'Understanding PKI'

Computerworld - This book excerpt is from Chapter 6 "Certificates and Certifications" of the newly released Understanding PKI, Second Edition: Concepts, Standards, and Deployment Considerations. It is posted with permission from Addison-Wesley Professional.

As we discussed in Chapter 2, public-key cryptography involves the use of public/private-key pairs to facilitate digital signature and key management services. The fundamental principle that enables public-key technology to scale is the fact that the public component of the public/private-key pair may be distributed freely among the entities that need the public component to use the underlying security services. (See Chapters 4 and 5 for more information regarding security services enabled through the use of a PKI.)

However, distribution of the public component without some form of integrity protection would defeat the very foundation for these security services. Thus, the public-key component must be protected in such a way that it will not impact the overall scalability that public-key cryptography techniques offer. Further, we need to bind certain attributes with the public key.

Thus, a data integrity mechanism is required to ensure that the public key (and any other information associated with that public key) is not modified without detection. However, a data integrity mechanism alone is not sufficient to guarantee that the public key belongs to the claimed owner. A mechanism that binds the public key to the claimed owner in a trustworthy manner is also required. In the end, the goal is to provide a single mechanism by which a relying party (that is, the "user" of the key and associated data, as defined in [RFC2527] is assured that

• The integrity of the public key (and any other associated information) is sound.






• The public key (and any other associated information) has been bound to the claimed owner in a trusted manner.

Certificates

Kohnfelder first introduced the concept of using a signed data structure or certificate to con-vey the public key to a relying party in his 1978 bachelor's thesis entitled "Towards a Practical Public-Key Cryptosystem" [Kohn78]. Thus, over two decades ago, it was recognized that a scalable and secure method (from an integrity perspective) would be required to convey the public keys to the parties that needed them. Simply stated, public-key certificates are used to bind an entity's name (and possibly additional attributes associated with that entity) with the corresponding public key.