@Misc{AHR05a,
  author = 	 { Ben Adida and Susan Hohenberger and Ronald L. Rivest },
  title = 	 { Ad-Hoc Group Signatures from Hijacked Keypairs },
  howpublished = { Unpublished draft.
                   A preliminary version was presented by Ben Adida at the
                   April 14--15, 2005 DIMACS Workshop on Theft in E-Commerce.
                 },
  date =         { 2005-06-24 },                  
  OPTmonth = 	 { June 24, },
  OPTyear = 	 { 2005 },
  eventtitle =   { DIMACS Workshop on Theft in E-Commerce: Content, Identity, and Service },                  
  eventdate =    { 2005-04-14/2005-04-15 },                  
  venue =        { Rutgers, Piscataway, New Jersey },                  
  organizers =   { Drew Dean and Markus Jakobsson },                  
  urla =         { <a href="http://dimacs.rutgers.edu/Workshops/Intellectual/program.html">workshop</a> },                  
  abstract =     {
        Ad-hoc-group signatures enable an individual to sign on behalf of a group without requiring prior
        group membership setup. Such signatures are used to provide credibility -- the signer must be one of the
        group members -- combined with some degree of anonymity -- the identity of the signer within the group
        cannot be determined. Thus, in many instances, other group members might not cooperate in the creation
        of such a signature. They may even wish to interfere with its creation, refusing to generate keypairs of a
        form that might facilitate such activity.
        \par                  
        We present a combination of techniques for efficiently coercing any user into an ad-hoc signatory
        group, using only that user's public key. This public key may correspond to almost any signature or
        encryption scheme, as long as there exists an efficient Special Honest Verifier Zero Knowledge Proof
        of Knowledge protocol for the secret key, or, alternatively, a hash-and-sign algorithm for that keypair
        type. Our approach effectively hijacks any public key for the purpose of building an ad-hoc group
        signature. We also present a new proof protocol that enables, within our framework, the hijacking of
        Boneh-Franklin and Waters identity-based encryption keys, as well as Camenisch-Lysyanskaya signature
        keys.     
                 },                  
}