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atical : D (C) = M
Encrypt and then decrypt the message first , the original plaintext will be recovered , expressed mathematically as:
 D (E (M)) = M
E is the encryption function , D is the decryption function .
Encryption and decryption operations are typically under the control of the key , the encryption and decryption keys used in the process are known as the encryption key and decryption key .

As can be seen from the figure , the data encrypted ciphertext is stored , even if they are stolen , copied , confidential data will not be hostile to obtain . Because then they get , and just a bunch of almost unbreakable password, so rational database encryption technology is an effective means of protecting sensitive data . Here used in the encryption of the plaintext through a certain algorithm and encryption key , resulting ciphertext ; ciphertext decryption algorithm and through certain decryption key to decrypt , resulting plaintext. Data privacy encryption is directly dependent on the cryptographic algorithms and key lengths .

Different types according to the key data encryption algorithm can be divided into two categories : symmetric key algorithms and asymmetric key algorithm.

Sometimes also called symmetric key algorithms traditional cryptographic algorithm , the encryption key is the decryption key can be derived from the opposite is true . In most symmetric algorithms , the encryption and decryption keys are the same . Symmetric key cryptosystem model .

A symmetric key cryptosystem workflow is: Assume that A and B are two systems , the two decided to conduct secure communications . A and B are some way a shared secret key that only the A and B are known , the other users do not know . A or B by using the access key to encrypt the information sent to the other party , the other party can decrypt the information only , other users can not decrypt the message.

The advantage of symmetric key algorithms : computational overhead is small, encryption and decryption speed ( encryption and decryption speed can reach to tens of Mbps or more ) , the algorithm is simple and suitable for encrypting large amounts of data .
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