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The Death Throes of crypt()
dex writes "Tom Perrine and Devin Kowatch of the San Diego Supercomputer Center have issued "Teracrack:
Password cracking using TeraFLOP and PetaByte Resources" (PDF, HTML version via Google). Using SDSC's
prodigious computing facilities, they precomputed 207 billion crypt() hashes in
80 minutes."
Mirrored here:
http://home.twcny.rr.com/scooper2/teracrack.pdf
- Sometimes you're the pidgeon, sometimes you're the statue.
Read the PDF. The first page tell us that:
Using the Blue Horizon supercomputer at the San Diego Supercomputer Center, we found that pre-computing the 207 Billion hashes for over 50 million passwords can be done in about 80 minutes. Further, this result shows that for about $10K anyone should be able to do the same in a few months time, using one uni-processor machine.
Remember that many glibc2 "overloads" crypt() to be able to deal with MD5 hashes. I wonder how many MD5 hashes they can generate...
If I understand the article correctly, they're using serious computer power to develop a database of all passwords and their resulting hashes. In doing so, they can reverse engineer any hash back into a password via a 1 to 1 lookup. The only problem is that the attacker still needs physical access to your password hashes. In other words, this is much more serious for "insider" hacks where a system user wants root control.
Correct me if I'm wrong, but wasn't the point of moving the hashes from passwd to another root protected file (like "master.passwd") to prevent this sort of problem?
Javascript + Nintendo DSi = DSiCade
Solaris uses PAM, so its trivial to add any kind of authentication method that you want.
Sure, MD5 strings are a little longer, but still (I'm pretty sure) less than 80 characters.
md5 strings are 32 characters. And most linux distros use md5 for their shadow files already.
DES is the Digital Encryption Standard. IIRC, it's a 56-bit symmetric-key encryption method, and is considered insecure, as a high-end desktop machine can crack anything encrypted with it in under 24 hours.
"They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
and System Administration Guide: Security Services
Funny, we did this work almost a year ago, and someone finally notices :-(
:-)
Yes, this is a very small part of the total theorectical key space.
But its exactly the part of the space that is most "interesting"; this is the part that will most likely be searched by an attacker AND the part that is most likely to have a real, user-selected password.
The original goal (years ago) was to allow us to verify that our users weren't using passwords that would be likely to be found by an attacker.
Yes, passwords are *supposed* to be stored in shadow files that are not accessible, except by root, but in practice, it is often discovered out in the Real World, especially at larger multi-vendor sites, that user password hashes are copied between machines, stored in databases, and in general available to an attacker who does not yet have root.
These are the same sites that often can't or haven't converted to md5() hashes, as they have older legacy OSes that don't do md5(). Note that even though Sun "supports" md5() hashes, they don't support them everywhere and it certainly isn't seamless. Don't get me started about AIX. Linux and the *BSD folks are way ahead of most of the commercial UNIX variants.
As for the scalability, read the whole paper. We used the largest single machine at SDSC, but its rather dated in terms of crypt() performance. A distributed.net-style project using typical home machines would win, IF you could get a thousand or so people to cooperate.
The Terabytes of storage in a single filesystem didn't hurt in the sort/merge phases either.
Personally, I'm a Kerberos fan
With a password hash, all hashes generated are of the same length. Therefore someone bruteforcing the hash will take the same amount of time no matter what the password is. A longer password though may save you from a dictionary attack, especially passphrases, as it greatly reduces the chance of a brute force dictionary crack finding your password.
Actually, it's worse than that. You don't have to test every number between 1 and sqrt, just the primes.
I recall reading somewhere that it takes about ten bits to double the security of a public key, rather than one. I don't know if that's actually true.
You want the truthiness? You can't handle the truthiness!
This statement starts off true and ends up totally false. A high end desktop machine cannot "crack" DES in under 24 hours. It can't even "crack" DES in under 24 years.
1) DES has never been "cracked". It has been brute forced.
2) A single machine would take on the order of 600 to 1200 years to brute force a single 56-bit key. Obviously, this number changes with the method used to brute force and the machine used.
There has never been a machine demonstrated capable of cracking 56-bit DES in under 24 hours. The EFF built a DES Cracker which could search the entire key space in 9 days.
DES is not considered insecure. Many applications would likely benefit from another choice however.
You're overlooking the random salt value, which is different on each machine, or even the same machine for different accounts. So, generally you would have a hash of "$salt-$password".
The problem mentioned with crypt() is that the $salt value is very small (1.5 bytes), thus making dictionary attacks feasible. If MySQL is not using salt values, then they risk similar attacks.
