Abstract: In the banking and non-financial world, DES algorithm is increasingly used. DES is called Data EncrypTIon Standard. Let's talk about the application misunderstanding and security analysis of the DES algorithm. The DES algorithm converts a 64-bit plaintext input block into a 64-bit ciphertext output block. The key used is also 64 bits. The main flow chart of the whole algorithm is as follows: Its function is to recombine the input 64-bit data block in bits, and divide the output into two parts, L0 and R0. Each part is 32 bits long. The replacement rules are as follows: 58,50,12,34,26,18,10,2,60,52,44,36,28,20,12,4, 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 58th place to be entered is changed to the first place, and the 50th place is changed to the second place. . . And so on, the last one is the original seventh. L0 and R0 are the two parts after the transposition output. L0 is the left 32 bits of the output, and R0 is the right 32 bits. For example, the input value before the change is set to D1D2D3. . . . .D64, the result after the initial replacement is: L0=D58D50. .D8; R0=D57D49. .D7. After 26 iterations. Obtain L16 and R16, take this as an input, and perform inverse permutation to obtain ciphertext output. The inverse permutation is exactly the inverse of the initial set. For example, after the first bit is subjected to the initial permutation, it is at the 40th position, and by the inverse permutation, the 40th bit is replaced by the first bit. The inverse permutation rule is as shown in the following table. : 40,8,48,16,56,24,64,32,39,7,47,15,55,23,63,31, 38,6,46,14,54,22,62,30,37,5,45,13,53,21,61,29, 36,4,44,12,52,20,60,28,35,3,43,11,51,19,59,27, 34,2,42,10,50,18,58 26,33,1,41, 9,49,17,57,25, Magnification table 32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9, 8, 9, 10,11, 12,13,12,13,14,15,16,17,16,17,18,19,20,21,20,21, 22,23,24,25,24,25,26,27,28,29,28,29,30,31,32, 1, Simple transposition table 16,7,20,21,29,12,28,17, 1,15,23,26, 5,18,31,10, 2,8,24,14,32,27, 3, 9,19,13,30, 6,22,11, 4,25, In the f(Ri, Ki) algorithm description diagram, S1, S2. .S8 is a selection function whose function is to convert 6-bit data into 4-bit data. The function table for the selection function Si (i = 1, 2, . . . . . . 8) is given below: Selection function Si S1: 14,4,13,1,2,15,11,8,3,10,6,12,5,9,0,7, 0,15,7,4,14,2,13,1,10,6,12,11,9,5,3,8, 4,1,14,8,13,6,2,11,15,12,9,7,3,10,5,0, 15,12,8,2,4,9,1,7,5,11,3,14,10,0,6,13, S2: 15,1,8,14,6,11,3,4,9,7,2,13,12,0,5,10, 3,13,4,7,15,2,8,14,12,0,1,10,6,9,11,5, 0,14,7,11,10,4,13,1,5,8,12,6,9,3,2,15, 13,8,10,1,3,15,4,2,11,6,7,12,0,5,14,9, S3: 10,0,9,14,6,3,15,5,1,13,12,7,11,4,2,8, 13,7,0,9,3,4,6,10,2,8,5,14,12,11,15,1, 13,6,4,9,8,15,3,0,11,1,2,12,5,10,14,7, 1,10,13,0,6,9,8,7,4,15,14,3,11,5,2,12, S4: 7,13,14,3,0,6,9,10,1,2,8,5,11,12,4,15, 13,8,11,5,6,15,0,3,4,7,2,12,1,10,14,9, 10,6,9,0,12,11,7,13,15,1,3,14,5,2,8,4, 3,15,0,6,10,1,13,8,9,4,5,11,12,7,2,14, S5: 2,12,4,1,7,10,11,6,8,5,3,15,13,0,14,9, 14,11,2,12,4,7,13,1,5,0,15,10,3,9,8,6, 4,2,1,11,10,13,7,8,15,9,12,5,6,3,0,14, 11,8,12,7,1,14,2,13,6,15,0,9,10,4,5,3, S6: 12,1,10,15,9,2,6,8,0,13,3,4,14,7,5,11, 10,15,4,2,7,12,9,5,6,1,13,14,0,11,3,8, 9,14,15,5,2,8,12,3,7,0,4,10,1,13,11,6, 4,3,2,12,9,5,15,10,11,14,1,7,6,0,8,13, S7: 4,11,2,14,15,0,8,13,3,12,9,7,5,10,6,1, 13,0,11,7,4,9,1,10,14,3,5,12,2,15,8,6, 1,4,11,13,12,3,7,14,10,15,6,8,0,5,9,2, 6,11,13,8,1,4,10,7,9,5,0,15,14,2,3,12, S8: 13,2,8,4,6,15,11,1,10,9,3,14,5,0,12,7, 1,15,13,8,10,3,7,4,12,5,6,11,0,14,9,2, 7,11,4,1,9,12,14,2,0,6,10,13,15,3,5,8, 2,1,14,7,4,10,8,13,15,12,9,0,3,5,6,11, Here we use S1 as an example to illustrate its function. We can see that in S1, there are 4 rows of data, named 0, 1, 2, 3 rows; each row has 16 columns, named 0, 1, 2, 3 ,. . . . . . , 14, 15 columns. The current input is: D=D1D2D3D4D5D6 