The Key Your Own Code Is Not Allowed to Read

Subtitle: A key can be usable without being readable.

• THE BOUNDARY - HAND WORK ACROSS:
• crypto.subtle returns Promises
• Work may leave the JavaScript thread
• CryptoKey is a handle, not raw bytes
• Secure contexts only; plain HTTP refuses

• NON-EXTRACTABLE - WHAT IT MEANS:
• Set extractable to false at creation
• sign, verify, encrypt, decrypt still work
• exportKey rejects every raw-byte request
• Stolen script may spend, not steal, the key

• FALSIFY THE COMFORT:
• Hidden bytes do not mean safe use
• Injected script can sign while the page lives
• Client code cannot be a trust boundary
• No bcrypt, Argon2, or scrypt lives here
• Password checks belong off the client

• HONEST TEST + ONE EXCEPTION:
• Generate a non-extractable key
• Sign a message: success
• Call exportKey: rejection
• Those two results are the security model
• getRandomValues is sync and outside subtle
• Never replace it with Math.random