Blind decoding, blind undeniable signatures, and their applications to privacy protection

  • Kouichi Sakurai
  • Yoshinori Yamane
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 1174)


A cryptographic concept, blind decoding is discussed: a client has a message encrypted with a server's public key and the client asks the server to decode the message without revealing what is the decoded plaintext nor learning the server's secret key. Blind decoding is a useful tool for protecting user's privacy in on-line shopping over the Internet. The RSA-based blind decoding is easily converted from the similar protocol as the Chaum's blind signature scheme, and a blind decoding protocol for the ElGamal encryption scheme is newly proposed. Moreover, the practical gap between the known RSA-based blind decoding and our ElGamal-based scheme is discussed in the application to protecting copyright matter of electronic documents.

In blind decoding scheme, undetectability of the decrypted message has both negative and positive aspects: a negative aspect is considered as the problem of spotting the oracle and a positive aspect is applicable to making undeniable signatures blind against the signer.

Key words

Blind decoding undeniable signatures ElGamal encryption privacy protection online shopping digital money 


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Copyright information

© Springer-Verlag Berlin Heidelberg 1996

Authors and Affiliations

  • Kouichi Sakurai
    • 1
  • Yoshinori Yamane
    • 1
  1. 1.Dept. of Computer Science and Communication EngineeringKyushu UniversityJapan

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