Now do the wrench attack.
Decoy hard drives may work against coercion
Becoming physically immune to brute-force attacks (2021)
31–40 of 72 posts
Re: Becoming physically immune to brute-force attacks (2021)
#32I can't say I understood and evaluated all the physics here (I skimmed parts) but I was pretty surprised by how small the estimate was. I would've assumed that, were we to have one or two thousand years more cryptographic history, we'd end up using ginormous keys (maybe on the order of 1 MiB?). But this suggests that 512 or 1024 bits might be all we need.
Re: Becoming physically immune to brute-force attacks (2021)
#33Now do the wrench attack.
I thought we had already established that the best way to beat that one is to have two passwords. First is Hunter2 and unlocks the keyboard for the second one: A variation of the Moonlight Sonata in off key.
Re: Becoming physically immune to brute-force attacks (2021)
#34I suspect this can be bypassed with knowledge about the size of the target system. Intuitively, there are a finite number of passwords that can be stored on earth, so a large enough system should be able to enumerate them? Whilst also existing in the observable universe.
You only have to store a single 340-bit password (or something equivalent) in order to secure something with a 340-bit password. You can do this by, for example, writing down a 103-bit number on paper, which you can do on a business card with a pencil. Your argument seems to depend on the defender needing to store all possible 340-bit passwords, which they don't.
Re: Becoming physically immune to brute-force attacks (2021)
#35Is this proof that the universe cannot understand itself? It seems weird that there can be a set of information in the universe that can be hidden from the rest of the universe.
Re: Becoming physically immune to brute-force attacks (2021)
#36I could be wrong (my physics background isn't that strong either) but I think Dyson's "time without end" paper http://www.aleph.se/Trans/Global/Omega/dyson.txt shows that eventually the universe will cool down enough to make all keys brute-force-attackable despite Bremermann's limit.
Given a finite amount of attacker computation you're willing to defend against, you can get a real advantage from key stretching (though not from mere salting). If you want a password strength of 256 bits, you can memorize a password of 226 bits and require work equivalent to 2³⁰ key-hashing operations to derive the actual encryption key or crypted password. This is normally called a KDF; reasonable ones are scrypt, bcrypt, and Argon2, in ascending order of goodness.
If you make the work factor unreasonably large, you won't be able to use the password in practice, because you have to do that work every time you use it. For example, if you try to memorize 170 bits of password and use a 2¹⁷⁰ work factor in your KDF to reach the 340-bit security level, recommended here, you have to do 2¹⁷⁰ work on your laptop every time you log in. Assuming a trillion operations per second (a safe upper bound for current laptops) each login will take about 47 nonillion years, about a sextillion times longer than the history of the universe so far and about 50 times longer than the expected lifetime of the last galaxies (see https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future). It may be inconvenient to wait that long.
For the same reason that a KDF is a safe way to derive keys for decrypting data at rest, in a client-server system, you can generally do this work on the client safely, so it doesn't pose a denial-of-service risk.
Re: Becoming physically immune to brute-force attacks (2021)
#37I can't say I understood and evaluated all the physics here (I skimmed parts) but I was pretty surprised by how small the estimate was. I would've assumed that, were we to have one or two thousand years more cryptographic history, we'd end up using ginormous keys (maybe on the order of 1 MiB?). But this suggests that 512 or 1024 bits might be all we need.
This is because exponential growth is counter-intuitive. A 256 bit key is not 2x more secure than 128 bit, it is 340282366920938463463374607431768211456x more secure.
Re: Becoming physically immune to brute-force attacks (2021)
#38Earlier quoted context omitted.
By "target system" you mean "system from which the password originated", right? But unless you think true randomness is impossible, and also that all possible sources of pseudo-random input on Earth come from terrestrial sources and not, say, incoming cosmic radiation, then knowing the size of the "Earth" system is no constraint at all. A heuristic for focusing your search, maybe, if you think the password is likely…
> By "target system" you mean "system from which the password originated", right? Yeah that’s correct. > The phrase "stored on Earth" is a red herring. You don't need to store all possible passwords for those passwords to be possible to generate here. A password used to protect a system must be persistently stored inside that system. The number of passwords that can be generated on earth is greater than the number th…
You're still essentially bound by having to consider all the passwords that could be generated. Let's say that passwords are limited to 2048 bits, but you can only store 2^128 passwords. The problem is that you don't know which 2^2048 passwords have been stored, so you have to go through them all anyway.
Re: Becoming physically immune to brute-force attacks (2021)
#39Is this proof that the universe cannot understand itself? It seems weird that there can be a set of information in the universe that can be hidden from the rest of the universe.
This is why it annoys me when journalists say P!=NP is about scheduling flights.
Re: Becoming physically immune to brute-force attacks (2021)
#40Loving reading this but.. 'TLDR - at the bottom' is wicked
There are a couple of other worthy jokes in the text, BTW.
One example unbreakable password:
>An excerpt from a religious text with a trailing space:
>"I'd just like to interject for a moment. What you’re referring to as Linux, is in fact, GNU/Linux, "
Followed by the deadpan sage advice:
>Don’t use actual excerpts from pre-existing works as your password.
IOW don't try this yourself unless you make up your own religion. Established scriptures of all other kinds have been completely compromised long ago ;)