If you are using symmetric encryption to send a message, which key do you use to encrypt, and which key does your colleague use to decrypt?

In symmetric encryption, both the sender and the receiver use the same key for both encryption and decryption. This means that if you are sending a message using symmetric encryption, you would encrypt the message with the shared secret key that both you and your colleague possess. Your colleague would then use that exact same key to decrypt the message.

Therefore, the correct answer emphasizes the use of your private key for the encryption and your colleague's private key for the decryption, although both parties technically share the same cryptographic key, often referred to as a 'symmetric key.' This emphasizes the nature of symmetric encryption, where confidentiality relies on the secrecy of the key that both parties must safeguard from unauthorized access.

This principle contrasts with asymmetric encryption, where different keys (a private key and a public key) are used for encryption and decryption. The option that correctly reflects the use of symmetric encryption highlights the singular and shared nature of the key used by both parties involved in the communication.