write a c programme to chnage password of linux

raksha singh · 12-14-2012, 01:25 AM

i am new to c program and i want to write a c program to change the linux password
example
----------------------
passwd raksha
Changing password for user raksha.
enter new password
---------------------

program should be like that it should do above mention thing

acid_kewpie · 12-14-2012, 02:01 AM

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jpollard · 12-14-2012, 03:26 PM

Second, you are writing a program that uses an encryption procedure... NOT something simple to do and get right.

Wim Sturkenboom · 12-14-2012, 11:28 PM

Disclaimer: I've never used it, so there is a chance that I put you on the wrong track.

You need this: http://www.kernel.org/doc/man-pages/...3/crypt.3.html; pay attention to the glibc notes at the end.

I would start testing by just verifying a password; your application should anyway prompt the user for his/her current password.

Read the id and the salt from the file where the password is stored
Call the crypt function with $id$salt$ as the salt and the provided password as the key
Verify the returned result against the encrypted password in the filewhere the passwords are stored

Wim Sturkenboom · 12-15-2012, 08:30 AM

Just tested and validation works; crypt() however does not return the encrypted password but the string $id$salt$encryptedpassword.

And a note: use a random salt when using crypt() to generate the encrypted password.

Other functions used for the verification
fopen/fgets/fclose
strchr (strtok can also do the trick and might be the better choice)