Vault vs. Keywhiz
Keywhiz is a secret management solution built by Square. Keywhiz has a client/server architecture based on a RESTful API. Clients of Keywhiz access secrets through the API by authenticating with a client certificate or cookie. To allow for flexible consumption of secrets by arbitrary software, clients may also make use of a FUSE filesystem to expose secrets as files on disk, and use Unix file permissions for access control. Human operators may authenticate using a cookie-based authentication either via command line utilities or through a management web interface.
Vault similarly is designed as a comprehensive secret management solution. The client interaction with Vault is flexible both for authentication and usage of secrets. Vault supports mTLS authentication along with many other mechanisms. The goal is to make it easy to authenticate as a machine for programmatic access and as a human for operator usage.
Vault and Keywhiz expose secrets via an API. The Vault ACL system is used to protect secrets and gate access, similarly to the Keywhiz ACL system. With Vault, all auditing is done server side using audit devices.
Keywhiz focuses on storage and distribution of secrets and supports rotation through secret versioning, which is possible in the Keywhiz UI and command-line utilities. Vault also supports dynamic secrets and generating credentials on-demand for fine-grained security controls, but adds first class support for non-repudiation. Key rotation is a first class concern for Keywhiz and Vault, so that no external systems need to be used.
Lastly, Vault forces a mandatory lease contract with clients. All secrets read from Vault have an associated lease which enables operators to audit key usage, perform key rolling, and ensure automatic revocation. Vault provides multiple revocation mechanisms to give operators a clear "break glass" procedure after a potential compromise.