There are often claims of "No Key" versions or updates of Delta Executor. These versions either bypass the advertisement system or use a different installation method that integrates the key during the initial setup. However, official versions frequently revert to the key system to maintain development funding.
The next time your phone updates with just a 100 MB delta, remember—the Keystore’s TEE just performed a cryptographic handshake to ensure that every single byte of that delta is exactly what the OEM intended. delta android keysystem link