Symmetric cryptosystem vs Public-key cryptography system

Flaws in the symmetric cryptography system:
Key allocation problem: the communication between two parties to encrypt communication, the need to negotiate the encryption key through a secret secure channel, and this secure channel may be difficult to achieve key management problems: In a network with multiple users, any two users need to have a shared key, when the network of users n is very large, the number of keys to manage is very large , there is no signature function for n (n-1)/2: When subject a receives the electronic document (electronic data) of subject B, it is unable to prove to the third party that the electronic documents do originate from B. Public key cryptography system focuses on three areas of the problem: Key exchange: The communication between the two parties to exchange the session key to encrypt the communication between the two subsequent connections transmitted information. Each logical connection uses a new session key, which is discarded when it is exhausted. Communication confidentiality: The public key as the encryption key, the private key as the decryption key, the communication between the two parties do not need to exchange the key to achieve secure communication. Digital signature: The private key is used as the encryption key, and the public key is used as the decryption key, which can be interpreted by one user to encrypt the data. Throughout the history of cryptography in the public key cryptography, all cryptographic algorithms, including classical and modern passwords, are based on two basic tools of substitution and substitution. The public key cryptosystem provides a new theoretical and technical basis for the development of cryptography, on the one hand, the basic tool of public key cryptography is no longer substitution and substitution, but the mathematical function, on the other hand, the public key cryptography algorithm uses two keys in asymmetric form, two keys are used for confidentiality, key assignment, signature, Certification and so on have a profound significance.

Public key algorithm encryption and decryption slow. MYTH: Public key cipher algorithm more secure public key password makes symmetric key password obsolete