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MD5 Collision Source Code Released
SiliconEntity writes "The crypto world was shaken to its roots last year with the announcement of a new algorithm to find collisions in the still widely-used MD5 hash algorithm. Despite considerable work and commentary since then, no source code for finding such collisions has been published. Until today! Patrick Stach has announced the availability of his source code for finding MD5 collisions and MD4 collisions (Coral cache links provided to prevent slashdotting). MD4 collisions can be found in a few seconds (but nobody uses that any more), while MD5 collisions (still being used!) take 45 minutes on a 1.6 GHz P4. At last we will be able to implement various attacks which have been purely hypothetical until now. This more than anything should be the final stake in the heart of MD5, now that anyone can generate collisions whenever they want."
So is SHA1 the recommended alternative?
Bradley Holt
(With sincere apologies to Bryce Jasmer.)
Carousel is a lie!
It's important news but not really that shocking. MD5 was not something professionals would recommend for a few years already.
Any half-way intelligent cryptographer would have suggested SHA-1, TIGER or perhaps HAVAL since quite some time already.
Tom
Someday, I'll have a real sig.
Keeping in mind where MD5 is broken is important, so that good uses for this tool are not disposed of out-of-hand.
md5 is still good for keeping track of if your files have changed. It should not be used for document signing.
I'm essentially crypto ignorant. About all I've known to do was verify MD5 hashes on downloads. Now that this is by-and-large pointless, how to check the veracity of things like Linux ISO's, video drivers, etc, ad inifintum?
blarg.
Great. Now that MD5 is dead, the slow/theoretical attacks on SHA1 can be the focus of collision research. I look forward to changing hash algorythms again from SHA1 in a year. :-/
"Fight for lost causes. You may discover they weren't."
This is all really interesting theoretically, but who has the money to run a 1.6 GHz P4?
Recommended replacements are SHA (preferably SHA-2), WHIRLPOOL and/or RIPEMD.
http://en.wikipedia.org/wiki/SHA-2
http://en.wikipedia.org/wiki/WHIRLPOOL
http://en.wikipedia.org/wiki/RIPEMD-160
Why not just use 2 different algorithms? Yes, it's possible. Or hell, use 3. Can some one tell me why not this isn't a standard practice? Even if one has a weakness, you still have the other to back it up
I use HMAC-SHA-256 with PasswordMaker.
https://passwordmaker.org/passwordmaker.html
In other words, right now it's time to...
...LICK OUT THE KAMS, NOTHERGUCKERS!
doesn't bittorrent use md5 to verify the sections of files it has downloaded? will this facilitate poison seeds? or does BT use something more complex than md5?
I guess someone thinks he's a little too cool to comment his code properly. Yeah, like "/* B2 */" tells me anything useful you insensitive clog!
Hero of Allacrost, a FOSS RPG for *NIX/*BSD/OS X/Win
This new algorithm does not ruin the usefulness of MD5 hashes. The algorithm can generate two documents that have the same MD5 hash, an MD5 collision. But it can NOT generate an MD5 collision starting with an existing document. In practical terms, this means a file that has been signed with an MD5 hash is STILL secure. Nobody can replace the file with a different file that will have the same MD5 hash. However someone can prepare in advance two documents with the same MD5 hash and trick someone into believing one document is really the other. So if you trust the original source (a Linux distro for example) you can be confident you are downloading the original document.
- For the complete works of Shakespeare: cat
This more than anything should be the final stake in the heart of MD5, now that anyone can generate collisions whenever they want.
/.'d), but unless they have made an enormous breakthrough since this was last reported, this attack has very little implications for those of us who use MD5).
No, no, no. This does not allow an attacker to generate any collision they like. They cannot find data that collides with a piece of data I provide them with. All they can do is provide me with 2 pieces of data that happen to collide.
This means that an attacker can theoretically provide 2 different documents to people with the same hash, but they cannot easily produce a document that has the same hash as a document I have written.
(Disclaimer: I haven't actually been able to RTFA (it's
This program is an efficient way to generate two source blocks with the same resulting MD5. This program does NOT allow you to match an arbitrary MD5 hash. That may come some day, but unless I've missed a very important paper somewhere, it has not happened yet.
