[an error occurred while processing this directive] History of PGP:

Back in 1976, a man by the name of Martin Hellman, along with Whitfield Diffie brought Public Key Cryptography into the world of mathematics. It is a concept where something is encrypted with one key, but decrypted with another. Therefore, two keys are needed for the whole process.

Then, in 1977 Ron Rivest, Adi Shamir, and Len Adleman developed an advance in the public key system, which they called RSA (for their initials). They worked for MIT as researchers. When the NSA got wind of their accomplishment, it warned them to not publish the result, as it could be a significant threat to national security. They ignored the NSA and published a document titled "New Directions in Cryptography" in 1977.

Moving on to 1991, the United States Senate was working on bill 266. If it had passed, this bill would have required makers of all encryption systems to insert trap doors into their systems so that the government could intercept and read all communications.

Phil Zimmerman, frightened by the restrictions this or a bill like it would place on the encryption community, was prompted to write PGP Version One.

What PGP did that no other (unclassified) software package to date had done was to allow people to have two distinct keys, one that would be kept secret, and another that would be given away. A message encrypted with one key can only be decrypted with the other. The same key cannot encrypt and decrypt a message. This allows people two new freedoms:

To "sign" a message, guaranteeing to a recipient that it in fact came from them. This is accomplished by encrypting the message with a private key, which only the sender knows. The only code that can decrypt the message is the public key, which the recipients know belongs to the sender.
To send someone a message so that only the recipient could view it. If it was intercepted, and the spy knew the public key used to encrypt the message, it could not be decrypted. Only the private key can be used to decrypt a message encrypted with the public key. The key used to encrypt a message cannot be used to decrypt it.

Eventually, the United States government decided that it didn't like PGP, probably because it made the NSA's job a lot harder. The United States then started investigating possible violations of cryptography control laws, but the investigation was later halted.

Currently, it is legal to use PGP both inside and outside the Unted States. You have to get a special version to use outside the U.S., though. If you live within the United States, it is illegal to export PGP yourself. For this reason, we cannot include a PGP example applet. Violation of this law has a maximum penalty of $1,000,000 in fines and 10 years in prison.

The math behind all this cryptography is actually quite straightforward. It revolves around the theory that all non-prime numbers can be represented as a product of a unique set of prime numbers. This is the same as the prime factorization trees we all learned in elementary school. Those trees are unique to every composite number.

In order to break a PGP encrypted system, all you have to do is find the prime factorization of a key. However, this is extremely difficult for large numbers. It cannot be done in any practical amount of time, which is what makes PGP encryption very strong.