In the near future, there will be a rapid increase in number of users communicating over the same channel which increases security threats. So an efficient broadcast channel is needed for the group of users to communicate securely. Internet Multicasting Bone and satellite television are the important domain applications effected by this insecure communications over a channel [1]. Multicasting bone is a kind of virtual network that facilitates multicasting to the internet [4].
An efficient mechanism is to be designed as a solution to target the existing problems of both the domain applications. The designed system should use single key generator where each user keep only a limited number of keys in the entire key life cycle [1].
Broadcast encryption mechanism encrypts the keys for all the domain applications such as satellite TV or Internet Multicasting Bone. Every broadcast network is accommodated with set-top terminal (STT). The broadcast channel transmits the key in encrypted format and STT is used to decrypt that key. STT is capable of communicating only in one direction. In case of satellite television, broadcast encryption generates the key for that billing period or another new unique key for that particular pay-per-view band-width. Assumption was made in such a way that subscriber acquires the unique broadcast key from the service provider using different service contact channels. Service provides sets the target and sends the encrypted key over the broadcast network excluding unsubscribed users. Encrypted key transmission should be done only to the users who are subscribed to that channel. If any unsubscribed user decrypts the transmitted key then he will be able to use the channel over a period with no cost which has high financial value. [1]
The service provider use key encryption mechanism so that only subscribed users can have access to channel. When a key transmission is done over a channel subscribed users have to decrypt the encrypted key to unlock the broadcasting channel. The set-top terminal (STT) is capable of storing encrypted key information called entitlement. Each user is provided with one STT to decrypt the stored encrypted key. For security reasons each STT is provided with a secure chip or a smart-card which are tamper-resistant, readable, writable and non-volatile. Each secure chip or smart card is provided with some secure memory to store the encrypted key information. In this secure chips memory is limited to a few KB (Kilo Byte). It is difficult to store all the encrypted key information in a single STT because for each billing cycle there will be hundreds of keys to be stored in each STT. The memory management is primary issue for key transmissions over a channel. [2]
Flexibility: Service providers should make subscribers flexible to the broadcast network. Instead of making key transmissions for every channel, service provider should create a package having group of programs with a single key, if the user is subscribed to a package, they can have an access to every program in that package. By this we can reduce number of key transmissions done and there is no need for set-top terminal (STT) to store key for every program. [6]
Security: Even though the secure chips in set-top terminal (STT) are tamper-resistant there is chance of decrypting the keys that are transmitted. Many security hackers who are familiar with the system can easily decrypt the encrypted keys that are transmitted over a channel. The best solution would be even though hackers break into system they may not be able to decrypt the encrypted keys. [6]
In this process of sharing the group keys to all the subscribed users need messages to be encrypted with the separate keys for each package. Encrypted messages are sent separately using unicast for all the users who are not subscribed to the package. Alternatively, the shared messages are sent to all the group members using multicast. The cost of communication is proportional to the group size. As Security is the major issue in group communication. To attain high level security, the group key should be modified for each and every transmission, so no new member will gain access to the communication channel once they leave the group. [5].
Operational overview:
The operational design uses different tree structured mechanisms for securing all the multicast communications to the group.
