## CryptoDB

### Willi Meier

#### Publications

Year
Venue
Title
2019
TOSC
The conditional cube attack on round-reduced Keccak keyed modes was proposed by Huang et al. at EUROCRYPT 2017. In their attack, a conditional cube variable was introduced, whose diffusion was significantly reduced by certain key bit conditions. The attack requires a set of cube variables which are not multiplied in the first round while the conditional cube variable is not multiplied with other cube variables (called ordinary cube variables) in the first two rounds. This has an impact on the degree of the output of Keccak and hence gives a distinguisher. Later, the MILP method was applied to find ordinary cube variables. However, for some Keccak based versions with few degrees of freedom, one could not find enough ordinary cube variables, which weakens or even invalidates the conditional cube attack.In this paper, a new conditional cube attack on Keccak is proposed. We remove the limitation that no cube variables multiply with each other in the first round. As a result, some quadratic terms may appear in the first round. We make use of some new bit conditions to prevent the quadratic terms from multiplying with other cube variables in the second round, so that there will be no cubic terms in the first two rounds. Furthermore, we introduce the kernel quadratic term and construct a 6-2-2 pattern to reduce the diffusion of quadratic terms significantly, where the Θ operation even in the second round becomes an identity transformation (CP-kernel property) for the kernel quadratic term. Previous conditional cube attacks on Keccak only explored the CP-kernel property of Θ operation in the first round. Therefore, more degrees of freedom are available for ordinary cube variables and fewer bit conditions are used to remove the cubic terms in the second round, which plays a key role in the conditional cube attack on versions with very few degrees of freedom. We also use the MILP method in the search of cube variables and give key-recovery attacks on round-reduced Keccak keyed modes.As a result, we reduce the time complexity of key-recovery attacks on 7-round Keccak-MAC-512 and 7-round Ketje Sr v2 from 2111, 299 to 272, 277, respectively. Additionally, we have reduced the time complexity of attacks on 9-round KMAC256 and 7-round Ketje Sr v1. Besides, practical attacks on 6-round Ketje Sr v1 and v2 are also given in this paper for the first time.
2018
EUROCRYPT
2018
CRYPTO
A fast correlation attack (FCA) is a well-known cryptanalysis technique for LFSR-based stream ciphers. The correlation between the initial state of an LFSR and corresponding key stream is exploited, and the goal is to recover the initial state of the LFSR. In this paper, we revisit the FCA from a new point of view based on a finite field, and it brings a new property for the FCA when there are multiple linear approximations. Moreover, we propose a novel algorithm based on the new property, which enables us to reduce both time and data complexities. We finally apply this technique to the Grain family, which is a well-analyzed class of stream ciphers. There are three stream ciphers, Grain-128a, Grain-128, and Grain-v1 in the Grain family, and Grain-v1 is in the eSTREAM portfolio and Grain-128a is standardized by ISO/IEC. As a result, we break them all, and especially for Grain-128a, the cryptanalysis on its full version is reported for the first time.
2018
CRYPTO
In this paper, we propose a key-recovery attack on Trivium reduced to 855 rounds. As the output is a complex Boolean polynomial over secret key and IV bits and it is hard to find the solution of the secret keys, we propose a novel nullification technique of the Boolean polynomial to reduce the output Boolean polynomial of 855-round Trivium. Then we determine the degree upper bound of the reduced nonlinear boolean polynomial and detect the right keys. These techniques can be applicable to most stream ciphers based on nonlinear feedback shift registers (NFSR). Our attack on 855-round Trivium costs time complexity $2^{77}$. As far as we know, this is the best key-recovery attack on round-reduced Trivium. To verify our attack, we also give some experimental data on 721-round reduced Trivium.
2018
CRYPTO
The cube attack is an important technique for the cryptanalysis of symmetric key primitives, especially for stream ciphers. Aiming at recovering some secret key bits, the adversary reconstructs a superpoly with the secret key bits involved, by summing over a set of the plaintexts/IV which is called a cube. Traditional cube attack only exploits linear/quadratic superpolies. Moreover, for a long time after its proposal, the size of the cubes has been largely confined to an experimental range, e.g., typically 40. These limits were first overcome by the division property based cube attacks proposed by Todo et al. at CRYPTO 2017. Based on MILP modelled division property, for a cube (index set) I, they identify the small (index) subset J of the secret key bits involved in the resultant superpoly. During the precomputation phase which dominates the complexity of the cube attacks, $2^{|I|+|J|}$2|I|+|J| encryptions are required to recover the superpoly. Therefore, their attacks can only be available when the restriction $|I|+|J|<n$|I|+|J|<n is met.In this paper, we introduced several techniques to improve the division property based cube attacks by exploiting various algebraic properties of the superpoly. 1.We propose the “flag” technique to enhance the preciseness of MILP models so that the proper non-cube IV assignments can be identified to obtain a non-constant superpoly.2.A degree evaluation algorithm is presented to upper bound the degree of the superpoly. With the knowledge of its degree, the superpoly can be recovered without constructing its whole truth table. This enables us to explore larger cubes I’s even if $|I|+|J|\ge n$|I|+|J|≥n.3.We provide a term enumeration algorithm for finding the monomials of the superpoly, so that the complexity of many attacks can be further reduced. As an illustration, we apply our techniques to attack the initialization of several ciphers. To be specific, our key recovery attacks have mounted to 839-round Trivium, 891-round Kreyvium, 184-round Grain-128a and 750-round Acornrespectively.