This does not totally invalidate MD5 for verification. This attack still does not let you poison a torrent feed, etc, unless you are the author of the original source data and you engineered the data specifically to be vulnerable to this attack.
This more than anything should be the final stake in the heart of MD5
No, no it won't be. It won't be, because MD5 is useful for many things where the existance of an "easy" (in quotes because easy is relative) method of generating colisions is irrelavant.
It won't even kill off the use of MD5 checksums as a signature for verifying authenticity, because if your data is smaller than the checksum there may not be a colision at all, and an exploit wouldn't matter.
This is an important discovery, but it doesn't make MD5 useless any more than CRC32 is useless.
OK, so clearly a scripted attack against MD5 is bad.
But aren't most people using MD5 using salted (as opposed to unsalted) hashes? (for those unclear on the difference, a "salted" has basically uses a local seed as part of it's MD5 hash, in addition to the value to be encrypted)
Doesn't seem likely that salted hashes can be easily broken by this technique, although clearly it's a concern that, should the salt value become known, all your passwords, etc, become breakable...
The only attacks that these md5 collisions allow are denial-of-service/destruction-of-data attacks, they don't generally allow the compromise of protected data or access to systems or suchlike. The collision blocks that are generated are effectively random data. It has yet to be shown how to -craft- a collision block.
/dev/random as out of a collision block.
If we could craft a collision block that contained a specified string at a specified position, that would be another issue altogether.
The ability to find collision blocks easily does suggest that crafted collision blocks might be possible, but for now, you have as good a chance of getting a viable exploit out of
This doesn't mean we shouldn't look to other options for the newest releases of high-security software, but it doesn't mean that the md5 algorithm should be purged from our systems altogether either. It's still extremely valuable at detecting accidental corruption, and useful-with-caveats at detecting malicious corruption (45 minutes to discover a block of data that matches the sum is not really useful in either speed or resulting data for any kind of man in the middle attack, for example, so using md5 to validate network packets is safer than using it to validate disk files).
Of course, the black hats may know more than we do about md5 weaknesses, but 'may know' is just as true of any other algorithm.
--Parity
'Card carrying' member of the EFF.
Just because collisions can be generated doesn't mean that MD5 is dead.
It might only take minutes to calculate two random strings with the same hash, but it would still take a very long time to calculate a second string that collides with a pre-existing string. So even though it is now cryptographically weak, it can still be used effectively to check the integrity of files.
(Coral cache links provided to prevent slashdotting)
Im sorry, you must be new here.
"In the game of life, someone always has to lose. To me, if life were fair, that someone would always be Oklahoma." -DKR
TIGER is good, as is Whirlpool. Whirlpool has the advantage that it uses AES as the basis, and AES is regarded as secure. It was also certified for secure work by NESSIE - a European group trying to do for the EU what NIST does for the US - which means that it's probably certified for use in secure environments in Europe.
According to the Hashing Function Lounge, there are other hashing functions that have not been broken (eg: cellhash and fft-hash) but these are sufficiently obscure that a lack of a known exploit may be through lack of study and not through the presence of good security. It would make them good for beating skript-kiddies, as they won't have the skills to find exploits and those skilled enough at finding them aren't studying those algorithms much. (I don't like security through obscurity, but technically these aren't obscured as anyone CAN study the algorithm.)
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Maybe someone could explain why collisions are a serious problem for MD5. Or at least in what instances they are. I can see that in some cases, such as password hashing this could be a problem. But for many other uses I don't see what harm a collision has. Maybe I misunderstand but as I understand it MD5s are normally used in a checksum manner to sign or provide a fingerprint of a document. If you have an original document and compute it's MD5 then it can match some certified MD5 check sum. If someone were to generate a fake document they coul dnot design it to match the MD5 fingerprint. They could create some bit of gibberish that did match it but not a document that was useful as a forgery.
I guess if one were trying to deliberately pedal gibberish, like say if you were the RIAA trying to destabilize a torrent net then that would be all you care about. But for more general issues I don't get it.
