What a lovely hat

We present the first comprehensive study on thresholdizing practical OV-based signature schemes, specifically focusing on MAYO and UOV. Our approach begins by addressing the challenges associated with thresholdizing algorithms that sample solutions to linear equation systems of the form $Ax = y$, which are fundamental to OV-based signature schemes. Previous attempts have introduced levels of leakage that we deem insecure. We propose a novel minimum-leakage solution and assess its...

In this poster, we present a Jasmin implementation of Mayo2, a multivariate quadratic(MQ) based signature scheme. Mayo overcomes the disadvantage of the Unbalanced oil and vinegar(UOV) scheme by whipping the UOV map to produce public keys of sizes comparable to ML-DSA. Our Jasmin implementation of Mayo2 takes 930 μs for keygen, 3206 μs for sign, 480 μs for verify based on the average of 1,00,000 runs of the implementation on a 2.25GHz x86 64 processor with 256 GB RAM. To this end, we have a...

Unbalanced Oil and Vinegar (UOV) is one of the oldest, simplest, and most studied ad-hoc multivariate signature schemes. UOV signature schemes are attractive because they have very small signatures and fast verification. On the downside, they have large public and secret keys. As a result, variations of the traditional UOV scheme are usually developed with the goal to reduce the key sizes. Seven variants of UOV were submitted to the additional call for digital signatures by NIST, prior to...

The National Institute for Standards and Technology (NIST) initiated a standardization procedure for additional digital signatures and recently announced round-2 candidates for the PQ additional digital signature schemes. The multivariate digital signature scheme Unbalanced Oil and Vinegar (UOV) is one of the oldest post-quantum schemes and has been selected by NIST for Round 2. Although UOV is mathematically secure, several side-channel attacks (SCA) have been shown on the UOV or UOV-based...

Multivariate cryptography currently centres mostly around UOV-based signature schemes: All multivariate round 2 candidates in the selection process for additional digital signatures by NIST are either UOV itself or close variations of it: MAYO, QR-UOV, SNOVA, and UOV. Also schemes which have been in the focus of the multivariate research community, but are broken by now - like Rainbow and LUOV - are based on UOV. Both UOV and the schemes based on it have been frequently analyzed regarding...

Digital signature schemes based on multivariate- and code-based hard problems are promising alternatives for lattice-based signature schemes, due to their smaller signature size. Hence, several candidates in the ongoing additional standardization for quantum secure digital signature (DS) schemes by the National Institute of Standards and Technology (NIST) rely on such alternate hard problems. Gaussian Elimination (GE) is a critical component in the signing procedure of these schemes. In this...

In the present work, we establish a new relationship among the Beyond UnForgeability Features (BUFF) introduced by Cremers et al. (SP’21). There, the BUFF notions have been shown to be independent of one another. On the other hand, the analysis by Aulbach et al. (PQCrypto’24) reveals that one of the BUFF notions—message-bound signatures (MBS)—is achieved by most schemes. To achieve BUFF security, there is the generic BUFF transform that achieves all the beyond unforgeability features. The...

SNOVA is one of the submissions in the NIST Round 1 Additional Signature of the Post-Quantum Signature Competition. SNOVA is a UOV variant that uses the noncommutative-ring technique to educe the size of the public key. SNOVA's public key size and signature size are well-balanced and have good performance. Recently, Beullens proposed a forgery attack against SNOVA, pointing out that the parameters of SNOVA can be attacked. Beullens also argued that with some slight adjustments his attacks...

In 2022, Wang et al. proposed the multivariate signature scheme SNOVA as a UOV variant over the non-commutative ring of $\ell \times \ell $ matrices over $\mathbb{F}_q$. This scheme has small public key and signature size and is a first round candidate of NIST PQC additional digital signature project. Recently, Ikematsu and Akiyama, and Li and Ding show that the core matrices of SNOVA with $v$ vinegar-variables and $o$ oil-variables are regarded as the representation matrices of UOV with...

Hash-and-Sign with Retry is a popular technique to design efficient signature schemes from code-based or multivariate assumptions. Contrary to Hash-and-Sign signatures based on preimage-sampleable functions as defined by Gentry, Peikert and Vaikuntanathan (STOC 2008), trapdoor functions in code-based and multivariate schemes are not surjective. Therefore, the standard approach uses random trials. Kosuge and Xagawa (PKC 2024) coined it the Hash-and-Sign with Retry paradigm. As many attacks...

In this paper, we present an efficient attack against ${\tt PROV}$, a recent variant of the popular Unbalanced Oil and Vinegar (${\tt UOV}$) multivariate signature scheme, that has been submitted to the ongoing ${\tt NIST}$ standardization process for additional post-quantum signature schemes. A notable feature of ${\tt PROV}$ is its proof of security, namely, existential unforgeability under a chosen-message attack (${\tt EUF-CMA}$), assuming the hardness of solving the system formed by the...

Multivariate cryptography is one of the main candidates for creating post-quantum public key cryptosystems. Especially in the area of digital signatures, there exist many practical and secure multivariate schemes. The signature schemes UOV and Rainbow are two of the most promising and best studied multivariate schemes which have proven secure for more than a decade. However, so far the security of multivariate signature schemes towards physical attacks has not been appropriately assessed....

In this work, we study the singular locus of the varieties defined by the public keys of UOV and VOX, two multivariate quadratic signature schemes submitted to the additional NIST call for signature schemes. Singular points do not exist for generic quadratic systems, which enables us to introduce a new algebraic attack against UOV-based schemes. We show that this attack can be seen as an algebraic variant of the Kipnis-Shamir attack, which can be obtained in our framework as an...

The submission of the Triangular Unbalanced Oil and Vinegar (TUOV) digital signature scheme to the NIST competition in 2023 claims that if the Multivariate Quadratic (MQ) problem (with suitable parameters) is hard, then the TUOV problem must also be hard. We show why the proof fails and why the claimed theorem cannot be true in general.

VOX is a UOV-like signature scheme submitted to Round 1 additional signatures of NIST PQC standardization process. In 2023 Furue and Ikematsu proposed a rectangular MinRank attack on VOX, resulting in the submitters changing their parameters to counter this attack. In this paper we propose a new type of MinRank attack called padded MinRank attack. We show that the attack is highly efficient in its running time, taking less than one minute to break eight of nine parameters and about eight...

SNOVA is a variant of a UOV-type signature scheme over a noncommutative ring. In this article, we demonstrate that certain parameters provided by authors in SNOVA fail to meet the NIST security level, and the complexities are lower than those claimed by SNOVA.

SNOVA is a multivariate signature scheme submitted to the ad- ditional NIST PQC standardization project started in 2022. SNOVA is con- structed by incorporating the structure of the matrix ring over a finite field into the UOV signature scheme, and the core part of its public key is the UOV public key whose coefficients consist of matrices. As a result, SNOVA dramatically reduces the public key size compared to UOV. In this paper, we recall the construction of SNOVA, and reconsider its...

VOX has been submitted to the NIST Round 1 Additional Signature of the Post-Quantum Signature Competition in June 2023. VOX is a strengthened variant of UOV which uses the Quotient-Ring (QR) setting to reduce the public-key size. At the end of August 2023, Furue and Ikamatsu posted on the NIST mailing-list a post, indicating that the parameters of VOX can be attacked efficiently using the rectangular attack in the QR setting. In this note, we explain the attack in the specific case of...

This paper presents MQ on my Mind (MQOM), a digital signature scheme based on the difficulty of solving multivariate systems of quadratic equations (MQ problem). MQOM has been submitted to the NIST call for additional post-quantum signature schemes. MQOM relies on the MPC-in-the-Head (MPCitH) paradigm to build a zero-knowledge proof of knowledge (ZK-PoK) for MQ which is then turned into a signature scheme through the Fiat-Shamir heuristic. The underlying MQ problem is non-structured in the...

NIST issued a new call in 2023 to diversify the portfolio of quantum-resistant digital signature schemes since the current portfolio relies on lattice problems. The MAYO scheme, which builds on the Unbalanced Oil and Vinegar (UOV) problem, is a promising candidate for this new call. MAYO introduces emulsifier maps and a novel 'whipping' technique to significantly reduce the key sizes compared to previous UOV schemes. This paper provides a comprehensive analysis of the implementation...