Group Secure Channel (GSC) is to be initiated for secure group communication startup. Access control list (ACL) in GSC sets the security policy for the subscribers who got access for the group communication. Once the service is started all the new Group Security Intermediaries (GSI) and users can submit their request to join the group. The service providers can also check if any subgroup members other than GSI's are interested in joining the group. [3]
The subscriber tracks the Group Security Agent (GSA) location so that they can send their JOIN request using secure unicast channel. GSA checks the records of every user in the database and approves the request. The key is generated for each new member (MBR) by the GSA (KGSA-MBR). The generated secret key is also stored in the database with subscriber records. Key transmission is done using secure broadcast channel from GSA to new member. GSA multicasts the updated key information using Group Key Update (GRP_KEY_UPDATE). It sends the encrypted key to all the subgroup (K'SGRP) members. The new subscriber uses the encrypted key (K'SGRP) to complete the JOIN request. [3] Example of join request using GRP_KEY_UPDATE
FIGURE 1: GRP_KEY_UPDATE message on JOIN [3]
Each new key generated for JOIN request is associated with the expiration time. GSA sends REFRESH message if any user wants to continue in the group for secure broadcasting. All the subgroup members divided from the main group are removed from the broadcast network after expiration time. Performing LEAVE request from the group can occur in two conditions 1.User sends LEAVE request to Group Security Agent (GSA). 2. GSA can remove user from the group for some security reasons. Users expelled will be sent notification by the GSA. In both the conditions the subgroup encrypted key (K'SGRP) will be changed. So user uses new (KGSA-MBR) key to multicast one message with many copies of encrypted subgroup key (K'SGRP). The Group key Update (GRP_KEY_UPDATE) is done after encrypting all the subgroup keys by (KGSA-MBR).
FIGURE 2: GRP_KEY_UPDATE message on LEAVE
Encrypting and decrypting data by Group Security Intermediaries (GSI) is inefficient. Instead of sending the encrypted key, sender generates one time random key which is used to encrypt the data. This encrypted data is used by the subgroup channel where K'SGRP is used to encrypt the key. The random key is decrypted by Group Security Agent (GSA). There is no need to decrypt the whole packet. GSA needs to verify the signature on the packet before transmitting it to the valid user. This makes sender to validate the encrypted group key before transmitting it to the subscribers. One way of multicasting is done directly without the help of GSI. In direct multicasting sender directly sends the random key to the users to encrypt the data. The other way of multicasting is GSA-assisted multicasting. In GSA-assisted multicasting the sender transmits the random key to GSI's and GSI's verify the information and sends the key directly to GSA. GSA verifies the information and send messages to all the users. [3]
FIGURE 3: Two methods to send. [3]
GSA sends the Group End (GRP_END) notification to all the users when they want to end the multicasting session to the subgroup members in top-level. The group members who receive the GRP_END message SHUTDOWNS their multicast to the bottom-level. This is tree structured process which ends in the similar way down to the group at bottom-level. We can start membership with new GSA, if one GSA is overloaded with subscriptions. [3]
BROADCAST ENCRYPTION USING SMART CARDS: 8
Broadcast encryption using smart cards is a revolutionary scheme which presents the encryption mechanism using smart cards and key management technique using in-band. In the basic model of encryption mechanism uses secure chip to encrypt the data which is capable of producing a new key for every user. This mechanism allows any number of security hackers to decrypt the encrypted key which is stored in secure chip memory. The current scheme of using smart cards is only for small scale system parameters. Broadcast encryption using smart card allows utmost 100 hackers to withdraw at a time before all cards needed to be replaced. Based on this revocation scheme we can develop the system which allows hundreds of hackers to withdraw from the system before all cards could be replaced. By this we can make a proper assumption about the threat rate for the broadcast channel while transmitting the encrypted data and keys. [8]
ATTACK AND DEFENSE MODELS:
ATTACK MODEL:
The most common issue in multimedia distribution systems and digital systems is Piracy. Piracy is to duplicate the original content and sell the key or data to the users. Service providers lose millions of dollars every year because of this piracy. The most common attack performed by the pirates is they extract or decrypt the keys from Secure Chip and create large number of duplicates for that Secure Chip. There are several ways that pirate could easily break into the Secure Chip (SC) even though it was tamper-resistant. Pirates encrypt the data from smaller Security chip and then duplicate it on to a large Security Chip. If the main key in the security chip is modified then it revokes all the duplicate keys. The original SC that is decrypted by the pirate is primary thing to be maintained securely than the cloned SC. [8]
Revocation Process:
