Nous considerons des mecanismes pour le probleme du bureaucrate paresseux. Des agents, responsabl... more Nous considerons des mecanismes pour le probleme du bureaucrate paresseux. Des agents, responsables d'une tâche doivent communiquer la duree de leur tâche a un ordonnanceur. Son objectif est de selectionner un sous ensemble de tâches maximal pour l'inclusion, dont la duree totale n'excede pas son budget et est minimum. Nous nous interessons aux mecanismes a veracite garantie, pour lesquels les agents n'ont pas interet a mentir sur la duree de leurs tâches afin d'appartenir a l'ensemble des tâches selectionnees.
In this chapter we consider the design of Secure Broadcast protocols in generic networks of known... more In this chapter we consider the design of Secure Broadcast protocols in generic networks of known topology. Studying the problem of Secure Message Transmission (SMT) proves essential for achieving Broadcast in incomplete networks. We present a polynomial protocol that achieves parallel secure message transmissions between any two sets of nodes of an incomplete network provided that the weakest connectivity conditions which render the Broadcast problem solvable hold. Using the above, we show that the SMT protocol can be used as a subroutine for the simulation of any known protocol for complete networks, which leads us to protocols for generic networks which remain polynomial with respect to the measures of consideration. We extend our result to the case of wireless networks by exploiting the fact that participants are committed to perform local broadcasts, which greatly facilitates achieving an agreement.
This work formalizes Publicly Auditable Conditional Blind Signatures (PACBS), a new cryptographic... more This work formalizes Publicly Auditable Conditional Blind Signatures (PACBS), a new cryptographic primitive that allows the verifiable issuance of blind signatures, the validity of which is contingent upon a predicate and decided by a designated verifier. In particular, when a user requests the signing of a message, blinded to protect her privacy, the signer embeds data in the signature that makes it valid if and only if a condition holds. A verifier, identified by a private key, can check the signature and learn the value of the predicate. Auditability mechanisms in the form of non-interactive zero-knowledge proofs are provided, so that a cheating signer cannot issue arbitrary signatures and a cheating verifier cannot ignore the embedded condition. The security properties of this new primitive are defined using cryptographic games. A proof-of-concept construction, based on the Okamoto–Schnorr blind signatures infused with a plaintext equivalence test is presented and its security is analyzed.
An important objective of research in counting complexity is to understand which counting problem... more An important objective of research in counting complexity is to understand which counting problems are approximable. In this quest, the complexity class \(\mathsf {TotP}\), a hard subclass of \(\#\mathsf {P}\), is of key importance, as it contains self-reducible counting problems with easy decision version, thus eligible to be approximable. Indeed, most problems known so far to admit an fpras fall into this class.
Nous considerons des mecanismes pour le probleme du bureaucrate paresseux. Des agents, responsabl... more Nous considerons des mecanismes pour le probleme du bureaucrate paresseux. Des agents, responsables d'une tâche doivent communiquer la duree de leur tâche a un ordonnanceur. Son objectif est de selectionner un sous ensemble de tâches maximal pour l'inclusion, dont la duree totale n'excede pas son budget et est minimum. Nous nous interessons aux mecanismes a veracite garantie, pour lesquels les agents n'ont pas interet a mentir sur la duree de leurs tâches afin d'appartenir a l'ensemble des tâches selectionnees.
In this chapter we consider the design of Secure Broadcast protocols in generic networks of known... more In this chapter we consider the design of Secure Broadcast protocols in generic networks of known topology. Studying the problem of Secure Message Transmission (SMT) proves essential for achieving Broadcast in incomplete networks. We present a polynomial protocol that achieves parallel secure message transmissions between any two sets of nodes of an incomplete network provided that the weakest connectivity conditions which render the Broadcast problem solvable hold. Using the above, we show that the SMT protocol can be used as a subroutine for the simulation of any known protocol for complete networks, which leads us to protocols for generic networks which remain polynomial with respect to the measures of consideration. We extend our result to the case of wireless networks by exploiting the fact that participants are committed to perform local broadcasts, which greatly facilitates achieving an agreement.
This work formalizes Publicly Auditable Conditional Blind Signatures (PACBS), a new cryptographic... more This work formalizes Publicly Auditable Conditional Blind Signatures (PACBS), a new cryptographic primitive that allows the verifiable issuance of blind signatures, the validity of which is contingent upon a predicate and decided by a designated verifier. In particular, when a user requests the signing of a message, blinded to protect her privacy, the signer embeds data in the signature that makes it valid if and only if a condition holds. A verifier, identified by a private key, can check the signature and learn the value of the predicate. Auditability mechanisms in the form of non-interactive zero-knowledge proofs are provided, so that a cheating signer cannot issue arbitrary signatures and a cheating verifier cannot ignore the embedded condition. The security properties of this new primitive are defined using cryptographic games. A proof-of-concept construction, based on the Okamoto–Schnorr blind signatures infused with a plaintext equivalence test is presented and its security is analyzed.
An important objective of research in counting complexity is to understand which counting problem... more An important objective of research in counting complexity is to understand which counting problems are approximable. In this quest, the complexity class \(\mathsf {TotP}\), a hard subclass of \(\#\mathsf {P}\), is of key importance, as it contains self-reducible counting problems with easy decision version, thus eligible to be approximable. Indeed, most problems known so far to admit an fpras fall into this class.
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