Or is it now possible to generate a collision that also contains some intentional content like a binary program or source code or bank statement. That woul dbe be bad.
It seems like even in the case of gibberish generation that some simple hacks could extend the useful life of this. For example, if you were to MD5 a whole document and then MD5 the concatenation of every other byte in the document, it woul dbe pretty hard to find two collisions that had that property simulateously. Sure I wont doubt there are better ways to hash something than adding hacks to MD5. I'm just saying that it seems like a simple hack might well be good enough to extend its useful lifespan for passwords and file shareing.
But I invite you to explain to me why I'm wrong.
Some drink at the fountain of knowledge. Others just gargle.
No. This only helps you find collisions in two randomly generated strings.
It is still very difficult to produce a colliding file given a pre-existing file on the network.
It should also be noted that edonkey splits a file into 9500KB chunks, and then into smaller chunks again, and hashes each one. It would be far more difficult to produce a chunk that causes collisions on all three levels.
Anyway, I expect an eMule extension will come out soon to allow for sharing of SHA1 hashes between clients (if it doesn't already exist).
This code is weak. I fired it up like 20 minutes ago and still haven't r00ted my box.
t's also the default algorithm to hash passwords (i.e. if you type in your password, it gets hashed into an MD5 sum which is then compared to what the MD5-ed password should be, thereby avoiding plaintext password storage).
Doesn't matter. This attack has no significant effect on password hashing, with or without salt.
This attack allows you to find a pair of plaintexts that hash to the same value; you don't get to pick either the plaintexts or the hash value. It does not help you find a plaintext that hashes to a given value. To use this to attack an unsalted password hashing system you would need to first generate a collision, then convince the target of your attack to set one of those plaintexts to be his/her password, then you could log in using the other plaintext. But if you can convince the target to use a particular password, why not just use that to log in?
This is not an insignificant cryptologic result, and people should move away from MD-5 as fast as practically possible (actually, people have been moving away from it for years due to some results against MD-4, which MD-5 is very similar to) but it doesn't really have any practical implications right now.
Note to ACs: I usually delete AC replies without reading them. If you want to talk to me, log in.
Question: Does this mean all my MD5 passwords for all my users can be cracked?
Answer: The short answer is yes, they can be cracked. The long answer is no, not if you used a salt, and the attacker has to get those md5 hashes first. You are not safe you are storing your user's password field input directly to the database ala the php/sql method of:
Question: How should I remedy this?
Answer: Always use a salt or salts. For example in the case above you could use this php/sql method instead:
Question: How/Why is this safer?
Answer: Collisions are only direct input for the md5 function to get the same md5 hash. So in the above case, $password was directly taken from the user and made into a hash. Assuming an attacker got an SQL injection in and grabbed the database, they could run this collision creator on a hash and produce an input that gave that exact hash.
But, this would be much more difficult with any code that introduced a salt. That is why the second code is better, it includes two salts that the attacker (through his SQL injection) is unable to account for.
MD5 is dead. SHA-1 is currently dying. They're both based on the same fundamental math, and the attacks on SHA1 are getting stronger and stronger. Now would be a really good time to get off of that entire family of hashes if you can (MD4, MD5, RIPEMD-* SHA-*, etc).
The crypto world is in a little bit of a bind when it comes to strong hashes now. We simply don't have any left that both have a long proven track record of analysis and haven't been seriously compromised. Best bet, IMHO, is to go with a new-blood hash algorithm. They seem to be the answer we're looking for - but of course what they lack is more years of intensive study by the experts for flaws they themselves might harbor.
So if you want to give them a whirl, I'd recommend looking at Tiger and Whirlpool:
http://en.wikipedia.org/wiki/Tiger_(hash)
http://en.wikipedia.org/wiki/Whirlpool_(algorithm
11*43+456^2
Ah! That's a very good point.
now if you you were a software company you could put torrents out (I assume they use blocks of MD5sum), and then after the torrent becomes popular start randomly seeding people with blocks that hash correctly but are complete garbage (since you can't pick what exactly you hash). if you do it right you would have games out there that would still mostly run. but would crash, or have garbled game data, etc.
