Shulou(Shulou.com)06/01 Report--

1. Encryption algorithm terminology

Suppose we replace each letter in ABCD with the second letter after it, for example, A with C, and finally ABCD with CDEF.

Clear text: ABCD

Encryption algorithm: letter substitution

Key: replace each letter with the second letter after it

Ciphertext: CDEF

Encryption: ABCD-- > CDEF

Decryption: CDEF-- > ABCD

2. Classification of encryption algorithms

Encryption algorithms are divided into symmetric encryption algorithm (private key encryption) and asymmetric encryption algorithm (public key encryption).

2.1. Symmetric encryption algorithm (private key encryption)

Encryption and decryption use the same key.

DES (Data Encryption Standard)

There are three forms of DES encryption, which are DES (40-bit length encryption), DES (56-bit length encryption) and 3DES (3x 56-bit length encryption, that is, 168-bit length encryption).

AES (Advanced Encryption Standard)

There are three forms of AES encryption, which are AES 128 (128-bit length encryption), AES 192 (192-bit length encryption) and AES 256 (256-bit length encryption).

2.2. Asymmetric encryption algorithm (public key encryption)

Different keys are used for encryption and decryption, the key used for encryption is called public key, the key used for decryption is called private key, the public key is used for encryption, and the private key is used for decryption.

The basic idea is: a sends the public key to B, B encrypts the data with the public key, and sends the data to A. even if others intercept the data, because there is no key, they can not get the content of the data.

The name of the RSA public key encryption algorithm is the name of the inventor: Rivest, Shamir and Adleman. The length of the algorithm varies and is defined manually.

3. Encryption algorithm selection

Although the public key encryption algorithm is more secure than the private key encryption algorithm, the speed of the public key encryption algorithm is slow. So the usual practice is to use the public key encryption algorithm to securely transmit the key of the private key encryption algorithm, and then use the private key encryption algorithm to encrypt the data. This method not only ensures the security of the key, but also speeds up the speed of data encryption.

4. Hash algorithm

The corresponding hash value is calculated before the data is sent, and the receiver also calculates the hash value after receiving the data. if the two are inconsistent, the data has been tampered with in the process of transmission. The characteristic of Hash algorithm is that the length of Hash value calculated by any size of data is the same, only according to the hash value, the data content can not be calculated, and the data content can not be restored. Hash is mostly used for authentication, when authentication peers authenticate each other, they only need to exchange the hash value of the password, but there is no need to exchange the password, so as to prevent the password from being stolen.

MD5 (Message Digest 5)

Output the hash value of the 128-bit length after any data is calculated.

SHA-1 (Secure Hash Algorithm 1)

160-bit digest calculates any data and outputs the 160-bit length hash value.

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