What Is Java\'s Default Crypto/AES Behavior Without Further Configuration?

Java's Default Crypto/AES Behavior Unraveled

When working with Java's Cryptography API, the behavior of the default settings for AES encryption can be a little enigmatic. Here's a deeper dive into what's going on:

Question: What is the default Java crypto behavior for the following:

<code class="java">SecretKeySpec localSecretKeySpec = new SecretKeySpec(arrayOfByte, "AES");
Cipher localCipher = Cipher.getInstance("AES");</code>

Specifically, how do these classes generate the Initialization Vector (IV) and what is the default encryption mode when "AES" is specified without further clarification?

Answer:

For Oracle JDK 7, the default cipher used for AES encryption is AES/ECB/PKCS5Padding. Surprisingly, this information is not explicitly stated in the Java Security documentation. Instead, it requires some hands-on testing to unravel:

<code class="java">Cipher cipher = Cipher.getInstance("AES");
System.out.println(cipher.getAlgorithm());
// Outputs: AES/ECB/PKCS5Padding</code>

In this default configuration:

• No IV generation occurs by default. This is because ECB mode (Electronic Codebook Mode) does not utilize an IV for encryption.
• The specified encryption mode is ECB (Electronic Codebook Mode), which processes each block of data independently without chaining dependencies.

It's important to note that while this default behavior may suffice for basic scenarios, it is generally not considered secure for most applications due to the lack of IV generation and the potential for data leakage in ECB mode. To address these security concerns, it is recommended to explicitly define the encryption mode and IV generation strategy that aligns with your specific requirements.

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