**Chinese Remaindering with Errors **

*Oded Goldreich, Dana Ron and Madhu Sudan *

**Abstract: **The Chinese Remainder Theorem states that a positive integer m is
uniquely specified by its remainder modulo k relatively prime integers
p_1,...,p_k, provided m < \prod_{i=1}^k p_i. Thus the residues of m
modulo relatively prime integers p_1 < p_2 < ... < p_n form a
redundant representation of m if m <= \prod_{i=1}^k p_i and k <
n. This suggests a number-theoretic construction of an
``error-correcting code'' that has been implicitly considered often in
the past. In this paper we provide a new algorithmic tool to go with
this error-correcting code: namely, a polynomial-time algorithm for
error-correction. Specifically, given n residues r_1,...,r_n and an
agreement parameter t, we find a list of all integers m <
\prod_{i=1}^k p_i such that (m mod p_i) = r_i for at least t values of
i in {1,...,n}, provided t = Omega(sqrt{kn (log p_n)/(log p_1)}). We
also give a simpler algorithm to decode from a smaller number of
errors, i.e., when t > n - (n-k)(log p_1)/(log p_1 + \log p_n). In
such a case there is a unique integer which has such agreement with
the sequence of residues.

One consequence of our result is that is a strengthening of the relationship between average-case complexity of computing the permanent and its worst-case complexity. Specifically we show that if a polynomial time algorithm is able to guess the permanent of a random n x n matrix on 2n-bit integers modulo a random n-bit prime with inverse polynomial success rate, then #P=BPP. Previous results of this nature typically worked over a fixed prime moduli or assumed very small (though non-negligible) error probability (as opposed to small but non-negligible success probability).

**Category / Keywords: **Algorithms, Error correcting codes, List decoding, Number theory, Lattice reduction.

**Publication Info: **Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive.

**Date: **received Feb 8th, 1999. Also appears as ECCC TR98-062.

**Contact author: **madhu at theory lcs mit edu

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