Update January 16, 2018: Oracle released Java 8 u162. In this version, the unlimited policy is enabled by default. You no longer need to install the policy file in the JRE or set the security property
When you use the Java Cryptography Extension (JCE), you may already know that the Java runtime out of the box enforces a limitation on specific key length parameters.
When you look at the following program that encrypts and decrypts a string with AES it works fine when you use a key length of 128 bits (
byte input = "My super secret text".getBytes(); SecureRandom random = SecureRandom.getInstanceStrong(); KeyGenerator keyGen = KeyGenerator.getInstance("AES"); keyGen.init(128, random); SecretKey key = keyGen.generateKey(); Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "SunJCE"); byte iv = new byte; random.nextBytes(iv); GCMParameterSpec spec = new GCMParameterSpec(128, iv); cipher.init(Cipher.ENCRYPT_MODE, key, spec); byte cipherText = cipher.doFinal(input); // Decrypt cipher.init(Cipher.DECRYPT_MODE, key, spec); byte plainText = cipher.doFinal(cipherText); System.out.println(new String(plainText));
But when you change the key length to 192 (
keyGen.init(192, random);) or 256 (
keyGen.init(256, random);) bits the java runtime throws an exception:
Exception in thread "main" java.security.InvalidKeyException: Illegal key size
To solve that you have to go to this website, download the Unlimited Strength Jurisdiction Policy Files, unzip it, go to the
<java-home>/lib/security directory, and replace the two files
US_export_policy.jar with the two files from the download.
With this change, you can now use AES with key sizes 192 and 256 without exception.
This behavior changed in the u151 and u152 version of Java 8. Since this version, it is no longer necessary to download the policy files from the Oracle website and install it. You can now set the unlimited policy directly in your application with this one-liner:
Make sure that this code runs before the JCE framework has been initialized.
Alternatively you can set the unlimited policy in the
<jre_home>/lib/security/java.security file without changing any application. Search for the line
#crypto.policy=unlimited and remove the
# character to uncomment it.
Since Java 9, the policy is set to unlimited by default, so you don't have to change anything or add any code to your program when you use the latest Java version.