Jacob is concerned that the password used for one of his organization's services is weak, and he wants to make it harder to crack by making it harder to test possible keys during a brute-force attack. What is this technique called?

Key stretching makes potentially weak keys more resistant to brute-forcing and often involves using a hash or block cipher repeatedly to make the original value harder to crack. Key rotation is the process of changing keys on a periodic basis to limit the impact of potential exposure. Master keying and passphrase armoring are not commonly used concepts for information security, although master keys are used for physical locks.