Affiliations: Key Laboratory of Information and Network Security, Engineering College of Chinese Armed Police Force, Xi'an, 710086, P. R. China. [email protected]
Note: [] Address for correspondence: Key Laboratory of Information and Network Security, Engineering College of Chinese Armed Police Force, Xi'an, 710086, P. R. China
Abstract: In Informatica 32 (2008), Ren and Gu proposed an anonymous hierarchical identity based encryption scheme based on the q-ABDHE problem with full security in the standard model. Later in Indocrypt'08, they proposed another secure hierarchical identity based encryption scheme based on the q-TBDHE problem with full security in the standard model. They claimed that their schemes have short parameters, high efficiency and tight reduction. However, in this paper we give attacks to show their schemes are not secure at all. Concretely, from any first level private key, the adversary can easily derive a “private key” which can decrypt any ciphertexts for the target identity. That is to say, a query on any first level identity is enough to decrypt any ciphertext in the system.
Keywords: Cryptography, hierarchical identity based encryption, fully secure, attack
