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Security Issues in Multimedia Transmission
We will represent an introduction of 802.11n. We will show some of the most important techniques like MIMO, frame aggregation and channel bonding, which are responsible for the higher throughput and longer range. Afterwards we will discuss the benefits of this new system and we will explain the importance of 802.11n. Finally, we will discuss some considerations about the implementations in network designing with the 802.11n network.
802.11n, Channel bonding, High throughput, MRC, STBC, RIFS, Frame Aggregation, MIMO,
Receiver Access Control
The popularity of multimedia transmissions have grown dramatically over the years. Examples include IP-TV, live-radio, webcasting, video conference, online video games and video on demand. Multicast transmission is the base for all the above multimedia applications. With all these tremendous growth of these applications it is very important to develop a security environment for the multicast transmissions. There are many security issues and in this article we interrogate the available solutions for providing security multicast transmissions and discussed the fundamental principles of three secure multicast routing protocols ,,.
We present receiver access control. MACs and digital signatures for the source authentication problem. We discuss how to join or remove users from a group.
The most important security requirements for a multicast transmission are secrecy and authenticity. Secrecy means that only the group members should be able to decode the transmitted data. Authenticity has two senses . The group authenticity, which means that every member of the multicast group can recognize if the message was sent by another member of the group. And the source authenticity, which means that every member of the multicast group can recognize the particular member of the group which sends the message.
Another concern has to do with anonymity. Anonymity has two senses. Anonymity may means that the identity of the members of the multicast group is secret from outsiders, or maybe it means that the identity of the message sender is secret.
Moreover access control which means that only registered members have access to the communication addressed. Traffic analysis and service availability are some additional security issues which we have to face off.
There are many multicast routing protocols. These protocols must be informed for the members of the group in order to deliver packets to the members. The IGMP is the mechanism which is responsible for this. The mechanism of this protocol allows a host to inform the routing system that it should receive packets addressed to a specific multicast group. The most common technique used to protect the data is to encrypt them and provide decryption keys to the members of the multicast group.
The multicast receiver access control has some certain functionalities . Firstly it has the group policy function. It's an access control policy which specifies the hosts who have access rights to become member of the group. Secondly it has the access request function, when a host notifies the system that it wants to be a member of a specific group. Thirdly it has the access control functions. It receives the request from the host authenticates him and performing the authorization with the group policy functions.
Hash Based & MAC-Based Schemes
In the following paragraphs we briefly discuss two proposed solutions. Hardjono and Cain  solution based on access control list. A host sends a request which includes the token to the router. The router verifies if the access token is in the list.
Ballardie and Crowcroft  present another survey about another version of IGMP. In this case the host who wants to join a group sends a request to an authorization server. The host receives an authorization stamp, this stamp is a part from the join request sent to the router, then the router forwards the request from the host to the authorization server for approval.
It is very important for the members of a multicast group to identify the sender of a packet. In multicast transmission the group key distribute a shared secret key, with this key the message authentication verifies only that the sender is a member of the same group, but not who exactly is the sender. It is important for some applications the receiver to identify the specific sender of a message.
The properties of a source authentication method should include the following.
Authenticity: The receiver verifies the sender of a packet.
Integrity: The receiver is able to verify that the message received without being modified.
Non repudiation: The sender cannot deny that has sent a particular message.
Some other properties are Efficiency, Collusion resistance, Minimal latency and robustness against unreliable communication. These properties discussed in detail from Paul Judge and Mostafa Ammar .
Hash-based and Mac-based are the two approaches in source authentication for multicast transmission. In the following section we briefly discuss these schemes and some proposed solutions.
The first approach in multicast source authentication schemes is hash-based. Digital signatures aren't a very practical solution for authentication but it is a simple solution.
Packet Chaining: In paper  proposed an efficient solution to authenticate digital streams. A stream of data packets separated into chains, and every packetin the chain has a hash of the next data packet. So only the 1st packet in every chain must be signed.
Tree Chaining: In paper  C.Wong and S. Lam proposed the tree chaining technique. In this technique a stream of data packets partitioned into blocks and create a tree structure to perform the authentication. Every block of k messages is authenticated by one signature.
There are also some other techniques like the P. Golle and N. Modadugu  that designed to be stable against bursty packet loss.
The second approach in multicast source authentication schemes is MAC-Based Schemes. Below we briefly discuss two MAC-Based schemes.
Efficient MACs: In paper  Ran Canetti et al. proposed a Mac-Based scheme. The sender keeps a set of k Mac keys, and every member of the group keeps a subset of the k MAC keys. Every message is “MACed” with every k keys, and the MAC is verified by the recipient with the keys it holds.
Tesla: Adrian Perrig et al. presented a scheme with low computation overhead and stable at packet loss. <<Tesla is based on loose time synchronization between the sender and the receivers.>>