MAYO is a topical modification of the established multivariate signature scheme UOV. Signer and Verifier locally enlarge the public key map, such that the dimension of the oil space and therefore, the parameter sizes in general, can be reduced. This significantly reduces the public key size while maintaining the appealing properties of UOV, like short signatures and fast verification. Therefore, MAYO is considered as an attractive candidate in the NIST call for additional digital signatures...

Unbalanced Oil and Vinegar is a multivariate signature scheme that was introduced in 1999. Most multivariate candidates for signature schemes at NIST's PQC standardization process are either based on UOV or closely related to it. The UOV trapdoor is a secret subspace, the "oil subspace". We show how to recover an equivalent secret key from the knowledge of a single vector in the oil subspace in any characteristic. The reconciliation attack was sped-up by adding some bilinear equations...

MQ-Sign is a variant of the UOV singature scheme proposed by Shim et al. It has been suggested as a candidate for the standardization of post-quantum cryptography in Republic of Korea (known as KpqC). However, recently Aulbach et al. proposed a practical key recovery attack against MQ-Sign-RS and MQ-Sign-SS with a simple secret key $\mathcal{S}$. In this paper, we propose another attack that is valid for the case of a general secret key $\mathcal{S}$.

We present an optimized constant-time implementation of the MAYO signature scheme on ARMv7-M. MAYO is a novel multivariate proposal based on the trapdoor function of the Unbalanced Oil and Vinegar scheme. Our implementation builds on existing techniques for UOV-based schemes and introduces a new approach for evaluating the polar forms of quadratic maps. We modify MAYO's original parameters to achieve greater benefits from the proposed optimizations, resulting in slightly larger keys and...

In this paper we describe attacks on the UOV-based signature scheme called MQ-Sign. MQ-Sign was submitted by Shim, Kim, and An as a a first-round candidate for standardization in the (South) Korean post-quantum cryptography competition (KpqC). The scheme makes use of sparseness of the secret central polynomials and equivalent key construction to reduce the size of the private key. The authors propose four variants exploiting different levels of sparsity, MQ-Sign-SS, MQ-Sign-RS, MQ-Sign-SR,...

Due to recent cryptanalytical breakthroughs, the multivariate signature schemes that seemed to be most promising in the past years are no longer in the focus of the research community. Hence, the cryptographically mature UOV scheme is of great interest again. Since it has not been part of the NIST process for standardizing post-quantum cryptography so far, it has not been studied intensively for its physical security. In this work, we present a side-channel attack on the latest...

In this paper, we propose a simple noncommutative-ring based UOV signature scheme with key-randomness alignment: Simple NOVA, which can be viewed as a simplified version of NOVA[48]. We simplify the design of NOVA by skipping the perturbation trick used in NOVA, thus shortens the key generation process and accelerates the signing and verification. Together with a little modification accordingly, this alternative version of NOVA is also secure and may be more suitable for practical uses. We...

A hash-and-sign signature based on a preimage-sampleable function (Gentry et al., STOC 2008) is secure in the quantum random oracle model if the preimage-sampleable function is collision-resistant (Boneh et al., ASIACRYPT 2011) or one-way (Zhandry, CRYPTO 2012). However, trapdoor functions in code-based and multivariate-quadratic-based signatures are not preimage-sampleable functions; for example, underlying trapdoor functions of the Courtois-Finiasz-Sendrier, Unbalanced Oil and Vinegar...

NOVA signature scheme is a UOV-type signature scheme over a non-commutative coefficient ring with a novel structural map. In this article we show that a randomly generated central map for the scheme is very likely insecure and may suffer from a forgery attack in polynomial time.

In this paper, we propose a noncommutative-ring based unbalanced oil and vinegar signature scheme with key-randomness alignment: NOVA (Noncommutative Oil and Vinegar with Alignment). Instead of fields or even commutative rings, we show that noncommutative rings can be used for algebraic cryptosystems. At the same or better level of security requirement, NOVA has a much smaller public key than UOV (Unbalanced Oil and Vinegar), which makes NOVA practical in most situations. We use Magma to...

