“Key certificates are an important element in the use of
public-key cryptography (PKC). Your browser, when it visits a
secure site, checks for a key certificate from a small number of
commercial certificate providers. The instructions that came with
PGP described how to sign keys, and explained the importance of
doing so. The concept of a public-key infrastructure (PKI) refers
to what is essentially a way to facilitate key certification,
perhaps with government assistance.”
“This is because of what would otherwise be a fatal weakness in
public-key cryptography.”
“Using ordinary cryptography, that is, a conventional or
symmetric algorithm, you and the person with whom you are
exchanging messages are the only two people who share the secret
key that had to have been exchanged in advance, face to face, ahead
of time.”
“Public key cryptography removes the need for a face to face
meeting in advance. Preparing a secret message only requires the
use of the public key, but unscrambling it again requires the
private key, and it is not feasible to derive the private key from
the public key. So, to send a message to someone, you use that
person’s public key to encipher it, and then he or she can use his
or her own private key to read it.”