When implementing cryptographic algorithms, always verify the exact behavior and return values of security-critical functions. Misinterpreting how functions signal success or equality can lead to severe security vulnerabilities. In particular: - Confirm whether comparison functions return true/false or 0/non-0 for equality - Implement security checks with precise understanding of function semantics - Follow relevant cryptographic standards (RFCs) meticulously - Use constant-time operations for cryptographic comparisons to prevent timing attacks Example of a potential error in a security check: ```cpp // INCORRECT: Misinterpreting constantTimeMemcmp which returns 0 for equality if (derivedKey->size() != expectedOutputSize || !constantTimeMemcmp(derivedKey->span(), zeros)) { // Handle insecure all-zeros key case } // CORRECT: Properly checking for equality with constantTimeMemcmp if (derivedKey->size() != expectedOutputSize || constantTimeMemcmp(derivedKey->span(), zeros) == 0) { // Handle insecure all-zeros key case } ``` Security-critical checks must be implemented correctly the first time - cryptographic vulnerabilities can be subtle and devastating.