Скачать или смотреть How to Perform AES-256 Encryption in Java with Correct IV Handling

Learn how to properly implement `AES-256 encryption` in Java, ensuring that your IV is set up correctly for consistent results with PHP.
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This video is based on the question https://stackoverflow.com/q/67429570/ asked by the user 'Pim H' ( https://stackoverflow.com/u/10481878/ ) and on the answer https://stackoverflow.com/a/67429972/ provided by the user 'Topaco' ( https://stackoverflow.com/u/9014097/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

In today's digital world, data security is paramount. Encryption often plays a crucial role in protecting sensitive information. However, when transitioning code from one language to another, such as from PHP to Java, discrepancies can arise, leading to different encryption results. In this post, we will address a common question related to performing AES-256 encryption in Java, following a PHP example. Specifically, we will explore why the Java implementation returns a different result than the PHP code and how to fix it.

Understanding the Problem

In the provided PHP code, the openssl_encrypt function successfully encrypts a string using AES-256 in OFB (Output Feedback) mode. The PHP implementation creates a secret key and an initialization vector (IV) effectively, but the translation of this code to Java leads to unexpected results.

Here’s a simplified summary of the PHP encryption flow:

A secret key is defined and hashed using SHA-256.

An IV is generated from the key.

The openssl_encrypt function encrypts the input data.

The result is encoded in Base64.

Despite following a similar logic in Java, the output is not matching the expected result from the PHP code.

Debugging the Java Code

Key Issues Identified

Incorrect IV Generation:
In Java, the line keyHashed.toString().getBytes() is mistakenly used to derive the IV. This does not yield the expected result from the hashed key but rather returns a string representation of the object, resulting in an incorrect IV.

Security Concerns:
The approach taken to generate the IV is insecure. By using the same password, you would generate the same key/IV pair, which compromises security. It is vital to derive the key securely, using a reliable key derivation function along with a random salt.

Missing Character Encoding:
Encoding and decoding without specifying the character set may lead to cross-platform inconsistencies. Always specify the encoding, such as StandardCharsets.UTF_8, to maintain compatibility across platforms.

Solution Steps

To correctly implement AES-256 encryption in Java that matches the output of the PHP version, follow these steps:

Correct the IV Generation

Replace:

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

With:

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

Use Secure Key Derivation

Consider using functions like PBKDF2, bcrypt, or Argon2 to derive the key securely. Randomly generate a salt and store it alongside the cipher text.

Specify Character Encoding

Ensure that encoding is explicitly defined when converting strings:

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

Conclusion

When performing encryption tasks and translating from one programming language to another, paying attention to the implementation details is crucial. By correctly generating the IV, ensuring secure key derivation, and specifying character encoding, you can achieve consistent and secure results between PHP and Java.

With these changes, you should now achieve matching encrypted outputs from both your PHP and Java implementations. Always prioritize security and test your changes to ensure that they meet the required standards.

Remember, encryption is not just about writing code; it’s about ensuring your data remains safe in an ever-evolving landscape of threats!