Rainbow, a multivariate digital signature scheme and third round finalist in NIST's PQC standardization process, is a layered version of the unbalanced oil and vinegar (UOV) scheme. We introduce two fault attacks, each focusing on one of the secret linear transformations $T$ and $S$ used to hide the structure of the central map in Rainbow. The first fault attack reveals a part of $T$ and we prove that this is enough to achieve a full key recovery with negligible computational effort for all...

We present here the analysis of a new perturbation, that seems to strengthen significantly the security of some families of multivariate schemes. Thanks to this new perturbation, we are indeed able to get interestingly efficient signature and encryption public key schemes, in particular when combining this perturbation to the well known trapdoors HFE and UOV. We present here the best attacks that we know against these variant schemes and we give practical examples of parameters for current...

QR-UOV is a variant of UOV with smaller keys proposed at Asiacrypt 2021. In this paper, we show that QR-UOV can be constructed by a smaller UOV over an extension field.

The Oil and Vinegar signature scheme, proposed in 1997 by Patarin, is one of the oldest and best understood multivariate quadratic signature schemes. It has excellent performance and signature sizes but suffers from large key sizes on the order of 50 KB, which makes it less practical as a general-purpose signature scheme. To solve this problem, this paper proposes MAYO, a variant of the UOV signature scheme whose public keys are two orders of magnitude smaller. MAYO works by using a UOV map...

In this paper, we present a new secret trapdoor function for the design of multivariate schemes that we call ``Onyx'', suitable for encryption and signature. It has been inspired by the schemes presented in Ariadne Thread and Pepper: New mul-tivariate cryptographic schemes with public keys in degree 3. . From this idea, we present some efficient encryption and signature multivariate schemes with explicit parameters that resist all known attacks. In particular they resist the two main (and...

The problem of solving a system of multivariate quadratic equations over a finite field is known to be hard in general. However, there have been several algorithms of solving the system of quadratic equations efficiently when the number of variables is sufficiently larger than the number of equations (e.g., Kipnis et al., Eurocrypt 1999, Thomae-Wolf, PKC 2012, Cheng et al., PQCrypto 2014 and Furue et al., PQCrypto 2021). In the present paper, we propose a new algorithm which is available...

In 2019, Tao proposed a new variant of UOV with small keys, called Hufu-UOV. This paper studies its security.

In this paper, we present a new perturbation for the design of multivariate schemes that we call ``Pepper''. From this idea, we present some efficient multivariate signature schemes with explicit parameters that resist all known attacks. In particular they resist the two main (and often very powerful) attacks in this area: the Gröbner attacks (to compute a solution of the system derived from the public key) and the MinRank attacks (to recover the secret key). Pepper can also be seen as a new...

Solving a polynomial system over a finite field is an NP-complete problem of fundamental importance in both pure and applied mathematics. In~particular, the security of the so-called multivariate public-key cryptosystems, such as HFE of Patarin and UOV of Kipnis et~al., is based on the postulated hardness of solving quadratic polynomial systems over a finite field. Lokshtanov et al.~(2017) were the first to introduce a probabilistic algorithm that, in the worst-case, solves a Boolean...

In this paper, we present two new perturbations for the design of multivariate schemes that we call ``Ariadne Thread'' and ``Pepper''. From these ideas, we present some efficient multivariate encryption and signature schemes with explicit parameters that resist all known attacks. In particular they resist the two main (and often very powerful) attacks in this area: the Gröbner attacks (to compute a cleartext from a ciphertext) and the MinRank attacks (to recover the secret key). Ariadne...

The contributions of this paper are twofold. First, we simplify the description of the Unbalanced Oil and Vinegar scheme (UOV) and its Rainbow variant, which makes it easier to understand the scheme and the existing attacks. We hope that this will make UOV and Rainbow more approachable for cryptanalysts. Secondly, we give two new attacks against the UOV and Rainbow signature schemes; the intersection attack that applies to both UOV and Rainbow and the rectangular MinRank attack that applies...

