Generalization of symmetric and asymmetric cryptography

Symmetric encryption Meaning: Symmetric encryption is the fastest and easiest way to encrypt encryption (encryption) and decryption (decryption) with the same key (secret key), this method is called symmetric encryption algorithm in cryptography. Symmetric encryption has many algorithms, and because of its high efficiency, it is widely used in the core of many cryptographic protocols. Asymmetric encryption Meaning: Asymmetric encryption provides a very secure way to encrypt and decrypt data, using a pair of keys, public key, and private key. The private key can only be safely kept by one party and cannot be compromised, while the public key may be sent to any person requesting it. Asymmetric encryption uses one of these keys to encrypt, while decryption requires another key. For example, you ask the bank for the public key, the bank sends you the public key, you encrypt the message using the public key, then only the holder of the private key-the bank can decrypt your message. Unlike symmetric encryption, the bank does not need to send the private key over the network, so security is greatly improved.
Common Symmetric cryptography:

1). Des:java6 only supports example 56-bit key lengths, which can be increased by bounvycastle to 64 bits. Example: http://blog.csdn.net/u013791374/article/details/51970860

2). 3-heavy des: as des improved (core or DES), for the DES key length is short, the number of iterations is small, and other problems have been improved, the key length from 56 to 112 or 168 bits, the advantages: anti-poor lifting capacity significantly increased, disadvantage: encryption inefficient, processing speed is slow. Example: http://blog.csdn.net/u013791374/article/details/51971188.

3). The basic requirements for AES:AES are: faster than triple DES, at least as secure as Sanchong des, data packet lengths of 128 bits, and a key length of 128/192/256 bits. Advantages: The key set-up time is short and storage requirements are low. commonly used asymmetric encryption:

1). RSA: Secret key length 1024 bits. Example: http://blog.csdn.net/u013791374/article/details/51980724

Summary

(1) Symmetric encryption and decryption using the same key, so fast, but because the need to transfer the key in the network, so security is not high.
(2) Asymmetric encryption uses a pair of keys, public and private keys, so security is high, but encryption and decryption slow.
(3) The solution is to encrypt the symmetric encryption key using the asymmetric encryption of the public key, and then send it out, the receiver uses the private key to decrypt the symmetric encryption key, and then the two sides can use symmetric encryption to communicate.