# The Science Of Cryptography Computer Science Essay

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Cryptography is the science of using mathematics to encrypt and decrypt data. It is a method of protecting sensitive data in an unreadable manner. Cryptography has a history began around 2000 B.C. in Egypt. The Hieroglyphics was used to decorate tombs to know about history of Egypt. Cryptography has made many changes through our centuries because keeping secrets of civilization was important. Cryptography helped people to know history in better way.

Cryptography was first used in Hieroglyphics. In ancient time Cryptography was first used on stones and wood by carving messages by people but Cryptography which is using now a day is totally different from ancient Cryptography. The main purpose of Cryptography is exchanging messages between two people in such a way that cannot be understood by others. The analyzing and breaking secure communication is known as Cryptanalysis.

Cryptography is mainly used to store sensitive information in unreadable format. The data can be sent through insecure networks, so that cannot be read by anyone except the intended recipient. Cryptographic algorithm used in converting of cleartext to ciphertext is encryption and the same cryptographic algorithm used to convert the ciphertext to the cleartext is decryption. The encryption and decryption which is provided by a system is nothing but Cryptosystem.

The main concept is to encode the cleartext (original text, plaintext) to ciphertext (altered text). This process is called Encoding or Enciphering and decoding the cipher text to clear text is known as Deciphering. Ciphertext is encrypted plaintext which is sent to the receiver. When once cleartext is altered to ciphertext no human can properly process until the ciphertext is decrypted to cleartext or original text. There two method of transmitting the file format. They are:-

A) Encryption

B) Decryption

## ENCRYPTION:-

Encryption is a translation of file format (encrypted format). The encrypted file can be stored in the computer and also we can send the encrypted file through unsecure networks. To represent the character of file format we use common encoding format such as ASCII (American Standard code for Information Interchange) and Unicode. The translation of ciphertext is done by this encryption algorithm and an encryption key. The process of converting or transmitting cleartext to ciphertext is encryption.

Cleartext------------&gt; Encryption ------------&gt;Ciphertext

## DECRYPTION:-

Decryption is the translation of encrypted message (Ciphertext) to plaintext. The Ciphertext is decrypted by Decryption key and Decryption algorithm. The process of converting the ciphertext to cleartext (plaintext) is decryption.

Ciphertext--------------&gt;Decryption-----------------&gt;Cleartext

## Public key cryptography:-

Public key cryptography solves the problems in key distribution. Some of the public key cryptosystems are

A) Whitfield Diffie and Martin Hellman introduced the concept public key cryptography in 1975.

B) RSA algorithm was introduced by Ron Rivest, Adi Shamir, and Leonard Adleman in 1977.

C) Elgamal was introduced by Taher Elgamal.

D) DSA (Digital Signature algorithm) is introduced by David Kravitz.

In this concept pair of keys used for encryption and decryption. The public key is the key which encrypt data. The private key is the key which is for decryption. The person who know public key can encrypt data but without knowing private key we cannot decrypt data.

The cleartext is encrypted with session key and it is encrypted with public key. Then the recipient&acirc;€™s private key is used to decrypt session key after this the session key is used to decrypt ciphertext. By this process the ciphertext is translated to cleartext.

Private key

key

Public key

Cleartext -----&gt;Encryption ------&gt;Ciphertext ------&gt;Decryption ------&gt;Cleartext

Ron Rivest (Ronald Linn Rivest) is a cryptographer, born in 1947. He is specially known for symmetric key encryption algorithms .Symmetric key algorithm that uses same key to encrypt and decrypt data. RC2, RC4, RC5 are the symmetric key encryption algorithms developed by Ronald Linn Rivest and he was the co-inventor of RC6. RC stands for Rivest cipher or Ron&acirc;€™s Code.

Cipher is a cryptographic algorithm used for encryption and decryption. He also introduced RC3 algorithm but it was broken at RSA security during the development of this algorithm. Similarly, there was same problem with RC1 algorithm which was never published. Ron Rivest also developed cryptographic hash functions (MD2, MD4, MD5, and MD6). Algorithms used for encryption in the company which was developed by Ronald Linn Rivest. So, depending on Ron Rivest algorithms encryption was done. In 1987 RC2 algorithm was developed and it is a 64-bit block cipher and RC4 algorithm is a widely used stream cipher in the world.

RC4 algorithm:-

RC4 algorithm is a algorithm which protect internet traffic and also secure wireless networks.

RC4 algorithm is also known as ARC4 (Alleged RC4) algorithm. In some protocols RC4 algorithm is used such as SSL (Secure Socket Layer), WEP (Wired Equivalent Privacy). Secure Sockets Layer protocols provide security over internet. But sometimes using of RC4 algorithm may lead to very insecure cryptosystems. The long-term key can be generated by analyzing large number of messages encrypted with this key. To generate RC4 key, long-term key and nonce (number used once) are concatenated. These are some of the effects which are used to break WEP encryption used with WLAN( Wireless Local Area Network). But only once we can use particular RC4 key.

RC5 algorithm:-

RC5 algorithm is a suitable implementation of software and hardware by fast symmetric block cipher. For encryption and decryption, same secret cryptographic key is used in this algorithm. The RC5 algorithm consisting of three components: A) A key expansion algorithm B) Encryption algorithm C) Decryption algorithm.