CS 596 Client-Server Programming
CS 596 Client-Server Programming
What is security?
From Webster's College Dictionary:
security, n.
Before we can talk about security related to computers and networks, we need to
know what we are trying to secure:
Some different types:
Physical security:
Prevent access to physical devices (network, computers, etc.) with:
Software security:
Some common methods of "attack":
Network sniffing is the gathering of information on a network not designated
for you.
Ethernet is a broadcast network: All machines on a segment can see all traffic
on that segment.
Some solutions:
Authentication is performed to ensure that a user or program has specific
access to a resource or data.
Examples:
The authentication process normally relies on some sort of shared (between
resource provider and resource seeker) secret or irreproducible attribute:
How is authentication over a network different?
Network packets can travel through many "unknown" (read untrusted) routers and
computers.
What are the added risks?
Some issues:
Username and password
Protocols we have seen that use this:
Problems?
The more frequent the authentication information is sent over the network, the
higher the chance that it will be sniffed.
A security token is given to a client by a server. The client can then use
this token to uniquely identify itself to the server in the future.
The APOP command was introduced to the POP3 protocol to prevent the frequent
sending of username and passwords over the network.
The client only logs in once a day and gets a special token which it will use
the rest of the day.
Some requirements for security tokens:
Why?
How can a server identify a client with a token?
Rely on a piece of information that is hard to change: IP address of the
client.
The server somehow needs to correlate the token with the address when the
client uses it.
How does a server create a token?
Random string approach:
One-way scambling approach:
Weakness of this approach?
Time-sharing machines can run multiple clients
Why is this a problem?
After a client has been authenticated, the traffic on the network can still be
sniffed.
A solution is encryption of all traffic.
This can be done at any layers of the protocol stack
Two basic types of encryption:
Shared key encryption:
One key both encrypts and decrypts
Public/Private key encryption:
One key encrypts, another decrypts
A public key is something that is well known, i.e. published.
A client can send authentication information by encrypting the info with the
server's public key.
The server will then use its own private key to decrypt the information.
Advantages:
The same encryption method can be used to authenticate a message:
A client encrypts information with its own private key.
The server will lookup the client's published public key and decrypt the
information.
Advantages:
This is a digital signature.
A combination of the previous two methods allows for mutual authentication.
Kerberos is an authentication and session encryption system.
Three levels of security:
The actual algorithms used are complicated.
Look at
http://www.ov.com/misc/krb-faq.html
for more information about the workings.
Kerberos uses a separate ticket granting server that gives a ticket to a user
or application.
This ticket can then be used for any number of resources on the network.
If a client wants to talk to a server, both the client and the server will talk
to the authentication server to establish that the client is authorized.
Advantages of kerberos:
Disadvantages:
Points to keep in mind when dealing with security:
Some existing tools to look at: