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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?

#121

Post by Buge »

lucasgonze wrote: post #2

That inspired this idea: make all password databases public, in an encrypted form. Just post them in a standard location. This is to get rid of the fiction that these are ever private and to eliminate an incentive to break in.

That's essentially what brainwallet did. Your bitcoin private key was deterministicly generated by your password. So using a list of common passwords, private keys could be pregenerated by attackers. So anyone who "created" a brainwallet with a weak password would get their money stolen the second they deposited it. Brainwallet got so much hate from people that used weak passwords and got their money stolen that it was shut down.

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

#122

Post by forgotpwtomain »

throwaway2016a wrote: post #112
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

In reality while that would be really easy to crack (measured in minutes as others pointed out). However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary. [not quite right see edit] Rainbow tables are just giant tables where the key is the hash and the value is the string that generated it. How…

>However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary.

Umm what? Even assuming a limited set of ASCII i.e. Base64, on what magical medium do you suppose a 64^10 rainbow table is stored?

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

#123

Post by agwa »

throwaway2016a wrote: post #112
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

In reality while that would be really easy to crack (measured in minutes as others pointed out). However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary. [not quite right see edit] Rainbow tables are just giant tables where the key is the hash and the value is the string that generated it. How…

> However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary.

Really? Storing every possible 10 character long printable ASCII password plus its MD5 hash would require approximately 1.5 zettabytes[1].

[1] 95^10 * (16+10)

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

#124

Post by morecoffee »

agwa wrote: post #123
throwaway2016a wrote: post #112

Earlier quoted context omitted.

In reality while that would be really easy to crack (measured in minutes as others pointed out). However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary. [not quite right see edit] Rainbow tables are just giant tables where the key is the hash and the value is the string that generated it. How…

> However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary. Really? Storing every possible 10 character long printable ASCII password plus its MD5 hash would require approximately 1.5 zettabytes[1]. [1] 95^10 * (16+10)

Rainbow tables are formed by chains of passwords and their hashes. The rainbow table only includes the ends of the chains, so you can throw away the middle of the chain.

Rainbow tables are a tradeoff between storing every hash, and generating them during cracking. You get to pick how much space you want to spend to speed up cracking.

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

#125

Post by tatersolid »

CiPHPerCoder wrote: post #39
lucasgonze wrote: post #2

That inspired this idea: make all password databases public, in an encrypted form. Just post them in a standard location. This is to get rid of the fiction that these are ever private and to eliminate an incentive to break in.

Instead of password hashes, why don't we just use Argon2id as a KDF to produce an Ed25519 keypair, and then publish the (salt, memcost, opscost, Ed25519 public key)? I can throw this into a structure indistinguishable from a blockchain if any VCs want to invest ;)

You've just described SQRL

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

#126

Post by morecoffee »

forgotpwtomain wrote: post #122
throwaway2016a wrote: post #112

Earlier quoted context omitted.

In reality while that would be really easy to crack (measured in minutes as others pointed out). However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary. [not quite right see edit] Rainbow tables are just giant tables where the key is the hash and the value is the string that generated it. How…

>However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary. Umm what? Even assuming a limited set of ASCII i.e. Base64, on what magical medium do you suppose a 64^10 rainbow table is stored?

Any medium really. Rainbow tables are compressed (by throwing away most of the hashes). The amount you throw away determines how long it takes to crack.

For example, A rainbow table might use chain lengths of 10,000. This means that for every 10,000 hashes calculated, only 1 (really 2) are kept. Each chain ends up as a row in the table, which is then sorted. When cracking, the target hash is hashed and reversed up to 10,000 times looking through the table.

The more compression the less space needed, but longer look up. The original Windows XP rainbow table cracking CD published along with the Rainbow table paper was only ~500Mb, but was able to crack pretty much every windows password.

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

#127

Post by throwaway76543 »

Retric wrote: post #114
TheCoelacanth wrote: post #103

Earlier quoted context omitted.

That's only 43 years and it was only 25 GPUs. Bump that up to 12000 GPUs and you could do it in about a month. It's also an unsalted hash, so you could brute force an unlimited number of passwords at the same time without additional resources. Someone with a budget of a few million dollars could break every password in the world in a month. So in other words, definitely don't publicize unsalted MD5 hashes of your pas…

We can't really store that many passwords. It's even just 30^14 = 500 exabytes per byte and MD5 is 16 bytes at a minimum so you need 8000+ exabytes = 8,000,000,000+ Terabytes. Note: only "In the third quarter of 2016, approximately 144.6 million hard disk drives were shipped worldwide" aka something like all HDD ever produced might fit that much data. PS: Plus that 30 was low balling for a full search space it's 26 (…

There's no need to store anything. You have a list of hashes you'd like to reverse. You compute the entire search space and compare each.

No storage, other than the hashes you're attempting to reverse -- which for a data dump from even a large site like Yahoo wouldn't be very large at all. Megabytes.

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

#128

Post by TheCoelacanth »

Retric wrote: post #114
TheCoelacanth wrote: post #103

Earlier quoted context omitted.

That's only 43 years and it was only 25 GPUs. Bump that up to 12000 GPUs and you could do it in about a month. It's also an unsalted hash, so you could brute force an unlimited number of passwords at the same time without additional resources. Someone with a budget of a few million dollars could break every password in the world in a month. So in other words, definitely don't publicize unsalted MD5 hashes of your pas…

We can't really store that many passwords. It's even just 30^14 = 500 exabytes per byte and MD5 is 16 bytes at a minimum so you need 8000+ exabytes = 8,000,000,000+ Terabytes. Note: only "In the third quarter of 2016, approximately 144.6 million hard disk drives were shipped worldwide" aka something like all HDD ever produced might fit that much data. PS: Plus that 30 was low balling for a full search space it's 26 (…

You don't have to store all of the possible passwords, just the hashes for all of the real passwords that you are trying to crack.

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

#129

Post by throwaway76543 »

Retric wrote: post #115
throwaway76543 wrote: post #107

Earlier quoted context omitted.

Keep in mind article is from 5 years ago.

Sure, but "25 machine cluster which would reverse your hash in about 12 minutes -- regardless of your password features." is clearly wrong as GPU's are not that much faster and the article is talking about 25 GPU's.

You're right, that should read "25 machine cluster which would reverse your hash in about 12 minutes -- assuming similar password features"

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

#130

Post by Godel_unicode »

morecoffee wrote: post #126
forgotpwtomain wrote: post #122

Earlier quoted context omitted.

>However, any possible password with a standard printable ASCII character set will typically be found in Rainbow tables up to 10 characters long making expensive cracking unnecessary. Umm what? Even assuming a limited set of ASCII i.e. Base64, on what magical medium do you suppose a 64^10 rainbow table is stored?

Any medium really. Rainbow tables are compressed (by throwing away most of the hashes). The amount you throw away determines how long it takes to crack. For example, A rainbow table might use chain lengths of 10,000. This means that for every 10,000 hashes calculated, only 1 (really 2) are kept. Each chain ends up as a row in the table, which is then sorted. When cracking, the target hash is hashed and reversed up to…

An md5 rainbow table for lower alphanumeric which covers passwords of length 9 is 63gb. Length 10 is 316gb. You can see where this is going. It's important to note the caveat upfront; lower case-only plus numbers. No upper case, no symbols.

http://project-rainbowcrack.com/table.htm

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