Is it possible to create a MD5 collision based on a known input value?
So for example I have input string abc with MD5 900150983cd24fb0d6963f7d28e17f72.
Now I want to add bytes to string def to get the same MD5 900150983cd24fb0d6963f7d28e17f72.
(I know this is possible by bruteforcing and waiting a long time; I want to know if there is a more efficient way in doing this)
Unitl now no algorithm has been discovered that allows you to find a matching input that will generate a given md5 hash.
What has been proven is that you can create md5 collisions quite easily, for example with what is known as chosen-prefix-collision: you can create two files yielding the same md5 hash by appending different data to a specified file. If you want to know more or get the program to try it, look here.
Related
I have a project where we are supposed to find a sha256 from another sha256.
For example we have
hash1 = "45f1bc22c29626c6db37d483273afbe0f6c434de02fe86229d50c9e71ed144fc"
and we would have to find
hash0 = "5495a885b7f445a198cc5b67a517a0e0536792ab3e7ead18a12c75f8310a9b89"
hash1 is just the hash0 used in a sha256 function.
Initially, I went on to redo every possibility of sha256 but it may do a lot and take a lot of time.
If you have any idea how I could do this, even see if it's possible?
It's impossible, hashes can't be inverted, regardless if they're hashes of hashes or of other content. You could try all the combinations, sure, knowing that the source is a 256-bit sequence, but this is practically prohibitive, although there's always a possibility of 1 out of 2^256 that you guess it at the first try :-)
The input strings have the following conditions:
Only contain alphanumericals ([a-zA-Z0-9])
The size of a string is always less than 256 bytes
Total number of input strings is less then 1000,000
So what is the conflict probability of md5 digestion if the input strings are all under the above conditions? Can I just assume that there has no conflict?
If the inputs are random the likelihood of a collision in that input set is very low. That being said MD5 is a broken algorithm and a human can easily use software to find a collision. So you probably just shouldn't use MD5, but it depends on what you're using it for. I'm not sure why you would ever want to use MD5 anymore. You should look into the blake2 family or the newer SHAs (SHA256, SHA512, not SHA-1). If these are passwords you should pretty much definitely be using a hash designed for passwords like PBKDF2 or one of the Argons. To be honest I'd recommend just using libsodium's defaults for most things.
I wish to know how do software verify the downloaded files are not corrupt by using hash functions?
You should read http://en.wikipedia.org/wiki/File_verification,
"Hash-based verification ensures that a file has not been corrupted by comparing the file's hash value to a previously calculated value. If these values match, the file is presumed to be unmodified." That's how
Consider password hash verfication process....
you signup to "www.example.com" and they ask for your password
"your-secret-password" >> gets hashed and becomes gn234hs (for example)
You now have a "reference" hash
you come back a month later and as long as you provide same password the hash function will produce the same output gn234hs - which matches the original and verifies that what you entered is the same as what was entered last time.
No big insights there....
what if, instead of feeding in a password - someone feed a binary representation of a file or a collection of text files into the hashing function.
[010101001010101... huge number] >> hash function
hash function produces 32j4h234j234k23j4h23k4h23kj423kj4h3
you now have a "reference hash" for that file.
Now you get a file off the internet
If you run the file through the same hashing function and you get
32j4h234j234k23j4h23k4h23kj423kj4h3 - same as for a password - you know the file is a bit for bit representation of the original.
So the question is, I get how a hash can represent a password thats only a few characters , but how can a hash represent an unbelievably huge binary sequence or text file, be "sensitive" enough to detect changes and still have a unique quality?
Basically, because of the "randomness" of the output of cryptographic hash functions (as distinct from ordinary hashes) and the number of possible combinations a hash can have is so huge, that whilst its possible for different permutations of the items being hashed to result in the same hash - its so small as to be considered statistically insignificant.
Its a bit oversimplified, but hopefully that helps.
There (obviously) is tons of info on the subject if you google it, e.g. the wiki article linked to already.
I received a MD5 hash and a Regular Expression which have the same plaintext..
How do I use the Regular Expression to crack the MD5 hash and find the text behind the MD5?
b89e49cab317f2681be60fb3d1c0f8f8
[(a|c|d)n-t\|]{8}
The idea would be to use the regex as a template and generate inputs that satisfy it.
You can search for a regex visualizer to see this, but what that one says is any of the characters ()acd| or any character between n and t (inclusive) in any order, repeated eight times. I tested this in hashcat, and the regex is correct despite it looking like it means something else. A shorter way to write that would be [acd|()n-t]{8}.
So you start generating 8 character strings with those values and taking the md5 of them. You can do this in almost any programming language but Python is a good choice. Look up the hashlib library, it has a function md5. You'll call the function hexdigest on that and compare it to the provided hash.
>>> import hashlib
>>> hashlib.md5(b'cybering').hexdigest()
'61e4feebe66ad22349e292d1462afd3a'
Additionally, if you want to use cracking software, look up JohnTheRipper or hashcat. You should be able to provide them a dictionary and have it attempt to break the hash. I was able to solve this with hashcat on my 980ti in ~5 seconds. This tutorial helped me set up the custom charset and mask to perform the attack.
Have fun!
One approach would be to generate all possible eight-character combinations (with repetition) of the 19 characters allowed by the regex. Test each combination by computing the md5 hash and comparing it to the one you were given.
That would be 13^8 = 815,730,721 possible combinations to check. The answer will likely be found before checking all of them.
I was able to whip out a little Node.js program on my laptop that found the solution in about 4 minutes (I split the problem up using workers to take advantage of multiple CPU cores).
Edit: I thought the regex had n-z instead of n-t so the search space was actually much smaller.
You cant crack the md5 hash value it has used one way hashing algorithm.
I'm writing a file system deduper. The first pass generates md5 checksums, and the second pass compares the files with identical checksums.
Is there a collection of strings which differ but generate identical md5 checksums I can incorporate into my test case collection?
Update: mjv's answer points to these two files, perfect for my test case.
http://www.win.tue.nl/~bdeweger/CollidingCertificates/MD5Collision.certificate1.cer
http://www.win.tue.nl/~bdeweger/CollidingCertificates/MD5Collision.certificate2.cer
You can find a couple of different X.509 certificate files with the same MD5 hash at this url.
I do not know of MD5 duplicate files repositories, but you can probably create your own, using the executables and/or the techniques described on Vlastimil Klima's page on MD5 Collision
Indeed MD5 has been know for its weakness with regards to collision resistance, however I wouldn't disqualify it for a project such as your file system de-duper; you may just want to add a couple of additional criteria (which can be very cheap, computationally speaking) to further decrease the possibility of duplicates.
Alternatively, for test purposes, you may simply modify your MD5 compare logic so that it deems some MD5 values identical even though they are not (say if the least significant byte of the MD5 matches, or systematically, every 20 comparisons, or at random ...). This may be less painful than having to manufacture effective MD5 "twins".
http://www.nsrl.nist.gov/ might be what you want.