Scalable Wildcarded Identity-Based Encryption

Wildcarded identity-based encryption allows a sender to simultaneously encrypt messages to a group of users matching a certain pattern, defined as a sequence of identifiers and wildcards. We propose a new wildcarded identity-based encryption scheme with generalized key delegation, which reduces the ciphertext size to be constant. To the best of our knowledge, our proposal is the first wildcarded identity-based encryption scheme that generates a constant size ciphertext regardless of the depth of the identities. The proposed scheme also improves the decryption time by minimizing the wildcard conversion cost. According to our experiment results, decryption of the proposed scheme is 3, 10, and 650 times faster than existing WIBE, WW-IBE, and CCP-ABE schemes. The proposal also subsumes the generalized key derivation naturally by allowing wildcards in the key delegation process. We prove CPA security of the proposed scheme and extend it to be CCA secure.