gpg4win

Gpg4win allows users to move emails and files securely with the help of encryption and digital signatures.  Encryption protects content from being read by an unintended party.  Digital signatures allow you to ensure that the signature has not been altered and comes from a specific sender.

  Gpg4win supports relevant encryption standards, OpenPGP and S/MIME (X.509), and is the official GnuPG distribution for Windows.  Maintained by the developers of GnuPG.  Gpg4win and the software included in Gpg4win are Free Software (Open Source; free for all commercial and non-commercial purposes, among others).