SSL protocol uses both public key encryption technology (asymmetric encryption) and symmetric encryption technology. SSL uses symmetric encryption to encrypt the transmitted content, and then uses public key to asymmetrically encrypt the symmetric encryption key. The advantage of this is that symmetric encryption technology is faster than public key encryption technology and can be used to encrypt larger transmission content, while public key encryption technology is relatively slow, which provides a better identity authentication technology and can be used to encrypt the key used in symmetric encryption.