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API Authentication & Webhook Security
HMAC Message Authentication Generator
Compute HMAC-SHA256, HMAC-SHA512, and HMAC-SHA1 signatures client-side using WebCrypto with instant Hex and Base64 outputs.
Message & Secret Key
Computed HMAC Signature
0 characters
HMAC-SHA256 in Modern API Security & Webhooks
When third-party webhooks (such as Stripe payment confirmations, GitHub commit pushes, or Shopify order creations) hit your server, your application must verify that the incoming HTTP payload actually came from the authentic provider and was not forged or altered by an attacker in transit. The service signs the body using a shared secret and HMAC-SHA256, passing the signature in an HTTP header (e.g. X-Hub-Signature-256 or Stripe-Signature).
Frequently Asked Questions
No! Standard string comparison (
a === b) terminates at the first differing character, leaking information about matching prefixes through execution timing (timing attacks). In production applications, always use constant-time comparison methods such as crypto.timingSafeEqual() in Node.js, hash_equals() in PHP, or hmac.compare_digest() in Python.
HMAC-SHA256 is the universal industry standard recommended by NIST, AWS, and modern web platforms. HMAC-SHA512 is also widely utilized for high-security environments, while HMAC-SHA1 is deprecated and should only be used for backwards compatibility.