Paper 2006/122

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

Eike Kiltz


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.

Note: Note: parts of this unpublished pre-print appeared as follows: Eike Kiltz and Yevgeniy Vahlis.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.

Available format(s)
Public-key cryptography
Publication info
Published elsewhere. Unknown where it was published
Chosen-ciphertext securityIdentity-Based EncryptionBilinear Maps
Contact author(s)
kiltz @ cwi nl
2008-11-19: last of 5 revisions
2006-03-29: received
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      author = {Eike Kiltz},
      title = {Chosen-Ciphertext Secure Identity-Based Encryption in the Standard Model with short Ciphertexts},
      howpublished = {Cryptology ePrint Archive, Paper 2006/122},
      year = {2006},
      note = {\url{}},
      url = {}
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