Symmetric key distribution for asymmetric ciphers

Because the public key encryption system is inefficient, it is seldom used for the direct encryption of large data blocks, but is often used in the encryption of small chunks, one of the most important applications is for key distribution, such as the main key distribution of the KDC.

A simple Key distribution scheme

　　

1, a generates a public private key pair {Pua,pra}, and then sends the public key and A's identity information to B.

2, B generates a session key, and A's public key is encrypted to a. Because only A's private key can be decrypted, a can get a session key.

Defects:

This scheme can easily be attacked by middlemen. The role of a middleman playing both B and a is to communicate with a and B, respectively, to obtain the session key. The root cause is that the program lacks certification.

Key distribution system to ensure confidentiality and identity authentication

　　

　　

Symmetric key distribution for asymmetric ciphers