des加密密碼補位

This is a Data Encryption Standard that is the asymmetric key generation for the encryption of digital data in cryptography. Therefore, its short key length of 56 bits of character criticized from the beginning or starting makes it too insecure or safe for most current applications to use, it has been highly influential in the advancement of modern cryptography in the cryptoanalysis.

這是一種數據加密標準 ，它是用于加密中數字數據加密的非對稱密鑰生成。 因此，從一開始或一開始就批評它的56位字符的短密鑰長度使其對于大多數當前應用程序來說太不安全或太安全了，它在密碼分析的現代密碼學發展中具有很大的影響力。

It was developed in the early 1970s at IBM and depends on an earlier design by Horst Feistel, the algorithm was submitted to the-National Bureau of Standards (NBS) following the agency's invitation to propose a candidate for the protection of sensitive, unclassified electronic government data in the cryptography. It will be developed in 1976, cryptography after consultation with the National Security Agency(NSA), the NBS eventually selected a slightly modified version in the cryptography as strengthened against differential cryptoanalysis, but weakened against brute force attack, which was described as an official Federal Information Processing Standard (FIPS) for the United States in 1977 in the whole world.

它是在1970年代初期由IBM開發的，并依賴于Horst Feistel的較早設計，該算法是在該機構邀請提出保護敏感的，未分類的電子政府的候選人之后，提交給國家標準局(NBS)的。加密中的數據。 它是在與國家安全局(NSA)協商后于1976年開發的密碼學，國家統計局最終在密碼學中選擇了一個經過稍微修改的版本，以增強對差分密碼分析的抵抗力，但對暴力破解的抵抗力卻減弱了，這被描述為官方的聯邦1977年，美國在全球范圍內采用了信息處理標準(FIPS)。

加密過程 (Encryption Process)

It is a DES which is a block cipher, and encrypts data in blocks of size of 64 bit each of the messages, means 64 bits of plain text or original text goes as the input into the DES, which produces 64 bits of the character of ciphertext. A similar algorithm and key are used for encryption and decryption with minor differences between them. Here, the key length is 56 bits longs uses in cryptography in cryptoanalysis.

它是一種DES ，是一種分組密碼，它以每個消息64位大小的塊對數據進行加密，這意味著64位純文本或原始文本將作為DES的輸入，產生64位的字符。密文。 類似的算法和密鑰用于加密和解密，它們之間的差別很小。 在此，密鑰長度為56位長，用于密碼分析中的密碼學。

Here, DES is depended upon the Feistel Cipher, all that is required to specify DES in that way as,

此處，DES依賴于Feistel密碼 ，以這種方式指定DES所需的全部條件如下：

• Key Generation

  密鑰生成

• Round function

  圓形功能

• Any additional processing ? Initial and final permutation

  任何其他處理-初始和最終置換

密鑰生成 (Key Generation)

The round-key generator forms sixteen 48-bit keys out of a 56-bit cipher key in the cryptography. The process of key generation is depicted in the following steps,

圓形密鑰生成器在密碼學中的56位密碼密鑰中形成16個48位密鑰。 以下步驟描述了密鑰生成的過程：

• Initially key is of 64 bits.

  最初，密鑰為64位。

• Then it goes under PI(1) and after that, it develops key of 56 bits

  然后進入PI(1)，此后，開發出56位的密鑰

• Then 56 bit of key divide into two half: left of 28 bit and right of 28 bit.

  然后將56位密鑰分成兩半：28位的左側和28位的右側。

• In both half do the circular left shift according to the round with we perform.

  在兩半中，根據我們執行的回合，圓形左移。

• As we perform 1,2,9,16 we do circular left shift by one bit and remaining round circular left shift by 2 bit.

  當我們執行1,2,9,16時，我們將循環左移一位，而將剩余的循環左移2位。

• After that combine the left and right half and form again 56 bit of key.

  之后，將左右一半結合起來再形成56位鍵。

• Then again 56 bit of key goes under PI(2) as form a key of 48 bit.

  然后再將56位密鑰作為48位密鑰進入PI(2)。

• This key is used in the DES block diagram.

  該密鑰在DES框圖中使用。

舍入函數 (Round Function)

The main or important or we can say that the heart of this cipher is the DES function, (f). This DES function applies 48-bit key cryptography to the rightmost 32 bits to produce a 32-bit output as a right.

主要的或重要的，或者我們可以說此密碼的核心是DES函數( f) 。 此DES函數將48位密鑰加密應用于最右邊的32位，以產生32位的輸出作為右邊。

This function follows some steps,

此功能遵循一些步驟，

• Expansion Permutation box

  擴展排列框

• Xor with the key of 48 bit.

  使用48位密鑰進行異或。

• Substitution Box

  替代箱

• Permutation box.

  排列框。

• Expansion Permutation Box

  擴展排列框

  Here, right half input is 32-bit and the round key is a 48-bit, we first need to expand right half input to 48 bits.

