Timed release cryptography from bilinear pairings using hash chains

Abstract

We propose a new Timed Release Cryptography (TRC) scheme which is based on bilinear pairings together with an S/Key-like procedure used for private key generation. Existing schemes for this task, such as time-lock puzzle approach, provide an approximate release time, dependent on the recipients' CPU speed and the beginning time of the decryption process. Additionally, some other server-based schemes do not provide scalability and anonymity because the server is actively involved in the encryption or the decryption. However, there are already protocols based on bilinear pairings that solve most of the problems referred. Our goal is to extend and combine the existing protocols with desirable properties in order to create a secure, fast and scalable TRC scheme applied to dependent or sequential events. For this purpose we used continuous hashed time-instant private keys (hash chain) in the same way the S/Key system works. Our approach decreases dramatically the number of past time-instant private keys the server stores and only two keys are needed, the last one to construct the previous keys and the first one to recursively verify the authenticity of the next keys. © IFIP International Federation for Information Processing 2006.