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You are dangerously bad at cryptography

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Re: You are dangerously bad at cryptography

#141

Post by terolacu »

jiggy2011 wrote: post #90
bashinator wrote: post #84

Earlier quoted context omitted.

Funny story - quite a few years back I was a sysadmin for a company that was compiling their own PHP with a couple of patches. When I asked about it, my co-worker said it was to suppress some warnings that were spamming the logs whenever someone created an account. Yes, those warnings were telling us that we weren't using an initialization vector (IV, aka a salt) when hashing the passwords. Facepalm. I suppose that d…

Once you are choosing salts that is almost level 4 knowledge. This is one of the problems with "raw" PHP development, there's no way to say "this is a password field, make it secure" only "hash this with algorithm X". To be fair though , I believe recent releases have addressed this and frameworks like symphony give you a default user class to inherit from that does things sensibly. It also sticks a seed for the salt…

> This is one of the problems with "raw" PHP development

... or any other language.

Re: You are dangerously bad at cryptography

#142

Post by terolacu »

carbocation wrote: post #137
jiggy2011 wrote: post #90

Earlier quoted context omitted.

Once you are choosing salts that is almost level 4 knowledge. This is one of the problems with "raw" PHP development, there's no way to say "this is a password field, make it secure" only "hash this with algorithm X". To be fair though , I believe recent releases have addressed this and frameworks like symphony give you a default user class to inherit from that does things sensibly. It also sticks a seed for the salt…

Hmm, unfortunately I think Symfony2 runs passwords through 1 round of SHA1 unless a custom password "encoder" is used [1]. [1] = http://symfony.com/doc/2.0/book/security.html#encoding-the-u...

Bcrypt and PBKDF2 are not custom, they are part of the framework:

http://symfony.com/doc/current/reference/configuration/secur...

Re: You are dangerously bad at cryptography

#143

Post by carbocation »

terolacu wrote: post #142
carbocation wrote: post #137

Earlier quoted context omitted.

Hmm, unfortunately I think Symfony2 runs passwords through 1 round of SHA1 unless a custom password "encoder" is used [1]. [1] = http://symfony.com/doc/2.0/book/security.html#encoding-the-u...

Bcrypt and PBKDF2 are not custom, they are part of the framework: http://symfony.com/doc/current/reference/configuration/secur...

Those were added in Symfony2.2; my last experience was with 2.1. Also, I understand that neither of those is default; one should be.

Re: You are dangerously bad at cryptography

#144

Post by bigiain »

jarrett wrote: post #95
tptacek wrote: post #79

Earlier quoted context omitted.

Just accept the fact that people who say "don't use crypto" aren't saying "don't hash passwords", nor are they saying "don't generate random numbers", and move on.

Sure, but then what are they saying? "Dont use cryptography" is a quotation taken verbatim from the OP, and I've heard similar statements all around in the last few years. A reasonable person reading that statement would interpret it at face value: "Don't use cryptography" means that very thing. So what I'm suggesting is that the "don't use crypto" meme should go away and be replaced with something more helpful and m…

Isn't the actual meme "Don't build your own crypto", rather than "don't use crypto"?

I remember at least 10 years ago getting (and seeing a lot) the advice "use SSL for data in transit, use GPG for data at rest". Those two principles, combined with the somewhat more recent "just use (b|s)crypt" for password hashes would still provide your average non-crypto-expert developer with a pretty good fundamental starting place.

Re: You are dangerously bad at cryptography

#145

Post by scythe »

anonymouz wrote: post #122
scythe wrote: post #70

Earlier quoted context omitted.

The biggest candidate: * Pure mathematics: Consider e.g. the difficulty in verifying the recent proofs of Fermat's Last Theorem (Wiles-Taylor-Frey theorem?), the Poincaré conjecture (Perelman-Hamilton-Thurston theorem?), and now the ABC conjecture (Mochizuki-Szpiro theorem?): there is essentially no indication of the correctness of a mathematical proof besides simply having a whole lot of smart people look at it and…

If I understood your proposed system correctly, the following seems to be a deal-breaking weakness: Given a number of polynomials representing encrypted messages, (x-z) is a common factor of all of them. The GCD of a set of polynomials can very efficiently be computed. Thus, an attacker observing different messages encrypted with the same key over time gets a better and better idea of what the key is (how quickly dep…

In this case, simply computing the GCD may require "non-obvious" intuition, since the polynomials do not act over the real numbers, but the algebraic closure of an unknown finite field. But I wouldn't bet my data on it, at least, not until I am a lot more confident in my understanding of abstract algebra.

Re: You are dangerously bad at cryptography

#146

Post by unethical_ban »

tptacek wrote: post #107
jarrett wrote: post #95

Earlier quoted context omitted.

Sure, but then what are they saying? "Dont use cryptography" is a quotation taken verbatim from the OP, and I've heard similar statements all around in the last few years. A reasonable person reading that statement would interpret it at face value: "Don't use cryptography" means that very thing. So what I'm suggesting is that the "don't use crypto" meme should go away and be replaced with something more helpful and m…

It really seems like this is an argument that seeks to make it harder to understand a problem, rather than easier. I'm just not interested in the semantic debate, sorry.

