Bio

Ewa Syta is a PhD candidate in the Computer Science Department at Yale University. She is co-advised by Professors Michael Fischer and Bryan Ford. Prior to joining Yale, she earned her B.S. and M.S. in Computer Science and Cryptology from Military University of Technology in Warsaw, Poland. Her research interests lie in computer security. She is particularly interested in the security and privacy issues users face as a result of engaging in online activities. She has been working on developing stronger anonymous communication technologies, privacy-preserving biometric authentication schemes, anonymous and deniable authentication methods as well as different ways to generate good and verifiable randomness in a distributed setting.

Certificate Cothority: Towards Trustworthy Collective CAs

Certificate Cothority: Towards Trustworthy Collective CAs

Certificate Authorities (CAs) sign certificates attesting that the holder of a public key legitimately represents a name such as google.com, to authenticate SSL/TLS connections. Only if a server can produce a certificate signed by a trusted CA, will the client’s browser accept it and establish a secure connection.

Current web browsers directly or indirectly trust hundreds of CAs, any one of which can issue fake certificates for any domain. Consequently, it takes only one compromised or malicious CA to threaten the security of the entire PKI and in turn, everyone on the Internet. Due to this “weakest-link” security, hackers have stolen the “master keys” of CAs such as DigiNotar and Comodo and successfully generated fake certificates for website spoofing and man-in-the-middle attacks.

We propose to replace current, high-value certificate authorities with a certificate cothority (CC) — a practical system, which embodies strongest-link security by allowing all participants to validate certificates before they are issued and endorsed, and therefore proactively prevent their misuse.

We build certificate cothorities using an instantiation of a collective authority (cothority), an architecture we propose to enable thousands of participants to witness, validate, and co-sign an authority’s public actions, with moderate delays and costs.

Each of potentially thousands of hosts comprising a certificate cothority independently validates each new batch of certificates, either contributing a share of a collective digital signature or withholding it and raising an alarm if misbehavior is detected. This collective signature attests to the client that not just one but many (ideally thousands) well-known servers independently checked and signed off on a certificate. Therefore, a certificate cothority guarantees strongest-link security whose strength increases as the collective grows, instead of decreasing to weakest-link security as in today’s CA system.