[PLUG] linux uses md5 for password encryption

[archana acharya]

Hello all,
I am trying to write a php script which would enable me to change
linux users password,
from what I have understood so far linux uses md5 encryption for example
$1$PzWoHIp0$OBl0/opUYe7ciRrfQsPuk1
$1$-depicts that this is a md5 encryption
PzWoHIp0-this is the 8 charecter salt
OBl0/opUYe7ciRrfQsPuk1-this is the 22 character encrypted password
now when i use this code to generate the encrypted password **********
if (CRYPT_MD5==1)
$hashed= crypt($pasword);
then i get an encryted password in a similar format but when i try n
substitute this value for a particular user in /etc/shadow file and
then try loggin in as the concerned user my login fails.
Please do let me know if u have any clue as to why this is happening.
am using rhel4