2. Name Certification
Certificates were originally viewed as having one function: binding names to keys or keys to names. This thought can be traced back to the paper by Diffie and Hellman introducing public key cryptography in 1976. Prior to that time, key management was risky, involved and costly, sometimes employing special couriers with briefcases handcuffed to their wrists.
Diffie and Hellman thought they had radically solved this problem. "Given a system of this kind, the problem of key distribution is vastly simplified. Each user generates a pair of inverse transformations, E and D, at his terminal. The deciphering transformation, D, must be kept secret but need never be communicated on any channel. The enciphering key, E, can be made public by placing it in a public directory along with the user's name and address. Anyone can then encrypt messages and send them to the user, but no one else can decipher messages intended for him." [DH]
This modified telephone book, fully public, took the place of the trusted courier. This directory could be put on-line and therefore be available on demand, worldwide. In considering that prospect, Loren Kohnfelder, in his 1978 bachelor's thesis in electrical engineering from MIT [KOHNFELDER], noted: "Public-key communication works best when the encryption functions can reliably be shared among the communicants (by direct contact if possible). Yet when such a reliable exchange of functions is impossible the next best thing is to trust a third party. Diffie and Hellman introduce a central authority known as the Public File."
2.1 First Definition of CERTIFICATE
Kohnfelder then noted, "Each individual has a name in the system by which he is referenced in the Public File. Once two communicants have gotten each other's keys from the Public File they can securely communicate. The Public File digitally signs all of its transmissions so that enemy impersonation of the Public File is precluded." In an effort to prevent performance problems, Kohnfelder invented a new construct: a digitally signed data record containing a name and a public key. He called this new construct a CERTIFICATE. Because it was digitally signed, such a certificate could be held by non-trusted parties and passed around from person to person, resolving the performance problems involved in a central directory.