mcrypt is intended to be a replacement of the old unix crypt(1) under theÂ GNU General Public License. Unix Crypt(1) was a popular(?) file encryption program in unix boxes. It was based on the enigma encryption algorithm but it was considerable trivialized. Since this was not adequate, even for individual privacy needs, I decided to create a similar program using some modern block encryption algorithms. Mcrypt also has a compatibility mode with unix crypt(1) and with solaris des(1). It supports all the algorithms and modes found in libmcrypt and it is very extendable. At the time writing this, it supports the algorithms:Â BLOWFISH,TWOFISH,Â DES,Â TripleDES,Â 3-WAY,Â SAFER,Â LOKI97,Â GOST,Â RC2,Â MARS,Â RIJNDAEL,Â SERPENT,Â CAST,Â ARCFOUR andÂ WAKE.
Block algorithms are implemented in modes: CFB, CBC, CTR, ECB, OFB (8 bit and n bit, where n is the size of the algorithm’s block length). For a brief description of the algorithms and the modes look at the mcryptmanpage (this may be out of date). In mcrypt it is on the user to decide which algorithm he considers best for encrypting his data
More about mcryptÂ HERE