Скачать или смотреть AES Decryption Issues: Solving the CFB Mode Error with No Padding

Struggling with AES encryption and decryption in CFB mode? Discover why your code isn't working and how to fix it efficiently!
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This video is based on the question https://stackoverflow.com/q/70035143/ asked by the user 'Palak' ( https://stackoverflow.com/u/4078362/ ) and on the answer https://stackoverflow.com/a/70035470/ provided by the user 'gthanop' ( https://stackoverflow.com/u/6746785/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding AES Encryption and Decryption Issues

When working with symmetric encryption using the Advanced Encryption Standard (AES), you may encounter specific challenges, particularly when using modes such as CFB (Cipher Feedback) without padding. One common issue is that the encryption and decryption processes do not work correctly, which can lead to confusion and frustration.

In this guide, we'll dissect common problems faced during AES encryption and decryption in CFB mode, specifically when you find that your decryption isn't returning the original data.

The Problem: Encryption to Decryption Doesn't Work

Let's explore the initial concern presented: the encryption and decryption methods were implemented but returned incorrect results. The provided code attempts to encrypt a value and then decrypt it, expecting to retrieve the original plaintext. However, our encryption and decryption operations are not aligned because new keys are being generated for each process.

Here’s a simplified outline of your original method's key issues:

New Secret Key Created for Each Operation: The encryption and decryption processes require the same symmetric key; however, the key is generated anew in both functions.

Constant IV (Initialization Vector): While using a constant IV for AES is technically possible, it typically leads to reduced security and should be handled more carefully in production environments.

The Solution: Proper Key and IV Handling

To fix the problem, we must ensure that the same symmetric key and IV are used for both encryption and decryption. This means generating them once and reusing them in both processes.

Revised Code Implementation

Here’s the updated code that resolves the issue:

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

Breakdown of the Code

Secret Key Generation:

The key is generated once using a KeyGenerator, which ensures consistency across encryption and decryption.

Initialization Vector (IV):

The IV is also created once and passed to both encrypt and decrypt methods. This maintains the security integrity of the operation.

Functionality:

The encrypt method takes the secret key and IV to process the value.

The decrypt method does precisely the opposite, ensuring that the operations are perfectly mirrored.

Conclusion

In summary, when working with AES encryption in CFB mode, it’s crucial to use the same symmetric key and IV for both encryption and decryption processes. By ensuring these elements are consistent, you can effectively resolve issues where the decryption does not produce the original plaintext.

Always remember: consistency in key and IV usage is paramount in symmetric encryption algorithms.

By following the revised implementation, you can successfully perform AES encryption and decryption, paving the way for more secure applications.