Resolving the Python cryptography Error: 'Expected instance of hashes.HashAlgorithm'

Learn how to fix the `Unexpected Error Derived Key` issue in Python's cryptography library when updating from Fedora 38 to Fedora 39.
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Resolving the Python cryptography Error: "Expected instance of hashes.HashAlgorithm"

When dealing with encryption in Python, it's not uncommon to encounter unexpected errors, especially after updates to libraries or operating systems. Recently, users faced a frustrating issue upgrading from Fedora 38 to Fedora 39 with the cryptography library, specifically with the error message: "Expected instance of hashes.HashAlgorithm."

In this guide, we'll dive into the cause of this error and explore a straightforward solution to get your code back up and running.

Understanding the Problem

After upgrading to Fedora 39, many users reported that existing encryption code suddenly began failing. The error occurs within the authentication process when trying to derive keys. Below is a sample of the error message:

[[See Video to Reveal this Text or Code Snippet]]

An Example Code Snippet

Here's a simplified version of the code that exemplifies the issue:

[[See Video to Reveal this Text or Code Snippet]]

In this case, hashes.SHA256 is passed incorrectly, which leads to the error.

Solution: How to Fix the Error

To resolve this issue, you need to provide an instance of hashes.HashAlgorithm, which can be achieved by changing the way you instantiate the algorithm. Follow the steps below:

Step 1: Correct the Instantiation

Update the line where you create the PBKDF2HMAC object as follows:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Explanation of the Change

Old Approach: hashes.SHA256 returns a class that describes the hash, but not an instance you can work with.

New Approach: By using hashes.SHA256() you are calling the class constructor to create an instance of the hashing algorithm, which is what the PBKDF2HMAC function requires.

Updated Example Code

Here’s an updated snippet incorporating the fix:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Upgrading to new software versions may often lead to challenges with existing code. In this instance, updating to Fedora 39 highlighted a crucial requirement in the instantiation of hash algorithms in the cryptography library.

By ensuring you instantiate the hash algorithm correctly, you can continue using this essential library without interruptions. Always remember to check the library documentation for any breaking changes or updates when performing upgrades.

Feel free to leave your comments or questions below, and happy coding!