對稱密碼和非對稱密碼體系

Cryptography is a study of different techniques used for encryption and decryption of the text to convert the plain text into ciphertext and vice-versa. There are many different cryptographic techniques and algorithm which have been developed so far.

密碼術(shù)是對用于文本加密和解密以將純文本轉(zhuǎn)換為密文，反之亦然的不同技術(shù)的研究。 到目前為止，已經(jīng)開發(fā)了許多不同的密碼技術(shù)和算法。

These are broadly classified into two types,

這些大致分為兩種類型，

Symmetric key cryptography

對稱密鑰加密

Asymmetric key cryptography

非對稱密鑰加密

The sole difference between lies between the pair of keys used for encryption and decryption process.

兩者之間唯一的區(qū)別在于用于加密和解密過程的一對密鑰之間。

1)對稱密鑰加密 (1) Symmetric key cryptography)

In the symmetric key cryptography, the same key is used for encryption as well as decryption. To maintain the security levels, this key is kept private so that no third party or unauthorized member can access the data.

在對稱密鑰密碼術(shù)中，相同的密鑰用于加密和解密。 為了維持安全級別，此密鑰保持私密，因此任何第三方或未經(jīng)授權(quán)的成員都無法訪問數(shù)據(jù)。

There are further two types of symmetric key encryption techniques,

還有另外兩種類型的對稱密鑰加密技術(shù)，

Substitution technique

替代技術(shù)

In the substitution technique, the letters of the plain text are substituted by some other letters. This substitution is done with the help of a key and a suitable algorithm, and the decryption is also performed using the same key and just by reversion of the order of steps performed in the algorithm.

在替換技術(shù)中，純文本字母被其他一些字母替換。 借助于密鑰和適當?shù)乃惴▉硗瓿稍撎鎿Q，并且還使用相同的密鑰并且僅通過還原算法中執(zhí)行的步驟的順序來執(zhí)行解密。

The substitution technique may also not be consistent throughout in all cases, i.e. the letter which is used for substituting any letter say

替代技術(shù)在所有情況下也可能不一致，例如，用于替換任何字母的字母

'm' at a position may or may not be the same letter for substituting 'm' at some different position of the plain text. According to this, there are 2 ways in which the substitution technique can be performed.

“M”的位置可以是或者可以不是用于在純文本的一些不同位置取代的“m”相同的字母。 據(jù)此，有兩種可以執(zhí)行替換技術(shù)的方式。

Mono-alphabetic Cipher: Here, in this case, a single cipher alphabet for each plain text alphabet throughout the text.單字母密碼 ：在這種情況下，這里是整個文本中每個純文本字母的單個密碼字母。 Eg. If we are substituting 例如。 如果我們用'm' by “ z”代替'z', then this substitution will take place throughout the encryption process.“ m” ，那么這種替換將在整個加密過程中進行。 Example: Caeser cipher 示例 ：Caeser密碼

Poly-alphabetic Cipher: Here, in the case of a poly-alphabetic cipher, no fixed cipher alphabet is used for substituting the plain text alphabets. Different alphabets can substitute the same alphabet of plain text at different places.多字母密碼 ：在此情況下，對于多字母密碼，不使用固定密碼字母來代替純文本字母。 不同的字母可以在不同的地方替換相同的純文本字母。 Eg. If we are substituting 例如。 如果我們在某個位置用'm' by “ z”替換'z' at a place, then it may happen that “ m” ，則可能在其他位置用'm' is being substituted by some other letter say “ y”替換其他字母'y' at some other place.“ m” 。 Example: 示例 ： Playfair cipher Playfair密碼

Transposition technique

換位技術(shù)

The transposition technique includes performing some sort of permutation on the plain text letters. It should be noted that the length of plain text and cipher text remains the same in this technique.

換位技術(shù)包括對純文本字母執(zhí)行某種置換。 應(yīng)該注意的是，在這種技術(shù)中，純文本和密文的長度保持不變。

Eg. 'NAME' can be encrypted as 'MNAE' or 'EANM' etc.

例如。 可以將“ NAME”加密為“ MNAE”或“ EANM”等。

Examples: Rail-fence cipher

示例 ： 圍欄密碼

2)非對稱密鑰加密 (2) Asymmetric key cryptography)

In the asymmetric key cryptography, a pair of different keys are used for encryption and decryption process. Usually, one of these keys is kept public, i.e. which is made available to all and the other is kept private, i.e. is available only to the authorized members. To maintain confidentiality and authentication, it is a convention that the encryption is done by the public key and the decryption with the help of the private key.

在非對稱密鑰加密中，一對不同的密鑰用于加密和解密過程。 通常，這些密鑰中的一個保持公開狀態(tài)，即對所有人開放，而另一個保持私有，即僅對授權(quán)成員可用。 為了保持機密性和身份驗證，一種慣例是，加密由公鑰完成，并在私鑰的幫助下進行解密。

Examples: Diffie Hellman Cipher, Elliptic curve cryptography

示例： Diffie Hellman密碼 ， 橢圓曲線密碼學

翻譯自: https://www.includehelp.com/cryptography/types-of-cryptography-symmetric-and-asymmetric.aspx

對稱密碼和非對稱密碼體系

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