# Scalable Wildcarded Identity-Based Encryption

## Abstract

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.

## Keywords

Wildcard identity based encryption Constant ciphertext Key delegation Pattern## Notes

### Acknowledgement

This work was supported by Institute for Information and communications Technology Promotion (IITP) grant funded by the Korea government (MSIT) (No. 2016-6-00599, A Study on Functional Signature and Its Applications and No. 2017-0-00661, Prevention of video image privacy infringement and authentication technique), by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2017R1A2B4009903 and No. 2016R1D1A1B03934545), and by Basic Research Laboratory Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (MSIP) (No. 2017R1A4A1015498).

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