Can you break md5

MD5 is a digest algorithm. Think of it as converting a cow into a steak. Now try to reverse that. And even if you did, you wouldn't be able to go in reverse, because the algorithm purposefully loses information.

TrimikhaValentius MD5 is a digestive algorithm. Show 6 more comments. Active Oldest Votes. Once a piece of data has been run through a hash function, there is no going back. Improve this answer. Adam Batkin Adam Batkin It is no longer considered optimal as the best hash for passwords.

Since most passwords are shorter than the MD5 hash, there is usually only one password for each hash. And finding one, even if it is not the original one, is enough to access the account.

The point of being one-way function is not there are multiple different preimages, so we can't know which one was the original one , but it is really hard to find even one original value.

Olathe - I'm not sure I agree. There are usually an infinite number of inputs that produce every possible hashed output. I said generally because, if you know for example that you are looking for a string of ASCII characters, and it's less than, say, 12 bytes, it is probable that there is only one input that produces a given output. But there are always going to be collisions infinite , and unless you have some external constraint like in my example you will never know which is right — Adam Batkin.

This can be done using after-the-fact probabilities rather than prechosen constraints. It obviously can't be done in general, but it is still quite useful. Show 5 more comments. MD5 is a bad hash to use for passwords: It's fast, which means if you have a "target" hash, it's cheap to try lots of passwords and see whether you can find one which hashes to that target.

Salting doesn't help with that scenario, but it helps to make it more expensive to try to find a password matching any one of multiple hashes using different salts.

I believe it has known flaws which make it easier to find collisions, although finding collisions within printable text rather than arbitrary binary data would at least be harder. Jon Skeet Jon Skeet 1. Yes, there are other methods, but you need to understand what Jon said above - 'you shouldn't email them their password - that's sensitive information which might remain sensitive. A password should stay as secure as possible - usually by keeping it as a hash only in a database.

And also the fact that if the password can be reversed, that means anyone who gets access to your database can get at users' passwords. Not a good idea. One way passwords should be the norm; only keep the real password even encrypted if you absolutely have to e.

I've seen antispam-measures where the receivers webserver denies an incoming mail just to wait for the sender's mailserver to retry spambots usually only try once. That could easily exceed your 10 minute timeout. There's no guarantee that it's the original plaintext value. If the password is unknown, you can't know whether the one revealed is the original one or not.

But the point is that one way hashes like MD5 by definition lose information. The fact that sites like this can come up with a matching password is just good evidence of MD5 being a bad algorithm to use for security reasons. Show 7 more comments. Chris Huang-Leaver 5, 6 6 gold badges 38 38 silver badges 66 66 bronze badges. Daniel May Daniel May 8, 1 1 gold badge 31 31 silver badges 43 43 bronze badges.

I've got a few nitpicks. Rainbow tables are not brute forcing. There are actually programs and sites that do brute force very simple passwords of a few characters generally they just loop over a few hours or days, and you can fill in a hash and hope it comes up in the loop. And unfortunately, given the lack of quality of many passwords, the chance that one pops up is not "a very small chance".

I have to interject: Reversing MD5 is not malicious by nature. How you use this ability is what determines malice or good intent. If some one figured out how to reverse it and shared that with the world, they could win a nobel prize or something. That is how we all get better. But if you find a reverse to MD5 and then use it for personal gain, then yes, you are being malicious.

Add a comment. I would add that finding another value that hashes to the same output is called a "collision". This is the most common method of breaking MD5-hashed systems. Renesis, finding data that hashes to a previously known value is called a "preimage", actually, and it's much, much harder than just a collision. No preimage attack has yet been demonstrated against MD5, but collision attacks have been used. The point of hash functions when used for password storage is not that there are lots of possible passwords which give the same hash there are, but most of them are longer than the hash itself , but that it is hard to find even one of them which would be enough to access the system.

And yes, because of rainbow tables you don't use unsalted hashes. To be technical, you can't perform MD5 with certainty, because the hardware might have malfunctioned. In the same way, you may not be able to be certain that the password was password rather than all the other infinite inputs that produce the same hash but which all look quite random, but you can be close enough.

The pigeonhole principle applies of course, but it is still computationally infeasible to find a second input that hashes to a certain value, e. If you find an X that hashes to a given H X then you can be certain that X is the correct input. This makes the whole first section of this answer and most of the rest incorrect. Not possible, at least not in a reasonable amount of time. Matthew Groves Matthew Groves If the hash wasn't salted, you'd be surprised how often all it takes is a google search for the hashed value Not really practical for a password retrieval system though, even an unsalted one : — Matthew Groves.

You can't revert a md5 password. Nettogrof Nettogrof 2, 2 2 gold badges 15 15 silver badges 22 22 bronze badges. Nix the rainbow table idea.

If you're salting -- and you should be -- then it wouldn't work, anyhow. StevenSudit If they are still using MD5 to hash passwords instead of using a strong password hash, then you cannot assume they are using a salt.

Maybe they do, probably they don't. No, he must have been confused about the MD5 dictionaries. Robert Greiner Robert Greiner Sinan Taifour Sinan Taifour 9, 3 3 gold badges 28 28 silver badges 29 29 bronze badges. MD5 is a hashing algorithm, you can not revert the hash value. Rivest, R.

In: Menezes, A. Wang, X. Rump session of Crypto , E-print Google Scholar. Zheng, Y. In: Zheng, Y. Xiaoyun Wang 1 Hongbo Yu 1 1. Shandong University Jinan China. Personalised recommendations. Cite paper How to cite? ENW EndNote. This is important as we don't want the new line characters to be hashed with our password.

For demonstration purposes, we'll create multiple MD5 hashes containing different strength passwords and output them to a file called hashes :. If you already have a list of words then the following bash script can be used to automate the MD5 generation, reading each line in a file, then generating a file off the resulting hashes.

Replace 'wordlist' with the file path of your word list. If you do not have md5sum on your machine, you can copy and paste the hashes above and save it in a file called "hashes". If you want to hash different passwords than the ones above and you don't have md5sum installed, you can use MD5 generators online such as this one by Sunny Walker.

Now we can start using hashcat with the rockyou wordlist to crack the MD5 hashes. Do they contain emails someone sent you? Bzzzt : Not fine. Do they contain a browser cache from web sites you have visited?

Do they contain Git repositories you've cloned from someone? For general-purpose tools like rsync one stands on very shaky ground when one asserts it's OK—it's not security-related. Show 5 more comments. Active Oldest Votes. Improve this answer. Squeamish Ossifrage Squeamish Ossifrage Do you have a reference for an efficient parallelized version?

I misquoted the paper I cited. Fixed now. If, for example, a site is distributing an executable binary and publishes the size and an MD5 hash of the file, the attacker's goal wouldn't be to find the original input, but would rather be to create a malicious file of the same size that produces the same hash that they could trick users into downloading and executing.

The OP's question seemed to be about recovering what the original plaintexts were, so I focused on that goal. What you describe is similar to a , except instead of learning what the original input was, we don't care and just fill it with garbage to match a target hash, like a Bitcoin block. Show 3 more comments. Sign up or log in Sign up using Google.