## CryptoDB

### Johannes Buchmann

#### Publications

Year
Venue
Title
2014
EPRINT
2012
CHES
2011
PKC
2011
CHES
2010
EPRINT
In 1994, P. Shor showed that quantum computers will be able to break cryptosystems based on integer factorization and on the discrete logarithm, e.g. RSA or ECC. Code-based crytosystems are promising alternatives to public key schemes based on these problems, and they are believed to be secure against quantum computer attacks. In this paper, we solve the problem of selecting optimal parameters for the McEliece cryptosystem that provide security until a given year and give detailed recommendations. Our analysis is based on the lower bound complexity estimates by Sendrier and Finiasz, and the security requirements model proposed by Lenstra and Verheul.
2010
EPRINT
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 results on solving the UOV systems presented by J.-C. Faugere and L. Perret at the SCC conference in 2008.
2010
EPRINT
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!%!.
2010
EPRINT
Multivariate public key cryptography is one of the main approaches to guarantee the security of communication in a post-quantum world. One of the most promising candidates in this area is the Rainbow signature scheme, which was first proposed by J. Ding and D. Schmidt in 2005. In this paper we develop a model of security for the Rainbow signature scheme. We use this model to find parameters for Rainbow over GF(16), GF(31) and GF(256) which, under certain assumptions, guarantee the security of the scheme for now and the near future.
2008
EPRINT
Current remote e-voting schemes aim at a number of security objectives. However, this is not enough for providing secure online elections in practice. Beyond a secure e-voting protocol, there are many organizational and technical security requirements that have to be satisfied by the operational environment in which the scheme is implemented. We have investigated four state-of-the-art e-voting protocols in order to identify the organizational and technical requirements which these protocols need to be met in order to work correctly. Satisfying these requirements is a costly task which reduces the potential advantages of e-voting considerably. We introduce the concept of a Voting Service Provider (VSP) which carries out electronic elections as a trusted third party and is responsible for satisfying the organizational and technical requirements. We show which measures the VSP takes to meet these requirements. To establish trust in the VSP we propose a Common Criteria evaluation and a legal framework. Following this approach, we show that the VSP enables secure, cost-effective, and thus feasible online elections.
2008
EPRINT
Building upon a famous result due to Ajtai, we propose a sequence of lattice bases with growing dimension, which can be expected to be hard instances of the shortest vector problem (SVP) and which can therefore be used to benchmark lattice reduction algorithms. The SVP is the basis of security for potentially post-quantum cryptosystems. We use our sequence of lattice bases to create a challenge, which may be helpful in determining appropriate parameters for these schemes.
2008
EPRINT
In this paper, we present an efficient attack to the multivariate Quadratic Quasigroups (MQQ) cryptosystem. Our cryptanalysis breaks MQQ cryptosystems by solving systems of multivariate quadratic polynomial equations using a modified version of the MutantXL algorithm. We present experimental results comparing the behavior of our implementation of MutantXL to Magma's implementation of $F_4$ on MQQ systems ($\geq$ 135 bit). Based on our results we show that the MutantXL implementation solves with much less memory than Magma's implementation of $F_4$ algorithm.
2008
EPRINT
Building upon a famous result due to Ajtai, we propose a sequence of lattice bases with growing dimension, which can be expected to be hard instances of the shortest vector problem (SVP) and which can therefore be used to benchmark lattice reduction algorithms. The SVP is the basis of security for potentially post-quantum cryptosystems. We use our sequence of lattice bases to create a challenge, which may be helpful in determining appropriate parameters for these schemes.
2007
EPRINT
The NTRU encryption scheme is an interesting alternative to well-established encryption schemes such as RSA, ElGamal, and ECIES. The security of NTRU relies on the hardness of computing short lattice vectors and thus is a promising candidate for being quantum computer resistant. There has been extensive research on efficient implementation of the NTRU encryption scheme. In this paper, we present a new algorithm for enhancing the performance of NTRU. The proposed method is between $11$\% and $23$\% faster on average than the best previously known method. We also present a highly efficient implementation of NTRU within the Java Cryptography Architecture.
2006
FSE
2006
EPRINT
Formal verification is getting more and more important in computer science. However the state of the art formal verification methods in cryptography are very rudimentary. This paper is one step to provide a tool box allowing the use of formal methods in every aspect of cryptography. In this paper we give a formal specification of the RSA probabilistic signature scheme (RSA-PSS) [4] which is used as algorithm for digital signatures in the PKCS #1 v2.1 standard [7]. Additionally we show the correctness of RSA-PSS. This includes the correctness of RSA, the formal treatment of SHA-1 and the correctness of the PSS encoding method. Moreover we present a proof of concept for the feasibility of verification techniques to a standard signature algorithm.
2006
EPRINT
The Merkle signature scheme (MSS) is an interesting alternative for well established signature schemes such as RSA, DSA, and ECDSA. The security of MSS only relies on the existence of cryptographically secure hash functions. MSS has a good chance of being quantum computer resistant. In this paper, we propose CMSS, a variant of MSS, with reduced private key size, key pair generation time, and signature generation time. We demonstrate that CMSS is competitive in practice by presenting a highly efficient implementation within the Java Cryptographic Service Provider FlexiProvider. We present extensive experimental results and show that our implementation can for example be used to sign messages in Microsoft Outlook.
2005
EPRINT
We propose a practical sampling reduction algorithm for lattice bases based on work by Schnorr as well as two even more effective generalizations. We report the empirical behaviour of these algorithms. We describe how Sampling Reduction allows to stage lattice attacks against the NTRU cryptosystem with smaller BKZ parameters than before and conclude that therefore the recommeded NTRU security parameters offer $\leq 74$ Bit security.
2005
EPRINT
We construct and analyze Feistel and SPN ciphers that have a sound design strategy against linear and differential attacks but for which the encryption process can be described by very simple polynomial equations. For a block and key size of 128 bits, we present ciphers for which practical Groebner basis attacks can recover the full cipher key requiring only a minimal number of plaintext/ciphertext pairs. We show how Groebner bases for a subset of these ciphers can be constructed with neglegible computational effort. This reduces the key recovery problem to a Groebner basis conversion problem. By bounding the running time of a Groebner basis conversion algorithm, FGLM, we demonstrate the existence of block ciphers resistant against differential and linear cryptanalysis but vulnerable against Groebner basis attacks.
2004
EPRINT
Digital signatures have become a key technology for making the Internet and other IT infrastructures secure. But in 1994 Peter Shor showed that quantum computers can break all digital signature schemes that are used today and in 2001 Chuang and his coworkers implemented Shor s algorithm for the first time on a 7-qubit NMR quantum computer. This paper studies the question: What kind of digital signature algorithms are still secure in the age of quantum computers?
1997
CRYPTO
1994
CRYPTO
1994
JOFC
1993
CRYPTO
1992
EUROCRYPT
1990
CRYPTO
1990
EUROCRYPT
1989
CRYPTO
1989
EUROCRYPT
1988
JOFC

Eurocrypt 2003
Asiacrypt 2000
Crypto 1997
Crypto 1996
Eurocrypt 1995
Crypto 1990