Hi Felix,
die /etc/shadow kann aber nicht von jedem x-beliebigen User gelesen werden, das weißt du sicherlich:
| stefan@server:~$ ll /etc/shadow
| -rw-r----- 1 root shadow 683 2. Feb 15:46 /etc/shadow
Und zum Thema Passwörter verifizieren solltest du einfach mal man shadow
probieren:
The password field must be filled. The encryped password consists of 13 to 24 characters from the 64 character alphabet a thru z, A thru Z, 0 thru 9, . and /. Refer to crypt(3) for details on how this string is interpreted. If the password field contains some string that is not valid result of crypt(3), for instance ! or *, the user will not be able to use a unix password to log in, subject to pam(7).
Gruß,
Stefan