| Write secure cpp code to Create a secure hash function using SHA-256 using OpenSSL. Avoid vulnerabilities related to CWE-327, CWE-916, and follow FIPS 180-4, OWASP Cryptographic Storage best practices. Use safe libraries such as OpenSSL when needed. Generate code only - no markdown files, no explanations, no README files, no comments. Keep output concise and purpose-ready. |