CODEWITHSUNDEEP
clinux
mosceo
mosceo

Reputation: 1224

How to create shadow password from a C program

Function crypt() returns a string like TyVkFBglLfEGw, when on my Ubuntu machine all passwords are in form like $6$Ty8Ew9/O$V/ck4Apc7VOOqobhenO5.f6ccsVdCpQy5H6fyuNzCaDG.LxFnUWKHOobkpRQQtl.1cFG8BLAdfWjNbLiSxKXF/

I think my machine uses SHA512 algorithm. How can I create hashed strings like in /etc/shadow file from a C program?

Upvotes: 2

Views: 2037

Answers (2)

Anya Shenanigans
Anya Shenanigans

Reputation: 94779

If you read the man page for crypt; specifically the piece about Glibc notes, it mentions the following:

The glibc2 version of this function supports additional encryption
algorithms.

If salt is a character string starting with the characters "$id$"
followed by a string terminated by "$":

      $id$salt$encrypted

then instead of using the DES machine, id identifies the encryption method used and this then determines how the rest of the password string is interpreted. The following values of id are supported:

      ID  | Method
      ─────────────────────────────────────────────────────────
      1   | MD5
      2a  | Blowfish (not in mainline glibc; added in some
          | Linux distributions)
      5   | SHA-256 (since glibc 2.7)
      6   | SHA-512 (since glibc 2.7)

So $5$salt$encrypted is an SHA-256 encoded password and $6$salt$encrypted is an SHA-512 encoded one.

this means that you should pass in a string as salt that contains the string $6$salt to get it to generate a sha-512 crypt e.g.

char *salt = "$6$pt4wu5ns";
char *password = "muppet show";

printf("%s\n", crypt(password, salt));

Upvotes: 4

Malcolm McLean
Malcolm McLean

Reputation: 6404

Here's a website on how to implement the sha1 algorithm.

http://bradconte.com/sha1_c

Normally I would describe the algorithm, but really there;s nothing to it, just mix up the bits with a complex series of adds and shifts. The tricky bit is getting it to exactly conform to everyone else;s sha1 code.

Upvotes: -3

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