5 ms·

In other words: a maintenance nightmare, filled with security gotchas, difficult to scale, and hard to write. So is the alternative the author describes (excep

In other words: a maintenance nightmare, filled with security gotchas, difficult to scale, and hard to write. So is the alternative the author describes (except for scaling). HMACs for temporary credentials are clever and simple, if you're already versed in crypto primitives. But to anyone else, they're magic security sauce: "But why can't I just use MD5? Wait, no, that's broken somehow - what about SHA? What do I include in the HMAC? Do I have to use a new key every time?" The solution trades implementation complexity for arcane knowledge. The author is so confident that his solution is superior because he already has that arcane knowledge. That said, a well-implemented HMAC-based password reset flow is probably more bulletproof than a well-implemented DB-based flow. So if you're implementing AWS, go for HMAC. If you're implementing a blog, go with whatever you feel like. Just implement it well.

morgante 12y ago
I don't really consider HMACs to be particularly arcane knowledge. They're easy to generate in any language and straightforward to work with. While I consider myself to be a pretty good developer, I'm definitely not well-versed in crypto and math isn't my strongest skill. Despite that, I've had no problem using crypto for several of the obvious use cases (ex. password resets).
- Terr_ 12y ago
  Arcane to use as the consumer of a library, or arcane to implement on your own? The most important rule of thumb for crypto is that you'll probably mess up doing it yourself.
  - williamcotton 12y ago
    That rule if for like, implementing AES on your own, not just using HMAC! No one is saying roll your own HMAC!
    - lvh 12y ago
      That's a common misconception. While designing your own cipher or implementing AES is a terrible idea, it's fairly easy to produce broken systems with strong primitives like AES or HMAC, and the brokenness would not have anything to do with the implementation of those primitives.
      - tomjen3 12y ago
        How will you make a broken system with HMAC? Other than exposing the key or the data inside there really isn't that much you can do wrong with HMAC.
  - tripzilch 12y ago
    You shouldn't implement HMAC yourself, of course. I repeat: you should not do this. However, if you read Wikipedia on HMAC, you'll find that HMAC is in fact probably one of the easier crypto primitives to understand and implement (as a TOY project). As long as you do the padding thing exactly as specified. But really, use a library.
sk5t 12y ago
Are you arguing in favor of developer laziness? An average programmer should be able to understand the use cases for HMAC within a couple hours or so, given nothing but the Wikipedia page and an IDE or REPL, and knowing about MACs might prevent him from cooking up all manner of broken security protocols in the future.
- tinco 12y ago
  The risk is that a developer might not realize there is a significant difference between just encrypting something, and using a MAC.
  - deleted 12y ago
    [deleted]
- michael_storm 12y ago
  Well, I'm certainly not in favor of name-calling like that. HMACs don't provide any greater provable security guarantees than a database row in this scenario, so it comes down to implementation. HMACs are harder if you're not familiar with them, but almost everyone is familiar with a database. On the other hand, HMACs make the security of the overall system easier to verify, assuming HMACs are used correctly - but it's harder for newcomers to use them correctly. I'm saying that in this scenario, it doesn't make much of a difference which system is used. So the author shouldn't be quite so forceful in telling people to use a crypto primitive outside of their comfort zone for minimal benefit. I'd rather use a system written by someone confident in their DB solution, rather than someone who learned their HMAC solution in a couple of hours on Wikipedia.
- skybrian 12y ago
  How confident should the average developer be that they are able to create a secure crypto implementation in a couple of hours, based on some possibly-dubious advice they read in Wikipedia? I would argue that they shouldn't be very confident in this. The first thing you learn about crypto is that it's harder than it looks and best left to experts. Knowing when it's actually okay is difficult. At the very least, I'd expect that they ask for a review from someone who does know what they're doing, and how many developers who don't work at a big Internet company have a spare security expert handy?
jakejake 12y ago
I felt like the article sounded like an infomercial- making an ordinary task sound incredibly bothersome when it really isn't. Signed URLs are incredibly useful, but the examples given dont seem that compelling to me.
hvidgaard 12y ago
This is a valid and very real concern and one of the reasons that a lot of companies want to hire CS graduates as developers. They have an idea of what this is, and any reasonable CS grad would know where to look for this, if they aren't already well versed in the crypto world.

morgante 12y ago

I don't really consider HMACs to be particularly arcane knowledge. They're easy to generate in any language and straightforward to work with. While I consider myself to be a pretty good developer, I'm definitely not well-versed in crypto and math isn't my strongest skill. Despite that, I've had no problem using crypto for several of the obvious use cases (ex. password resets).

Terr_ 12y ago
Arcane to use as the consumer of a library, or arcane to implement on your own? The most important rule of thumb for crypto is that you'll probably mess up doing it yourself.
- williamcotton 12y ago
  That rule if for like, implementing AES on your own, not just using HMAC! No one is saying roll your own HMAC!
  - lvh 12y ago
    That's a common misconception. While designing your own cipher or implementing AES is a terrible idea, it's fairly easy to produce broken systems with strong primitives like AES or HMAC, and the brokenness would not have anything to do with the implementation of those primitives.
    - tomjen3 12y ago
      How will you make a broken system with HMAC? Other than exposing the key or the data inside there really isn't that much you can do wrong with HMAC.
- tripzilch 12y ago
  You shouldn't implement HMAC yourself, of course. I repeat: you should not do this. However, if you read Wikipedia on HMAC, you'll find that HMAC is in fact probably one of the easier crypto primitives to understand and implement (as a TOY project). As long as you do the padding thing exactly as specified. But really, use a library.

sk5t 12y ago

Are you arguing in favor of developer laziness? An average programmer should be able to understand the use cases for HMAC within a couple hours or so, given nothing but the Wikipedia page and an IDE or REPL, and knowing about MACs might prevent him from cooking up all manner of broken security protocols in the future.

tinco 12y ago
The risk is that a developer might not realize there is a significant difference between just encrypting something, and using a MAC.
- deleted 12y ago
  [deleted]
michael_storm 12y ago
Well, I'm certainly not in favor of name-calling like that. HMACs don't provide any greater provable security guarantees than a database row in this scenario, so it comes down to implementation. HMACs are harder if you're not familiar with them, but almost everyone is familiar with a database. On the other hand, HMACs make the security of the overall system easier to verify, assuming HMACs are used correctly - but it's harder for newcomers to use them correctly. I'm saying that in this scenario, it doesn't make much of a difference which system is used. So the author shouldn't be quite so forceful in telling people to use a crypto primitive outside of their comfort zone for minimal benefit. I'd rather use a system written by someone confident in their DB solution, rather than someone who learned their HMAC solution in a couple of hours on Wikipedia.
skybrian 12y ago
How confident should the average developer be that they are able to create a secure crypto implementation in a couple of hours, based on some possibly-dubious advice they read in Wikipedia? I would argue that they shouldn't be very confident in this. The first thing you learn about crypto is that it's harder than it looks and best left to experts. Knowing when it's actually okay is difficult. At the very least, I'd expect that they ask for a review from someone who does know what they're doing, and how many developers who don't work at a big Internet company have a spare security expert handy?

jakejake 12y ago

I felt like the article sounded like an infomercial- making an ordinary task sound incredibly bothersome when it really isn't. Signed URLs are incredibly useful, but the examples given dont seem that compelling to me.

hvidgaard 12y ago

This is a valid and very real concern and one of the reasons that a lot of companies want to hire CS graduates as developers. They have an idea of what this is, and any reasonable CS grad would know where to look for this, if they aren't already well versed in the crypto world.