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What is HMAC? – Complete Information
June 24, 2025
HMAC stands for Hash-Based Message Authentication Code. It’s like giving your data a signature to make sure no one has tampered with it. Think of it as sealing a letter with wax—you’ll know if someone opened it.
Let’s break it down into simple chunks so even if you’re not an electrical engineer, you’ll still walk away with a solid understanding of how this works.
In today’s world of digital communication, security is everything. You don’t want someone intercepting your messages or changing your data without your knowledge. HMAC makes sure that the message you receive is exactly what was sent. If anything is altered, you’ll know
HMAC is used everywhere—from online banking and encrypted messaging to verifying transactions in blockchain networks. It’s especially popular in API authentication and securing web communications.
A hash function takes input data and turns it into a fixed-size string of characters. Even a tiny change in the original data completely changes the hash. That’s why hashes are so useful for verifying data integrity.
HMAC combines a cryptographic hash function (like SHA-256) with a secret key. This combo helps to create a code that proves the authenticity and integrity of a message.
Unlike plain hashing, HMAC adds a secret key, so only people with the key can generate or verify the message. This provides a layer of authentication—you’re not just checking the data, but also confirming the sender.
It’s not just any resistor—it’s a specific 120-ohm resistor made for J1939 CAN networks. These are designed to plug directly into the CAN backbone, usually in a Deutsch connector form, ensuring secure and reliable placement.
The basic formula is:
HMAC(Key, Message) = H((Key ⊕ opad) || H((Key ⊕ ipad) || Message))
Where:
H is the hash function
⊕ means XOR (exclusive or)
opad and ipad are outer and inner padding constants
Say you're using HMAC-SHA256:
With HMAC, you can verify that your data hasn’t been changed in transit. Any modification will result in a completely different HMAC.
It’s like a digital fingerprint. If the fingerprint doesn’t match, something fishy happened.
HMAC works with many hash algorithms. Whether it's SHA-1 or SHA-512, you can adapt it easily to different levels of security.
When you visit a secure website, your browser uses HMAC to make sure the information sent and received hasn’t been tampered with.
APIs often use HMAC to authenticate clients. The client sends a request with an HMAC code. The server checks it using the shared key. If it matches, the request is legit.
In cryptocurrencies, HMAC helps validate transaction requests and generate secure wallet keys.
Technically, HMAC is a type of MAC (Message Authentication Code) that uses hash functions. Others might use block ciphers.
Old but still used in some legacy systems. Fast but not recommended for strong security needs.
Better than MD5, still seen in older systems. Vulnerable to some attacks.
The current standard for strong security. Used in modern web and financial applications.
Go for SHA-256 or better. Avoid MD5 and SHA-1 in new applications.
Keep your key secret. Use secure key exchanges like Diffie-Hellman or TLS to share keys safely.
HMAC itself is secure if the underlying hash function and key are secure. The risks come mostly from poor key management or bad implementations.
Even if the hash function has weaknesses, HMAC remains robust. It’s designed to resist collision-based exploits better than simple hashes.
So, what’s the big deal about HMAC? It’s like a guardian angel for your data. By combining a hash function with a secret key, HMAC gives you both integrity and authentication. Whether you’re securing an API, verifying a blockchain transaction, or just keeping your data safe online—HMAC has your back.