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I mean, why not tell everyone our password hashes?

theobsidiantower.com

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Re: I mean, why not tell everyone our password hashes?

#161

Post by Retric »

TheCoelacanth wrote: post #159
Retric wrote: post #153

Earlier quoted context omitted.

If you mean after generating a hash you can compare it to your list of hashes then that saves time for cracking every password, but it's slower than cracking one password. Assuming you wanted to crack every Facebook password this way, that's not going to fit into cache and a binary search into RAM is actually rather slow. Yea, you could have more computers doing just this, but it's much slower than computing the hash…

You wouldn't need to do a binary search. The values are already MD5 hashes. You could do a hash table lookup in just a few CPU cycles since computing the hash is free.

Good point, though at a minimum you need to touch main memory twice which is 200+ clock cycles. And in practice that O(1) has an much worse constant factor.

Re: I mean, why not tell everyone our password hashes?

#162

Post by Retric »

TheCoelacanth wrote: post #158
Retric wrote: post #152

Earlier quoted context omitted.

Not at the same hash rate. Sure you can do binary search, but 100^14 or even 30^14 such searches is not fast. So, it's about as fast if you want 2 passwords but not 2 billion passwords.

It wouldn't be a binary search, the values are already hashes, so you could do a hash table lookup very cheaply. MD5 isn't great by cryptological standards, but it is extremely robust by hash table standards. While no extra resources might not have been strictly accurate, the lookup would be practically free compared to the time it takes to compute the hash.

In the example I gave the hashes don't fit on GPU's and for your hash table lookup you would need ~64GB of ram to do the hash table lookups. You can scale this across multiple machines but even the ideal case of 2 lookups to main memory * 100^14 is slow and thus expensive.

Re: I mean, why not tell everyone our password hashes?

#163

Post by snakeanus »

irundebian wrote: post #146
snakeanus wrote: post #119

Earlier quoted context omitted.

For now. https://www.keylength.com/en/compare/ Why risk it when generating an ed25519 or rsa4096 keypair is cheap?

The same logic would apply to an 8192 bit key. One more bit doubles the key space. Someone who is be able to crack 2048 bit keys, probably also has the opportunity to crack 4096 bit keys. It may not be cheap for your communication partners to use your 4096 bit key. Smartphones and embedded devices want to use as less energy as possible. With an 4096 bit key, you force your communication partners to spent an unnecessa…

> One more bit doubles the key space

Yes, except that a 4096 bit key is not just "one more bit", it's double the amount of bits.

> Someone who is be able to crack 2048 bit keys, probably also has the opportunity to crack 4096 bit keys

No, it would require an impossibly large amount of effort to crack 4096 bit keys compared to 2048 bit keys.

> Smartphones and embedded devices want to use as less energy as possible

They can use ed25519 then.

> With an 4096 bit key, you force your communication partners to spent an unnecessary amount of energy.

They spend more energy by running ad-ridden "apps" and electron monstrosities.

Re: I mean, why not tell everyone our password hashes?

#165

Post by royce »

analogist wrote: post #139
LeoPanthera wrote: post #88

Earlier quoted context omitted.

It's my understanding that even an MD5 hash of a not-terrible password is still virtually impossible to crack, is that wrong? Here's an md5 sum of a not-that-great password I just made up. It's 14 characters long, but has plenty of guessable features. Is it crackable? 1cf016ea3cb1f2aa2ccb59c196d0e704

That's pretty much correct, yeah. Due to exponentiation, length is almost everything in password security. Which means there's going to be a bunch of lengths at which brute force cracking is trivial, and then a very sharp rise in complexity, after which brute force cracking quickly becomes astronomical, and then absolutely impossible. If you look at the current cracking benchmarks of GPUs ( https://gist.github.com/ep…

A fantastic overview - clear and informed. Thanks very much for this.

Re: I mean, why not tell everyone our password hashes?

#166

Post by someone_elses »

jbg_ wrote: post #147
someone_elses wrote: post #141

Earlier quoted context omitted.

Basically you can take ownership of their IP ranges, modify routing information, etc. Even if you took a small percentage of the IP addresses in Europe, this could have a snowball effect. You take the IP addresses belonging to a popular mail service used by other domains, then you use admin email addresses to reset and eventually Europes internet is stolen.

It's not quite that simple. The RIPE database stores mostly administrative information, and doesn't _directly_ affect Internet routing. In order to "steal" IP addresses (get them routed to you) you would need to buy a connection to at least one exchange point, probably several if you want all the traffic for the target to route to you and not just some traffic from some networks. You'd need to buy rackspace somewhere…

Thank you!

Re: I mean, why not tell everyone our password hashes?

#167

Post by maccard »

Govindae wrote: post #156
maccard wrote: post #150

Earlier quoted context omitted.

I think it's a reasonable point. There's lots of armchair experts saying that md5 is broken, unusable, and anyone can reverse it, and here we are 14 hours later and nobody has proven it. Given that the claim was 12 minutes on a 25 machine cluster, that would imply 300 minutes of compute time which is 6 hours. This is hacker news, if it's not going to be done here, then no armchair enthusiasts are going to do it. If s…

https://hashcat.net/hashcat/ I haven't used it, but FAQs, Forums, wikis, and tutorials are all out there.

I will give it a try this weekend, thanks!
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