Digital Signature Methods

U ovom radu smo se upoznali s digitalnim potpisom, objasnili zašto nam je važan te koje su njegove prednosti. Neki od kriptosustava zasnivaju se na problemu faktorizacije, a najpoznatiji od njih su svakako RSA te Rabinov kriptosustav. Oni su predstavljeni u prvom poglavlju rada. Nakon što smo se upoznali s njima, promotrili smo i istoimene sheme potpisa koje su nastale od tih kriptosustava. U drugom je poglavlju naglasak bio na DSA shemu potpisa koja je nastala prema ElGamalovom kriptosustavu, odnosno ElGamalovoj shemi potpisa. Za razliku od RSA i Rabinovog kriptosustava, ElGamalov kriptosustav je zasnovan na problemu diskretnog logaritma kojeg smo također spomenuli u radu. U sljedeća dva poglavlja definirana je nepobitna shema potpisa te fail-stop shema potpisa. Nepobitna shema potpisa za potrebu provjere traži suradnju potpisnika, dok fail-stop potpisi pružaju dodatnu sigurnost od krivotvorenja. Za sve navedene sheme priložen je ilustrativni primjer na kojem su uočljive karakteristike promotrenog potpisa.In this paper we introduced digital signature, explain its importance and its advantages. Some of the cryptosystem are based on the factorization problem and few of them are RSA and Rabin cryptosystem. They are represented in the first chapter as well as corresponding signature schemes. The basis of the second chapter is the DSA signature scheme which is related to the ElGamal cryptosytem and signature scheme. ElGamal cryptosystem is based on the discrete logarithm problem which is also one of the topics in the paper. In addition is defined an undeniable signature scheme and a fail-stop signature scheme. For every scheme that is mentioned in this paper there is corresponding illustrative example

That’s not my signature! Fail-stop signatures for a post-quantum world

The Snowden\u27s revelations kick-started a community-wide effort to develop cryptographic tools against mass surveillance. In this work, we propose to add another primitive to that toolbox: Fail-Stop Signatures (FSS) [EC\u2789]. FSS are digital signatures enhanced with a forgery-detection mechanism that can protect a PPT signer from more powerful attackers. Despite the fascinating concept, research in this area stalled after the \u2790s. However, the ongoing transition to post-quantum cryptography, with its hiccups due to the novelty of underlying assumptions, has become the perfect use case for FSS. This paper aims to reboot research on FSS with practical use in mind: Our framework for FSS includes ``fine-grained\u27\u27 security definitions (that assume a powerful, but bounded adversary e.g: can break $128$-bit of security, but not $256$-bit). As an application, we show new FSS constructions for the post-quantum setting. We show that FSS are equivalent to standard, provably secure digital signatures that do not require rewinding or programming random oracles, and that this implies lattice-based FSS. Our main construction is an FSS version of SPHINCS, which required building FSS versions of all its building blocks: WOTS, XMSS, and FORS. In the process, we identify and provide generic solutions for two fundamental issues arising when deriving a large number of private keys from a single seed, and when building FSS for Hash-and-Sign-based signatures

Short One-Time Signatures

We present a new one-time signature scheme having short signatures. Our new scheme supports aggregation, batch verification, and admits efficient proofs of knowledge. It has a fast signing algorithm, requiring only modular additions, and its verification cost is comparable to ECDSA verification. These properties make our scheme suitable for applications on resource-constrained devices such as smart cards and sensor nodes. Along the way, we give a unified description of five previous one-time signature schemes and improve parameter selection for these schemes, and as a corollary we give a fail-stop signature scheme with short signatures

Model-based Testing

This paper provides a comprehensive introduction to a framework for formal testing using labelled transition systems, based on an extension and reformulation of the ioco theory introduced by Tretmans. We introduce the underlying models needed to specify the requirements, and formalise the notion of test cases. We discuss conformance, and in particular the conformance relation ioco. For this relation we prove several interesting properties, and we provide algorithms to derive test cases (either in batches, or on the fly)