Section 13.9. Other Security Topics

13.9. Other Security Topics

The specifications discussed in this chapter provide a strong foundation to secure Web services interactions, supporting sophisticated, automated business-to-business interactions. Additional technologies, not explicitly covered in the specifications discussed here, provide support for specific circumstances that often arise in the course of a business transaction. This section discusses the use of public key cryptography and how to provide non-repudiation capabilities in Web services interactions.

13.9.1. Public-Key Cryptography

Public-key cryptography was introduced in the mid-1970s by Whitfield Diffie and Martin Hellman. The concept is simple and elegant, yet it has had a huge impact on the science and applications of cryptography. It's based on the idea of encryption keys, private and public, as related pairs. The private key remains concealed by its owner, while the public key is freely disseminated to various partners. Data encrypted using the public key can be decrypted only by using the associated private key, and vice versa. Because the key used to encrypt plain text is different from the key used to decrypt the corresponding cipher text, this is also known as asymmetric cryptography.

The premise behind public-key cryptography is that it should be computationally infeasible to obtain the private key simply by knowing the public key. Modern public-key cryptography derives from sophisticated mathematical foundations, which are based on the one-way functions existing in the abstractions of number theory. A one-way function is an invertible function that is easy to compute but computationally hard to invert. A one-way trapdoor function is a one-way function that can be inverted only if one knows a secret piece of information, known as the trapdoor. Encryption is the easy one-way trapdoor function; its inverse, decryption, is the hard function. The only way to make the decryption as easy as the encryption is to have the private key.

Two of these one-way functions, factoring large numbers and computing discrete logarithms, form the basis of modern public-key cryptography. Factoring large numbers is a one-way trapdoor function, whereas computing discrete logarithms is a one-way function with no trapdoors.