Unless a user has a secret key, encryption denies users any access to an encrypted file. Only knowledge of the secret key allows that user the access to decrypt the encrypted file (Bates, 2000). Encryption comes in two categories, symmetric encryption and asymmetric encryptionIt is a form of art or science whose main and basic capability is to change the form of one unintelligible message to an intelligible message which can be read by everyone and after getting the information of the message, converting it to its creative form. The ways in which Encryption technique works are:
- Plain text- The original intelligible message.
- Cipher text- The converted message.
- Cipher- An algorithm used for converting the message in intelligible form.
- Encode-Way of converting the plain text into cipher text.
- Decode-Way of converting a cipher text into plain text again.
- Code breaking-Transforming unintelligible message again to intelligible one without the use of key.
Symmetric encryption allows both Alice (sender) and Bob (receiver) to encrypt and decrypt data using a shared key via a secret channel. Two types of symmetric encryption algorithms are stream ciphers and block ciphers. Symmetric encryption algorithms are highly effective at processing large quantities information and require less time/power to process through a CPU in comparison to asymmetric encryption techniques. However, shared key should be altered frequently, kept secure and distributed carefully as they can be cracked via brute force attack; once this key is then identified communication can be compromised.In this process a secret key is been used, it sets all the parameters which are to be used by the encoding algorithm. The most important point referred in the classical cryptography is that the keys are both the same which is used in both encryption and decryption (Hunter, 2004). That is classical cryptography is also called as the symmetric key cryptography. Basic terminology in Symmetric encryption are Plaintext, Cipher text, cipher, Key, Converting the plain text into cipher text, recovering the cipher text from the plain text.
Stream ciphers are naturally faster than block clock ciphers .One of the most important classes of cipher algorithm is called as stream cipher. One of the major roles played in the modern cryptosystem is the symmetric key cryptosystem. Stream ciphers helps to process the plain text given to it in to very small boxes which sometimes is about a size of a single bit. The stream chippers has the ability to keep some sort of memory as it gives the idea to process the plain text and uses the state as input in the process of chipper algorithm. There are two types of stream chipper-Synchronous stream chipper and self-synchronising stream chipper.
Block ciphers require more memory It is a very easy process and is used generally the plain text are converted generally in large boxes. The work of the encryption is always the same in each and every block. These block chippers are also characterized by a bijective function. It accepts as input asset of plain text which is of a fixed size, and a key, and it gives output in the form of cipher text (Knipp & Danielyan, 2002). The block ciphers are mainly of two types Feistel block cipher and non Feistel block cipher. The main goal of a Block cipher is to go over DES, Data Encryption Standard.
Types of Symmetric encryption
The normal process of encrypting data was through the symmetric algorithm also known as Data encryption standard (DES). Data Encryption Standard (DES) cipher is an outdated symmetric encryption method that uses a 56 bit algorithm and one key to encrypt and decrypt. This has been now replaced with a new standard known as Advanced Encryption Standard (AES). Due to the increase in computer processing power DES can be deciphered by using the brute force attack. DES is built on a cipherknown as the Feistel Block Cipher. In most of the Encryption Schemes the DES expects to be two inputs- the normal text that is to be encrypted and the secret key.
Triple DES is a block cipher that had been enhanced due to the DES being susceptible to brute force attacks. Triple DES used the same algorithm as the DES cipher. However, it uses a key length of 168 bits opposed to the previous 56 bit length DES utilizes. This was achieved by enlarging the key space of 3DES to three times the size of the outdated 56 bit Des and resulted in greater protect against attack.
The growth of RC2 was backed by Lotus. RC2 all so known as Rons Code and Rivest Cipher is a 64 bit block cipher, key size can vary from 40 to 128 bits by incrementing by 8. And it was exported by NSA as their new Lotus software. The algorithm of RC2 was kept secret in the beginning but on 26th January 1996 it was openly spread in the internet. RC2 is 64bit cipher having a flexible size key. It has 18 rounds organized by heavy system, having 16 rounds of the similar type, interposed by 2 rounds of a different type. There are four application in the mixing round having different transformation .
The RIjndael algorithm is a symmetric encryption of Block cipher of 10, 12, 14 rounds. It can encrypt the block of 128, 192 or 256 bits correspondingly using the symmetric keys of 128,192 or 256 bits. The Rijndael algorithm is now known as the AES Algorithm. It has a better performance in both hardware and software stage (Nozaki & Tipton, 2000). It cannot be broken easily only brutal attack can break it. Rijndael is completely free for the purpose of any use may it be public, private, commercial or non-commercial.
Asymmetric encryption allows both Alice (sender) and Bob (receiver) to encrypt and decrypt data via two separate keys, one key being used to encrypt and the second to decrypt. Due to using to these two keys, asymmetric encryption doesn’t require a secret channel when sending out the public key as the private key is also needed to decrypt (Security Risk Management, 2011). Disadvantage is the amount of CPU power and time to process the encryption and decryption of the communication.
Types of Asymmetric encryption
RSA generates two keys, a public and private key. These keys are based on large prime numbers that are mathematically related. The public key is shared to the public whereas the private key is kept secret. RSA keys are 1024 to 2048 bits long and provides encryption and digital signature functions for protocols such as SSH, SSL/TLS as well as browsers.
Advanced Encryption standard was to replace DES. AES is a block cipher that uses a 256 bit key and encrypts data in blocks of 128 bits. The AES was built by two Belgian cryptographers. The algorithm that has been described by AES is a symmetric key algorithm.Substitution permutation network is the principle design of the AES. AES operates on a 4x4 column major order matrix of bytes.
Blowfish is a symmetric key block cipher. Blowfish is a commonly used algorithm due to no unauthorised user being able to successfully decrypt. The secret key cipher encrypts the variable numbers of bits ranging from 16 to 448 bits sixteen times (Stallings, 1993). The encryption rate in software is good by Blowfish. Blowfish has a 64bit block size, which uses fixed s-boxes. In Blowfish the decryption is same as encryption, but in a reverse order.
Diffie Hellmon key exchange
Diffie Hellmon key exchange method allows both Alice (sender) and Bob (receiver) to create a shared secret key together over an insecure channel having no previous familiarity of each other. Once this key has been created, the following communications will be encrypted using a symmetric key cipher. Exchanging of cryptographic keys are completely secured in the Diffie-hellmon key exchange. Through the help of this secret data can be shared from one person to another over a public network.
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