[Resource Topic] 2009/356: A Domain Extender for the Ideal Cipher

Welcome to the resource topic for 2009/356

Title:
A Domain Extender for the Ideal Cipher

Authors: Jean-Sebastien Coron, Yevgeniy Dodis, Avradip Mandal, Yannick Seurin

Abstract:

We describe the first domain extender for ideal ciphers, {\sl i.e.} we show a construction that is indifferentiable from a 2n-bit ideal cipher, given a n-bit ideal cipher. Our construction is based on a 3-round Feistel, and is more efficient than first building a n-bit random oracle from a n-bit ideal cipher and then a 2n-bit ideal cipher from a n-bit random oracle (using a 6-round Feistel). We also show that 2 rounds are not enough for indifferentiability by exhibiting a simple attack. We also consider our construction in the standard model: we show that 2 rounds are enough to get a 2n-bit tweakable block-cipher from a n-bit tweakable block-cipher and we show that with 3 rounds we can get beyond the birthday security bound.

ePrint: https://eprint.iacr.org/2009/356

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