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See detailMeet-in-the-Middle Attacks and Structural Analysis of Round-Reduced PRINCE
Derbez, Patrick UL; Perrin, Léo Paul UL

in Leander, Gregor (Ed.) Fast Software Encryption - 22nd International Workshop, FSE 2015, Istanbul, March 8-11, 2015 (2015, March)

NXP Semiconductors and its academic partners challenged the cryptographic community with finding practical attacks on the block cipher they designed, PRINCE. Instead of trying to attack as many rounds as ... [more ▼]

NXP Semiconductors and its academic partners challenged the cryptographic community with finding practical attacks on the block cipher they designed, PRINCE. Instead of trying to attack as many rounds as possible using attacks which are usually impractical despite being faster than brute-force, the challenge invites cryptographers to find practical attacks and encourages them to actually implement them. In this paper, we present new attacks on round-reduced PRINCE including the ones which won the challenge in the 6 and 8-round categories --- the highest for which winners were identified. Our first attacks rely on a meet-in-the-middle approach and break up to 10 rounds of the cipher. We also describe heuristic methods we used to find practical SAT-based and differential attacks. Finally, we also present an analysis of the cycle structure of the internal rounds of PRINCE leading both to a low complexity distinguisher for 4-round PRINCE-core and an alternative representation of the cipher valid in particular contexts and which highlights, in this cases, a poor diffusion. [less ▲]

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See detailDifferential Analysis and Meet-in-the-Middle Attack against Round-Reduced TWINE
Biryukov, Alex UL; Derbez, Patrick UL; Perrin, Léo Paul UL

in Leander, Gregor (Ed.) Fast Software Encryption - 22nd International Workshop, FSE 2015, Istanbul, March 8-11, 2015 (2015, March)

TWINE is a recent lightweight block cipher based on a Feistel structure. We first present two new attacks on TWINE-128 reduced to 25 rounds that have a slightly higher overall complexity than the 25-round ... [more ▼]

TWINE is a recent lightweight block cipher based on a Feistel structure. We first present two new attacks on TWINE-128 reduced to 25 rounds that have a slightly higher overall complexity than the 25-round attack presented by Wang and Wu at ACISP 2014, but a lower data complexity. Then, we introduce alternative representations of both the round function of this block cipher and of a sequence of 4 rounds. LBlock, another lightweight block cipher, turns out to exhibit the same behaviour. Then, we illustrate how this alternative representation can shed new light on the security of TWINE by deriving high probability iterated truncated differential trails covering 4 rounds with probability $2^{-16}$. The importance of these is shown by combining different truncated differential trails to attack 23-rounds TWINE-128 and by giving a tighter lower bound on the high probability of some differentials by clustering differential characteristics following one of these truncated trails. A comparison between these high probability differentials and those recently found in a variant of LBlock by Leurent highlights the importance of considering the whole distribution of the coefficients in the difference distribution table of a S-Box and not only their maximum value. [less ▲]

Detailed reference viewed: 214 (12 UL)