Many law enforcement agencies are striving hard to fight piracy by capturing the cloned Security Chips (SC). Content provider analyses these cards and differentiates the cloned card from the original pirated card. Revocation process is to create a new key unknown to the pirates where all the valid users can have access to the broadcast channel. If an original pirated card is traced then the key modification can be done for next revocation round. If the Security chip is revoked immediately there will potential revenue loss which allow pirate users to watch everything without any subscription. [8]
User PROFILES IN BROADCAST ENCRYPTION:
Complete Sub tree (CS) and the subset difference (SD) are the efficient broadcast encryption schemes till date. In this encryption schemes user preferences are not considered. Complete sub tree and subset difference techniques can be implemented effectively if user preferences are taken into consideration. For this technology the relation between user profiles and transmission cost is established. Implementing optimization algorithm reduces the bandwidth for each broadcast using CS and SD. Bandwidth is more crucial to accommodate more number of users on a single broadcasting channel. [7]
Broadcast encryption enables secure data transmission and allows the valid users to decrypt the key. Data transmission may be of secure streaming or internet multicasting. Set-top box is given to all the users which contain the set of already installed keys. These keys are later decrypted by the authorized users. The users with the right set-top box content only can decrypt the broadcast channel transmission. The authorized users are called "privileged users". If an unauthorized user tries to decrypt the data, the system immediately revokes that user to decrease the entire system cost. [7]
Many factors such as size, security level, bandwidth, hardware affect the design of BE system. The memory used in secure chips for storing the encrypted keys is non-volatile and tamper-resistant. In Secure Chips long term storage of encrypted key is not possible because of its non-volatile memory. Theoretical schemes are implemented most efficiently using broadcast encryption schemes. Subset Difference scheme is best application used by many broadcasting channels. [7]
BROADCAST ENCRYPTION AND MULTICAST SCENARIOS:
Multicasting scenarios are derived from the Internet Multicasting Bone (MBONE). Any multicast terminology is adopted from the internet audio and video applications. Internet Multicasting is used to develop secure group communication and developing many internet protocols. The delivery services for all the domain applications like broadcast transmission and conference in the same group are provided by multicasting. Multicasting is well known for its group communication standards. [4]
Internet Multicasting is the best multicast scenario in which group communication channel control all the decryption mechanisms and transmit the data flow through the broadcast channel. The work is divided among different work groups where one service member acts as a group controller and takes the responsibility of handling all the encryption and decryption mechanisms. Group controller has the right to accept or deny the subscriber request. If the subscriber leaves the group the group controller should stop routing packet to the subscriber. This case would fail if the information transmitted over the broadcast channel is confidential. Rekeying operation should be performed for transmitting such confidential messages . If rekeying operation is performed the new subscriber is not allowed to access the content of the previous user. All the data can be revoked if the new user wants to perform further communication in the group using the same channel. [9]
In Internet Multicasting rekeying schemes are based on Logical Key Hierarchy (LKH) algorithm. Generally LKH scheme was implemented using secure multicast which builds secure broadcast communication channel. In LKH scheme each personal key is composed of log n keys and the tree structure is maintained for all the keys by group controller. Each and every modification in the keys must be recorded by the group controller; changes should be done from leaf to root in the tree. When modification is done in the tree all the non revoked users must change their personal keys to avoid the intersection of keys in the tree. After revoking all the keys from leaf to root, each user is left with O (log n) keys. [9]
CONCLUSIONS AND FUTURE WORK:
The Proposed systems and different algorithms can effectively decrease the transmission problem in broadcast encryption. The algorithms defined are capable of reducing the transmission time; bandwidth used and increases the security for the system. Using these algorithms there will be limited number of unauthorized users who can gain access to the broadcast channel. Encryption and decryption phases play a major role in broadcast encryption. The single key that is transmitted from the broadcast channel maintains the entire system. The Subset difference scheme helps the broadcast channel to lower the transmission rates and to determine what kind of broadcast channel is transmitting messages in the group. [7]
Future work in broadcast encryption should be designed in such a way that any kind of broadcast system should be capable of transmitting messages or keys only to the authorized users. Broadcast encryption in case of smart cards can be advanced as if each and every subscriber can deposit some digital cash into their own smart card and use it for monthly subscription and it sometimes helps in purchasing access to certain pay-per-view programs. [2]
