Proving Security of Tor ’ s Hidden Service Identity Blinding Protocol

Tor’s Hidden Services allow a server to offer a service anonymously through the Tor network. Hidden Services are associated with an identity key and need to publish descriptors that allow clients to locate introduction points to which the hidden service has already established anonymous circuits. As Biryukov et al. show [2], in the current Hidden Service design, a Tor Node that is in position to publish the descriptor for a hidden service can learn the identity key of the service and launch further attacks that could allow it to de-anonymize the service. This report analyzes the security of a new design proposed by Robert Ransom [3] and specified in full as Tor Proposal 224 to eliminate these attacks.