Order: column = D2D3D4D5 Line = D1D6 The corresponding number is then found in the S1 table, represented by a 4-bit binary, which is the output of the selection function S1. The generation algorithm of subkey Ki (48bit) is given below. From the description of the generation algorithm of the subkey Ki, we can see that the initial Key value is 64 bits, but the DES algorithm specifies that the eighth, 16, and . . . . . The .64 bit is a parity bit and does not participate in the DES operation. Therefore, the actual number of available digits of the Key is only 56. That is, after the transformation of the reduced transposition table 1 is changed, the number of digits of the Key is changed from 64 bits to 56 bits. The 56 bits are divided into two parts, C0 and D0, each of which is 28 bits, and then the first cycle is shifted to the left. Get C1 and D1, combine C1 (28 bits) and D1 (28 bits) to obtain 56 bits, and then select the transposition 2 by narrowing down, so that the key K0 (48 bits) is obtained. And so on, you can get K1, K2. . . . . . , K15, but it should be noted that the number of left shifts corresponding to the left shift of 16 cycles is based on the following rules: Cycle left shift number 1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1 The encryption process of the DES algorithm is described above. The decryption process of the DES algorithm is the same, the only difference is that the sub-key K15 is used in the first iteration, and the second time K14. . . . . . The last time you used K0, the algorithm itself did not change. Since the first public invention of the block cipher (DES algorithm) in 1977, it has attracted extensive attention from the academic and business circles. The academic community has conducted in-depth research on DES cryptography, and has launched a fierce debate around its security and deciphering methods. In a certain sense, it has also promoted the theoretical research of cryptography. At the same time, people have been skeptical about the security of DES, and have different opinions on the length of the key, the number of iterations, and the design of the S-box. DES is a symmetric block cipher algorithm. The main problem with symmetric block cipher algorithms is that since both encryption and decryption use the same key, the key must be distributed before sending and receiving data. Therefore, the distribution of keys becomes the weakest and most risky part of the encryption system. It is difficult for all basic means to ensure the security of the work, thus lengthening the key update period and deciphering others. The key provides an opportunity. In fact, this is not much different from traditional secrecy methods. In the historical war, the record of breaking the intelligence of other countries is nothing more than two ways: one is to intercept the other party's password book in the process of the enemy replacing the "password book"; the other is that the enemy key change period is too long and is long-term Track, find the law and be cracked. In the symmetric algorithm, although the chance of tracking and finding out the law to crack the key is greatly reduced due to the enhancement of the key strength, the difficulty of key distribution is almost impossible to solve. For example, if n parties participate in communication, if the n parties use the same symmetric key, once the key is cracked, the whole system will collapse; if different symmetric keys are used, n(n-1) keys are needed. The number of keys is proportional to the square of the number of people involved in the communication, which makes the management of large system keys almost impossible. 2835 Single Color Led Strip,Single Red Led Light,Single Color Led,Single Blue Led Light NINGBO SENTU ART AND CRAFT CO.,LTD. , https://www.lightworld-sentu.com