26-07-2012, 12:38 PM
Video Encryption Techniques
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INTRODUCTION
Cryptography is the art and science of protecting information from undesirable individuals by converting it into a form non-recognizable by its attackers while stored and transmitted. Data cryptography mainly is the scrambling of the content of data, such as text, image, audio, video and so forth to make the data unreadable, invisible or unintelligible during transmission or storage called Encryption. The main goal of cryptography is keeping data secure form unauthorized attackers. The reverse of data encryption is data Decryption, which recuperate the original data. Since cryptography first known usage in ancient Egypt it has passed through different stages and was affected by any major event that affected the way people handled information. In the World War II for instance cryptography played an important role and was a key element that gave the allied forces the upper hand, and enables them to win the war sooner, when they were able to dissolve the Enigma cipher machine which the Germans used to encrypt their military secret communications [1].
In modern days cryptography is no longer limited to secure sensitive military information but recognized as one of the major components of the security policy of any organization and considered industry standard for providing information security, trust, controlling access to resources, and electronic financial transactions. The original data that to be transmitted or stored is called plaintext, the one that can be readable and understandable either by a person or by a computer. Whereas the disguised data so-called ciphertext, which is unreadable, neither human nor machine can properly process it until it is decrypted. A system or product that provides encryption and decryption is called cryptosystem. Cryptosystem uses an encryption algorithms which determines how simple or complex the encryption process will be, the necessary software component, and the key (usually a long string of bits), which works with the algorithm to encrypt and decrypt the data [2] [3]. In the 19th century, a famous theory about the security principle of any encryption system has been proposed by Kerchhoff. This theory has become the most important principle in designing a cryptosystem for researchers and engineers. Kirchhoff observed that the encryption algorithms are supposed to be known to the opponents. Thus, the security of an encryption system should rely on the secrecy of the encryption/decryption key instead of the encryption algorithm itself. For even though in the very beginning the opponent doesn’t know the algorithm, the encryption system will not be able to protect the ciphertext once the algorithm is broken. The security level of an encryption algorithm is measured by the size of its key space [3]. The larger size of the key space is, the more time the attacker needs to do the exhaustive search of the key space, and thus the higher the security level is. In encryption, the key is piece of information (value of comprise a large sequence of random bits) which specifies the particular transformation of plaintext to ciphertext, or vice versa during decryption. Encryption key based on the keyspace, which is the range of the values that can be used to assemble a key. The larger keyspace the more possible keys can be constructed (e.g. today we commonly use key sizes of 128,192,or 256 bit , so the key size of 256 would provide a 2256 keyspace) [3][4]. The strength of the encryption algorithm relies on the secrecy of the key, length of the key, the initialization vector, and how they all work together. Depend on the algorithm, and length of the key, the strength of encryption can be considered. Assume that if the key can be broken in three hours using Pentium 4 processor the cipher consider is not strong at all, but if the key can broken with thousand of multiprocessing systems within a million years, then the cipher is pretty darn strong. There are two encryption/decryption key types: In some of encryption technologies when two end points need to communicate with one another via encryption, they must use the same algorithm, and in the most of the time the same key, and in other encryption technologies, they must use different but related keys for encryption and decryption purposes. Cryptography algorithms are either symmetric algorithms, which use symmetric keys (also called secret keys), or asymmetric algorithms, which use asymmetric keys (also called public and private keys).
Symmetric key Algorithms
In symmetric key encryption, the sender and receiver use the same key for encryption and decryption. As shown in figure 1. symmetric key encryption is also called secret key, because both sender and receiver have to keep the key secret and properly protected[4][5] Basically, the security level of the symmetric keys encryption method is totally depend on how well the users keep the keys protected. If the key is known by an intruder, then all data encrypted with that key can be decrypted.
Symmetric key Algorithms
This is what makes it more complicated how symmetric keys are practically shared and updated when necessary. Symmetric keys can provide confidentiality but they can not provide authentication, because there is no way to prove through cryptography who actually sent a massage if two people are using the same key. Due to that, with all the problem and defects that symmetric keys have they still used in many applications, because they are so fast and can be hard to break if using a large key size. Symmetric keys can handle a large amount of data that would take an unacceptable amount of time with asymmetric keys to encrypt and decrypt.
The most popular symmetric key algorithms are Data Encryption Standard (DES), Triple DES, and Advance Encryption.
The Data Encryption Standard (DES)
DES is one of the most important examples of a block cipher. DES was the result of a contest set by the U.S. National Bureau of Standards (now called the NIST) in 1973, and adopted as standard applications in 1977. The winning standard was developed at IBM, as a modification of the previous system called LUCIFER. The DES is widely used for encryption of PIN numbers, bank transactions, and the like. The DES is an example of a block cipher, which operates on blocks of 64 bits at a time, with an input key of 64 bits. Every 8th bit in the input key is a parity check bit which means that in fact the key size is effectively reduced to 56 bits[6][7].
Advance Encryption Standard (AES)
In 1997, the NIST called for submissions for a new standard to replace the aging DES. The contest terminated in November 2001with the selection of the Rijndael cryptosystem as the Advanced Encryption Standard (AES) [4] [8]. The Rijndael cryptosystem operates on 128-bit blocks, arranged as 4 × 4 matrices with 8-bit entries. The algorithm can use a variable block length and key length; the latest specification allowed any combination of keys lengths of 128, 192, or 256 bits and blocks of length 128, 192, or 256 bits
Asymmetric key Algorithms
Asymmetric key algorithm is also called public key algorithm. Public Key Cryptography was first described publicly by Stanford University professor Martin Hellman and graduate student Whitfield Diffie in 1976[9]. They described a two-key crypto system in which two parties could securely communicate over a non-secure communications channel without having to share a secret key and address the problem of secret key distribution by using two keys instead of a single key . In public key algorithm there are two keys are used. A public key, which can be known by everyone, and a privet key, which should be kept secret known only by the owner.