What Is HMAC And How Does It Secure File Transfers? | JSCAPE (2024)

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HMAC, or Keyed-Hashing for Message Authentication, enhances secure file transfers by ensuring data integrity and message authenticity via cryptographic hash functions and a shared secret key. In protocols like FTPS, SFTP, and HTTPS, HMAC checks prevent tampered data and authenticate the message source.

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What Is HMAC And How Does It Secure File Transfers? | JSCAPE (1)

An Overview of HMAC

Data integrity checks are vital to secure communications. They enable communicating parties to verify the integrity and authenticity of the messages they receive. In secure file transfer protocols like FTPS, SFTP, and HTTPS, data integrity/message authentication is usually achieved through a mechanism known as HMAC (Hash-based message authentication code). In this post, we explain what HMAC is, its basic inner workings, and how it secures data transfers.

Importance Of Data Integrity Checks In Secure File Transfers

Business decisions and processes are highly dependent on accurate and reliable data. If data gets tampered with and these changes go unnoticed, it could affect decisions and processes down the line. So if your data has to be transmitted over a network, especially one as perilous as the Internet, you must take precautionary measures to preserve its integrity or at least know if it has been hacked or altered.

This is precisely the reason why secure file transfer protocols like FTPS, SFTP, and HTTPS are equipped with mechanisms for preventing threats to data integrity. The most commonly used mechanism today is HMAC. Interested in seeing how HMAC can enhance the security of your file transfers? Book a demo with us today and discover the robust security features our solutions offer to protect your data in transit.

What Is HMAC?

HMAC stands for Keyed-Hashing for Message Authentication. It's a message authentication code obtained by running a cryptographic hash function (like MD5, SHA1, and SHA256) over the data (to be authenticated) and a shared secret key. HMAC is specified in RFC 2104.

HMACs are almost similar to digital signatures. They both enforce integrity and authenticity. They both use cryptography keys. And they both employ hash functions. The main difference is that digital signatures use asymmetric keys, while HMACs use symmetric keys (no public key).


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How HMAC Works

To understand how HMAC works, let's first examine how a hashed function (on its own) could conduct a data integrity check on a file transfer. Let's say a client application downloads a file from a remote server. It's assumed that the client and server have already agreed on a common hash function, for example, SHA2.

Before the server sends out the file, it first obtains a hash of that file using the SHA2 hash function. It then sends that hash (ex., a message digest) along with the file itself. Upon receiving the two items (ex., the downloaded file, and the hash), the client obtains the SHA2 hash of the downloaded file and then compares it with the downloaded hash. If the two matches, then that would mean the file was not tampered with.

What Is HMAC And How Does It Secure File Transfers? | JSCAPE (2)

If an attacker manages to intercept the downloaded file, alter the file's contents, and then forward the altered file to the recipient, that malicious act won't go unnoticed. That's because once the client runs the tampered file through the agreed hash algorithm, the resulting hash won't match the downloaded hash. This will let the receiver know the file was tampered with during transmission.

So a hash function should protect your files, right? Not so fast. While a hash function can establish data integrity, it can't establish authenticity. How would the client know the message it received came from a legitimate source?

That's why secure file transfer protocols like FTPS, SFTP, and HTTPS use HMACs instead of just hash functions. When two parties exchange messages through those secure file transfer protocols, those messages will be accompanied by HMACs instead of plain hashes. An HMAC employs both a hash function and a shared secret key.

A shared secret key provides exchanging parties a way to establish the authenticity of the message. That is, it provides the two parties a way of verifying whether both the message and MAC (more specifically, an HMAC) they receive really came from the party they're supposed to be transacting with.

The secret key enables this capability because it's generated during key exchange, a preliminary process that requires the participation of the two parties. Only those two parties participating in the key exchange would know the shared secret key. In turn, they would be the only ones who would be able to arrive at the same result if they computed the message's corresponding MAC using the shared secret key.

Why Is HMAC Suitable For File Transfers?

Aside from its ability to enable data integrity and message authentication, another reason why HMAC is an excellent file transfer data integrity-checking mechanism is its efficiency. As discussed in the article Understanding Hashing, hash functions can take a message of arbitrary length and transform it into a fixed-length digest. That means that even if you have relatively long messages, their corresponding message digests can remain short, allowing you to maximize bandwidth.

Choosing An HMAC Function

Because an HMAC's properties (especially its crypto strength) is highly dependent on its underlying hash function, a particular HMAC is usually identified based on that hash function. So we have HMAC algorithms that go by the names of HMAC-MD5, HMAC-SHA1, or HMAC-SHA256.

You've probably heard about the collision-related vulnerabilities of MD5. It's worth noting that HMAC-MD5, in spite of its underlying MD5 hash function, isn't as affected by those vulnerabilities. Regardless, SHA-1 is still cryptographically stronger than MD5, and SHA-2 (and its different forms, like SHA-224, SHA-256, and SHA-512) is likewise cryptographically stronger than SHA1, so you will want to take that into consideration.

So which HMAC should you use? You would normally choose an HMAC based on its underlying hash function. So, for example, you would want to use HMAC-MD5 if performance is more critical to you than security. On the other hand, if security is more critical, then you might want to use HMAC-SHA256 instead.

Get Your Free Trial

Would you like to try this yourself? JSCAPE MFT Server is platform-agnostic and can be installed on Microsoft Windows, Linux, Mac OS X and Solaris, and can handle any file transfer protocol and multiple protocols from a single server.

Additionally, JSCAPE enables you to handle any file type, including batch files and XML.

