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5 min read
Thinking about using Hash-Based Message Authentication Codes? Here’s what you need to know about using this message authentication method.

What is Hash-Based Message Authentication Codes (HMAC)?

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When building apps and web-based platforms, protecting the integrity of data and information communicated online has never been more important.

One mechanism for checking integrity is hash-based message authentication codes (HMAC) which use a cryptographic technique that uses combines three elements: a message, a secret key, and a hash function.

The goal of HMAC is to aid companies with data integrity, ensuring information isn’t tampered with. If data and information have been tampered with, HMAC allows you to see those data changes with ease.

How HMAC works

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HMAC is a message-based authentication code that uses a hash function in combination with a cryptographic key. HMAC provides the server and the client with a private key that is specific to the server and client.

The three elements that make HMAC possible are:

  1. The message: this is the data that is being authenticated or verified to ensure it is stored and shared securely.
  2. Secret keys: this is used to create the HMAC value and is a specific value only known to the parties that are authorized to use it.
  3. Cryptographic hash function: the process of hashing involves turning input data (the message and the key) into a new output value (HMAC value). What makes this process important is that it safeguards the integrity of a message, as HMAC values can’t be reversed to gain access to the original message or key.

This means that HMAC is what’s known as a symmetric key algorithm, using the same secret key to both create and verify the HMAC value.

The goals of HMAC

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HMAC keeps messages safe, secure, and free from external interference.

When messages are transmitted, there is the potential for outside intruders to intercept and corrupt this data (often to gain unauthorized access to secure platforms). HMAC helps to prevent this by hashing messages and combining these with secret keys during transmission.

Once received, the other party can verify if the contents of this message are accurate by using the same secret key to digest and verify this message. Through the process of recomputing the hash using the same secret key, the receiver can spot any modifications that might have been made by attackers.

If the hash matches the transmitted HMAC value, it’s clear that the message wasn’t altered and tampered with during transmission. However, if things don’t match the receiver knows something has gone wrong (whether that was a transmission error or a hacker intercepting this message).

This can help to reduce the chance of hackers gaining access to secure systems, as receivers can reject messages that they believe have been tampered with during the transmission process.

Why HMAC is important

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You want to protect your data and ensure it doesn’t get interfered with. Plus, if your data has been interfered with, you want to ensure you can easily spot those changes, too. The HMAC process ensures that your data isn’t open to attacks and safeguards its integrity.

When the HMAC process is finished the message becomes permanently hashed, meaning it can only be accessed and unlocked with the right secret key. This process is a helpful way to lower the chance of security breaches, including message modification, replay attacks as well as man-in-the-middle attacks.

The other key benefits of using HMAC during your app development include:

  • Ensure safe communications: using HMAC to verify message authenticity can give you the confidence to know that your apps and services are sharing data securely. Plus, this approach can dramatically lower the chance of sensitive data being intercepted, too.
  • Boost compliance: if you need to remain compliant with standards (such as GDPR), using a cryptographic algorithm can help you remain compliant with these regulations and ensure your app only interacts with trusted services.
  • Easy integration: as a widely used algorithm, HMAC is supported by a range of programming languages and can easily integrate with your existing workflows.

The drawbacks of HMAC

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Although HMAC offers various benefits in protecting the integrity of data, like all things, it’s not without its drawbacks and limitations.

The biggest drawback is HMAC’s reliance on a secret key. If this key is shared with an unauthorized user, it can compromise the integrity of messages. This means it’s essential to have processes in place to securely store and manage any secret keys you’re using.

HMAC also has some limitations when it comes to the type of attacks it can protect against. While it does offer some protection for identifying and detecting replay attacks, it can’t stop them altogether.

In the case of denial-of-service attacks, social engineering attacks, and side-channel attacks, HMAC can only go as far as detecting message tampering. This means HMAC should be used alongside other protections and protocols to keep your app safe and secure.

Implementing HMAC

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There are three key sections to implementing HMAC:

  • Choose a hash function (such as SHA-256 or SHA-512) to compute the message.
  • Choose a secret key that is randomly generated, with the length dependent on the level of security your platform needs.
  • Combine the message and secret key using the hash function to create an HMAC value.

This HMAC value is what is transmitted and verified, using the same hash function. If the values match, the message is seen as authentic. If not, it’s clear the message has been tampered with.

Ultimately, HMAC provides a great layer of security for companies that have sensitive data that needs protecting. It’s an important measure to protect data integrity from attackers and offers a clear indication if data has been compromised.

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