Most writers regard truth as their most valuable possession, and therefore are most economical in its use - Mark Twain
hummmm, i would beg to differ with the 'iamdrscience' post.
.000007%
You are thinking about normal computer science hashes not cryptographic hashes.
207 billion is a very small portion of the possible hash relations.
I worked on a project similar to this, a distributed password cracker.
They calculated 50million passwords and 4096 salts this gives ~207Billion hashes.
There are ~7.32*10^14 possible passwords (quick approximation) with the 4096 possible salts.
That gives ~2.99*10^18 possible hashes.
I think the author of the other post was thinking there would be a lot of collisions.
There are 2^64 possible permutations of the DES 'cipher text' which gives ~1.8*10^19 possible 'cipher text' final state.
This means there are six times as many theoretical hashes as there are actual password hashes.
That and the nature of the DES algorithm would make colusion not very likely.
Anyway back to the point... 207 billion hashes would be 2.07*10^11.
2.07*10^11/2.99*10^18 =
This is NOT a substantial portion of the search space.
-Nick
*cipher text is refering to the initial 64 zeros cipher text used in the DES password encryption.
There has never been a machine demonstrated capable of cracking 56-bit DES in under 24 hours. The EFF built a DES Cracker which could search the entire key space in 9 days.
Naw, the EFF machines was later upgraded, and combined with distributed.net was able to crack a DES encoded message in 22 hours
AccountKiller
Back in 1994 I wrote the MD5 based crypt() which it seems almost everybody has adopted from FreeBSD by now: *BSD, Linux/GLIBC, Cisco and appearantly even Solaris.
:-)
The important properties of a good crypt() algorithm are still:
1. Input password is not length or charset restricted.
2. The algorithm is complex enough to not lend itself easily to hardware implementations (FPGAs etc).
3. The Salt is big enough that precomputing dictionaries is not feasible.
You will notice that apart from #1, these are not quantified, DES-based crypt() fulfilled #2 and #3 back in its days, but no longer does so. In a similar way, some day we will declare my MD5 based password scrambler as failing one or both of those criteria because password scrambling is not a case of finding "the" algorithm and putting a checkmark in the box, it needs to on periodically evaluated and improved every decade or so.
That is why I put the $1$ prefix on my MD5-based crypt(), so that you can update to a better algorithm when you need to. OpenBSD has already added a couple of stronger SHA based algorithms ($2...) and more can be added in the future.
In the absense of any other "IANA" for this, I would appreciate if you would register your "magic strings" with me so we don't have collisions.
If you're still using DES-based crypt(), switch to MD5 based crypt() now. Don't wait any longer, you are already 9 years late (IMO).
It's even "free as in free beer"
Poul-Henning Kamp -- FreeBSD since before it was called that...
In standard crypt() format, the salt is the first two characters of the hash.
The canonical way hash a password using crypt():
The characters "xo" are chosen at random when the password is first hashed. Note how they are the first two characters of the hash. The canonical way to check if a given password matches a hash is:Note how I use the entire hash as the salt. Only the first two characters of the salt are actually used by crypt(). Actually, only twelve bits from the first two characters are used for the salt: Two different salts resulted in the same hashes: this shows that crypt() does not use the entire 16 bits of the two characters (indeed, not even the entire 14 bits of the characters as US-ASCII). Only twelve bits are in fact used.Also, the entire password is not used: in fact, only the first eight characters of the password are used:
Since slashcode strips un-american characters, I cannot demonstrate the the top bit of each character in the passphrase is discarded.
Now, we can do some math: if 12 bits of salt is used, we have 4096 possible salts (2 ^ 12). If 7 bits of 8 characters are used, we have 7 * 8 = 56 bits of possible password. Thus, we have 2 ^ 56 * 4096 = 295147905179352825856 possible passwords (295 quintillion).
Now, these numbers don't match up with what's reported in the article description (207 billion hashes). It's possible that some combinations of passwords and salts produce identical hashes, but I would never expect nearly this many...time to read the article.
OK, I skimmed the article. They did not cover the entire keyspace of passwords. They only created a list of candidate passwords from a system dictionary using Crack's password generation routines. There are 1425835290 (1.4 billion) times more possible passwords than they tested. If they tried hashing all possible passwords, it would have taken them 217022 years at the rate they're going (80 minutes per 207 billion passwords). The storage of these hashes is out of the question (I don't know my metrics that high :).
Actually, on second thought, I can imagine a compression scheme that could drastically cut down on the storage involved: but this is irrelevant, the CPU time is still overwhelming.
Lesson learned: worry more about the quality of your passwords than the quality of your password hashing algorithm.
[Perhaps I missed something? Anyone care to check my arithmetic?]