Before data is written to the storage backend, the data is encrypted by which Vault...

Comprehensive and Detailed In-Depth Explanation:

Vault’s architecture includes a cryptographic barrier that encrypts all data before it’s written to the storage backend. This ensures that the backend (e.g., Consul, Filesystem) only stores encrypted data, enhancing security even if the backend is compromised. The barrier uses a master key (split into unseal keys via Shamir’s Secret Sharing) to encrypt a keyring, which in turn encrypts the data. TLS certificates secure network communication, not storage encryption. Unseal keys unlock the master key, not encrypt data directly. The Transit engine is for application-level encryption, not storage backend protection. The Vault architecture docs confirm the cryptographic barrier’s role.