HMAC stands for Hash-based Message Authentication Code. Unlike a simple checksum (which verifies data wasn't accidentally corrupted), HMAC verifies authenticity. By using a shared Secret Key, it proves that the message created could only have come from someone who knows the key.
Tool Capabilities
File Support
Verify the authenticity of downloaded firmwares, documents, or binaries. Drag and drop a file to calculate its HMAC signature instantly.
Instant Verification
Don't rely on visual checks. Paste your expected signature into the Verify field to perform an exact character-by-character comparison.
Output Formats
Toggle between standard Hexadecimal (used in most systems) and Base64 (common in web headers and JWTs).
Multi-Algorithm
Full support for SHA-256 (standard), SHA-512 (high security), SHA-1, and MD5 (legacy), ensuring compatibility with any system.
Common Use Cases
API Signatures
APIs (like Amazon AWS S3) require requests to be signed with HMAC to prove identity without sending the password over the wire.
Webhook Validation
Payment gateways (Stripe, PayPal) sign webhooks with HMAC. Receivers use the secret key to verify the notification is legitimate.
Session Integrity
Cookies and JWTs are signed with HMAC to prevent users from tampering with their session data (like changing user_id=1 to user_id=2).
Frequently Asked Questions
What is HMAC?
HMAC (Hash-based Message Authentication Code) is a cryptographic construction that combines a hash function (like SHA-256) with a secret key. It is used to verify both the data integrity and the authenticity of a message.
How does HMAC differ from a standard Hash?
A standard hash (e.g., MD5 sum) only proves that data hasn't been accidentally corrupted. HMAC uses a secret key to prove that the data was created by someone who holds that key, preventing malicious tampering.
Can I generate HMAC for a file?
Yes! Our tool supports file input. Simply drag and drop any file to calculate its HMAC signature using your secret key. This is done entirely in your browser for security.
Which algorithm should I choose?
SHA-256 is the industry standard for most modern applications (AWS, Stripe, JWT). SHA-512 is used for higher security needs. MD5 and SHA-1 are considered weak and should only be used for legacy compatibility.
How do I verify a signature?
After generating an HMAC, use the "Verify" field to paste an expected signature. The tool will compare them and instantly tell you if they match or if the data has been altered.
Is my Secret Key safe?
Yes. This tool runs 100% client-side. Your secret key and input data never leave your browser and use the standard CryptoJS library for calculation.
What is the difference between Hex and Base64 output?
Hex (hexadecimal) represents the hash as a string of 0-9 and a-f characters. Base64 encodes binary data into ASCII characters and is often used in web headers (like Authorization headers). You can toggle between them in the Configuration panel.
Can I calculate HMAC for multiple lines at once?
Yes, enable "Batch Mode" to treat each line of your input text as a separate message. The tool will output a separate HMAC for each line.
What requires HMAC signatures?
HMAC is commonly used in API authentication (signing requests), verifying webhooks (ensuring payloads are from trusted senders), and securing JSON Web Tokens (JWTs).
Is there a file size limit?
Since processing happens in the browser memory, extremely large files (GBs) might cause performance issues depending on your device RAM. For most documents and images, it works instantly.