US Patent 9721120 Preventing unauthorized calls to a protected function

An obfuscated program can be configured to resist attacks in which an attacker directly calls a non-entry function by verifying that an execution path to the function is an authorized execution path. To detect an unauthorized execution order, a secret value is embedded in each function along an authorized execution path. At runtime, the secrets are combined to generate a runtime representation of the execution path, and the runtime representation is verified against an expected value. To perform the verification, a verification polynomial is evaluated using the runtime representation as input. A verification value result of zero means the execution path is an authorized execution path.