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I want to set a user's password as MD5 hash value in Centos. I mean I don't know the password, but I have the hash MD5 value (md5sum). Is it possible?

Detailed explanation: New password I want to set: 123 MD5 value of '123' is: dak37yd2o9d8m2ype9n8283up1m2 I want to run a command like this:

echo dak37yd2o9d8m2ype9n8283up1m2 | passwd --stdin -md5 myuser

So myuser can login with password 123

  • The hash you have given is not a valid md5 hash. MD5 outputs 128 bits, or 32 hexadecimal chars. You have supplied 29. The hash of the string 123 is 202cb962ac59075b964b07152d234b70. – Cyclic3 Oct 2 '18 at 9:53
  • That was just a random value to explain my question, but thanks anyway :) – Hamid Reza Oct 3 '18 at 17:34
  • ah, I didn't realise – Cyclic3 Oct 3 '18 at 18:53
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A word of warning: As I am sure you have heard many a time, md5 is a broken hash function. Storing passwords hashed with it is only slightly better than plaintext.

After much researching, including trying things out on my own system, I was unable to find a way of using an existing hash that has not been salted. If you still have access to the password, or access to someone who knows it, you can use chpasswd -e to generate a salted hash.

If you have a salted hash, add the user to your system normally, if you haven't done so already. Pick any password you like, as we will overwrite it later. Open the /etc/shadow file, and edit the line starting with the username of your user. Replace the second field (after the first colon, and before the second) with this:

$1$salt$hash

Where $salt$ is your salt, and $hash$ is the md5 hash in crypt base-64 format (https://www.linuxquestions.org/questions/linux-security-4/how-can-i-convert-a-sha-512-etc-shadow-hash-to-base64-4175477045/).

If the hash is unsalted, and you cannot gain access to the password through normal means, using something like hashcat to break it for you could be a viable option.

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    You can use chpasswd -e to set a password hash without editing /etc/shadow yourself manually. Purely looking at man 3 crypt, empty salt should be allowed (0 is "up to 16"), so $1$$hash might work. If it doesn't, filing a bug against glibc will likely lead to a documentation clarification that salt can't be empty. – Ulrich Schwarz Sep 30 '18 at 11:03
  • @UlrichSchwarz I shall update my answer accordingly. I did try with an empty salt, but it gave me a different value that sha1sum, and I could not use it to log in. – Cyclic3 Sep 30 '18 at 12:02

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