What does the key mean?

It is a parameter input in the algorithm of converting plaintext into ciphertext or ciphertext into plaintext. Keys are divided into symmetric keys and asymmetric keys. A simple example of a public key can be represented by a prime number. The algorithm of multiplying prime numbers is used as the public key, and the algorithm of decomposing product into original prime numbers is used as the private key.

Encryption is to add a prime number to the information to be transmitted when encoding, and then transmit it to the receiver after encoding. Anyone who receives this information without the private key owned by the receiver will not be able to interpret it in the process of decryption (in fact, the process of finding prime numbers) because the process of finding prime numbers (decomposing prime factors) is too long. ? A digital certificate contains public key information to confirm the identity of the user who owns the key pair.

Asymmetric key encryption system

It needs to use different keys to complete encryption and decryption operations, one is publicly released, that is, the public key, and the other is privately kept by the user himself, that is, the private key. The sender of information uses public key encryption, while the receiver of information uses private key decryption. The public key mechanism is flexible, but the speed of encryption and decryption is much slower than that of symmetric key encryption.

Therefore, in practical applications, people usually use them together. For example, a symmetric key encryption system is used to store a large amount of data information, while a public key encryption system is used to encrypt keys. For ordinary symmetric encryption, the encryption operation and decryption operation use the same key.

The commonly used symmetric encryption algorithm is simple and efficient, with short key and extremely difficult to decipher. Because the security of the system mainly depends on the security of the key, it is a serious problem to transmit and save the key safely on the open computer network. Because both parties use the same key in symmetric cryptography, data signature and undeniable function cannot be realized.