HMAC Calculator

A precise HMAC calculator that computes keyed hashes using common algorithms to verify data integrity for API requests, webhooks, and secure messaging.

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About This Tool

This tool computes a keyed-hash message authentication code (HMAC) given a secret key, a message, and a chosen hash function. It supports SHA-1, SHA-256, SHA-384, and SHA-512, making it suitable for API signing, webhook validation, and payload integrity checks. Conceptually, HMAC combines the secret key with the message in a two-pass hashing process to produce a MAC that is resistant to length-extension and related attacks. The tool adheres to the RFC 2104 construction, including key normalization for keys longer than the block size and encoding handling for both input and output. Users can supply inputs as UTF-8 text or as hex-encoded bytes and can receive the digest as lowercase hex, uppercase hex, or base64, depending on the selected output encoding. Core differentiators include explicit support for multiple algorithms in a single interface, clear validation of inputs, and RFC-compliant results that facilitate cross-language verification and automated testing scenarios.

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How to Use

Provide inputs: key, message, and algorithm. Choose encoding if not UTF-
Run calculation to produce the HMAC digest. Read the digest in the desired encoding and length. Copy the result for verification in code or API tests. Validate that the length matches the selected algorithm’s hash output (e.g., 64 hex chars for SHA-
.

Frequently Asked Questions

Find Quick Answers

What is HMAC and why use it?

HMAC is a keyed-hash message authentication code that uses a secret key to produce a MAC for a message. It provides data integrity and authenticity, ensuring the message originates from a trusted source and has not been altered.

Which algorithms are supported and which should I choose?

Supported: SHA-1, SHA-256, SHA-384, SHA-512. SHA-1 is legacy and less preferred due to collisions; for new systems, choose SHA-256 or SHA-512 to maximize security and compatibility with modern APIs.

How should I handle the key for best security?

Use a strong, random key of sufficient length and never reuse keys across independent signing contexts. Treat the key as a secret and rotate it periodically. The key length should at least match common security goals for the chosen algorithm.

How are inputs encoded and what is the digest format?

Inputs are interpreted as bytes using the selected encoding (UTF-8 by default; hex is supported). The digest is emitted as lowercase hex by default, with options for uppercase hex or base64 depending on user preference.

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