Constant-Size Hierarchical Identity-Based Signature/Signcryption without Random Oracles

We construct the first constant-size hierarchical identity-based signature (HIBS) without random oracles - the signature size is $O(\lambda_s)$ bits, where $\lambda_s$ is the security parameter, and it is independent of the number of levels in the hierarchy. We observe that an efficient hierarchical identity-based signcryption (HIBSC) scheme without random oracles can be compositioned from our HIBS and Boneh, Boyen, and Goh\u27s hierarchical identity-based encryption (HIBE). We further optimize it to a constant-factor efficiency improvement. This is the first constant-size HIBSC without random oracles