The unbalanced oil and vinegar signature scheme (UOV) is a multivariate signature scheme that has essentially not been broken for over 20 years. However, it requires the use of a large public key; thus, various methods have been proposed to reduce its size. In this paper, we propose a new variant of UOV with a public key represented by block matrices whose components correspond to an element of a quotient ring. We discuss how it affects the security of our proposed scheme whether or not the...

In 2017, Ward Beullens \textit{et al.} submitted Lifted Unbalanced Oil and Vinegar (LUOV)\cite{beullens2017field}, a signature scheme based on the famous multivariate public key cryptosystem (MPKC) called Unbalanced Oil and Vinegar (UOV), to NIST for the competition for post-quantum public key scheme standardization. The defining feature of LUOV is that, though the public key $\mathcal{P}$ works in the extension field of degree $r$ of $\mathbb{F}_2$, the coefficients of $\mathcal{P}$ come...

A new multivariate cryptosystem based on a linear code was proposed by Smith-Tone and Tone quite recently. This short note points out that it is a variant of UOV.

Multivariate public key signature scheme has a good performance on speed and signature size. But most of them have a huge public key size. In this paper, we propose a new method to reduce the public key size of unbalance oil and vinegar (UOV) signature scheme. We can reduce the public key size of UOV scheme to about 4KB for 128 bits security level. This method can be used to reduce the public key sizes of other multivariate public key cryptosystems.

We introduce a new technique for compressing the public keys of the UOV signature scheme that makes use of block-anti-circulant matrices. These matrices admit a compact representation as for every block, the remaining elements can be inferred from the first row. This space saving translates to the public key, which as a result of this technique can be shrunk by a small integer factor. We propose parameters sets that take into account several important attacks.

Circulant UOV and Circulant Rainbow are new variants of UOV (unbalanced oil and vinegar signature scheme) and Rainbow respectively. In this short report, we study the security of these new variants Circulant UOV and Circulant Rainbow.

Most Multivariate Quadratic (MQ) signature schemes have a very large public key, which makes them unsuitable for many applications, despite attractive features such as speed and small signature sizes. In this paper we introduce a modification of the Unbalanced Oil and Vinegar (UOV) signature scheme that has public keys which are an order of magnitude smaller than other MQ signature schemes. The main idea is to choose UOV keys over the smallest field F2 in order to achieve small keys, but to...

As recently been emphasized by NSA and NIST, there is an increasing need for cryptographic schemes being secure against quantum computer attacks. Especially in the area of digital signature schemes, multivariate cryptography is one of the main candidates for this. At Inscrypt 2015, Nie et al. proposed a new multivariate signature scheme called CUOV, whose public key consists both of quadratic and cubic polynomials. However, the scheme was broken by an attack of Hashimoto. In this paper we...

The unbalanced oil and vinegar signature scheme (UOV) is one of signature schemes whose public key is a set of multivariate quadratic forms. Recently, a new variant of UOV called Cubic UOV was proposed at Inscrypt 2015. It was claimed that the cubic UOV was more efficient than the original UOV and its security was enough. However, an equivalent secret key of the cubic UOV can be recovered easily. In this note, we describe how to recover it. After we posted the first version of this note,...

Multivariate public key cryptography which relies on MQ (Multivariate Quadratic) problems is one of the main approaches to guarantee the security of communication in the post-quantum world. In this paper, we propose a combined MQ signature scheme based on the yet unbroken UOV (Unbalanced Oil and Vinegar) signature if parameters are properly chosen. Our scheme can not only reduce the public key size of the UOV signature, but also provide more tighter bound of security against chosen-message...

Multivariate cryptography is one of the main candidates to guarantee the security of communication in the post-quantum era. Especially in the area of digital signatures, multivariate cryptography offers a wide range of practical schemes. In \cite{PB12} and \cite{PB13} Petzoldt et al. showed a way to speed up the verification process of improved variants of the UOV and Rainbow signature schemes. In this paper we show how we can do even better by a slight variation of their algorithms.

The Rainbow Signature Scheme is a non-trivial generalization of the well known Unbalanced Oil and Vinegar (UOV) signature scheme (Eurocrypt '99) minimizing the length of the signatures. By now the Rainbow Band Separation attack is the best key recovery attack known. For some sets of parameters it is even faster than a direct attack on the public key. Unfortunately the available description of the attack is very ad hoc and does not provide deep insights. In this article we provide another...

