What is HMAC MD5?

HMAC MD5 is a cryptographic hashing technique that combines the MD5 hash function with a secret key to create a unique digital signature of a message. While MD5 alone is not secure for hashing passwords or storing sensitive data, using it in HMAC form is still viable for message verification where speed is important, and moderate security is acceptable.

How Does HMAC MD5 Work?

HMAC MD5 works by applying the HMAC construction to the MD5 algorithm:

1. Normalize the Secret Key:

   
   

   • If longer than 64 bytes, hash it.

   • If shorter, pad it with zeros.

   
   

2. Prepare Inner and Outer Padding:

   
   

   • ipad = 0x36 repeated

   • opad = 0x5C repeated

   
   

3. Apply Two-Step Hashing:

   
   
   

   inner = MD5((key ⊕ ipad) || message)
   final = MD5((key ⊕ opad) || inner)

   
   The output is a 128-bit (32-character hexadecimal) digest.

   
   

Converting a String to a Byte Array

Before plugging your key or message into the HMAC MD5 process, you’ll first need to transform it into a byte array—since cryptographic functions munch on bytes, not text. One common way is to use UTF-8 encoding, which is supported in languages like Python (), Java (), and C# ().

For example, to convert a string key to bytes in C#:

csharp byte[] keyBytes = System.Text.Encoding.UTF8.GetBytes("your-secret-key");

This same approach applies to your message data. Be sure the byte arrays you generate correspond to the exact key and message you intend, as even small differences in encoding can alter the HMAC output.

Use This Tool With Other Qodex Utilities:

• Base64 Encoder – Convert HMAC MD5 output to base64 for headers or URLs

• URL Encoder – Encode signed query parameters safely

• MD5 Hash Generator – Compare simple MD5 vs HMAC MD5

• HMAC SHA-256 Generator – For enhanced security when needed

HMAC Algorithm Support in OpenEdge: Limitations and Alternatives

If you're working with OpenEdge and need HMAC support, there are a few caveats to keep in mind. Native, direct HMAC algorithm functions are not broadly available in all OpenEdge versions. Specifically, earlier releases do not offer built-in HMAC operations, and even newer iterations (from version 11 onward) only enable HMAC-style message digest calculations through the function—primarily for HMAC-SHA256.

Key points to consider:

• There is no general-purpose HMAC constructor for various algorithms like MD5 or SHA1; you're mainly limited to HMAC-SHA256.

• To generate HMAC digests in supported OpenEdge environments, use the function and refer to the product documentation for usage details.

• For unsupported versions or more flexible algorithm options (like HMAC MD5), you may need to rely on external libraries, call out to command-line utilities, or integrate with other languages via APIs.

  
  

When OpenEdge's own capabilities fall short, common workarounds include:

• Creating a wrapper function that invokes a scripting language (such as Python or Node.js) that handles the HMAC operation, then passing the result back into OpenEdge.

• Leveraging well-established tools like OpenSSL for command-line HMAC generation.

Always ensure your implementation aligns with your organization's security requirements, as workarounds can introduce their own risks and maintenance demands.

Practical Examples

Example 1: Signing a REST API Request

Message:

action=delete-user&id=9841

Secret Key:

mySecretKey

Generated HMAC MD5:

a192c2cf8c2068c9f58c26b2d80bd3c3

This hash can be included in headers for signature verification on the server.

Example 2: Protecting Form Submission Data

You can hash form data (like username/email) along with a shared secret to ensure no one tampers with it between client and server.

Example 3: File Integrity Check

Generate an HMAC MD5 of file content with a known key. If the file is changed in any way, the hash won’t match when revalidated.

Example 4: Calculating HMAC MD5 in .NET with System.Security.Cryptography

Need to generate an HMAC MD5 hash for a string or file in .NET? The class makes it straightforward. Here’s how you can approach either scenario:

HMAC MD5 for a String

1. Prepare your secret key
   Convert your key to a byte array using UTF-8 encoding.

2. Prepare your message
   Take the string you want to hash and encode it as bytes.

3. Compute the HMAC MD5 hash
   Create a new object with your key and call on your data.

4. Format the result
   Convert the resulting byte array to a hexadecimal string for easy comparison or storage.

   
   

HMAC MD5 for a File

If you're hashing file contents, simply read the file into a string (or byte array), encode it, and follow the same process.

Sample Implementation in ABL (OpenEdge) using .NET:

DEFINE VARIABLE oMac    AS System.Security.Cryptography.HMACMD5 NO-UNDO.
DEFINE VARIABLE oKey    AS System.Byte[]                        NO-UNDO.
DEFINE VARIABLE oData   AS System.Byte[]                        NO-UNDO.
DEFINE VARIABLE oHash   AS System.Byte[]                        NO-UNDO.
DEFINE VARIABLE cHex    AS CHARACTER                            NO-UNDO.
DEFINE VARIABLE lcFile  AS LONGCHAR                             NO-UNDO.

/* Convert the secret key to bytes */
oKey = System.Text.Encoding:UTF8:GetBytes("yourSecretKeyHere").

 /* Load the file contents into a LONGCHAR variable */
COPY-LOB FROM FILE "path\to\your\file.txt" TO lcFile.

/* Convert the file contents to bytes */
oData = System.Text.Encoding:UTF8:GetBytes(lcFile).

/* Create the HMACMD5 object and compute the hash */
oMac = NEW System.Security.Cryptography.HMACMD5(oKey).
oHash = oMac:ComputeHash(oData).

