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Data Encryption Using DES/Triple-DES Functionality in Spartan-II Fpgas WP115 (V1.0) March 9, 2000 Author: Amit Dhir

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Data Encryption Using DES/Triple-DES Functionality in Spartan-II Fpgas WP115 (V1.0) March 9, 2000 Author: Amit Dhir White Paper: Spartan-II FPGAs R Data Encryption using DES/Triple-DES Functionality in Spartan-II FPGAs WP115 (v1.0) March 9, 2000 Author: Amit Dhir Summary Today’s connected society requires secure data encryption devices to preserve data privacy and authentication in critical applications. Of the several data encryption types, Data Encryption Standard (DES) and its variant Triple-DES (TDES) have emerged to be the most commonly used in varying applications. The Spartan™-II devices with their extensive features and cost effectiveness compete effectively against ASICs and ASSPs. Through the value proposition of the DES/TDES IP in a Spartan-II FPGA, the programmable ASSP message is further confirmed. There is an immense value in integrating critical IP solutions like Discrete Cosine Transform/Inverse DCT (DCT/IDCT) and DES within a Xilinx FPGA to enhance performance and security in communication applications. A FPGA-based DES/TDES solution provides the necessary scalability and flexibility to handle all these applications and allows for tracking of new standards. Introduction Data encryption is used pervasively in today’s connected society. The two most basic facets of modern day data encryption are data privacy and authentication. As modern society becomes more connected, and more information becomes available there is a need for safeguards which bring data integrity and data secrecy. In addition, authenticating the source of information gives the recipient, with complete certainty that the information came from the original source and that it has not been altered from its original state. Both, the needs for information privacy and data authentication has motivated cryptography. • Cryptosystem or cipher system - A method of disguising messages so that only certain people can see through the disguise. • Cryptography - The art of creating and using cryptosystems. • Cryptanalysis - The art of breaking cryptosystems, and seeing through the disguise even when you are not supposed to be able to. • Cryptology - The study of both cryptography and cryptanalysis. • Plaintext - The original message • Ciphertext - The disguised message • Encryption - A fundamental security mechanism in which the ordinary data (plaintext) are transformed by the encryption process into ciphertext. • Decryption - A procedure to convert ciphertext back into plaintext. Encryption techniques are used to safeguard information while it is stored within a network node or while it is in transit across communications media between nodes. A cryptosystem is usually a whole collection of algorithms. The algorithms are labeled; and the labels are called keys. The people who are supposed to be able to see through the disguise are called recipients. Other people are enemies, opponents, interlopers, eavesdroppers, or third parties. As an example, for a plaintext message being sent, if every A is replaced with a D, every B is replaced with an E, and so on through the alphabet, only someone who knows the "shift by 3" rule can decipher the messages. Hence a "shift by n’’ encryption technique can be performed for several different values of n. Therefore, n is the key here. © 2000 Xilinx, Inc. All rights reserved. All Xilinx trademarks, registered trademarks, patents, and disclaimers are as listed at http://www.xilinx.com/legal.htm. All other trademarks and registered trademarks are the property of their respective owners. WP115 (v1.0) March 9, 2000 www.xilinx.com 1 1-800-255-7778 Data Encryption using DES/Triple-DES Functionality in Spartan-II FPGAs R With the expansion of applications requiring data encryption, the number of different encrypting methods have also increased. Each method has its strengths and weaknesses. Some of the encryption methods are RSA (Rivest-Shamir-Adleman), Data Encryption Standard (DES), Diffie-Hellman, Secure Hashing Algorithm (SHA), Blowfish, RC4/RC5, Elliptic Curves, ElGamal, LUC (Lucas Sequence) and so on. This white paper discusses DES and its variant Triple-DES (TDES). The Spartan-II family, combined with a vast soft IP (Intellectual Property) portfolio is the first programmable logic solution to effectively penetrate the ASSP (Application Specific Standard Products) marketplace. The DES and TDES solutions presented from Xentec, when ported on a Spartan-II device are good examples highlighting the concept of a programmable ASSP. Xentec is a member of the Xilinx AllianceCORE™ program and has a wealth of IP cores in other applications. Xentec, Inc., founded in 1995, provides solutions for the design and development of analog/ digital ASICs and FPGAs. The FPGA and ASIC solutions developed by Xentec are being used in multimedia, telecommunications, and cryptoprocessor designs. The company has over 50 analog and digital projects to its credit, ranging from developing test programs to full turnkey IC designs. Xentec provides cores in Xilinx-specific formats as well as in RTL HDL to suit