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    Adaptive Key Protection in Complex Cryptosystems with Attributes

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    In the attribute-based encryption (ABE) model, attributes (as opposed to identities) are used to encrypt messages, and all the receivers with qualifying attributes can decrypt the ciphertext. However, compromised attribute keys may affect the communications of many users who share the same access control policies. We present the notion of forward-secure attribute-based encryption (fs-ABE) and give a concrete construction based on bilinear map and decisional bilinear Diffie-Hellman assumption. Forward security means that a compromised private key by an adversary at time t does not break the confidentiality of the communication that took place prior to t. We describe how to achieve both forward security and encryption with attributes, and formally prove our security against the adaptive chosen-ciphertext adversaries. Our scheme is non-trivial, and the key size only grow
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