You were recently hired as a Cryptography Engineer at SecureIoT, a start$-$up company that specialises in building solutions to secure IoT devices. You are asked to secure the wireless communication between two devices which already share a private key. The deployed solution needs to ensure that messages between the devices remain confidential and that the devices can verify that the messages they receive are from the other device sharing the private key with it$.$ The devices are deployed in an uncontrolled environment and hence the communications between them may be observed, blocked, or modified by third parties.

question: Identify the cryptographic primitive that can guarantee the above security requirements and the notion of security that the primitive needs to achieve. Briefly justify your answer by discussing attack vectors that could arise in practice.