At times you want to use encryption in software and looking for time tested libraries  for various algorithms.
Two such open source libraries are NSS from Mozilla and crypto from openssl.org.
Whether you want MD4,MD5,SHA-1 for secure hash
or 
DES, tripple DES, AES, IDEA, Blowfish for symmetric encryption,
nss and crypto are there for you.

You get good documentation for both.

NSS is coming from long old days and more mature but openssl.org has nice 
commandline options and also there are some algorithms avaialable in one 
and not in the other. So check them both and decide.