customers' needs. Xentec also offers comprehensive design services and support. For more information regarding Xentec and their IP portfolio for Xilinx products please visit http:// www.xilinx.com/products/logicore/alliance/xentec/xentecinc.htm. The X_DES Cryptoprocessor and X_3DES Triple DES Cryptoprocessor cores are developed, sold, and supported by Xentec. The Spartan-II devices which implement these cores support the X9.52 standard and are NIST (National Institute of Standards and Technology) certified. These cores are available immediately for use in Spartan-II FPGAs and can be purchased directly from Xentec. The X_DES application note can be obtained from http://www.xilinx.com/ products/logicore/alliance/xentec/xdes.pdf. The X_3DES application note can be obtained from http://www.xilinx.com/products/logicore/alliance/xentec/x3des.pdf. Data Encryption The DES is based on the work of IBM Corporation, and was adopted as the American National Standard Standard (ANSI) X3.92-1981/R1987. The DES algorithm was adopted by the U.S. government in 1977, as the federal standard for the encryption of commercial and sensitive-yet-unclassified government computer data and is defined in FIPS 46 (1977). (FIPS are Federal Information Processing Standards published by NIST). A "block cipher" refers to a cipher that encrypts a block of data all at once, and then goes on to the next block. The DES, which is a block cipher, is the most widely known encryption algorithm. In block encryption algorithms, the plaintext is divided into blocks of fixed length which are then enciphered using the secret key. The DES is the algorithm in which a 64-bit block of plaintext is transformed (encrypted/enciphered) into a 64-bit ciphertext under the control of a 56-bit internal key, by means of permutation and substitution. It has been mathematically proven that block ciphers are completely secure. The DES block cipher is highly random, nonlinear, and produces ciphertext which functionally depends on every bit of the plaintext and the key. At least five rounds of DES are required to guarantee such dependence. In this sense, a product cipher should act as a "mixing" function which combines the plaintext, key, and ciphertext in a complex nonlinear fashion. The DES has more than 72 quadrillion (72 x 1015) possible encryption keys that can be used. For each given message, the key is chosen at random, from among this enormous number of keys. Like other private key cryptographic methods, both the sender and the receiver must know and use the same private key. The process can run in several modes and involves 16 rounds or operations. The DES algorithm is widely used and is still considered reasonably dependable but a more secure variant, which applies DES three times with different keys in succession called Triple-DES (TDES). The Xilinx Spartan-II FPGAs and Xentec soft IP present a solution for both DES and TDES. 2 www.xilinx.com WP115 (v1.0) March 9, 2000 1-800-255-7778 Data Encryption using DES/Triple-DES Functionality in Spartan-II FPGAs R The DES cryptographic algorithm converts plaintext to ciphertext using the 56-bit key in the encryption process. The same algorithm is reused with the same key to convert ciphertext back to plaintext, in the decryption process. The key is given in a 64-bit word, of which eight are parity bits, at locations 8, 16, 24,…, 64. The algorithm consists of 16 "rounds" of operations that mix the data and key together in a prescribed manner using the fundamental operations of permutation and substitution. The goal is to completely scramble the data and key so that every bit of the ciphertext depends on every bit of the data plus every bit of the key. Authorized users of encrypted computer data must have the key that was used to encrypt the data in order to decrypt it. The unique key chosen for use in a particular application makes the results of encrypting data using the algorithm unique. Using a different key causes different results. The cryptographic security of the data depends on the security provided for the key used to encrypt and decrypt the data. FIPS 171 (Key Management Using ANSI X9.17) provides approved methods for managing the keys used by the DES. There are four official DES operating modes (provided in FIPS 81) to encrypt or decrypt data: ECB (Electronic Codebook), CBC (Cipher Block Chaining), OFB (Output Feedback) and CFB (Cipher Feedback). The security provided by a cryptographic system depends on the mathematical soundness of the algorithm, length of the keys, key management, mode of operation, and implementation. The DES was originally developed to protect unclassified computer data in federal computer systems against a number of (passive and active) attacks in communications and computer systems. It was assumed that a knowledgeable person might seek to compromise the security system by employing resources commensurate with the value of the protected information. Agencies determining that cryptographic protection is needed based on an analysis of risks and threats can use the DES for applications such as electronic funds transfer, privacy protection of personal information, personal authentication, password protection, and access control.
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