@Misc{BJRS13a,
  author =    { John G. Brainard and Ari Juels and Ronald L. Rivest and Michael Szyldo },
  title =     { User Authentication Based on Voucher Codes },
  howpublished = { U.S. Patent 8,438,617. Issued May 7, 2013. },
  date =      { 2013-05-07 },                  
  OPTmonth =  { May 7, },
  OPTyear =   { 2013 },
  urla =      { <a href="http://www.google.com/patents/US8438617">google-patent-page</a> },                  
  abstract =  { An authentication server authenticates a first user,
                  and generates a voucher code that is provided to the
                  authenticated first user. The first user may provide
                  the voucher code to a second user, responsive to a
                  request by the second user for the first user to
                  vouch for the second user, to thereby allow the
                  second user to be authenticated. The authentication
                  server receives the voucher code from the second
                  user, and authenticates the second user based on the
                  voucher code. The authenticated second user may be
                  provided with a temporary password or other type of
                  code utilizable for at least one additional
                  authentication.  },
}