"Good thing Satoshi wasn't scared of cryptography or we wouldn't have bitcoin." ...a system for which there is no security definition, no security proof, a kno

"Good thing Satoshi wasn't scared of cryptography or we wouldn't have bitcoin." ...a system for which there is no security definition, no security proof, a known polynomial time attack (for some vague notion of "attack"), etc. I do not think this is the best example you can come up with. One of the problems here is that cryptography cannot just be cobbled together from component pieces. Things do not always compose securely. Bitcoin is not a signature system, so even if the ECDSA implementation is perfect it does not guarantee that Bitcoin is secure. One of the things that makes cryptography, especially in the public-key setting, difficult is the very precise assumptions and very precise definitions of security; it is easy to make an assumption that is not implied by a security definition, and very easy to violate a key assumption without even realizing it. Worse, cryptosystems must be composed with other software, and such compositions can be insecure (which is basically what happened with Skype). It's not that people should be scared away. Rather, we need to develop better tools that help programmers catch or avoid these kinds of bugs.