Efficient construction of infinite length hash chains with perfect forward secrecy using two independent hash functions

One-way hash chains have been used to secure many applications over the last three decades. To overcome the fixed length limitation of first generation designs, so-called infinite length hash chains have been introduced. Such designs typically employ methods of asynchronous cryptography or hash based message authentication codes. However, none of the proposed schemes offers perfect forward secrecy, keeping former outputs secret once the system got compromised. A novel algorithm for constructing infinite length hash chains with built-in support for perfect forward secrecy is presented in this work. Thereby, the scheme differs significantly from existing proposals by using a combination of two different hash functions. It avoids the computational complexity of public-key algorithms, utilises well studied standard hash functions and keeps the benefits of a hash chain without a length constraint.