Public Key Cryptography In Summary

• A public key is used to encrypt and a separate, different private key to decrypt the message.
   
  
• Each party involved generates a key pair.
   
  
• Each party publishes their public key.
   
  
• Each party secures their private key, which must remain secret.
   
  
• Assuming A desires to send a message to B, it first encrypts the message using B's public key.
   
  
• B can decrypt the message using its private key. Since no one else knows B's private key, this is absolutely secure -- no one else can decrypt it.
   
  
• There still remain difficult problems of authentication of public keys, compromised keys, bogus & out of date keys. Further, Public Key encryption is very, very slow compared to single key systems.
   
  
• A very useful way of using public key cryptography is as a means of distributing secret keys for conventional single key cryptography. The most common example of this, which most of us have probably used, is the Secure Sockets Layer (SSL) cryptography used in the World Wide Web, see later.