GnuPG (GNU Privacy Guard) is a GNU utility for encrypting data and
creating digital signatures. GnuPG has advanced key management
capabilities and is compliant with the proposed OpenPGP Internet
standard described in RFC2440. Since GnuPG doesn't use any patented
algorithm, it is not compatible with any version of PGP2 (PGP2.x uses
only IDEA for symmetric-key encryption, which is patented worldwide).