Elastic block ciphers

2009

Int. J. Inf. Secur.

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We introduce the concept of an elastic block cipher, which refers to stretching the supported block size of a block cipher to any length up to twice the original block size while incurring a computational workload that is proportional to the block size. Our method uses the round function of an existing block cipher as a black box and inserts it into a substitution-permutation network. Our method is designed to enable us to form a reduction between the elastic and the original versions of the cipher. Using this reduction, we prove that the elastic version of a cipher is secure against key-recovery attacks if the original cipher is secure against such attacks. We note that while reductionbased proofs of security are a cornerstone of cryptographic analysis, they are typical when complete components are used as sub-components in a larger design. We are not aware of use of such techniques in the case of concrete block cipher designs. We demonstrate the general applicability of the elastic block cipher method by constructing examples from existing block ciphers: AES, Camellia, MISTY1 and RC6. We compare the performance of the elastic versions to that of the original versions and evaluate the elastic versions using statistical tests measuring the randomness of the ciphertext. We also use our examples to demonstrate the concept of a generic key schedule for block ciphers. key words: elastic block ciphers, variable-length block ciphers, security analysis, reduction proof, key recovery attacks.

“…For the elastic versions of the ciphers, the percentage of samples passing each test was consistent across all block sizes and data sets. The detailed test results are available in [10].…”

Section: Randonmess Test Resultsmentioning

confidence: 99%

“…This work is an extended version of our previous work on elastic block ciphers, including a more detailed explanation for the selection of the basic structure utilized when creating elastic block ciphers, extended proofs of claims and extended descriptions of instantiations of the method from [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Elastic block ciphers: method, security and instantiations

2009

Int. J. Inf. Secur.

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“…We briefly review our method for creating elastic block ciphers [5]. The method converts the encryption and decryption functions of any existing block cipher to accept blocks of size b to 2b bits, where b is the block size of the original block cipher.…”

Section: Overviewmentioning

confidence: 99%

“…Elastic block ciphers are variable-length block ciphers created from existing block ciphers [5]. The elastic version of a block cipher supports any block size between one and two times that of the original block length, and results in a computational workload for encryption that is proportional to the actual block size.…”

Section: Introductionmentioning

confidence: 99%

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The Security of Elastic Block Ciphers Against Key-Recovery Attacks

Lecture Notes in Computer Science

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Abstract.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-permutation network. In this paper, we form a polynomial-time reduction between the elastic and original versions of the cipher by exploiting the underlying network structure. We prove that the elastic version of a cipher is secure against a given key-recovery attack if the original cipher is secure against such an attack. Our analysis is based on the general structure of elastic block ciphers (i.e., the network's structure, the composition methods between rounds in the network and the keying methodology) and is independent of the specific cipher.keywords: variable-length block ciphers, security analysis, reduction proof, key recovery attacks.

Elastic Block Ciphers in Practice: Constructions and Modes of Encryption

Proceedings of the 3rd European Conference on Computer Network Defense

2009

Self Cite

We demonstrate the general applicability of the elastic block cipher method by constructing examples from existing block ciphers: AES, Camellia, MISTY1 and RC6. An elastic block cipher is a variable-length block cipher created from an existing fixed-length block cipher. The elastic version supports any block size between one and two times that of the original block size. We compare the performance of the elastic versions to that of the original versions and evaluate the elastic versions using statistical tests measuring the randomness of the ciphertext. The benefit, in terms of an increased rate of encryption, of using an elastic block cipher varies based on the specific block cipher and implementation. In most cases, there is an advantage to using an elastic block cipher to encrypt blocks that are a few bytes longer than the original block length. The statistical test results indicate no obvious flaws in the method for constructing elastic block ciphers. We also use our examples to demonstrate the concept of a generic key schedule for block ciphers. In addition, we present ideas for new modes of encryption using the elastic block cipher construction.