Comprehensive and Detailed in Depth Explanation:
Vault supports auto-unseal to simplify operations. The HashiCorp Vault documentation states: "Vault supports opt-in automatic unsealing via cloud technologies: AliCloud KMS, AWS KMS, Azure Key Vault, Google Cloud KMS, and OCI KMS," and includes HSM and Transit as additional options. It explains: "Auto unseal is used to automatically unseal Vault using an HSM or cloud HSM service." The valid options are:
A (HSM): "HSM (Hardware Security Module) can automatically unseal Vault by securely storing and managing the master key used for encryption and decryption operations."
B (Azure KMS): "Azure KMS can automatically unseal Vault by utilizing Azure Key Management Service to manage the master key."
C (AWS KMS): "AWS KMS can automatically unseal Vault upon the start of the service by using AWS Key Management Service to manage the master key."
D (Transit): "Transit can automatically unseal Vault by using a pre-configured encryption key stored in Vault itself to encrypt the unseal key."
The documentation clarifies: "Key Shards require the user to provide unseal keys to reconstruct the master key," makingE (Key Shards)a manual process, not auto-unseal. Thus, A, B, C, and D are correct.
[Reference:, HashiCorp Vault Documentation - Seal Configuration, HashiCorp Vault Documentation - Auto Unseal Tutorial, HashiCorp Vault Documentation - Seal Concepts: Auto Unseal, ]
