Multi-grade cryptography

The recent development of powerful cryptographic techniques has caused a number of public policy issues to become significant. The three most prominent issues are (1) export control, (2) key escrow, and (3) anonymity. These represent tradeoffs between different societal objectives: (1) commerce/national-security and (2,3) privacy/law-enforcement. Some discussion of cryptographic policy issues can be found in Hoffman[3]. While the rapid development of cryptography is likely to make attempts to control it ultimately futile, it is interesting to see what technical possibilities there are for supporting compromise positions in each such trade-off. This paper presents a new paradigm for secret-key cryptography that may be useful for export control (and perhaps also for law-enforcement). We call it multi-grade cryptography because it makes a single cryptosystem appear to present multiple levels of security. It is not based on key-escrow, but rather on computational complexity.