Optical Cryptosystems. Naveen K. Nishchal
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Название: Optical Cryptosystems

Автор: Naveen K. Nishchal

Издательство: Ingram

Жанр: Отраслевые издания

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isbn: 9780750322201

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СКАЧАТЬ is a classical encryption method. It is referred to as a situation in which the key used for encryption is as used for decryption. In this case, key distribution must be performed prior to data transfer. Therefore, the security key plays a highly significant role because security directly depends on the nature of the key. Asymmetric key cryptography is an advanced encryption method. It is referred to as a situation in which the key used for encryption is different than the key used for decryption. In this case, a pair of keys, public and private keys, are used. The security is very high compared to the classical method of encryption.

      Of late, hash functions are also considered as a type of cryptography, which establishes the authenticity of the user [7].

      Symmetric key cryptography, also known as secret key cryptography or conventional cryptography, refers to an encryption system in which the sender and receiver share a single common key that is used to encrypt and decrypt the message. The process is shown in figure 1.3. The used algorithm is known as the symmetric algorithm or secret key algorithm. The key is defined as a piece of information (a parameter) that determines the functional output of a cryptographic algorithm or cipher. The key used for encrypting and decrypting a message has to be known to all the authentic recipients or else the message could not be decrypted by conventional means [6]. The examples of symmetric key cryptography are discussed below.

       Data encryption standard (DES): the DES was published in 1977 by the US National Bureau of Standards. It uses a 56-bit key and maps a 64-bit input block of plaintext onto a 64-bit output block of ciphertext. 56 bits is a rather small key for today’s computing power.

       Triple DES: it is an improved version created after overcoming the shortcomings of DES. Since it is based on the DES algorithm, it is very easy to modify existing software to use Triple DES. It has the advantage of proven reliability and a longer key length that eliminates many of the shortcut attacks that can be used to reduce the amount of time it takes to break the DES.

       Advanced encryption standard (AES): the AES is an encryption standard adopted by the US Government. The standard comprises three block ciphers, AES-128, AES-192, and AES-256. Each AES cipher has a 128-bit block size with key sizes of 128, 192, and 256 bits, respectively. The AES ciphers have been analyzed extensively and are now used worldwide.

       International data encryption algorithm (IDEA): the IDEA was developed in 1991. It uses a 128-bit key to encrypt a 64-bit block of plaintext into a 64-bit block of ciphertext. IDEA’s general structure is very similar to DES. It performs 17 rounds, each round taking 64 bits of input to produce a 64-bit output, using per-round keys generated from the 128-bit key.

      Figure 1.3. Symmetric key cryptography.

       Key management in symmetric key systems

      The symmetric key systems are simpler and faster but their main drawback is that the two parties must somehow exchange the key in a secure way and keep it secure after that. The key management caused a nightmare for the parties using the symmetric key cryptography. The worry was about how to get the keys safely and securely across all users so that the decryption of the message would be possible. This gave the chance for third parties to intercept the keys in transit to decode the secret messages. Thus, if the key was compromised, the entire coding system was compromised and a ‘secret’ would no longer remain a ‘secret’.

      Asymmetric key cryptography is also known as public key cryptography. It refers to a cryptographic algorithm which requires two separate keys, one of which is private and another is public. The public key is used to encrypt the message and the private one is used to decrypt the message. This method was developed to address the key management issue of symmetric key cryptography. The process of asymmetric cryptography is shown in figure 1.4. It is a very advanced form of cryptography. Officially, it was invented by Whitfield Diffie and Martin Hellman in 1975. The basic technique of public key cryptography was first discovered in 1973 by the British Clifford Cocks of Communications-Electronics Security Group but this was a secret until 1997. The examples of symmetric key cryptography are discussed below [6].

       Digital signature standard (DSS): the DSS is a digital signature algorithm developed by the US National Security Agency to generate a digital signature for the authentication of electronic documents. DSS was put forth by the National Institute of Standards and Technology (NIST) in 1994.

       RSA: (Rivest, Shamir, and Adleman who first publicly described it in 1977) It is an algorithm for public-key cryptography. It is the first algorithm known to be suitable for signing as well as encryption, and one of the first great advances in public key cryptography. RSA is widely used in electronic commerce protocols, and is believed to be secure given sufficiently long keys and the use of up-to-date implementations.

       ElGamal: ElGamal is a public key method. It is used in both encryption and digital signing. The encryption algorithm is similar in nature to the Diffie–Hellman key agreement protocol and is used in many applications and uses discrete logarithms. ElGamal encryption is used in the free GNU Privacy Guard software.

      Figure 1.4. Asymmetric key cryptography.

      A cryptographic hash function is a hash function that takes an arbitrary block of data and returns a fixed-size bit string, the cryptographic hash value such that any (accidental or intentional) change to the data will (with very high probability) change the hash value [7]. The data to be encoded is often called the message, and the hash values are sometimes called the message digest or simply digest. The ideal cryptographic hash function has four main properties:

       It is easy to compute the hash value for any given message.

       It is infeasible to generate a message that has a given hash.

       It is infeasible to modify a message without changing the hash.

       It is infeasible to find two different messages with the same hash.

      The examples of hash functions are discussed below.

       Secure hash algorithm (SHA): SHA hash functions are a set of cryptographic hash functions designed by the National Security Agency and published by the NIST as a US Federal Information Processing Standard. Because of the successful attacks on MD5, SHA-0 and theoretical attacks on SHA-1, NIST perceived a need for an alternative, dissimilar cryptographic hash, which became SHA-3. In October 2012, the NIST chose the Keccak algorithm as the new SHA-3 standard.

      As multimedia, image, and video are becoming increasingly part of modern economy and social companions, ensuring security from malicious interference, theft, and unauthorized use has become the demand of the hour. Encryption of images is one of the well-known mechanisms to preserve confidentiality of images/data over a reliable unrestricted public media, СКАЧАТЬ