CryptoDB

Raphael Overbeck

Publications

Year
Venue
Title
2009
EPRINT
In this paper we propose a conversion from signature schemes connected to coding theory into blind signature schemes. We give formal security reductions to combinatorial problems not connected to number theory. This is the first blind signature scheme which can not be broken by quantum computers via cryptanalyzing the underlying signature scheme employing Shors algorithms. We thus present a step towards diversifying computational assumptions on which blind signatures can be based. We achieve blind signatures by a different concept of blinding: Instead of blinding the message, we blind the public key, such that generating a (blind) signature for the blinded key requires the interaction of the holder of the original secret key. To verify the blind signature, the connection between the original and the blinded key is proven by a static ZK proof. The major ingredient for our conversion is the PKP protocol by Shamir.
2008
JOFC
2008
ASIACRYPT
2007
EPRINT
We present two efficient protocols for two flavors of oblivious transfer (OT): the Rabin and 1-out-of-2 OT using the McEliece cryptosystem and Shamir's zero-knowledge identification scheme based on permuted kernels. This is a step towards diversifying computational assumptions on which OT -- the primitive of central importance -- can be based. Although we obtain a weak version of Rabin OT (where the malicious receiver may decrease his erasure probability), it can nevertheless be reduced to secure 1-out-of-2 OT. Elaborating on the first protocol, we provide a practical construction for 1-out-of-2 OT.
2006
EPRINT
In this paper we give an overview of some of the cryptographic applications which were derived from the proposal of R.J. McEliece to use error correcting codes for cryptographic purposes. Code based cryptography is an interesting alternative to number theoretic cryptography. Many basic cryptographic functions like encryption, signing, hashing, etc. can be realized using code theoretic concepts. In this paper we briefly show how to correct errors in transmitted data by employing Goppa codes and describe possible applications to public key cryptography. The main focus of this paper is to provide detailed insight into the state of art of cryptanalysis of the McEliece cryptosystem and the effect on different cryptographic applications. We conclude, that for code based cryptography a public key of $88$KB offers sufficient security for encryption, while we need a public key of at least $597$KB for secure signing.
2006
EPRINT
In this paper we view interleaved Gabidulin codes and describe how to correct errors up to a rank equal to the amount of redundancy of the code with high probability. We give a detailed proof for our estimation of the probability of correct decoding. In a second part, we view the application to variants of the GPT cryptosystem. For GGPT this leads to an efficient attack on the remaining secure instances, whereas it allows to derive at least partial information of the plaintext in the case of RRC-GPT.
2005
EPRINT
In this paper we look at the Gabidulin version of the McEliece cryptosystem (GPT) and its variants. We propose a new polynomial time attack on the private key, which is applicable to all variants proposed so far, breaking some of them completely.
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?