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Public key cryptography (PKC) is a system based on pairs of keys, a
public key and a private key, rather than on a single secret key. The
keys are related in such a way that information that is encrypted with
the public key can only be decrypted with the private key. This means
that, if I have a pair of keys, I can make my public key freely
available to anyone who wants it without worrying about who else might
get it. If anyone wants to send me a secret message, they can use my
public key to encrypt the message. Only I can decrypt the message,
using my private key, which I keep safe.

The action of encrypting information with PKC keys is significantly
slower than encrypting with a secret key, such as a DES (Data
Encryption Standard) key. So, in practice, a system that uses PKC first
generates a secret key according to a method such as DES. It uses the
secret key to encrypt the message, and it uses the PKC key to encrypt
the secret key. Then, it attaches the PKC-encrypted secret key to the
secret key-encrypted message.

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*Denis Arnaud*

*12/19/1997*