International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Forward-Secure Signatures with Untrusted Update

Xavier Boyen
Hovav Shacham
Emily Shen
Brent Waters
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Abstract: In most forward-secure signature constructions, a program that updates a user's private signing key must have full access to the private key. Unfortunately, these schemes are incompatible with several security architectures including Gnu Privacy Guard (GPG) and S/MIME, where the private key is encrypted under a user password as a ``second factor'' of security, in case the private key storage is corrupted, but the password is not. We introduce the concept of forward-secure signatures with untrusted update, where the key update can be performed on an encrypted version of the key. Forward secure signatures with untrusted update allow us to add forward security to signatures, while still keeping passwords as a second factor of security. We provide a construction that has performance characteristics comparable with the best existing forward-secure signatures. In addition, we describe how to modify the Bellare-Miner forward secure signature scheme to achieve untrusted update.
  title={Forward-Secure Signatures with Untrusted Update},
  booktitle={IACR Eprint archive},
  keywords={public-key cryptography /},
  note={An extended abstract is to appear in ACM CCS 2006. 13390 received 30 Aug 2006},
  author={Xavier Boyen and Hovav Shacham and Emily Shen and Brent Waters},