Des 3g1h1i

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The Data Encryption Standard (DES) is a symmetrickey block cipher published by the National Institute of Standards and Technology (NIST).

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Encrypts 64 bit data under 56 bit key secret key.

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DES was published in the Federal in March 1975 as a draft of the Federal Information Processing Standard (FIPS).

Encryption and decryption with DES

The encryption process is made of two permutations (P-boxes), which we call initial and final permutations, and sixteen Feistel rounds.

F L O W C H A R T

58 50 42 34 26 18 10 2 60 52 44 36 28 20 12 4 62 54 46 38 30 22 14 6 64 56 48 40 32 24 16 8 57 49 41 33 25 17 9 1 59 51 43 35 27 19 11 3 61 53 45 37 29 21 13 5 63 55 47 39 31 23 15 7

The plaintext block undergoes an initial permutation.

 64 bits of the input data block are permuted according to the Initial Permutation Table

Split the block into two halves. The first 32 bits are called L[0], and the last 32 bits are called R[0]. Apply the 16 subkeys to the data block. Start with i = 1.

Get a 64-bit key from the .  Every 8th bit is considered as a parity bit.  For a key to have correct parity, each byte should contain an odd number of "1" bits

Perform the permutation PC-1 on 64 bit key. The parity bits are discarded reducing key to 56 bit. Bit 1 of the permuted block is bit 57 of the original key, bit 2 is bit 49, and so on 57 49 41 33 25 17 9 56 bit 64 bit permuted key 1 58 50 42 34 26 18 key PC-1 10 2 59 51 43 35 27 19 11 3 60 52 44 36 63 55 47 39 31 23 15 7 62 54 46 38 30 22 14 6 61 53 45 37 29 21 13 5 28 20 12 4

16 Sub keys calculation For key 1: Split the permuted key into two halves C[0] & D[0]. Perform one circular left shifts on both C[0] and D[0] to get C[1] and D[1].

14 3 23 16 41 30 44 46

17 11 24 28 15 6 19 12 4 7 27 20 52 31 37 40 51 45 49 39 56 42 50 36

1 5 21 10 26 8 13 2 47 55 33 48 34 53 29 32

 Concatenate C[1] D[1] which will be of 56 bits. Perform PC-2 to yield 48 bit K[1].

56 bit C[1] D[1]

48 bit K[1] PC-2

For key 2 : Perform one circular left shifts on both C[1] and D[1] to get C[2] and D[2]. Concatenate C[2] D[2] which will be of 56 bits. C2

D2 Perform PC-2 to yield 48 bit D2 K[2]. The number of shifts per iteration are given as: Iteration 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Left Shifts 1 1 2 2 2 2 2 2 1 2 2 2 2 2 2 1

T H E

The input to ffunction is 32 bit obtained from Right half of initially permuted block.

32

Expansion

F 48

F U N C T I O N

48

Key K

48 6

6

S1

…………………… ………..

S8 4

4 3 2 Permutation P

32

The 32 bit output is obtained using key, substitution box and permutation P.

E X P A N S I O N

32 bit input

Expansion

48 bit output

48 bit output

56 bit input

Key k 48 bit output

Xor

Expansion 32 bit input

48 bit output

48 bit input after Xor

8 blocks of 6 bits each 00

1 16

2

4*8=32 bit output After all the 8 substitution box

01 Substitution Box

1 0 11

Input bits

Bit 1

Bit 6

Output bits Bit 1 Bit 4

Left half

32 bit Input After substitution

32 32

32 bit output after xor

32 bit After xor Final output of 64 bits 32 bit

Main key: 133457799BBCDFF1 Data block: 0123456789ABCDEF

Cipher Text Obtained : 85E813540F0AB405

GENERAL APPLICATIONS –

Data Encryption: to encrypt a 64-bit plaintext Data Authentication: to produce cryptographic checksum. Data Encryption and Authentication: the same data can be protected b both encryption and authentication. SPECIFIC APPLICATIONS Data Storage and Mail Systems Electronic Funds Transfers (Retail and Wholesale) Electronic Business Data Interchange

DES is considered to be lacking strength for many applications, mainly due to the 56-bit key size being too small.

DES have been replaced by stronger encryption algorithms like AES and TDES.

We can extend this project by decrypting the encrypted data. It can be used in mobile encryption for secure communication. In recent years, the cipher has been superseded by the Advanced Encryption Standard (AES). Due to the limitations of DES on security context, we shall include Triple DES in the scope. Triple DES is a stronger form of DES algorithm.

[1] Waled Y. Zibideh, Mustafa M. Matalgah” ModifiedDES Encryption Algorithm with Improved BER Performance in Wireless Communication”, IEEE, Radio and Wireless Symposium (RWS), 2011 ,pp 219-222,jan 2011 [2] Ji Yaoa, Hongbo Kang “FPGA Implementation of Dynamic Key Management for DES Encryption Algorithm “IEEE, Electronic and Mechanical Engineering and Information Technology (EMEIT), 2011 International Conference on Vol. 9, pp. 4795 4798 ,Aug 2011

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