Get started with a free trial of JSCAPE MFT Server now.

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FAQs

What Is HMAC And How Does It Secure File Transfers? | JSCAPE? ›

HMAC, or Keyed-Hashing for Message Authentication

Message Authentication
In cryptography, a message authentication code (MAC), sometimes known as an authentication tag, is a short piece of information used for authenticating and integrity-checking a message. In other words, to confirm that the message came from the stated sender (its authenticity) and has not been changed (its integrity).
https://en.wikipedia.org › wiki › Message_authentication_code
, enhances secure file transfers by ensuring data integrity and message authenticity via cryptographic hash functions and a shared secret key. In protocols like FTPS, SFTP, and HTTPS, HMAC checks prevent tampered data and authenticate the message source.

What is HMAC and how does it work? ›

Hash-based message authentication code (or HMAC) is a cryptographic authentication technique that uses a hash function and a secret key. With HMAC, you can achieve authentication and verify that data is correct and authentic with shared secrets, as opposed to approaches that use signatures and asymmetric cryptography.

Why is HMAC more secure? ›

The strength of HMAC lies in its combination of both a secret key and a hash function. The secret key adds a layer of security by ensuring that only those with the key can generate or verify an HMAC. This aspect is particularly important in scenarios where confidentiality and data integrity are critical.

What is the HMAC of a file? ›

In cryptography, an HMAC (sometimes expanded as either keyed-hash message authentication code or hash-based message authentication code) is a specific type of message authentication code (MAC) involving a cryptographic hash function and a secret cryptographic key.

What is the difference between HMAC and SSL? ›

SSL/TLS provides end-to-end encryption and server authentication, while HMAC ensures message integrity and authenticity at the application level. Together, they form a robust security solution for your APIs.

What are the disadvantages of HMAC? ›

The drawbacks of HMAC

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.

When would you use HMAC? ›

When two parties exchange messages through those secure file transfer protocols, those messages will be accompanied by HMACs instead of plain hashes. An HMAC employs both a hash function and a shared secret key. A shared secret key provides exchanging parties a way to establish the authenticity of the message.

How is HMAC used in TLS? ›

HMAC is used in the TLS handshake, particularly in the “Finished” messages, where a MAC of the entire handshake up to that point is sent. HMAC is suitable for TLS for its many advantages: Flexibility: HMAC can work with a variety of hash functions such as SHA-256 or SHA-3.

What is the difference between SHA-256 and HMAC? ›

HMAC stands for "Hash-based Message Authentication Code," and SHA-256 refers to the Secure Hash Algorithm 256-bit variant. HMAC-SHA-256 combines the strength of SHA-256's cryptographic hashing with HMAC's ability to authenticate the integrity and source of a message.

What is the best practice for HMAC? ›

3 Best practices for HMAC

To use HMAC effectively and securely, it's recommended to use a strong hash function, such as SHA-256, SHA-384, or SHA-512. A secure key should be generated randomly, stored securely, and rotated periodically. The key should be long enough to prevent brute-force attacks.

Can you decode HMAC? ›

You can't decode it as it's a one way encryption. To validate you need to recreate the the HMAC_SHA256 on your side from the data that has been passed and a shared secret key. You then compare your calculated value to one provided and if they match you know the data hasn't been tampered with.

Is HMAC better than MAC? ›

The HMAC construction enhances the security of MACs by incorporating additional steps in the computation of the tag. It provides resistance against certain types of attacks and offers a higher level of security assurance compared to traditional MAC algorithms.

What is the security strength of HMAC? ›

The security strength of the HMAC algorithm4 is the minimum of the security strength of K and the value of 2L (i.e., security strength = min(security strength of K, 2L)). For example, if the security strength of K is 128 bits, and SHA-1 is used, then the security strength of the HMAC algorithm is 128 bits.

Why is HMAC more secure than hashing? ›

A hash lets you verify only the authenticity of the data (i,. e., that the data you received is what was originally sent). An HMAC lets you verify both the authenticity and the originator of the data.

What is HMAC for dummies? ›

HMAC (Hash-Based Message Authentication Code) is a cryptographic technique that ensures data integrity and authenticity using a hash function and a secret key. Unlike approaches based on signatures and asymmetric cryptography. Checking data integrity is necessary for the parties involved in communication.

Why does HMAC use two keys? ›

Cryptographic keys.

An encryption algorithm alters data, and a recipient needs a specific code (or key) to make it readable once more. HMAC relies on two sets of keys. One is public, and one is private.

What is the difference between sha256 and HMAC? ›

HMAC stands for "Hash-based Message Authentication Code," and SHA-256 refers to the Secure Hash Algorithm 256-bit variant. HMAC-SHA-256 combines the strength of SHA-256's cryptographic hashing with HMAC's ability to authenticate the integrity and source of a message.

What is the difference between HMAC and hashing? ›

They are message encryption, message authentication code, and hash functions. The major difference between MAC and hash (HMAC here) is the dependence of a key. In HMAC we have to apply the hash function along with a key on the plain text. The hash function will be applied to the plain text message.

What is the difference between a MAC and an HMAC? ›

A message authentication code (MAC) is similar to a cryptographic hash, except that it is based on a secret key. When secret key information is included with the data that is processed by a cryptographic hash function, the resulting hash is known as an HMAC.

What is the difference between HMAC and AES? ›

AES encryption is used to encrypt data while HMAC is used to authenticate data. Both operations use the same symmetric key, but they use the key in different ways. AES encryption uses the key to encrypt the data, while HMAC uses the key to generate a message authentication code (MAC) for the data.

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