Goal: prevent attackers from gaining privileges

Principle: Least privilege

Problem: Different code sections in a program may require different privileges.

Solution:
	1. Divide a program into different components.
	2. Grant proper privileges to each component.

Advantages:
	- Reduce amount of critical code

SSH:
	1. Listen to connection request
	2. User authentication
	3. Execute user commands
	4. Establish secure channel

where 1,2,3,4 relate to the above jobs of ssh server

First design:

Parent process
while(1)
{
	if(2)
		3;
}

Second design:

Parent process
while(1)
{
	fork()  //fork a new process that does 2 and 3	 
}

Child process:
if(2)
	3;

Third design:

Parent Process
while(1)
{
	if(2)
		fork()	//fork a new process that does just 3
}

Child process
3;

Fourth design:

Parent
while(1)
{
	fork()
}

Child1
4; //send callback to parent process asking for crypto
2; //send user info back to parent process if valid fork child 2
Child2
3;


Final design:

Parent
while(1)
{
	fork() //fork a process to do 4
	if(2);
		fork()
}

Child1
4; 	//send user info back to parent process

Child2
3;