## Cryptology ePrint Archive: Report 2014/394

**Relational Hash**

*Avradip Mandal and Arnab Roy*

**Abstract: **Traditional cryptographic hash functions allow one to easily check whether the original plain-texts are equal or not, given a pair of hash values. Probabilistic hash functions extend this concept where given a probabilistic hash of a value and the value itself, one can efficiently check whether the hash corresponds to the given value. However, given distinct probabilistic hashes of the same value it is not possible to check whether they correspond to the same value. In this work we introduce a new cryptographic primitive called \emph{relational hash} using which, given a pair of (relational) hash values, one can determine whether the original plain-texts were related or not. We formalize various natural security notions for the relational hash primitive - one-wayness, unforgeability and oracle simulatibility.

We develop a relational hash scheme for discovering linear relations among bit-vectors (elements of $\FF_2^n$) and $\FF_p$-vectors. Using these linear relational hash schemes we develop relational hashes for detecting proximity in terms of hamming distance. These proximity relational hashing scheme can be adapted to a privacy preserving biometric authentication scheme.

We also introduce the notion of \emph{relational encryption}, which is a regular semantically secure public key encryption for any adversary which only has access to the public key. However, a semi-trusted entity can be given a relational key using which it can discover relations among ciphertexts, but still cannot decrypt and recover the plaintexts.

**Category / Keywords: **public-key cryptography / Probabilistic Hash Functions, Biometric Authentication, Functional Encryption

**Date: **received 29 May 2014

**Contact author: **arnabr at gmail com

**Available format(s): **PDF | BibTeX Citation

**Version: **20140530:123641 (All versions of this report)

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