EFF is offering a number of Summer of Code projects for 2011. These include:
HTTPS Everywhere is a Firefox extension that automatically switches requests from HTTP websites to HTTPS versions. It uses rulesets to describe these transformations, which are sometimes quite complicated.
One possible Summer of Code project would be implementing context-dependent ruleset control and other UI improvements for HTTPS Everywhere, as discussed in the project's current roadmap.
The SSL Observatory
The EFF SSL Obseravtory is a project to collect and analyse complete lists of all the SSL/TLS certificates on the public web, in order to study the set of Certificate Authorities, check their work, and look for trends and problems in X.509 deployment.
We are building a decentralised version of the observatory, and could mentor GSOC students working on various aspects of that project.
Open-Source Security Auditing
In collaboration with computer security consulting firms, we will be auditing code for a number of security-critical free and open source software codebases. Google summer of code students interested in gaining experience in finding and fixing vulnerabilities could join us in this project.