What are "cryptographic keys" and why does stealing them matter?

Cryptographic keys are like master keys that unlock encrypted data and verify the authenticity of digital communications. In SharePoint's case, these keys (called ValidationKey and DecryptionKey) are used to ensure that requests to the server are legitimate. When hackers steal these keys, they can create fake but valid-looking requests that SharePoint will trust and process. It's like someone stealing the master key to your office building and being able to make perfect copies. Even after you change the locks (patch the vulnerability), they can still get in using their copied keys until you replace the entire locking system.