Forward-Secure Signatures with Untrusted Update

Package: libfssig-0.2.tar.gz
License: GPL
Developers: Emily Shen (primary), John Bethencourt (build system)
Added to ACSC: September 13, 2007
Last updated: October 22, 2007


This C library implements a forward-secure signature scheme that allows “untrusted updates”. In most forward-secure signature constructions, a program that periodically updates a user's private signing key must have full access to the private key. However, this prevents the common practice of encrypting it on disk under a passphrase. A scheme supporting untrusted updates, however, allows updates to the private key while it is encrypted.

The original author of the libfssig is Emily Shen. John Bethencourt packaged it up as a library and made some minor updates for releasing it.


Right now, the only documentation available is description of the provided functions in the README file within the source tarball. An example program, testfssig.c, is also included. This is probably all that is necessary, given the simplicity of the library.

Bugs and Limitations

None known, but like many other things on the ACSC this is research quality software and should not be used in any application actually requiring security. If you find any bugs, an email (or even a patch!) directed to John Bethencourt would be appreciated.


The scheme is implemented as described in the following paper.