As with hashing, you can use several algorithms for both symmetric and asymmetric
encryption. PHP??™s mcrypt library contains implementations of the most important symmetric
algorithms. No library in PHP deals with asymmetric encryption, but if you ever need to do
asymmetric encryption, you can use the Pretty Good Privacy (PGP) family of software (for
more information, see http://www.pgp.com) and GnuPG (http://www.gnupg.org).
Two of the more commonly used asymmetric algorithms are Digital Signature Algorithm
(DSA) and Rivest-Shamir-Adleman (RSA), named after its inventors, Ronald Rivest, Adi Shamir,
and Leonard Adleman. Of these, DSA can be used only to ???sign??? data so that its authenticity can
be verified, whereas RSA is more versatile (although slower than DSA when used to generate
digital signatures). DSA is the current standard for digital authentication used by the U.S. government.
Both the DSA and the RSA asymmetric algorithms are implemented in the PGP family
of software (PGP and GnuPG).
Some popular symmetric algorithms found in the mcrypt library are Data Encryption
Standard (DES), Triple DES (3DES), Ron??™s Code (RC2, or Rivest??™s Cipher, depending on who
you ask, also from Ronald Rivest), and Rijndael (from the names of its inventors, Joan Daemen
and Vincent Rijmen).
DES AND RIJNDAEL
DES has been the standard for some time now, although this is gradually changing.
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