Rupert Goodwins' diary

Wedneday 21/02/2001There's something about cryptography that drives men mad. Take Dr Michael Rabin, for example, a cryptographer who claims to have an new and unbreakable cypher.

Wedneday
21/02/2001 There's something about cryptography that drives men mad. Take Dr Michael Rabin, for example, a cryptographer who claims to have an new and unbreakable cypher. You take a random number, he says, and mix it with your message. Your friend has the same random number and mathematically unmixes it -- and there we go. Your original message restored. Hold on, isn't this the One Time Pad that's been used since before World War 1, and is still used even now? It is. Dr Rabin's trick addresses the problem that you have to get the random number to your pal in secret, as if the enemy get it then the system is useless. What happens, he says, is that you have a random number broadcast to everyone all the time: you and your pal merely agree on which point in the random number stream to start using it. The enemy won't know that point and thus won't have the number. Which is bonkers. First, if the enemy get at the random number and replace it with something that looks random, you're lost. Second, what if the enemy discovers big hard disks and records all the numbers around the time you're doing your message passing? But no, Dr Rabin says his scheme is absolutely safe. And I am a twenty-three year old ballerina from Kiev called Oblonska...