[Resource Topic] 2012/158: Efficient and Optimally Secure Key-Length Extension for Block Ciphers via Randomized Cascading

Welcome to the resource topic for 2012/158

Title:
Efficient and Optimally Secure Key-Length Extension for Block Ciphers via Randomized Cascading

Authors: Peter Gazi, Stefano Tessaro

Abstract:

We consider the question of efficiently extending the key length of block ciphers. To date, the approach providing highest security is triple encryption (used e.g. in Triple-DES), which was proved to have roughly k + min{n/2, k/2} bits of security when instantiated with ideal block ciphers with key length k and block length n, at the cost of three block-cipher calls per message block. This paper presents a new practical key-length extension scheme exhibiting k + n/2 bits of security – hence improving upon the security of triple encryption – solely at the cost of two block cipher calls and a key of length k + n. We also provide matching generic attacks showing the optimality of the security level achieved by our approach with respect to a general class of two-query constructions.

ePrint: https://eprint.iacr.org/2012/158

Talk: https://www.youtube.com/watch?v=xGY3vszsZTU

Slides: https://iacr.org/cryptodb/archive/2012/EUROCRYPT/presentation/24279.pdf

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