Digital Signature Schemes Based on Hash Functions

Cryptographers and security experts around the world have been awakened to the reality that one day (potentially soon) large-scale quantum computers may be available. Most of the public-key cryptosystems employed today on the Internet, in both software and in hardware, are based on number-theoretic problems which are thought to be intractable on a classical (non-quantum) computer and hence are considered secure. The most popular such examples are the RSA encryption and signature schemes, and the Elliptic Curve Diffie-Hellman (ECDH) key-exchange protocol employed widely in the SSL/TLS protocols. However, these schemes offer essentially zero security against an adversary in possession of a large-scale quantum computer. Thus, there is an urgent need to develop, analyze and implement cryptosystems and algorithms that are secure against such adversaries. It is widely believed that cryptographic hash functions are naturally resilient to attacks by a quantum adversary, and thus, signature schemes have been developed whose security relies on this belief. The goal of this thesis is to give an overview of hash-based cryptography. We describe the most important hash-based signature schemes as well as the schemes and protocols used as subroutines within them. We give a juxtaposition between stateful and stateless signature schemes, discussing the pros and cons of both while including detailed examples. Furthermore, we detail serious flaws in the security proof for the WOTS-PRF signature scheme. This scheme had the feature that its security proof was based on minimal security assumptions, namely the pseudorandomness of the underlying function family. We explore how this flawed security argument affects the other signature schemes that utilize WOTS-PRF

Analysis of code-based digital signature schemes

Digital signatures are in high demand because they allow authentication and non-repudiation. Existing digital signature systems, such as digital signature algorithm (DSA), elliptic curve digital signature algorithm (ECDSA), and others, are based on number theory problems such as discrete logarithmic problems and integer factorization problems. These recently used digital signatures are not secure with quantum computers. To protect against quantum computer attacks, many researchers propose digital signature schemes based on error-correcting codes such as linear, Goppa, polar, and so on. We studied 16 distinct papers based on various error-correcting codes and analyzed their various features such as signing and verification efficiency, signature size, public key size, and security against multiple attacks

On the security of digital signature schemes based on error-correcting codes

We discuss the security of digital signature schemes based on error-correcting codes. Several attacks to the Xinmei scheme are surveyed, and some reasons given to explain why the Xinmei scheme failed, such as the linearity of the signature and the redundancy of public keys. Another weakness is found in the Alabbadi-Wicker scheme, which results in a universal forgery attack against it. This attack shows that the Alabbadi-Wicker scheme fails to implement the necessary property of a digital signature scheme: it is infeasible to find a false signature algorithm D from the public verification algorithm E such that E(D*(m)) = m for all messages m. Further analysis shows that this new weakness also applies to the Xinmei scheme

Efficient Digital Signature Schemes

Digitálny podpis preberá vlastnosti klasického podpisu a slúži k zaisteniu obsahu dokumentov, ktoré by mohli byť v priebehu prenosu cez nezabezpečený kanál modifikované. Problémy poskytnutia bezpečnosti a ochrany komunikujúcich účastníkov sú riešené pomocou kryptografických technik. Overenie identity, integrity správ, dôveryhodnosť vlastníctva dokumentov a bezpečný prenos informácií cez nezabezpečený kanál, to všetko sú aspekty, ktorými sa zaoberá bezpečnosť komunikácie - infraštruktúra verejných kľúčov, ktorá používa digitálne podpisy. V dnešnej dobe digitálne podpisy majú veľký význam v zabezpečení dát v komunikácii cez nezabezpečený kanál. Cieľom nasledujúcej diplomovej práce je oboznámiť čitateľa s nutnými technologickými aspektmi digitálnych podpisov, ich výhodami a nevýhodami. Vzhľadom na stále zväčšujúceho výpočtového výkonu počítačov súčasné digitálne podpisy sa časom budú musieť vylepšovať a modifikovať tak, aby obstáli sofistikovanejším útokom. V tejto práci sú popísané aj návrhy nových efektívnych podpisových schém a ich porovnanie so súčasnými. Sú preskúmané aj ich aspekty pre výpočtovo slabé zariadenia, či nasadenie digitálneho podpisu v systémoch s nízkymi prenosovými rýchlosťami kanálu. Na základe objasnenia problematiky kryptografii a popísania jeho základných pojmov je následne zavedený pojem digitálneho podpisu. V kapitole 1 sú popísané aj formátovania a architektúry digitálneho podpisu. Druhá časť tejto diplomovej práce sa venuje súčasne používaným digitálnych podpisovým schémam a ich vlastnostiam. Kapitola 3 popisuje niektoré návrhy nových efektívnych digitálnych podpisových schém a ich porovnanie so súčasne používanými. V praktickej časti práce, ktorá je popísaná v kapitole 4 je predstavená implementácia (v prostredí .NET v jazyku C#) dvoch efektívnych podpisových schém v rámci aplikácii typu klient-server. Posledná časť sa zaoberá s porovnaním a analyzovaním vlastností implementovaných schém.Digital signatures, which take the properties of classical signatures, are used to secure the actual content of documents, which can be modified during transmission over an insecure channel. The problems of security and protection of communicating participants are solved by cryptographic techniques. Identity verification, message integrity, credibility, the ownership of documents, and the secure transmission of information over an unsecured channel, are all dealt with in secure communications - Public Key Infrastructure, which uses digital signatures. Nowadays digital signatures are often used to secure data in communication over an unsecured channel. The aim of the following master’s thesis is to familiarize readers with the necessary technological aspects of digital signatures, as well as their advantages and disadvantages. By the time digital signatures are being used they will have to be improved and modified to be secure against more sophisticated attacks. In this paper, proposals of new efficient digital signature schemes and their comparison with current ones are described. Also are examined their implications for computationally weak devices, or deployment in low speed channel transmission systems. After an explanation of cryptography and a description of its basic subjects, digital signatures are introduced. The first chapter describes the possible formatting and architecture of the digital signature. The second part of this master’s thesis is about current digital signature schemes and their properties. Chapter 3 describes some proposals of new efficient digital signature schemes and their comparison to those currently in use. In the practical part, the implementations (in the environment .NET in C#) of two effective digital signature schemes as part of a client-server application are presented and described (Chapter 4). In the last chapter the comparison and analysis of the implemented signature schemes are provided.

Improving the exact security of digital signature schemes

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (p. 28-30).by Leonid Reyzin.S.M

A Thesis: A CRYPTOGRAPHIC STUDY OF SOME DIGITAL SIGNATURE SCHEMES.

In this thesis, we propose some directed signature schemes. In addition, we have discussed their applications in different situations. In this thesis, we would like to discuss the security aspects during the design process of the proposed directed digital signature schemes. The security of the most digital signature schemes widely use in practice is based on the two difficult problems, viz; the problem of factoring integers (The RSA scheme) and the problem of finding discrete logarithms over finite fields (The ElGamal scheme). The proposed works in this thesis is divided into seven chapters