Security of public key schemes in a post-quantum world is a challenging task---as both RSA and ECC will be broken then. In this paper, we show how post-quantum signature systems based on Multivariate Quadratic (MQ) polynomials can be improved up by about 9/10, and 3/4, respectively, in terms of public key size and verification time. The exact figures are 88% and 73%. This is particularly important for small-scale devices with restricted energy, memory, or computational power. In addition, we...

Multivariate Cryptography is one of the alternatives to guarantee the security of communication in the post-quantum world. One major drawback of such schemes is the huge size of their keys. In \cite{PB10} Petzoldt et al. proposed a way how to reduce the public key size of the UOV scheme by a large factor. In this paper we extend this idea to the Rainbow signature scheme of Ding and Schmidt \cite{DS05}. By our construction it is possible to reduce he size of the public key by up to 62 \verb!%!.

In this paper we show that solving systems coming from the public key of the Unbalanced Oil and Vinegar (UOV) signature scheme is on average at least as hard as solving a certain quadratic system with completely random quadratic part. In providing lower bounds on direct attack complexity we rely on the empirical fact that complexity of solving a non-linear polynomial system is determined by the homogeneous part of this system of the highest degree. Our reasoning explains, in particular, the...

Many efficient attacks have appeared in recent years, which have led to serious blow for the traditional multivariate public key cryptosystems. For example, the signature scheme SFLASH was broken by Dubois et al. at CRYPTO'07, and the Square signature (or encryption) scheme by Billet et al. at ASIACRYPTO'09. Most multivariate schemes known so far are insecure, except maybe the sigature schemes UOV and HFEv-. Following these new developments, it seems that the general design principle of...

In this short note, we investigate the security of the Unbalanced Oil and Vinegar Scheme \cite{uov}. To do so, we use a hybrid approach for solving the algebraic systems naturally arising when mounting a signature-forgery attack. The basic idea is to compute Gröbner bases of several modified systems rather than a Gröbner basis of the initial system. It turns out that our approach is efficient in practice. We have obtained a complexity bounded from above by $2^{40.3}$ (or $9$ hours of...

Multivariate public key cryptography is one of the main approaches to guarantee the security of communication in a post quantum world. One of the major drawbacks in this area is the huge size of the public key. In this paper we present a new idea to create a multivariate signature scheme with an almost cyclic public key. The scheme is very similar to the UOV-Scheme of Kipnis and Patarin but reduces the size of the public key by about 83 \verb!%!.

In this paper ways to efficiently implement public-key schemes based onMultivariate Quadratic polynomials (MQ-schemes for short) are investigated. In particular, they are claimed to resist quantum computer attacks. It is shown that such schemes can have a much better time-area product than elliptic curve cryptosystems. For instance, an optimised FPGA implementation of amended TTS is estimated to be over 50 times more efficient with respect to this parameter. Moreover, a general framework for...

This thesis gives an overview of Multivariate Quadratic polynomial equations and their use in public key cryptography. In the first chapter, some general terms of cryptography are introduced. In particular, the need for public key cryptography and alternative schemes is motivated, i.e., systems which neither use factoring (like RSA, Rivest-Shamir-Adleman) nor the discrete logarithm (like ECC, elliptic curve cryptography). This is followed by a brief introduction of finite fields and a...

In this article, we show that public key schemes based on multivariate quadratic equations allow many equivalent, and hence superfluous private keys. We achieve this result by investigating several transformations to identify these keys and show their application to Hidden Field Equations (HFE), C$^*$, and Unbalanced Oil and Vinegar schemes (UOV). In all cases, we are able to reduce the size of the private --- and hence the public --- key space by at least one order of magnitude. We see...

The Unbalanced Oil and Vinegar scheme (UOV) is a signature scheme based on multivariate quadratic equations. It uses $m$ equations and $n$ variables. A total of $v$ of these are called ``vinegar variables". In this paper, we study its security from several points of view. First, we are able to demonstrate that the constant part of the affine transformation does not contribute to the security of UOV and should therefore be omitted. Second, we show that the case $n \geq 2m$ is particularly...