It's a secret (17)

So what can computers bring to the table?  Well for starters, they can lighten the load.  We have seen that using a series of random letters as your keystream results in a cipher which is unbreakable without the key.  But generating such a list of random letters (a one-time pad) is very time-consuming and getting such a list to your opposite number (the key distribution problem) is far from easy.  It is said that at the height of the Cold War, when the one-time pad was the cryptographic method of choice, on any given day there would be hundreds of people travelling round the world with metal cases chained to their wrists - they were couriers delivering one-time pads. Now a computer can be easily programmed to come up with a list of random numbers between 1 and 26, which can be treated as letters.  Strictly speaking, these numbers are not random but for all practical purposes can be treated as such.  To get the computer to do this, you first have to give it a starting number - called the "seed", and the point is that the same seed will always result in the same sequence of "random" numbers.  So you no longer have to spend time producing a one-time pad - you let the computer do it for you, and you no longer have to pass the whole sequence to your opposite number - you just have to give them the seed and their computer will do the rest.  But computers had much more to give...