I'm not sure if this is really all that useful. but this exploit certainly seems to make it easy to do.
“Common sense is not so common.” — Voltaire
Most document formats have lots of "dead space", parts you can pretty much modify at will without changing what the user actually sees. Comments in HTML or PostScript. Old junk data in Word documents. Executables can have just about anything you like added if you know your stuff. The MD5 attacks currently available only 128 "dead space" bytes to generate a collision. So far from being a gibberish document, one can generate almost any document you want. This page has a simple example with PostScript files. Both files have the same MD5 hash, but one is a relatively harmless letter of recommendation while the other is a grant of security clearance. Get your boss to sign your letter of recommendation digitally, swap in the security clearance file, and pass it on. This is a Big Deal and a Major Problem.
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The Coral Cache is extremely slow. Please point the links to the original site www.stachliu.com/collisions.html as the html is small/static and the machine it's sitting on has a decent (100mb) connection. Thanks.
The program generates byte stream A and B, both having the same hash C. You can't input C and get an arbitrary B out (with this algorithm).
Or you may have a brain tumor...
The generaly accepted definition for "cracking a password" is, given the encrypted password, being able to generate a password the once entered in the authentication system will generate the same encrypted form.
For the second time, this attack does not permit that. This attack permits build two byte streams that hashes to the same value. So in a password context, assuming the password system permits the entry permits more than 1024 bits of arbitrary data to be entered as password (I don't remind the details well, but I think this is the amount of data that you must be able to change between the two streams) one could generate to "passwords" (being that long they don't qualify for this name anymore IMHO) that would hash to the same value.
How does that amount to an attack on MD5 passwords again? Never at any point the attack had been being able given a unknown to him MD5 hash to produce a stream that would hash to the same value.
For the impatient, here is a summary for my recommendations for 2005-2006:
See the paper for mode details.
chongo (was here)
For one: any system that uses one-way hashed password storage or key generation mechanism, as many sites use, is now some percentage easier to violate because multiple strings may resolve to same hash.
It's the case with all one-way hashes that multiple strings hash to the same value. Since an n-bit hash function can only produce 2^n distinct hash values, if there are more than 2^n possible input plaintexts, than multiple plaintexts hash to single values. In fact, since MD5 and similar can hash inputs of any length, on average there are an infinite number of plaintexts that hash to any given n-bit value.
The existence of this attack doesn't change the existence or distribution of collsions... we always knew they existed. It just means that we can find some of them. Ideally, we'd like it to be practically impossible to find *any*, even though we know they exist.
Note to ACs: I usually delete AC replies without reading them. If you want to talk to me, log in.
While we might discover that "Donald Duck" has the same hash as "a", we don't get to choose either. We can't say "gimme a plaintext that hashes to this: 0x4faed...", all we can do so far is say "find two plaintexts that will give us the same hash"
Not that this doesn't mean this is a very serious matter. My take on the situation is: "Oh. Shit."
You don't seem to understand... Having the MD5 hash of a piece of software and the ability to generate a collision for that hash will--
Stop right there, because it's quite clear that the one who doesn't understand is you. Nobody has the ability to generate a collision for a given MD5 hash. All we have is the ability to generate two bits of random junk that share the same hash. This makes some attacks possible, but it does not make it possible for you to distribute a malicious version of someone else's software that has the same MD5 hash as their version.
The main problem with MD5 as it's used today comes when MD5 is used as a component of a digital signature scheme. Most digital signature schemes based on public key crypto work like this:
To verify a digital signature, the following is performed:
Now, it's easy to see why this spate of collision attacks on hashing algorithms is so deadly. If, given some signed document, you can produce another document that verifies to the same signature, well, I guess you're in a world of hurt. If these documents happen to be public key certificates, well, the whole PKI more or less collapses. And well, here's a bit of news: someone has done just that with X.509 certificates based on MD5.
Qu'on me donne six lignes écrites de la main du plus honnête homme, j'y trouverai de quoi le faire pendre.
