Hi Yolande,
This all, of course, depends on how your LDAP directory is configured. If you're running LDAP unsecured (i.e., the
ldap:// protocol), passwords are in the clear. If you're running LDAP secured (
ldaps://), passwords are encrypted.
Instructions for connecting Liferay in a secure way to LDAP are in Liferay's documentation here, and it uses Active Directory as the example:
http://www.liferay.com/documentation/liferay-portal/6.0/administration/-/ai/global-server-settin-4
Hope this helps!
--Rich