International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Secret Handshakes from CA-Oblivious Encryption

Claude Castelluccia
Stanislaw Jarecki
Gene Tsudik
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Abstract: Secret handshake protocols were recently introduced by Balfanz et al. [IEEE, Oakland 2003] to allow members of the same group to authenticate each other *secretly*, in the sense that someone who is not a group member cannot tell, by engaging some party in the handshake protocol, whether that party is a member of the group. On the other hand, any two parties who are members of the same group will recognize each other as members. Thus, secret handshakes can be used in any scenario where group members need to identify each other without revealing their group affiliations to outsiders. The secret handshake protocol of Balfanz et al. relies on a Bilinear Diffie-Hellman assumption (in ROM) on certain elliptic curves. We show how to build secret handshake protocols secure under more standard cryptographic assumption of Computational Diffie Hellman(CDH), using a novel tool of CA-oblivious public key encryption, which is an encryption scheme s.t. neither the public key nor the ciphertext reveal any information about the Certification Authority (CA) which certified the public key. We construct such CA-oblivious encryption, and hence a handshake scheme, based on CDH (in ROM). The new scheme takes 3 communication rounds like the scheme of Balfanz et al., but it is about twice cheaper computationally, and it relies on a weaker computational assumption.
  title={Secret Handshakes from CA-Oblivious Encryption},
  booktitle={IACR Eprint archive},
  keywords={cryptographic protocols / identification protocols, privacy, public-key cryptography},
  note={to be published in Asiacrypt 2004, preliminary one-page announcement in PODC 2004 12662 received 2 Jun 2004, last revised 1 Sep 2004},
  author={Claude Castelluccia and Stanislaw Jarecki and Gene Tsudik},