The Core Technology: Public-Key Cryptography

Microsoft Corporation

September 10, 1996

Cryptography provides a set of techniques for encoding data and messages such that the data and messages can be stored and transmitted securely. This section introduces the basic terminology of cryptography and explains some of the common methods used.

Cryptography can be used to achieve secure communications, even when the transmission media (for example, the Internet) is untrustworthy. You can also use cryptography to encrypt your sensitive files, so that an intruder cannot understand them.
Cryptography can be used to ensure data integrity as well as maintain secrecy.
Using cryptography, it becomes possible to verify the origin of data and messages. This is done using digital signatures.
When using cryptographic methods, the only part that must remain secret is the cryptographic keys. The algorithms, the key sizes, and file formats can be made public without compromising security.

Cryptography allows a series of operations or actions on data. The two fundamental operations are encryption (with decryption as its inverse) and signing (with verification of signature as its matching operation). Encryption is analogous to enclosing data in an opaque envelope; decryption is analogous to removing it from the envelope. Signature is similar to physically signing a document, and initialing each section to show that no portion of the document has changed. Verification of signature is roughly equivalent to matching the signature to a "signature on file" card, and verifying that no portion of the document has changed. Certificates are signed documents which match public keys to other information.

Here's a brief description of the core technology: