If you have sent any plaintext confidential emails to someone (most likely you did), have you ever questioned yourself about the mail being tampered with or read by anyone during transit? If not, you should!
Any unencrypted email is like a postcard. It can be seen by anyone (crackers/security hackers, corporations, governments, or anyone with the required skills), during its transit.
In 1991 Phil Zimmermann, a free speech activist, and anti-nuclear pacifist developed Pretty Good Privacy (PGP), the first software available to the general public that utilized RSA (a public key cryptosystem, will discuss it later) for email encryption and signing. Zimmermann, after having had a friend post the program on the worldwide Usenet, got prosecuted by the U.S. government; later he was charged by the FBI for illegal weapon export because encryption tools were considered as such (all charges were eventually dropped). Zimmermann later founded PGP Inc., which is now part of Symantec Corporation.
In 1997 PGP Inc. submitted a standardization proposal to the Internet Engineering Task Force. The standard was...