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Number one thing I learned from the Coursera class: don't build your own crypto.

cjg 14y ago
I've heard this said many times before and I agree. However, using crypto libraries does not solve the problem of vulnerabilities through cryptography misuse. For example, keys must be stored correctly, algorithms often need initialising in the correct mode for your specific application, IVs must not be repeated, and, as shown in this article, hashes should be used in specific ways to work correctly. There are many ways to fail with cryptography and avoiding them all takes considerable expertise. Using crypto libraries does not solve this problem.
- tptacek 14y ago
  This is the entire point of high-level crypto libraries, like Guttman's libcrypt and Google's Keyczar. So, yeah, don't use OpenSSL or javax::crypto or whatever .NET calls it; but, do consider using something like Keyczar, or, better yet, just use PGP/GPG to store data at rest, TLS for data in motion, and be done with it.
  - SoftwareMaven 14y ago
    Those still require key management. There is no way a developer can abdicate all responsibility for this stuff, no matter how high level (at least, not until we have good, common, trusted security as a service).
    - tptacek 14y ago
      Part of the point of Keyczar (note the name) is to make the right decisions about key management in advance and abstract them away from developers.
  - gambler 14y ago
    High-level libraries are definitely the way to go for a variety of reasons, but they don't replace understanding. Developers still need to understand what exactly is and is not guaranteed by cryptography involved, because that's the stuff protocols are build on. The root article is a great illustration of this.
    - tptacek 14y ago
      This is classic developerthink, and it's a good thing, but it doesn't serve you very well with crypto. The problem with crypto is that a partial understanding of the problems is actually worse than no understanding. You can be worse off learning crypto material than you were before you learned it. If you're interested in picking up crypto knowledge, my advice is to do so in the context of breaking systems, not building them. I spend a lot of time doing crypto stuff, and I don't feel qualified to build them. But needing to figure out how to break all the random systems that end up on my desk has taught me a lot about crypto.
- skibrah 14y ago
  Agreed- you can take an intro course in crypto and still find many ways of getting it wrong. My intro to crypto professor reiterated this fact almost ever class and noted that even seemingly small changes to a protocol can render it vulnerable to attack.
waterlesscloud 14y ago
Just finished the class today myself, and yep, that's the most repeated advice. The class repeats starting Monday, if anyone is interested in learning the basics of how all this stuff works. https://www.coursera.org/course/crypto https://www.coursera.org/course/crypto

cjg 14y ago

I've heard this said many times before and I agree. However, using crypto libraries does not solve the problem of vulnerabilities through cryptography misuse. For example, keys must be stored correctly, algorithms often need initialising in the correct mode for your specific application, IVs must not be repeated, and, as shown in this article, hashes should be used in specific ways to work correctly. There are many ways to fail with cryptography and avoiding them all takes considerable expertise. Using crypto libraries does not solve this problem.

tptacek 14y ago
This is the entire point of high-level crypto libraries, like Guttman's libcrypt and Google's Keyczar. So, yeah, don't use OpenSSL or javax::crypto or whatever .NET calls it; but, do consider using something like Keyczar, or, better yet, just use PGP/GPG to store data at rest, TLS for data in motion, and be done with it.
- SoftwareMaven 14y ago
  Those still require key management. There is no way a developer can abdicate all responsibility for this stuff, no matter how high level (at least, not until we have good, common, trusted security as a service).
  - tptacek 14y ago
    Part of the point of Keyczar (note the name) is to make the right decisions about key management in advance and abstract them away from developers.
- gambler 14y ago
  High-level libraries are definitely the way to go for a variety of reasons, but they don't replace understanding. Developers still need to understand what exactly is and is not guaranteed by cryptography involved, because that's the stuff protocols are build on. The root article is a great illustration of this.
  - tptacek 14y ago
    This is classic developerthink, and it's a good thing, but it doesn't serve you very well with crypto. The problem with crypto is that a partial understanding of the problems is actually worse than no understanding. You can be worse off learning crypto material than you were before you learned it. If you're interested in picking up crypto knowledge, my advice is to do so in the context of breaking systems, not building them. I spend a lot of time doing crypto stuff, and I don't feel qualified to build them. But needing to figure out how to break all the random systems that end up on my desk has taught me a lot about crypto.
skibrah 14y ago
Agreed- you can take an intro course in crypto and still find many ways of getting it wrong. My intro to crypto professor reiterated this fact almost ever class and noted that even seemingly small changes to a protocol can render it vulnerable to attack.

waterlesscloud 14y ago

Just finished the class today myself, and yep, that's the most repeated advice. The class repeats starting Monday, if anyone is interested in learning the basics of how all this stuff works. https://www.coursera.org/course/crypto https://www.coursera.org/course/crypto