  在這里，右半邊輸入是32位，而回合鍵是48位，我們首先需要將右半邊輸入擴展為48位。

  So, we have to expand the character as we take the 4 bit of 8 characters. In this, we simply convert the 4 bit of each character into 6 bit.

  因此，我們必須擴展字符，因為我們采用8位字符的4位。 在此，我們只需將每個字符的4位轉換為6位。

  So, we have to expand the 4 bit as in the starting put the bit which presents at the last character of the bit and in the end put the second character first bit.

  因此，我們必須擴展4位，就像在開始時將出現在該位的最后一個字符處的位放到最后將第二個字符在第一位中放置一樣。

  For example, we have text GIVE ME SOME MONEY, we write it in a four-bit as giving MESO MEMO NEYX now add the bits as tells you further as XGIVEM EMESOM OMEMON ONEYXG and here 16-bit convert into 24 bits.

  例如，我們有文本GIVE ME SOME MONEY，我們將其寫為四位，因為MESO MEMO NEYX現在將這些位添加為XGIVEM EMESOM OMEMON ONEYXG，并在此將16位轉換為24位。

• XOR

  異或

  After that the expansion permutation, DES does XOR operation on the expanded right section of 48 bit and the round key of 48 bit. The round key is used only in this operation and gave the output as 48 bit.

  在擴展排列之后，DES對48位的擴展右部分和48位的循環密鑰進行XOR操作。 回合密鑰僅在此操作中使用，并提供48位輸出。

• Substitution Boxes

  替代箱

  Thus, the S-boxes carry out the real mixing as confusion. DES uses 8 S-boxes, each with a 6-bit input as plaintext and a 4-bit output as it substitutes it. We have to simply convert 6 bit of character into 4 bit of character.

  因此，S盒作為混淆進行了真正的混合。 DES使用8個S盒，每個S盒具有6位純文本輸入和4位替代輸出。 我們必須簡單地將6位字符轉換為4位字符。

  As we take the first bit or last bit combine as a row and remaining middle four-bit as give a column.

  當我們將第一位或最后一位合并為行，其余的中間四位合并為列時。

  For example, 010010 110010 we take 1 character 00 as 0 rows and 1001 as 9 columns.

  例如，010010 110010我們將1個字符00作為0行，將1001作為9列。

• Permutation

  排列

  The 32-bit output of S-boxes is then subjected to the straight permutation as it has a table according to this we simply update the values by seen in the table and gave an output of 32 bit which further uses as of right.

  然后，S-box的32位輸出將進行直接置換，因為它具有一個根據此表的表，我們只需通過在表中看到的值來更新值，并給出32位的輸出，該輸出將繼續使用。

初始和最終排列 (Initial and Final Permutation)

Simply in starting we take plaintext of 64 bit and divide it into two halves as lest and right each of 32 bits. We use the right half and the key applies to the round function and gave the right half and after then it combines with as Xor of left and right. After that in the second round, left half with came after XOR become right half and original right half become left half and further do this process till round 16.

剛開始時，我們采用64位的明文，以免將其分為兩半，而正確地分為32位。 我們使用右半部分，并且將鍵應用于舍入函數，并給出右半部分，然后將其與左和右的Xor合并。 在第二輪之后，XOR變成右半，原來的右半變成左半之后再加上左半，然后繼續這一過程直到第16輪。

In the end, the same steps follow and at last left half and right half of 32 bits combine or merge and form a ciphertext of 64 bits in the cryptography in the cryptoanalysis.

最后，執行相同的步驟，最后在加密分析的密碼學中，32位的左半部分和右半部分組合或合并并形成64位的密文。

解密過程 (Decryption Process)

It is just the reverse of the encryption process it takes the ciphertext and gave the plain text by just follow the encryption process steps just reverse.

它只是加密過程的逆過程，它采用密文并通過遵循恰好相反的加密過程步驟來給出純文本。

DES分析 (DES Analysis)

This DES satisfies both the desired properties of a block cipher in cryptography. There are two properties make cipher very strong as,

該DES滿足密碼術中分組密碼的兩個所需特性。 有兩個屬性使密碼非常強大，因為：

• Avalanche effect: In this, a small change in plaintext results in a very great change in the ciphertext in the cryptography.

  雪崩效應 ：在這種情況下，明文的微小變化會導致密碼術中的密文發生很大的變化。

• Completeness: In each bit of ciphertext depends on many bits of plaintext in the cryptography.

  完整性 ：密文的每一位都取決于密碼術中許多明文。

Image references:

圖片參考：

• https://www.tutorialspoint.com/cryptography/data_encryption_standard.htm

  https://www.tutorialspoint.com/cryptography/data_encryption_standard.htm

翻譯自: https://www.includehelp.com/cryptography/data-encryption-standard-des-in-cryptography.aspx

des加密密碼補位

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