Elastic block ciphers: method, security and instantiations

Elastic Block Ciphers

We introduce the new concept of elastic block ciphers, symmetrickey encryption algorithms that (1) for a variable-size input do not expand the plaintext (i.e., do not require plaintext padding) and (2) adjust their computational load proportionally to the size increase. Contrary to stream ciphers, elastic block ciphers maintain the diffusion property and non-synchronicity of traditional block c...

A General Analysis of the Security of Elastic Block Ciphers

We analyze the security of elastic block ciphers in general to show that an attack on an elastic version of block cipher implies a polynomial time related attack on the fixed-length version of the block cipher. We relate the security of the elastic version of a block cipher to the fixed-length version by forming a reduction between the versions. Our method is independent of the specific block c...

The Security of Elastic Block Ciphers Against Key-Recovery Attacks

We analyze the security of elastic block ciphers against key-recovery attacks. An elastic version of a fixed-length block cipher is a variable-length block cipher that supports any block size in the range of one to two times the length of the original block. Our method for creating an elastic block cipher involves inserting the round function of the original cipher into a substitution-permutati...

Construction of Stream Ciphers from Block Ciphers and their Security

With well-established encryption algorithms like DES or AES at hand, one could have the impression that most of the work for building a cryptosystem -for example a suite of algorithms for the transmission of encrypted data over the internet is already done. But the task of a cipher is very specific: to encrypt or decrypt a data block of a specified length. Given an plaintext of arbitrary length...

Building Stream Ciphers from Block Ciphers and their Security