You made it a semantic debate.

  "Don't use crypto." - you  
  "That's terrible advice, we need crypto for x,y,z"  
  "I don't really mean don't use crypto"  
  "You just said that!"  
  "You're just talking semantics."

Re: You are dangerously bad at cryptography

#147

Post by kalleboo »

jarrett wrote: post #53

This argument keeps coming up, and while its premises are valid, its conclusion never sits right with me, namely: "Don't use cryptography." That advice isn't practical for developers. There are plenty of systems we have to design where crypto is not optional. Examples: * Storing passwords. You can't store them in plaintext. * Signing requests (like in the OP's example). What are the alternatives? You can store some k…

> * Storing passwords. You can't store them in plaintext.

Why not. Just write upfront on the signup form, "we don't hash or protect your passwords in any way. Do not reuse passwords from other sites. Create a unique password and retrieve it using a password manager."

Password hashing is a losing battle:

* the users who aren't educated enough to use unique passwords are the same ones who will always use a really weak one anyway, and those will always be crackable

* salting is nearly pointless. the GPU killed the rainbow table, the "bad passwords" keyspace is small enough it's easy enough to recompute, and in most hacks I've seen, the database has been compromised together with the source code so the salt is never really secret.

* the first advice after a hack is still always going to be "change your passwords".

Re: You are dangerously bad at cryptography

#148

Post by tptacek »

eridius wrote: post #138
andrewcooke wrote: post #132

Earlier quoted context omitted.

there are 6 levels. so presumably level 0 is people who started (ie requested) but did not complete level 1. a level is a day or two of work, in my experience (unless you get stuck and need to sleep on something, or get entertained and go off exploring something), but i doubt most people are doing them full-time, so timing data is going to reflect mostly how busy they were with other things.

Yeah, I've been at level 1 for quite a while, but that's because I haven't had much time available to spend working on it. When I get some time I try to work through one of the problems. Of course, I'm also doing it in Rust, so add in the extra time of learning a new language (especially one still in flux).

They're not going anywhere. Take your time!

Re: You are dangerously bad at cryptography

#149

Post by tptacek »

unethical_ban wrote: post #146
tptacek wrote: post #107

Earlier quoted context omitted.

It really seems like this is an argument that seeks to make it harder to understand a problem, rather than easier. I'm just not interested in the semantic debate, sorry.

You made it a semantic debate. "Don't use crypto." - you "That's terrible advice, we need crypto for x,y,z" "I don't really mean don't use crypto" "You just said that!" "You're just talking semantics."

Nobody dings developers for generating random numbers because they're "doing crypto".

Re: You are dangerously bad at cryptography

#150

Post by rwg »

dsl wrote: post #80
tptacek wrote: post #77

Note: we're still running these challenges: http://www.matasano.com/articles/crypto-challenges/ The current standings are: * level 0 (4362 players), * level 1 (335 players), * level 2 (123 players), * level 3 (40 players), * level 4 (21 players), * level 5 (23 players), * level 6 (32 players) We're still donating $20 to PIH or Watsi for everyone who finishes all 6 sets. The top languages finishers are using are (in o…

Just curious how far the Excel hacker(s) got... Also, have you made any hires from the contest yet?

The Excel thing started out as someone else's funny tweet and turned into me riding the bomb down while waving my cowboy hat, Slim Pickens style.

This tweet started the ball rolling:

https://twitter.com/sachinag/status/329701402546941953

The spreadsheets use no VBA or AppleScript or external code -- just Excel formulas and the functions Excel 2008 offers. I submitted the first four spreadsheets along with my "real" (Python) code/answers for set #2, just for the shock/horror value.

Later, despite what I said about giving up on Excel, I implemented the Mersenne Twister PRNG and single-block AES encryption (all three key sizes!):

https://twitter.com/areuugee/status/333344208154923008 https://twitter.com/areuugee/status/334142574296199168

One of these days, I'm going to start a blog just so I can write a series of posts about Excel. There are definitely limitations in what the design allows you to do, but it's more powerful than anyone gives it credit for. It'll also be cathartic to share how I made the AES and Mersenne Twister spreadsheets. (Spoiler: The C preprocessor was involved.)

That said, I don't think the Matasano people have to worry about me solving more problems in Excel. Programs that I could bang out in five minutes in Python turned into all-day, profanity-laden affairs with Excel, which turns Excel into a distraction from the crypto stuff.

Also, if anyone decides to give Matasano's crypto challenge a try, it's a great opportunity to learn a new programming language or a great excuse to get better at a programming language that you don't know so well. My Python knowledge was pretty minimal at best (the only languages I've ever really cared about are C, Fortran, Perl, and [spit!] PHP), but now I'm much more comfortable with it. In fact, if I ever finish, I might go back and redo everything in Ruby just to learn Ruby...

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