University of Virginia, Department of Computer Science
CS200: Computer Science, Spring 2003

Notes: Wednesday 23 April 2003

For my office hours today (after class) and Thursday (4-5:30), I will be either in my office or in Small Hall.

Asymmetric Cryptography

Use different keys for encryption and decryption. Reveal one of the keys (KU, the public key). Keep the other key secret (KR, the private key).

A message encrypted with the public key is decrypted with the private key. To send a confidential message to Alice, encrypt the message with her public key.

A message encrypted with the private key is decrypted with the public key. To sign a message, encrypt it with your private key. Some else can confirm that you wrote the message, but decrypting it using your public key. Only someone who knows the private key can create a message that can be decrypted with the corresponding public key.

Real mathematics has no effects on war. No one has yet discovered any warlike purpose to be served by the theory of numbers.

G. H. Hardy, The Mathematician's Apology, 1940.

We stand today on the brink of a revolution in cryptography. The development of cheap digital hardware has freed it from the design limitations of mechanical computing and brought the cost of high grade cryptographic devices down to where they can be used in such commercial applications as remote cash dispensers and computer terminals. In turn, such applications create a need for new types of cryptographic systems which minimize the necessity of secure key distribution channels and supply the equivalent of a written signature. At the same time, theoretical developments in information theory and computer science show promise of providing provably secure cryptosystems, changing this ancient art into a science.

Diffie and Hellman, November 1976.

CS 200

CS 200: Computer Science
Department of Computer Science
University of Virginia
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