(s): PDF | BibTeX Citation

Short URL: ia.cr/2016/514

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