@inproceedings{IACR:conf/eurocrypt2003/AhnEC03,
  author    = { Luis von Ahn and Manuel Blum and Nicholas J. Hopper and John Langford
               },
  title     = {CAPTCHA: Using Hard AI Problems for Security},
  booktitle = {EUROCRYPT},
  year      = {2003},
  pages     = {294-311},
  ee        = {http://www.iacr.org/archive/eurocrypt2003/26560294/26560294.pdf},
  crossref  = {IACR:conf/eurocrypt2003},
  bibsource = {IACR, http://www.iacr.org}
}

@proceedings{IACR:conf/eurocrypt2003,
  editor    = {Eli Biham},
  title     = {Advances in Cryptology - EUROCRYPT 2003, International Conference on
the Theory and Applications of Cryptographic Techniques, Warsaw,
Poland, May 4-8, 2003, Proceedings.},
  booktitle = {EUROCRYPT},
  publisher = {Springer},
  series    = {Lecture Notes in Computer Science},
  volume    = {2656},
  year      = {2003},
  isbn      = {3-540-14039-5},
  bibsource = {IACR, http://www.iacr.org}
}