What are the default settings for AES encryption in Java\'s cryptography classes?

Java Cryptography for AES

This question explores the default behavior of Java's cryptography classes, specifically for the Advanced Encryption Standard (AES).

Default Cipher for AES

As per the provided information, if you instantiate a SecretKeySpec object using the AES algorithm and then use it to create a Cipher instance without specifying a mode or initialization vector (IV), the default settings will be used.

For Oracle JDK 7, the default cipher for AES is AES/ECB/PKCS5Padding. This mode is Electronic Codebook (ECB), which encrypts each block of the plaintext independently, making it vulnerable to certain attacks. The padding specification is PKCS #5, which is a commonly used standard for padding plaintext data.

Generating the IV

In this case, you have not specified an IV, so the Java cryptography API will generate one automatically. For AES, the default IV size is 16 bytes. The specific mechanism used to generate the IV is not publicly documented but is likely to be based on a pseudorandom number generator (PRNG).

Importance of Using Strong Settings

It's important to note that the default settings in Java cryptography are not always considered strong or secure. For example, ECB mode is not recommended for use due to its susceptibility to certain attacks. It's best practice to specify explicit settings for both the encryption mode and the IV to ensure a secure and robust implementation.

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