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EDIT: also it is very important to seed with care if you are interested in security. Even a strong PRNG seeded with seed_prng(time(NULL)) will be an easy target for brute force attacks.
At least /dev/urandom should be used for seeding purposes in applications where you need an unguessable PRNG.
This is a pretty great post. We need lots more posts on practical exploit development for RNG flaws, because there are a lot of bad random number generators out there. I want to respond to this headline, though. Use of MT as a CSPRNG is very, very common in PHP applications. And it's also true that MT is the algorithm used by Ruby for it's "rand". But this is not a very common Ruby flaw, at least not like it is in PH…
For instance, you definitely need it in poker hand generation - would you need it for random loot generation in an MMO?
Also by "secure" you mean /dev/random, and /dev/urandom is used as if it was rand()?
This is a pretty great post. We need lots more posts on practical exploit development for RNG flaws, because there are a lot of bad random number generators out there. I want to respond to this headline, though. Use of MT as a CSPRNG is very, very common in PHP applications. And it's also true that MT is the algorithm used by Ruby for it's "rand". But this is not a very common Ruby flaw, at least not like it is in PH…
Is there any advice you're able to give on how to distinguish situations where you need secure RNG from those that don't matter? For instance, you definitely need it in poker hand generation - would you need it for random loot generation in an MMO? Also by "secure" you mean /dev/random, and /dev/urandom is used as if it was rand()?
/dev/urandom is fine; in Ruby apps, I'd use OpenSSL::Random.random_bytes or ActiveSupport::SecureRandom.random_number.
A PRNG based on RC4 should be very fast but much more secure than a MT or a LCG. EDIT: also it is very important to seed with care if you are interested in security. Even a strong PRNG seeded with seed_prng(time(NULL)) will be an easy target for brute force attacks. At least /dev/urandom should be used for seeding purposes in applications where you need an unguessable PRNG.
A PRNG based on RC4 should be very fast but much more secure than a MT or a LCG. EDIT: also it is very important to seed with care if you are interested in security. Even a strong PRNG seeded with seed_prng(time(NULL)) will be an easy target for brute force attacks. At least /dev/urandom should be used for seeding purposes in applications where you need an unguessable PRNG.
I usually consume /dev/urandom and convert it to the base I require, using that directly as my random number. When you say you should use it for seeding purposes, are you referring to using /dev/urandom as a seed for something like PHP's rand(), or do you mean something else?
Indeed as the author rightfully mentioned in his article this method is not designed for crypto purpose. One can use the following Python method instead random.SystemRandom().randint(...)
SystemRandom uses the system's urandom, which may not be ideal, either. (The man page for urandom mentions theoretical problems when system entropy pools are depleted.) The PyCrypto.Random.random option mentioned in another thread by wulczer might be better... but would love an authoritative recommendation from an expert.
A PRNG based on RC4 should be very fast but much more secure than a MT or a LCG. EDIT: also it is very important to seed with care if you are interested in security. Even a strong PRNG seeded with seed_prng(time(NULL)) will be an easy target for brute force attacks. At least /dev/urandom should be used for seeding purposes in applications where you need an unguessable PRNG.
> At least /dev/urandom should be used for seeding purposes in applications where you need an unguessable PRNG. I usually consume /dev/urandom and convert it to the base I require, using that directly as my random number. When you say you should use it for seeding purposes, are you referring to using /dev/urandom as a seed for something like PHP's rand(), or do you mean something else?
You're doing the right thing already.
http://news.ycombinator.com/item?id=639976
What's great about this blog post is that it attacks the underlying algorithm; the post you linked to is more fun, but this post is a little more useful.
In either case: just use random/urandom and this stuff is taken care of for you.
This is a pretty great post. We need lots more posts on practical exploit development for RNG flaws, because there are a lot of bad random number generators out there. I want to respond to this headline, though. Use of MT as a CSPRNG is very, very common in PHP applications. And it's also true that MT is the algorithm used by Ruby for it's "rand". But this is not a very common Ruby flaw, at least not like it is in PH…
Earlier quoted context omitted.
Is there any advice you're able to give on how to distinguish situations where you need secure RNG from those that don't matter? For instance, you definitely need it in poker hand generation - would you need it for random loot generation in an MMO? Also by "secure" you mean /dev/random, and /dev/urandom is used as if it was rand()?
You should pretty much just default to secure random. /dev/urandom is fine; in Ruby apps, I'd use OpenSSL::Random.random_bytes or ActiveSupport::SecureRandom.random_number.
Do those functions just read from /dev/urandom?