HMAC Generator / Verifier (SHA‑256 / SHA‑512)
Generate HMAC (Hash-based Message Authentication Code) using SHA-256 or SHA-512 algorithms. Verify message authenticity and integrity with shared secret keys. Essential for API authentication, webhook verification, and secure communications.
Secret key should be cryptographically random. Minimum 32 hex characters (16 bytes) recommended.
✅ Message Authentication Standard
- • Cryptographic authenticity: HMAC provides both integrity and authenticity verification
- • Tamper detection: Any modification to message or key produces completely different HMAC
- • Industry standard: Used in JWT tokens, API authentication, and secure protocols
- • Performance: Fast computation while maintaining strong security guarantees
- • Perfect for: API signatures, webhook verification, secure communications
About HMAC
- • Algorithm: Hash-based Message Authentication Code (RFC 2104)
- • Purpose: Verify message integrity and authenticity using shared secret
- • Construction: HMAC(K,m) = H((K ⊕ opad) || H((K ⊕ ipad) || m))
- • Key requirement: Shared secret key known only to sender and receiver
- • Security: Resistant to length extension and collision attacks
- • Deterministic: Same message and key always produce identical HMAC
- • Hash algorithms: Works with any cryptographic hash (SHA-256, SHA-512)
- • This tool uses the browser's native Web Crypto API for optimal security
HMAC Security Best Practices
Key Generation: Use cryptographically secure random number generator
Key Length: Minimum 32 bytes (256 bits) for SHA-256, 64 bytes for SHA-512
Key Storage: Store keys securely, separate from messages and HMACs
Key Rotation: Regularly rotate HMAC keys in production systems
Algorithm Choice: Prefer SHA-256 or SHA-512 for new implementations
Timing Attacks: Use constant-time comparison when verifying HMACs
⚠️ Security Considerations
Client-Side Processing: This tool runs in your browser - keys never leave your device
Key Secrecy: HMAC security depends entirely on keeping the secret key confidential
Key Distribution: Safely distribute shared keys using secure channels
Replay Protection: Consider adding timestamps or nonces to prevent replay attacks
Key Compromise: If key is compromised, all previous and future HMACs are invalid
Production Use: Implement proper key management and rotation policies
Common Use Cases
API Authentication: Sign API requests to verify sender identity
Webhook Verification: Validate incoming webhooks from trusted sources
JWT Tokens: Sign JSON Web Tokens for secure authentication
Message Integrity: Detect unauthorized modifications to data
Secure Protocols: TLS, IPSec, and other cryptographic protocols
File Verification: Verify file integrity during transfers
SHA-256 vs SHA-512 for HMAC
SHA-256: 64 hex character output, faster on 32-bit systems, widely supported
SHA-512: 128 hex character output, faster on 64-bit systems, higher security margin
Performance: SHA-256 generally preferred for network protocols due to smaller size
Security: Both provide excellent security; choose based on performance needs
Compatibility: SHA-256 has broader support across systems and libraries
Recommendation: Use SHA-256 for most applications, SHA-512 for maximum security
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