What are the Default Cryptographic Settings for AES in Oracle JDK?

Oracle JDK Default Crypto Behavior for AES

When instantiating a SecretKeySpec object for AES and a Cipher instance using the string "AES," Java crypto exhibits certain default behaviors. Understanding these behaviors, particularly with regard to IV generation and encryption mode, is crucial for effective encryption and decryption.

IV Generation

In Java, the default IV (initialization vector) generation scheme for AES depends on the underlying implementation. For Oracle JDK 7, the default cipher for AES is AES/ECB/PKCS5Padding. This cipher does not utilize an IV, as it operates in Electronic Codebook (ECB) mode.

Encryption Mode

The encryption mode refers to the specific algorithm used to encrypt data. When only "AES" is specified, Java crypto defaults to using the ECB mode. In ECB mode, each block of plaintext is encrypted independently, which can introduce security vulnerabilities when dealing with large blocks of data.

For secure encryption, it is recommended to explicitly specify a more robust encryption mode, such as CBC (Cipher Block Chaining) or GCM (Galois/Counter Mode). These modes provide better security guarantees by chaining data blocks and using a random IV, respectively.

Here's an example of how to specify a different encryption mode:

<code class="java">// Choose AES with Cipher Block Chaining mode and PKCS5Padding
Cipher localCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");</code>

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