Internet Security

74 3.3 RSA: public and private key

3.3

RSA: public and private key

We now have a better idea about how the public-private system works. It is

based on a technique patented by Diffie-Hellman in 1974 and formatted

into architecture by Rivest, Shamir, and Adelman (RSA Data Security,

Inc.). You can find more information at http://www.rsa.com and http://

www.verisign.com.

One example of the RSA implementation is PGP (Pretty Good Privacy).

Philip Zimmermann originally created PGP. Zimmermann was the first

person to make military-grade cryptography available to the general public.

PGP can be used to send encrypted messages via most any e-mail system.

All that is needed is software available from http://www.pgp.com and the

public key of the party to whom you want to send an encrypted message.

There are several methods to encrypt messages. One standard is S/

MIME. There are also secret key systems and other systems to encrypt data

as it travels from one location to another.

One process that can be used from a byproduct of public-private keys is

"digital signatures." Digital signatures can be used to authenticate messages

and prevent forgeries and/or tampering.

Following are encryption techniques that you will need to be familiar

with:

• DES~the U.S. government's data encryption standard, a cipher that

operates on 64-bit blocks of data using a 56-bit key. IBM developed

DES under contract to NIST (National Institute of Standards and

Technology).

• Triple DES~a cipher like DES that operates on 64-bit data blocks.

The difference is that Triple DES uses the basic DES cipher three times.

• RC2~a variable-key-size symmetric block cipher that can serve as a

replacement for DES.

• RC4~a variable-key-size symmetric stream cipher known for being

faster than DES.

• PEM~the Internet privacy-enhanced mail standard. PEM includes

encryption authentication and key management. The details of PEM

can be found in Internet RFCs (Requests for Comments) 1421

through 1424.

• S/MIME (Secure/Multipurpose Internet Mail Extensions)~provides

a method to send and receive secure MIME messages. S/MIME is