How many different keys will be required to give four people the ability to encrypt and decrypt the message using a symmetric cryptography algorithm?

ONE

Answer Explanation: Only one key would be required for everyone to be able to encrypt and decrypt the message. Symmetric cryptography uses the same "shared secret" key for encrypting and decrypting a message. A message encrypted using a symmetric encryption algorithm can be decrypted by anyone with the key. For this reason it is very important to ensure that the key is protected from unauthorized use. One of the primary security issues surrounding the use of symmetric cryptography is the method used to transport the key to users who need it, as most forms of communication are susceptible to eavesdropping.