What is Single Key Cryptography?

What is Single Key Cryptography?
It is also called Secret Key Cryptography or Symmetric Cryptography. They are the methods used for encryption/decryption in secure data transmission or storage, or for issues such as authentication. This method has a single non-public private key. Both the sender and receiver must know this key. Key distribution problem arises because this situation imposes a separate key requirement for each user pair. Due to this problem, double-key cryptography was developed.