"You can generate collisions at any point in a file simply by starting with the partial MD5 sum up to the point in the file that you want to insert the block at. //Initialize hash value for this chunk:
var int a := h0 := h1 := h2 := h3
//Main loop: := (b and c) or ((not b) and d) := i := (d and b) or ((not d) and c) := (5×i + 1) mod 16 := b xor c xor d
g := (3×i + 5) mod 16
else if 48 i 63 := c xor (b or (not d))
g := (7×i) mod 16
:= d := c := b := ((a + f + k(i) + w(g)) leftrotate r(i)) + b := temp
//Add this chunk's hash to result so far:
h0 := h0 + a := h1 + b := h2 + c := h3 + d := h0 append h1 append h2 append h3 //(expressed as little-endian)
What these guys have done is to find 512 bit blocks or larger that return the same hash given the same initial state h0, h1, h2, h3.
As u can see above, if you find a collision for state i, ho, h1, h2, h3 the same collision will not work for the different state MD5 will have say after processing a number of blocks.
It is computationally feasible to find many collisions for the initial state but to find collisions for all possible states and to have these collisions occuring in the original file is very hard.
So, no you cannot simply search the file for blocks that are among the blocks for which u found a collision and then simply replace them with their collision. The MD5 for which you found the collision and the MD5 that is used over the file are essentially two different functions and will not hash to the same value.
As for the rest of your comments: I hope you realize that you don't just give their program an MD5 hash and it outputs two values that hash to that output. MD5 has been shown not to be collision resistant but it is still preimage and second preimage resistant.
I explicitly said that we assume the signer is trusted, you did not need to say anything about trusted parties. If the signer is not trusted the whole signed code scheme is meaningless.
" That's incorrect. MD5 operates over 512-bit blocks and uses state generated from the hash of the previous blocks to generate the new state for the current block. The state is actually the 4 words of the 128 digest.
Here is the alg from wikipedia:
init h0
init h1
init h2
init h3
for each 512-bit chunk of message
break chunk into sixteen 32-bit little-endian words w(i), 0 i 15
var int b
var int c
var int d
for i from 0 to 63
if 0 i 15 then
f
g
else if 16 i 31
f
g
else if 32 i 47
f
f
temp
d
c
b
a
h1
h2
h3
var int digest
The parent comment, which I wrote, was based on a severe misunderstanding of the extent of the capability of the attack. In particular, I didn't realize that the attack could find collisions even with arbitrary, attacker-specified IVs. What that means is that it is indeed possible to generate x.509 certificates containing different keys but the same MD5 hash (and therefore the same signature). In fact, it's been done.
Note to ACs: I usually delete AC replies without reading them. If you want to talk to me, log in.
A lot of people have the programs md5sum and sha1sum installed, but they often don't have equivalent programs for the SHA-2 family. To calculate those you can use the command:
or you can download a dedicated program: http://www.ouah.org/~ogay/sha2/.
There's a hidden treasure in Python 3.x: __prepare__()
Is it advised to switch GnuPG from SHA-1 for signatures to SHA-256 (like immediately)? How can I make this configuration change?
(from material at the Pure Crypto Project - http://senderek.de/pcp/ )
Quote below from http://senderek.de/pcp/pcp-security.html
The nice thing about Adi Shamir's hash function is that it, as well as the RSA cryptosystem co-created with Rivest and Len Adleman is all based on simple modular exponentiation.
Too bad the Feds consider arbitrary precision mathematics used for encryption purposes to be 'a munition' and 'a controlled export'....
Years ago, they raked Phil Zimmerman over the coals over his email cryptosystem PGP then (eventually) left him alone.
Can't cryptosavvy individuals secure the details of their affairs with strong encryption WITHOUT being hassled by 'the Man'?...
P.S. However, Rivest came up with a scheme that gives you 'confidientiality *without* encryption' through a scheme he calls Chaffing and Winnowing
Enjoy!
Because that would require the hashed password and a preimage attack.
See here.
Summary for those who are lazy:
In conclusion, the value of this attack/exploit is only relative to how the hash function is used in an application. Just because this exploit and source code for it exists, that does not that these hashing algorithms are completely useless.