If i create a SHA-256 has in the terminal i get a nice looking hex hash:
echo -n ChillyWilly | sha256sum
4c74e3994a247dfc31a515721528c78bb6ec09ccdcfd894d09f4aa44131393a8 -
If i try to do the same with the crypt(3) function then i get something entirely different:
const char* what = crypt("ChillyWilly", "$5$");
printf("%s\n", what);
$5$$fQITOGYPwBrwOSpjX1Uhx5Ock/J84zbrqmTtg/SlvMB
It looks like Base64 but it's not.
My assumption is that if the key and salt are equal then i should get the same result. All SHA-256 hashers in the web will generate the same result from the same key/salt combination.
How can i get the same hex hash with the crypt(3) function? I have set the $5$ as instructed on the crypt manpage that should force the crypt function into SHA-256 mode.
I know there are a few similar questions here but they did not seem to contain the correct answers.
Thanks!
While crypt can use SHA-256 when in $5$ mode, they aren't the same thing.
SHA-256 is a hash function, designed to run quickly. But crypt is a key-derivation function intended for hashing passwords. As such, it runs SHA-256 a large number of times (5000 by default) to make it slower and less prone to brute-force attacks. So it will give a different result than a simple SHA-256 use. You can see the details of the algorithm here.
As you saw, crypt also doesn't output the result as hex, but as a Base64-like encoding (not the standard Base64 but based on a similar idea). There's no point in trying to convert to hex if you do this expecting to get the same result as SHA-256.
crypt() will in fact use the same SHA-256 algorithm - but it does not return the hash as you would expect. After computing the hash it does it applies another transformation to the result, as seen here.
So I wouldn't count on using it and getting the same result as sha256sum, since it's built for a different purpose. You might look into using the openssl SHA256 implementation, or something else if you need it to match.
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 :-)
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.
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 am basically creating an API in php, and one of the parameters that it will accept is an md5 encrypted value. I don't have much knowledge of different programming languages and also about the MD5. So my basic question is, if I am accepting md5 encrypted values, will the value remain same, generated from any programing language like .NET, Java, Perl, Ruby... etc.
Or there would be some limitation or validations for it.
Yes, correct implementation of md5 will produce the same result, otherwise md5 would not be useful as a checksum. The difference may come up with encoding and byte order. You must be sure that text is encoded to exactly the same sequence of bytes.
It will, but there's a but.
It will because it's spec'd to reliably produce the same result given a repeated series of bytes - the point being that we can then compare that results to check the bytes haven't changed, or perhaps only digitally sign the MD5 result rather than signing the entire source.
The but is that a common source of bugs is making assumptions about how strings are encoded. MD5 works on bytes, not characters, so if we're hashing a string, we're really hashing a particular encoding of that string. Some languages (and more so, some runtimes) favour particular encodings, and some programmers are used to making assumptions about that encoding. Worse yet, some spec's can make assumptions about encodings. This can be a cause of bugs where two different implementations will produce different MD5 hashes for the same string. This is especially so in cases where characters are outside of the range U+0020 to U+007F (and since U+007F is a control, that one has its own issues).
All this applies to other cryptographic hashes, such as the SHA- family of hashes.
Yes. MD5 isn't an encryption function, it's a hash function that uses a specific algorithm.
Yes, md5 hashes will always be the same regardless of their origin - as long as the underlying algorithm is correctly implemented.
A vital point of secure hash functions, such as MD5, is that they always produce the same value for the same input.
However, it does require you to encode the input data into a sequence of bytes (or bits) the same way. For instances, there are many ways to encode a string.
How can I encode a file using sha256 and c/c++ ???
Thanks!
SHA 256 stands for Secure Hash Algorithm ! It will only produce the hash of a given file . You can't retrieve the original file from a given hash otherwise hash functions are useless.
If you want to do encryption/decryption AES would be a better solution. Everything you need is in OpenSSL.
If you don't know what SHA is for, then you better ask someone who knows this stuff instead of doing it yourself. Even if you use a given library, chances are very high that you will produce snake oil. Security depends on much more than calling some encryption functions.