Cryptology ePrint Archive: Report 2015/1197

On-the-fly Homomorphic Batching/Unbatching

Yarkın Doröz and Berk Sunar and Gizem S. Çetin

Abstract: We introduce a homomorphic batching technique that can be used to pack multiple ciphertext messages into one ciphertext for parallel processing. One is able to use the method to batch or unbatch messages homomorphically to further improve the flexibility of encrypted domain evaluations. In particular, we show various approaches to implement Number Theoretic Transform (NTT) homomorphically in FFT speed. Also, we present the limitations that we encounter in application of these methods. We implement homomorphic batching in various settings and present concrete performance figures. Finally, we present an implementation of a homomorphic NTT method which we process each element in an independent ciphertext. The advantage of this method is we are able to batch independent homomorphic NTT evaluations and achieve better amortized time.

Category / Keywords: applications / Homomorphic encryption, homomorphic batching, homo- morphic number theoretic transform

Date: received 14 Dec 2015

Contact author: ydoroz at wpi edu

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Version: 20151216:042433 (All versions of this report)

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