/* Convert the hash bytes to a hex string */
cHex = System.BitConverter:ToString(oHash).
cHex = REPLACE(cHex, "-", ""). /* Removes dashes for a clean hex digest */

/* Optionally, create a GUID from the hash bytes if needed */

This process gives you a 32-character hexadecimal HMAC MD5 that can be used to verify data integrity or secure API communication.

Example 5: Generating HMAC MD5 in ABL (OpenEdge)

Need to sign your data with HMAC MD5 in an OpenEdge/ABL environment? Here’s a practical outline to create and verify an HMAC MD5 signature using .NET classes directly within your ABL code.

How it works:

1. Prepare Your Key and Data
   Convert your secret key and the data you want to hash into byte arrays using UTF-8 encoding.

2. Initialize HMAC MD5 Algorithm
   Use the System.Security.Cryptography.HMACMD5 .NET class, supplying your secret key.

3. Compute the Hash
   Feed your data into the hash algorithm to obtain the HMAC MD5 digest as a byte array.

4. Format the Output
   Convert the hash bytes to a hexadecimal string—remove any separator characters to match common API or DB formats. You can also convert directly to a GUID if needed for database storage or cross-system compatibility.

Sample Workflow:

• Encode your secret, e.g.,
  oKey = System.Text.Encoding:UTF8:GetBytes("YourSuperSecretKey").

• Encode your message (from a file or string).

• Create a new HMAC MD5 instance with your key.

• Compute the hash from the data bytes.

• Convert the resulting hash bytes to a hex string (and strip out dash characters if present).

• Optionally, instantiate a GUID from the hash bytes to use as a unique identifier.

This approach is especially useful for tasks like file integrity checks, tamper-proof signatures, and database row verification. HMAC MD5 is natively supported in .NET, making it a convenient option inside ABL environments that interoperate with .NET assemblies.

Converting HMAC MD5 to a GUID

In some applications, you may want to store your HMAC MD5 hash as a GUID (Globally Unique Identifier) in your database for consistency or compatibility—especially with systems or ORMs that expect a GUID column. Because both an MD5 hash and a GUID are 128 bits in size, this conversion is straightforward.

Here's how it works:

• Take the 16-byte raw output of your HMAC MD5 (not the hex string!)

• Use those 16 bytes directly to construct a GUID/UUID object

• Store this GUID in your database

Most programming languages and database libraries (for example, .NET’s System.Guid or Python’s uuid.UUID) allow you to create a GUID/UUID from a byte array. Just be aware: doing this means your "GUID" won’t follow the typical UUID generation patterns, but it will be a valid 128-bit value suitable for storage and retrieval.

Sample Code – HMAC MD5 in Python

import hmac
import hashlib

def hmac_md5(key, message):
    return hmac.new(key.encode(), message.encode(), hashlib.md5).hexdigest()

print(hmac_md5("mySecretKey", "action=delete-user&id=9841"))

This simple function demonstrates how to compute an HMAC MD5 hash in Python—pass in your secret key and message, and it returns the signature as a hexadecimal string.

Bonus: HMAC MD5 in ABL (OpenEdge Progress)

For those working in enterprise environments or dealing with legacy applications, you might encounter ABL (Advanced Business Language). Here’s how you can generate an HMAC MD5 of a file’s contents using ABL and .NET integrations:

DEFINE VARIABLE oMac        AS System.Security.Cryptography.HMACMD5 NO-UNDO.
DEFINE VARIABLE cGuid       AS System.Guid                          NO-UNDO.
DEFINE VARIABLE oKey        AS "System.Byte[]"                      NO-UNDO.
DEFINE VARIABLE oData       AS "System.Byte[]"                      NO-UNDO.
DEFINE VARIABLE oHashBytes  AS "System.Byte[]"                      NO-UNDO.
DEFINE VARIABLE cHex        AS CHARACTER                            NO-UNDO.
DEFINE VARIABLE lcFile      AS LONGCHAR                             NO-UNDO.

/* Convert secret key string to bytes */
oKey = System.Text.Encoding:UTF8:GetBytes(
    "abcedfghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ123456789012345678"
).

/* Load file contents into LONGCHAR */
COPY-LOB FROM FILE "your-file-path.txt" TO lcFile.

/* Convert file content to bytes */
oData = System.Text.Encoding:UTF8:GetBytes(lcFile).

/* Create HMAC-MD5 Algorithm */
oMac = NEW System.Security.Cryptography.HMACMD5(oKey).

/* Compute hash */
oHashBytes = oMac:ComputeHash(oData).

/* Convert to HEX string */
cHex = System.BitConverter:ToString(oHashBytes).
cHex = REPLACE(cHex, "-", ""). /* Remove dashes from hex string */

/* Optionally, convert to GUID for database storage */
cGuid = NEW System.Guid(oHashBytes)

Tip: In this example, replace with the actual path to your file. This script loads the file, computes the HMAC MD5, and outputs a hexadecimal digest—exactly what you’d use for integrity checks or digital signatures.

Whether you’re working in Python for API requests or in ABL to validate files, these code samples show how HMAC MD5 can be implemented across different technologies.

Why Use HMAC MD5?

Pro Tips

• Avoid using HMAC MD5 for password storage; use it only for integrity verification.

• Combine it with Base64 Encoder to transmit hashes in JSON or URLs.

• For more secure applications, consider HMAC SHA-1 or HMAC SHA-256.

• MD5 produces a 32-character digest, so always validate the length during implementation.

• Always keep your secret key securely stored (e.g., in environment variables, not front-end code).