## Cryptology ePrint Archive: Report 2006/122

Chosen-Ciphertext Secure Identity-Based Encryption in the Standard Model with short Ciphertexts

Eike Kiltz

Abstract: We describe a practical identity-based encryption scheme that is secure in the standard model against chosen-ciphertext (CCA2) attacks. Security is based on an assumption comparable to (but slightly stronger than) Bilinear Decisonal Diffie-Hellman (BDDH). A comparison shows that our construction outperforms all known identity-based encryption schemes in the standard model and its performance is even comparable with the one from the random-oracle based Boneh/Franklin IBE scheme. Our proposed IBE scheme has furthermore the property that it fulfills some notion of redundancy-freeness", i.e. the encryption algorithm is not only a probabilistic injection but also a surjection. As a consequence the ciphertext overhead is nearly optimal: to encrypt $k$ bit messages for $k$ bit identities and with $k$ bit randomness we get $3k$ bit ciphertexts to guarantee (roughly) $k$ bits of security.

Category / Keywords: public-key cryptography / Chosen-ciphertext security, Identity-Based Encryption, Bilinear Maps

Date: received 28 Mar 2006, last revised 19 Nov 2008

Contact author: kiltz at cwi nl

Available format(s): PDF | BibTeX Citation

Note: Note: parts of this unpublished pre-print appeared as follows:

Eike Kiltz and Yevgeniy Vahlis. CCA2 Secure IBE: Standard Model Efficiency through Authenticated Symmetric Encryption. Proceedings of CT-RSA 2008. Full version available on Cryptology ePrint Archive: Report 2008/020.

Short URL: ia.cr/2006/122

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