加密可以用來保護傳輸中的數據和存儲器中的數據。一些廠家提供硬件加密設備，用來加密和解密數據。也可買到軟件加密程序包或作為自由軟件免費獲得。
Encryption can be defined as the process of tasking information that exists in some readable form (plaintext) and converting it into a form (ciphertext) so that it cannot be understood by others.
加密可以定義為把現有的、以某種可讀形式(明文)的信息轉換成其他人不能理解的形式(密文)的過程。
In public key cryptosystem, the encryption and decryption keys were different, and plaintext encrypted with the public key can only be deciphered with the private key from the same pair. Conversely, plaintext encrypted with the private key can be decrypted only with the public key[4] ( it is used in electronic signatures). The notations for these are as follows.
C=E k (P) , P=D k1(C)=D k1 (E k (P)) or
C=D k1 (P), P=E k (C)=E k (D k1 (P))
在公鑰秘鑰系統中，加密和解密密鑰是不同的。并且用公開密鑰加密的明文只能用同一對密鑰中的秘密密鑰解密。相反，用私有密鑰加密的明文只能用公開密鑰解密(它用于電子簽名)。這些關系的表示法如下：(見上式)
Here k is a public key and k1 is private key( or secret key). Users can make their public keys freely available or place them at a key distribution center for others to access. However, the private key must be kept safe. In public-key systems there is no need to find a safe channel for communicating a shared secret key.
這里K是公開密鑰，K1是私有密鑰(或秘密密鑰)。用戶可以讓他們的公開密鑰自由地使用，或把它們放在密鑰分配中心供其他人存取。然而，私有密鑰必須安全的保存。在公開密鑰系統，無需找一條傳送共享的私有密鑰的安全通道。
文章來源于領測軟件測試網 http://www.kjueaiud.com/
