When he is saying

>Save yourself the trouble. Don't use cryptography. It is plutonium. There are millions of ways to mess it up and precious few ways of getting it right.

I am sure he means don't use your own homegrown cryptography solution. Use something established and well tested. Good advice, probably can't be repeated enough. I liked the exampled he gives, I didnt know for example that you can basically extend an MD5ed string and keep the original MD5 value. Then again, I know that MD5 isn't a secure cryptographic hash function so I wouldn't have used it from the start. Nice to know why thats the case.