Securing Traceability of Ciphertexts - Towards a Secure Software Key Escrow System (Extended Abstract)

The Law Enforcement Agency Field (LEAF), which in Clipper is appended to the ciphertext, allows the Law Enforcement Agency to trace the sender and receiver. To prevent users of Clipper to delete the LEAF, the Clipper decryption box will not decrypt if the correct LEAF is not present. Such a solution requires the implementation to be tamperproof. In this paper we propose an alternative approach to achieve traceability. Our solution is based on the computational complexity of some well known problems in number theory. So, our scheme does not require a tamperproof implementation, nor a secret algorithm. Its applications extend beyond key escrow.

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