Before the following command can be run to encrypt data, what (three) commands must be...

Comprehensive and Detailed in Depth Explanation:

To encrypt data using the Transit secrets engine, it must be enabled and configured. The HashiCorp Vault documentation states: "Enable the Transit secrets engine at the default path of ‘transit’ using the command vault secrets enable transit. Create an encryption key called ‘vendor’ using the command vault write -f transit/keys/vendor. Encode the string using base-64 encoding by using the command base64 <<< ‘hashicorp certified’." These steps are prerequisites for the given vault write transit/encrypt/vendor command:

A (base64 <<< "hashicorp certified"): The docs note, "All plaintext data must be base64-encoded. The reason for this requirement is that Vault does not require that the plaintext is ‘text’. It could be a binary file such as a PDF or image. The easiest safe transport mechanism for this data as part of a JSON payload is to base64-encode it." The provided plaintext aGFzaGljb3JwIGNlcnRpZmllZA== is the base64 encoding of "hashicorp certified."

D (vault secrets enable transit): "Before you can use the transit secrets engine, it must be enabled with vault secrets enable transit at the default path ‘transit/’."

E (vault write -f transit/keys/vendor): "An encryption key must be created before encryption can occur. Use vault write -f transit/keys/vendor to generate a key named ‘vendor’."

Bis the target command, not a prerequisite.C (vault secrets list)lists engines but doesn’t configure Transit. Thus, A, D, and E are correct.