CRYPTOGRAPHIC KEY RECOVERY SYSTEM

摘要

A cryptographic key recovery system for generating a cryptographic key for use by a pair of communicating parties while simultaneously providing for its recovery using one or more key recover agents. A plurality of m-bit shared key parts (P, Q) are generated which are shared with respective key recovery agents, while an n-bit nonshared key part (R) is generated that is not shared with any key recovery agent. The shared key parts (P, Q) are combined to generate an m-bit value which is concatenated with the nonshared key part (R) to generate an (m + n)-bit value from which an encryption key is generated. The cryptographic system has the effective work factor of an n-bit key to all of the key recovery agents acting in concert, but has the effective work factor of an (m + n)-bit to any other combination of third parties. The quantity n is selected to make authorized key recovery feasible, but not so trivial as to permit routine decryption of intercepted communications, while the quantity m is selected to make decryption by unauthorized third parties infeasible. Means are provided for verifying that the shared key parts have been shared with the key recovery agents before permitting encrypted communications using the thus generated key.