2018
TOSC
Energy optimization is an important design aspect of lightweight cryptography. Since low energy ciphers drain less battery, they are invaluable components of devices that operate on a tight energy budget such as handheld devices or RFID tags. At Asiacrypt 2015, Banik et al. presented the block cipher family Midori which was designed to optimize the energy consumed per encryption and which reduces the energy consumption by more than 30% compared to previous block ciphers. However, if one has to encrypt/decrypt longer streams of data, i.e. for bulk data encryption/decryption, it is expected that a stream cipher should perform even better than block ciphers in terms of energy required to encrypt. In this paper, we address the question of designing low energy stream ciphers. To this end, we analyze for common stream cipher design components their impact on the energy consumption. Based on this, we give arguments why indeed stream ciphers allow for encrypting long data streams with less energy than block ciphers and validate our findings by implementations. Afterwards, we use the analysis results to identify energy minimizing design principles for stream ciphers.
2017
CRYPTO
2017
TOSC
Time-memory-data (TMD) tradeoff attacks limit the security level of many classical stream ciphers (like E0, A5/1, Trivium, Grain) to 1/2n, where n denotes the inner state length of the underlying keystream generator. In this paper, we present Lizard, a lightweight stream cipher for power-constrained devices like passive RFID tags. Its hardware efficiency results from combining a Grain-like design with the FP(1)-mode, a recently suggested construction principle for the state initialization of stream ciphers, which offers provable 2/3n-security against TMD tradeoff attacks aiming at key recovery. Lizard uses 120-bit keys, 64-bit IVs and has an inner state length of 121 bit. It is supposed to provide 80-bit security against key recovery attacks. Lizard allows to generate up to 218 keystream bits per key/IV pair, which would be sufficient for many existing communication scenarios like Bluetooth, WLAN or HTTPS.
2017
TOSC
In this paper, we study the security of Grain-like small state stream ciphers by fast correlation attacks, which are commonly regarded as classical cryptanalytic methods against LFSR-based stream ciphers. We extend the cascaded structure adopted in such primitives in general and show how to restore the full internal state part-by-part if the non-linear combining function meets some characteristic. As a case study, we present a key recovery attack against Fruit, a tweaked version of Sprout that employs key-dependent state updating in the keystream generation phase. Our attack requires 262.8 Fruit encryptions and 222.3 keystream bits to determine the 80-bit secret key. Practical simulations on a small-scale version confirmed our results.
2015
EPRINT
2015
EPRINT
2015
EPRINT
2015
CRYPTO
2015
ASIACRYPT
2014
FSE
2013
JOFC
The need for lightweight (that is, compact, low-power, low-energy) cryptographic hash functions has been repeatedly expressed by professionals, notably to implement cryptographic protocols in RFID technology. At the time of writing, however, no algorithm exists that provides satisfactory security and performance. The ongoing SHA-3 Competition will not help, as it concerns general-purpose designs and focuses on software performance. This paper thus proposes a novel design philosophy for lightweight hash functions, based on the sponge construction in order to minimize memory requirements. Inspired by the stream cipher Grain and by the block cipher KATAN (amongst the lightest secure ciphers), we present the hash function family Quark, composed of three instances: u-Quark, d-Quark, and s-Quark. As a sponge construction, Quark can be used for message authentication, stream encryption, or authenticated encryption. Our hardware evaluation shows that Quark compares well to previous tentative lightweight hash functions. For example, our lightest instance u-Quark conjecturally provides at least 64-bit security against all attacks (collisions, multicollisions, distinguishers, etc.), fits in 1379 gate-equivalents, and consumes on average 2.44 μW at 100 kHz in 0.18 μm ASIC. For 112-bit security, we propose s-Quark, which can be implemented with 2296 gate-equivalents with a power consumption of 4.35 μW.
2011
FSE
2011
FSE
2010
ASIACRYPT
2010
CHES
2010
FSE
2010
FSE
2010
EPRINT
BLAKE is a hash function selected by NIST as one of the 14 second round candidates for the SHA-3 Competition. In this paper, we follow a bottom-up approach to exhibit properties of BLAKE and of its building blocks: based on differential properties of the internal function G, we show that a round of BLAKE is a permutation on the message space, and present an efficient inversion algorithm. For 1.5 rounds we present an algorithm that finds preimages faster than in previous attacks. Discovered properties lead us to describe large classes of impossible differentials for two rounds of BLAKEs internal permutation, and particular impossible differentials for five and six rounds, respectively for BLAKE- 32 and BLAKE-64. Then, using a linear and rotation-free model, we describe near-collisions for four rounds of the compression function. Finally, we discuss the problem of establishing upper bounds on the probability of differential characteristics for BLAKE.
