Authors : Amandeep Singh, Manu Bansal

International Journal of Scientific & Engineering Research, Volume 1, Issue 1, October-2010

ISSN 2229-5518

Cryptography includes two basic components: Encryption algorithm and Keys. If sender and recipient use the same key then it is known as symmetrical or private key cryptography. It is always suitable for long data streams. Such system is difficult to use in practice because the sender and receiver must know the key. It also requires sending the keys over a secure channel from sender to recipient [4]. The question is that if secure channel already exist then transmit the data over the same channel.

On the other hand, if different keys are used by sender and recipient then it is known as asymmetrical or public key cryptography. The key used for encryption is called the public key and the key used for decryption is called the private key. Such technique is used for short data streams and also requires more time to encrypt the data [3]. To encrypt a message, a public key can be used by anyone, but the owner having private key can only decrypt it. There is no need for a secure communication channel for the transmission of the encryption key. Asymmetric algorithms are slower than symmetric algorithms and asymmetric algorithms cannot be applied to variable-length streams of data. Section 1 includes the introduction of cryptography. Section 2 describes the cryptography techniques. Section 3 includes the analysis and implementation of DES Algorithm using Xilinx software. Conclusion and Future work has been included in Section 4.

**CRYPTOGRAPHY TECHNIQUES**Symmetric Cryptography

Asymmetric Cryptography

**DES ALGORITHM**Data Encryption Standard (DES) is a cryptographic standard that was proposed as the algorithm for the secure and secret items in 1970 and was adopted as an American federal standard by National Bureau of Standards (NBS) in 1973. DES is a block cipher, which means that during the encryption process, the plaintext is broken into fixed length blocks and each block is encrypted at the same time. Basically it takes a 64 bit input plain text and a key of 64-bits (only 56 bits are used for conversion purpose and rest bits are used for parity checking) and produces a 64 bit cipher text by encryption and which can be decrypted again to get the message using the same key. Additionally, we must highlight that there are four standardized modes of operation of DES: ECB (Electronic Codebook mode), CBC (Cipher Block Chaining mode), CFB (Cipher Feedback mode) and OFB (Output Feedback mode). The general depiction of DES encryption algorithm which consists of initial permutation of the 64 bit plain text and then goes through 16 rounds, where each round consists permutation and substitution of the text bit and the inputted key bit, and at last goes through a inverse initial permutation to get the 64 bit cipher text.

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