Tweakable Block Ciphers

We propose a new cryptographic primitive, the “tweakable block cipher.” Such a cipher has not only the usual inputs—message and cryptographic key—but also a third input, the “tweak.” The tweak serves much the same purpose that an initialization vector does for CBC mode or that a nonce does for OCB mode. Our proposal thus brings this feature down to the primitive block-cipher level, instead of incorporating it only at the higher modes-of-operation levels. We suggest that (1) tweakable block ciphers are easy to design, (2) the extra cost of making a block cipher “tweakable” is small, and (3) it is easier to design and prove modes of operation based on tweakable block ciphers.

• Type: Journal
• Year: 2011
• Where: JOC
• Authors: Moses Liskov, Ronald L. Rivest, David Wagner
• Keywords: Block Ciphers, Initialization Vector, JOC 2011, Nonce