Direct chosen-ciphertext secure identity-based key encapsulation without random oracles

We describe a practical identity-based encryption scheme that is secure in the standard model against chosen-ciphertext attacks. Our construction applies “direct chosen-ciphertext techniques” to Waters’ chosen-plaintext secure scheme and is not based on hierarchical identity-based encryption. Furthermore, we give an improved concrete security analysis for Waters’ scheme. As a result, one can instantiate the scheme in smaller groups, resulting in efficiency improvements.