Both PGP and S/MIME protocols are used for authentication and privacy of messages over internet. S/MIME protocol refers to Secure/Multipurpose Internet Mail Extensions which has been incorporated in the various main exchange software, incl. Outlook, Thunderbird & others And also incorporated in all major browsers (chrome, Mozilla, IE and others). S/MIME is based on IETF standards and defined in RFC 5751. RFC 5751 defined S/MIME as "S/MIME (Secure/Multipurpose Internet Mail Extensions) provides a consistent way to send and receive secure MIME data. Based on the popular Internet MIME standard, S/MIME provides the following cryptographic security services for electronic messaging applications: authentication, message integrity and non-repudiation of origin (using digital signatures), and data confidentiality (using encryption). As a supplementary service, S/MIME provides for message compression." PGP known as Pretty Good Privacy, is a data encryption and decryp