It's a secret (22 - and last)

PPK has one drawback - because it uses such enormously big numbers, encryption and decryption take time - particularly if all you've got is a standard desk-top computer.  And as we've already seen, time may be of the essence.  So enter Phil Zimmerman, an American who in 1991 posted a document on the internet entitled "Pretty Good Privacy".  He said - look, we've already got relatively quick "conventional" cryptography methods which are unbreakable without the key.  The problem is not passing the message, it's getting the key securely to the other side. Right then - why don't we use one of these methods to encrypt the message, and then send the key (which will be a relatively short file) by PPK?  This way we get the best of both worlds.  And this - known as PGP (for Pretty Good Privacy) - has become the cryptographic method of choice for sending secret messages over the internet. Which brings this series of posts full circle - it's all very well the Prime Minister saying that he intends to give the security services carte blanche to intercept such messages - but what use is that if they can't decipher them?