Security

Expressive Black-Box Traceable Ciphertext-Policy Attribute-Based Encryption

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Executive Summary

In a Ciphertext-Policy Attribute-Based Encryption (CP-ABE) system, decryption privileges are defined over attributes that could be shared by multiple users. If some of the users leak their decryption privileges to the public or to some third party, say for profit gain, a conventional CP-ABE has no tracing mechanism for finding these malicious users out. There are two levels of traceability for tackling this problem: given a well-formed decryption key, a White-Box tracing algorithm can find out the original key owner; and given a decryption-device while the underlying decryption algorithm or key may not be given, a Black-Box tracing algorithm, which treats the decryption-device as an oracle, can find out at least one of the malicious users whose keys have been used for constructing the decryption-device.

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