Feistel ciphers in East Germany in the communist era

Courtois, Nicolas T.; Drobick, Jörg; Schmeh, Klaus

doi:10.1080/01611194.2018.1428835

Cited by 14 publications

(23 citation statements)

References 5 publications

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“…Some polynomial invariant attacks work for a fraction of keys, other for all possible keys. According to [17,18,26], using longer keys in each round could be a good reason, why many ciphers are likely to be secure against non-linear attacks. However even when many key bits are used in each round, cf.…”

Section: Limitations and Vulnerabilitymentioning

confidence: 99%

“…exactly those where Z j () = 0, are called "transformable" polynomials 25 . Other polynomials Z i are non-zero 26 and they use the same set of input-side variables as Q i . Moreover we assume that for every Z j () this Boolean function is annihilated by product of (up to) all "transformable" polynomials Q k , or more precisely that:…”

Section: Our General Framework Theorem and Constructionmentioning

confidence: 99%

“…DES is one of the most widely used cryptographic algorithms of all times and there exists numerous modified versions of DES [26,33,34]. There are strong connections between various Feistel ciphers used in government communications during the Cold War cf.…”

Section: On Existence Of Polynomial Invariants In Desmentioning

confidence: 99%

“…There are strong connections between various Feistel ciphers used in government communications during the Cold War cf. [10,26]. In Eastern Germany DES was implemented inside a portable electronic cipher machine T-316 [26].…”

Section: On Existence Of Polynomial Invariants In Desmentioning

confidence: 99%

“…[10,26]. In Eastern Germany DES was implemented inside a portable electronic cipher machine T-316 [26]. Our methodology and notations emphasise similarities between different ciphers, and we do not believe that a cipher must necessarily be special or weak, in order to exhibit a large variety of polynomial invariants.…”

Section: On Existence Of Polynomial Invariants In Desmentioning

confidence: 99%

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Systematic Construction of Nonlinear Product Attacks on Block Ciphers

Courtois

Abbondati²,

Ratoanina

et al. 2020

Lecture Notes in Computer Science

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A major open problem in block cipher cryptanalysis is discovery of new invariant properties of complex type. Recent papers show that this can be achieved for SCREAM, Midori64, MANTIS-4, T-310 or for DES with modified S-boxes. Until now such attacks are hard to find and seem to happen by some sort of incredible coincidence. In this paper we abstract the attack from any particular block cipher. We study these attacks in terms of transformations on multivariate polynomials. We shall demonstrate how numerous variables including key variables may sometimes be eliminated and at the end two very complex Boolean polynomials will become equal. We present a general construction of an attack where multiply all the polynomials lying on one or several cycles. Then under suitable conditions the non-linear functions involved will be eliminated totally. We obtain a periodic invariant property holding for any number of rounds. A major difficulty with invariant attacks is that they typically work only for some keys. In T-310 our attack works for any key and also in spite of the presence of round constants.

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Section: Limitations and Vulnerabilitymentioning

confidence: 99%

Section: Our General Framework Theorem and Constructionmentioning

confidence: 99%

Section: On Existence Of Polynomial Invariants In Desmentioning

confidence: 99%

Section: On Existence Of Polynomial Invariants In Desmentioning

confidence: 99%

Section: On Existence Of Polynomial Invariants In Desmentioning

confidence: 99%

See 3 more Smart Citations

Systematic Construction of Nonlinear Product Attacks on Block Ciphers

Courtois

Abbondati²,

Ratoanina

et al. 2020

Lecture Notes in Computer Science

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show abstract

Feistel Networks

Easttom¹

2020

Modern Cryptography

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Can a Differential Attack Work for an Arbitrarily Large Number of Rounds?

Courtois

Quisquater

2021

Information Security and Cryptology – ICISC 2020

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Differential cryptanalysis is one of the oldest attacks on block ciphers. Can anything new be discovered on this topic? A related question is that of backdoors and hidden properties. There is substantial amount of research on how Boolean functions affect the security of ciphers, and comparatively, little research, on how block cipher wiring can be very special or abnormal. In this article we show a strong type of anomaly: where the complexity of a differential attack does not grow exponentially as the number of rounds increases. It will grow initially, and later will be lower bounded by a constant. At the end of the day the vulnerability is an ordinary single differential attack on the full state. It occurs due to the existence of a hidden polynomial invariant. We conjecture that this type of anomaly is not easily detectable if the attacker has limited resources.

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Feistel ciphers in East Germany in the communist era

Cited by 14 publications

References 5 publications

Systematic Construction of Nonlinear Product Attacks on Block Ciphers

Systematic Construction of Nonlinear Product Attacks on Block Ciphers

Feistel Networks

Can a Differential Attack Work for an Arbitrarily Large Number of Rounds?

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