CRYPTOGRAPHY used to be a cloak and dagger business, of interest only to spies and the security services. Not any more. The rise of e-commerce means that such everyday actions as withdrawing cash from ATM machines or buying goods on the Internet are mediated by cryptographic techniques that would be the wonder of WWII code breakers. The widespread deployment of such techniques, involved in millions of transactions each day, is testament to their basic soundness. "Good encryption, if implemented and used properly, very rarely, if ever, fails," to quote Andrew Clark, president of the International Association of Cryptographic Researchers. But there are problems. All these cryptographic techniques rely on keys - essentially very long numbers - to scramble (encrypt) information, into a form that cannot be understood by a hacker or eavesdropper. There are two basic approaches: classical cryptography, using a common secret key at both ends of the link, and public key cryptography, which uses a combination of private and public keys. The drawback to the classical approach is that it depends on having some secure means of getting the key to the two ends of the link - couriers handcuffed to briefcases have been used. Public key cryptography avoids the key distribution problem, but its security is reliant on the present formidable difficulties of separating a large number into its prime factors - difficulties which, at some point in the future, may be overcome.
展开▼
