Microsoft® Windows® 2000 Security Handbook

Keys and Key Length

A key is a value that works with a cryptographic algorithm to produce encrypted data. In the final analysis, keys are really just big, big numbers. Key size is measured in bits; the number representing a 1,024-bit key is bigger than most calculators can handle. In public key cryptography, the bigger the key, the more secure the encryption.

Note

All keys are not created equal. The size of a public key and the size of the more traditional secret key are unrelated. An 80-bit secret key has the equivalent strength of a 1,024-bit public key. Because the rule of thumb is bigger is better, it becomes obvious that your public keys will have to be an order of magnitude larger than their secret counterparts. This is part of the reason ...