Crypt

[Mauro Gatti]

Hi all,
I'd like to create a little C program that use the same crypt algorithm of passwd command.
The program must accept one argument that is the word to crypt and must return the encrypted word.

Do You could give me an Idea to do it?

[Bill McNAMARA_1]

man crypt ?

Later,
Bill

[Mauro Gatti]

I've already tried but crypt command do not use the same algorythm of passwd.
I've found in man 3c crypt the crypt() function but I'd like to see some example to understand how use it.

[A. Clay Stephenson · Accepted solution]

It's actually easy:

1) Extract the 1st two characters of the existing password (old_passwd) hash - this is the 'salt'.

2) char *passwd2 = crypt(plaintext,salt);

3) if (strcmp(old_passwd,passwd2) == 0)
{
printf("Password okay\n");
}

When choosing a new password, you are advised to create a new salt value. The attached snippet will prove useful.

[Jack Tan]

Be aware that passwords longer than 8 characters should be encrypted on trusted HP-UX using bigcrypt() instead of crypt(). On other platforms, other functions are used besides bigcrypt(), such as dispcrypt() on Tru64.

If you need a cross-platform solution, I'd suggest looking at the source code to sudo (http://www.courtesan.com/sudo/) and wu-ftpd (http://www.wu-ftpd.org/).