I want to know what are the permissions available in UNIX for achieving security? It would be nice if someone could share their thoughts about the UNIX permission usage in other words what level of access if provided to whom for security and how they are provided.

I think you can achieve the same by using chmod a command available in UNIX. But there is lot of permission commands available in UNIX which I am not aware. Hope to get it the knowledge in this discussion. All the above UNIX is a system designed for getting higher security.

Basically there are three types permission you can set on a file "read", "write" and "execute". These file permission can be changed with the help of command "chmod"
Ex: drwxrwxrwx 8 bin bin 8192 Mar 7 19:50 tmp

r=read=4
w=write=2
x=excecute=1

in the above example the first "d" say's tmp is a directory file and after that there are three set of "rwx" in which the first set is for user, the second one is for group and the third is one for others.

permission on a file can be changed by

$ chmod 644
6=read and write permission on the file to users
4=only read permission on the file to group
4=only read permission on the file to others.

for more information use "man"
$man chmod

chown and chgrp are two more of that kind.

athor type chmod