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1 to 7 of 7 results
  • Flexible anonymous subscription schemes

     González Vasco, Maria Isabel; Heidarvand, Somayed; Villar Santos, Jorge Luis
    Communications in computer and information science
    Date of publication: 2012
    Journal article

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  • Privacy-Providing Signatures and Their Applications

     Heidarvand, Somayed
    Defense's date: 2011-03-16
    Department of Applied Mathematics IV, Universitat Politècnica de Catalunya
    Theses

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  • A fair and abuse-free contract signing protocol from Boneh-Boyen signature

     Heidarvand, Somayed; Villar Santos, Jorge Luis
    Public Key Infrastructures, Services and Applications
    Presentation's date: 2010-09
    Presentation of work at congresses

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    A fair contract signing protocol is used to enable two mistrusted parties to exchange two signatures on a given contract, in such a way that either both of them get the other party’s signature, or none of them gets anything. A new signature scheme is presented, which is a variant of Boneh and Boyen’s scheme, and building on it, we propose a new signature fair exchange protocol for which all the properties of being optimistic, setup-free and abuse-free can be proved without random oracles, and it is more efficient than the known schemes with comparable properties.

  • Anonymous subscription schemes : a flexible fonstruction for on-line services access

     González Vasco, Maria Isabel; Heidarvand, Somayed; Villar Santos, Jorge Luis
    International Conference on Security and Cryptography
    Presentation's date: 2010-07
    Presentation of work at congresses

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    In traditional e-cash systems, the tradeoff between anonymity and fraud-detection is solved by hiding the identity of the user into the e-coin, and providing an additional triggering mechanism that opens this identity in case of double spending. Hence, fraud detection implies loss of anonymity. This seems to be a somewhat natural solution when universality of the e-coin is required (i.e., the use of the coin is not determined at the time the coin is generated). However, much simpler protocols may suffice if we only want to prevent that payments for accessing certain services are over-used, even when users' anonymity is perfectly preserved. In this paper we propose a simple and efficient Subscription Scheme, allowing a set of users to anonymously pay for and request access to different services offered by a number of service providers. In our approach, the use of the token is completely determined at issuing time, yet this final aim remains hidden to the issuing authority. Moreover, fraud detection here implies no loss of anonymity; as we make access tokens independent of the owner in a quite simple and efficient way. On the other hand, if different usages of the same token are allowed, these are fully traceable by the service providers.

  • CRIPTOGRAFIA DE CLAVE PUBLICA Y COMPARTICIÓN DE SECRETOS

     Morillo Bosch, Maria Paz; Gracia Rivas, Ignacio; Martí Farré, Jaume; Martin Mollevi, Sebastia; Padro Laimon, Carles; Saez Moreno, German; Herranz Sotoca, Javier; Rafols Salvador, Carla; Heidarvand, Somayed; Villar Santos, Jorge Luis
    Participation in a competitive project

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  • European Network of Excellence for Cryptology II

     Morillo Bosch, Maria Paz; Martí Farré, Jaume; Heidarvand, Somayed; Gracia Rivas, Ignacio; Padro Laimon, Carles; Martin Mollevi, Sebastia; Saez Moreno, German; Herranz Sotoca, Javier; Rafols Salvador, Carla; Villar Santos, Jorge Luis
    Participation in a competitive project

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  • Public verifiability from pairings in secret sharing schemes

     Heidarvand, Somayed; Villar Santos, Jorge Luis
    Lecture notes in computer science
    Date of publication: 2009
    Journal article

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    In this paper we propose a new publicly verifiable secret sharing scheme using pairings with close relations to Shoenmakers’ scheme. This scheme is efficient, multiplicatively homomorphic and with unconditional verifiability in the standard model. We formalize the notion of Indistinguishability of Secrets and prove that out scheme achieves it under the Decisional Bilinear Square (DBS) Assumption that is a natural variant of the Decisional Bilinear Diffie Hellman Assumption. Moreover, our scheme tolerates active and adaptive adversaries.