Extended dual system group and shorter unbounded hierarchical identity based encryption

This paper continued the research line of dual system groups (DSG) opened by Chen and Wee (CRYPTO, 2013 and IACR Cryptology ePrint Archive, 2014). Motivated by Lewko’s unbounded hierarchical identity based encryptions (HIBE) (EUROCRYPT, 2012), we extended Chen and Wee’s DSG and showed how to construct an unbounded HIBE from our extended DSG. Furthermore, an instantiation of our extended DSG was given using prime-order bilinear groups under the d-Lin assumption. These two results imply an adaptively secure unbounded HIBE in the standard model with not only shorter ciphertexts and user’s secret keys but also faster algorithms than Lewko’s construction.