Invertible Universal Hashing and the TET Encryption Mode

This work describes a mode of operation, TET, that turns a regular block cipher into a length-preserving enciphering scheme for messages of (almost) arbitrary length. When using an n-bit block cipher, the resulting scheme can handle input of any bit-length between n and 2 and associated data of arbitrary length. The mode TET is a concrete instantiation of the generic mode of operation that was proposed by Naor and Reingold, extended to handle tweaks and inputs of arbitrary bit length. The main technical tool is a construction of invertible “universal hashing” on wide blocks, which is as efficient to compute and invert as polynomial-evaluation hash.