2009
ASIACRYPT
2009
ASIACRYPT
2009
FSE
2008
FSE
2008
FSE
2008
EPRINT
This paper presents preimage attacks for the hash functions 3-pass HAVAL and step-reduced MD5. Introduced in 1992 and 1991 respectively, these functions underwent severe collision attacks, but no preimage attack. We describe two preimage attacks on the compression function of 3-pass HAVAL. The attacks have a complexity of about $2^{224}$ compression function evaluations instead of $2^{256}$. Furthermore, we present several preimage attacks on the MD5 compression function that invert up to 47 (out of 64) steps within $2^{96}$ trials instead of $2^{128}$. Though our attacks are not practical, they show that the security margin of 3-pass HAVAL and step-reduced MD5 with respect to preimage attacks is not as high as expected.
2008
EPRINT
In cryptology we commonly face the problem of finding an unknown key K from the output of an easily computable keyed function F(C,K) where the attacker has the power to choose the input parameter C. In this work we focus on self-synchronizing stream ciphers. First we show how to model these primitives in the above-mentioned general problem by relating appropriate functions F to the underlying ciphers. Then we apply the recently proposed framework at AfricaCrypt08 [4] (for dealing with this kind of problems) to the proposed T-function based self-synchronizing stream cipher by Klimov and Shamir at FSE05 [5] and show how to deduce some non-trivial information about the key. We also open a new window for answering an open question raised in [4].
2008
EPRINT
Bernstein's CubeHash is a hash function family that includes four functions submitted to the NIST Hash Competition. A CubeHash function is parametrized by a number of rounds r, a block byte size b, and a digest bit length h (the compression function makes r rounds, while the finalization function makes 10r rounds). The 1024-bit internal state of CubeHash is represented as a five-dimensional hypercube. The submissions to NIST recommends r=8, b=1, and h in {224,256,384,512}. This paper presents the first external analysis of CubeHash, with: improved standard generic attacks for collisions and preimages; a multicollision attack that exploits fixed points; a study of the round function symmetries; a preimage attack that exploits these symmetries; a practical collision attack on a weakened version of CubeHash; a study of fixed points and an example of nontrivial fixed point; high-probability truncated differentials over 10 rounds. Since the first publication of these results, several collision attacks for reduced versions of CubeHash were published by Dai, Peyrin, et al. Our results are more general, since they apply to any choice of the parameters, and show intrinsic properties of the CubeHash design, rather than attacks on specific versions.
2007
FSE
2007
EPRINT
The stream cipher Salsa20 was introduced by Bernstein in 2005 as a candidate in the eSTREAM project, accompanied by the reduced versions Salsa20/8 and Salsa20/12. ChaCha is a variant of Salsa20 aiming at bringing better diffusion for similar performance. Variants of Salsa20 with up to 7 rounds (instead of 20) have been broken by differential cryptanalysis, while ChaCha has not been analyzed yet. In this paper, we introduce a novel method for differential cryptanalysis of Salsa20 and ChaCha, inspired by correlation attacks and related to the notion of neutral bits. This is the first application of neutral bits in stream cipher cryptanalysis, and it allows us to present the first break of Salsa20/8, to bring faster attacks on the 7-round variant, and to break 6- and 7-round ChaCha. In a second part, we analyze the compression function Rumba, constructed as the XOR of four Salsa20 instances, and returning a 512-bit output. We find collision and preimage attacks for two simplified variants, then we discuss differential attacks on the original version, and exploit a high-probability differential to reduce complexity of collision search from 2^(256) to 2^(79) for 3-round Rumba. We give examples of collisions over three rounds for a version without feedforward, and near-collisions of weight 16 for three rounds of the original compression function, and of weight 129 for four rounds.
2006
EUROCRYPT
2006
FSE
2005
CRYPTO
2004
EUROCRYPT
2003
EUROCRYPT
2003
EUROCRYPT
2002
PKC
2002
EPRINT
At EUROCRYPT '96 J. Patarin introduced the "Isomorphisms of Polynomials (IP)" problem as a basis of authentication and signature schemes. We describe an attack on the secret key of "IP with one secret" and demonstrate its efficiency through examples with realistic parameter sizes. To prevent our attack, additional restrictions on the suggested parameters should be imposed.
2001
FSE
2000
FSE
1999
EUROCRYPT
1998
ASIACRYPT
1996
CRYPTO
1994
EUROCRYPT
1993
EUROCRYPT
1992
CRYPTO
1992
JOFC
1991
EUROCRYPT
1990
CRYPTO
1990
EUROCRYPT
1989
EUROCRYPT
1989
JOFC
1988
EUROCRYPT

FSE 2020
FSE 2019
Eurocrypt 2018
FSE 2018
FSE 2017
Eurocrypt 2017
Crypto 2016
Asiacrypt 2014
Asiacrypt 2013
Asiacrypt 2012
FSE 2012
Asiacrypt 2011
FSE 2010
FSE 2009
FSE 2008
FSE 2007
Asiacrypt 2006
Eurocrypt 2006
FSE 2006
FSE 2005
FSE 2004
Crypto 2004
FSE 2003
FSE 2002
Eurocrypt 2001
Eurocrypt 1999
Crypto 1995