Toward Fair International Key Escrow ⋆ – An Attempt by Distributed Trusted Third Agencies with Threshold Cryptography –

Abstract. We consider key escrow system for international communication between multiple domains with different policies. In intercepting international communications between two domains serious problems on unfairness may arise when one government has not authorized the message interception in legal. We solve this problem by incorporating a mechanism that allows message interception by law enforcement parties subject to the consent of both governments involved in the communication. That mechanism involves the establishment of an independent International Trusted Third Party (ITTP) that has the ultimate authority to check of the security policies of each country and permit or deny the interception of international messages. We present a scheme with multiple Diffie-Hellman type key distribution protocoland the ITTP copes with only the secret-key corresponding to its own public-key. We can also make the ITTP “multiple”, and we apply recent developed techniques on distributed (threshold) cryptography to our multiple ITTPs. Thus, the establishment and control of an international trusted third party can done with incorporating by each governments. Key Words: Key escrow/recovery system, Diffie-Hellman key distribution