Symmetric encryption (1) Basic principles of symmetric encryption

Symmetric encryption (1) Basic principles of symmetric encryption (1) Basic principles of symmetric encryption

Symmetric encryption is the oldest and most classic encryption standard in the computer encryption field. Although symmetric encryption is no longer considered as a secure encryption method, we still don't see any signs of its elimination until now. In many non-network encryption environments, symmetric encryption is sufficient to meet people's needs.

Symmetric encryption uses a single-key encryption method. Both encryption and decryption use the same key, that is, "one key opens a lock ". Symmetric encryption features simple operations, convenient management, and high speed. Its disadvantage is that keys are easily eavesdropped during network transmission, and each key can only be applied once, making key management difficult. Implementation form and encryption of symmetric encryptionAlgorithmThe openness makes it dependent on the security of the key, rather than the security of the algorithm.

A symmetric encryption system consists of five parts, which can be expressed

S = {M, C, K, E, D}

The meanings of each letter are as follows:

M: plaintext space, a set of all plain texts.

C: a set of ciphertext spaces.

K: key space, a set of all keys.

E: encryption algorithm.

D: decryption algorithm.

Symmetric encryption and decryption generally follow the process shown in 1-1.

 

 

Figure 1-1 symmetric encryption and decryption process

Now, the sender of the Data wants to send the data to the receiver securely, but there is no way to prevent attackers from listening to the network between the sender and receiver, data can only be encrypted. First, the sender uses the encryption algorithm e to encrypt the plaintext m to be sent using the key K to obtain the ciphertext C. This process can be simply expressed:

C = EK (m)

The sender transmits the ciphertext C to the receiver over the network. During the transmission process, if the attacker intercepts the sent information, only the ciphertext is displayed, and the plaintext content cannot be obtained without cracking. After receiving the ciphertext from the sender, the receiver cannot obtain the plaintext. The sender must send the key to the receiver through a special channel. The receiver uses the key K to obtain the plaintext using the decryption algorithm. This process can be expressed:

M = dk (c)

From this process, we can understand that key K transfer has become the most critical step. If an attacker acquires K, it will easily crack the ciphertext because the encryption algorithm is public.