When a user first moves into their residence, the user receives a key that unlocks and locks their front door. This key is only given to them but may be shared with others they trust. Which of the following cryptography concepts is illustrated in the example above?
A. Asymmetric key sharing
B. Exchange of digital signatures
C. Key escrow exchange
D. Symmetric key sharing

Based on the information provided within the question it can be said that the cryptography concept that is being illustrated in this example is called Symmetric key sharing. This is a cyrptography concept in which the sender and receiver of a message share a single common key that is used in order to be able to decrypt this message. This private key can be shared with any trusted individuals that need to be able to decrypt the message. Such as any trusted individual that need the key to the front door in question.