Verify cryptographic function behavior

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.

copy reviewer prompt

Prompt

Reviewer Prompt
Deploy Agent

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:

// 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.

Source discussions