What is the main role of a unseal key in HashiCorp Vault?

The main role of an unseal key in HashiCorp Vault is to unlock the Vault after it has been sealed. When Vault is sealed, it is in a state where no operations can be performed, and all secrets are secured. To access the secrets or perform any actions, the Vault must first be unsealed.

Unseal keys are critical for this process because they are required to decrypt the master key that Vault uses to secure its data. Upon initialization of Vault, a master key is split into several parts using Shamir's Secret Sharing scheme, and these parts are distributed as unseal keys. A specified number of these keys must be provided together to successfully unseal Vault and regain access to the stored secrets.

This process ensures that no single person has complete control over the Vault, enhancing security and accountability. Sealing and unsealing offer a way to protect sensitive data when the Vault is not actively in use or when it needs to be temporarily taken offline.