Until a few years ago there was no good way to do the latter,in the sense that any convenient encryption scheme could be broken by a sufficiently determined and resourceful opponent. That has changed with the growing popularity of the free software package PGP,authored by Philip Zimmermann, a programmer and small-computer consultant herein Boulder. In fact, this is my own public key. Users of PGP generate a pair of keys, onepublic and one secret. The two keys represent two very large numbers that arerelated mathematically but impossible to derive from one another using currenttechnology.
Individuals can share their public keys by post or e-mail, phoneor fax, billboard or skywriting.
Any eavesdropping thirdparty, who has only the two public keys, cannot unscramble the encryptedmessage. The scheme that can accomplish this magic is RSA, invented by Ron Rivest, AdiShamir, and Leonard Adleman, and published in 1977. The latter, which is like asuper-password, protects your secret key. Personal privacy sounds great, but remember that the same software can be usedby, say, terrorists and pornographers to keep their own files andcommunications secret. Some branches of government such as the NationalSecurity Agency, employer of the best cryptographic staff and hardware in theworld, are less than happy about such top-quality encryption being in the handsof everyone.