Contributions to fail-stop signature schemes

In an electronic world, a person can electronically sign a document such that the signature is verifiable by everyone. A problem may arise if an enemy who sees the electronic transaction has unlimited computational power: he can break the underlying computational assumption of the system and forge a signature. In this situation, there is no way to distinguish whether the signer is trying to deny his own signature, or someone else is trying to forge the signature. To protect against this problem, Fail-Stop Signature (FSS) schemes were introduced. A general construction proposed for FSS uses bundling homomorphisms. There has been two constructions for FSS schemes based on this general construction which can be proved to be secure. The main objective of this thesis is to find new efficient constructions for FSS. This includes finding new template constructions and also specific construction based on the known templates. A second objective is to propose FSS constructions that can cater for specific applications. In particular we will propose constructions of FSS that can be securely used in distributed environments, and FSS that can be efficiently used for signing long messages. Both these applications are of high interest in today\u27s distributed computer systems and as will be shown, pose new security and efficiency problems that require careful attention. W e prove security of all the proposed constructions and compare their efficiencies with other known schemes