InvalidKeyException Illegal key size

This error means that your Java virtual machine uses a policy that only allows restricted cryptography key sizes due to US export laws.

Java 9 and higher

The Unlimited Strength Jurisdiction Policy Files are included with Java 9 and used by default (see Security Updates in the Java 9 Migration Guide).

If you get this error with Java 9, it might mean the policy configuration has been changed to a more restrictive policy (limited), see the instructions from the migration guide:

JCE Jurisdiction Policy File Default is Unlimited

If your application previously required the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files, then you no longer need to download or install them. They are included in the JDK and are activated by default.

If your country or usage requires a more restrictive policy, the limited Java cryptographic policy files are still available.

If you have requirements that are not met by either of the policy files provided by default, then you can customize these policy files to meet your needs.

See the crypto.policy Security property in the <java-home>/conf/security/java.security file, or Cryptographic Strength Configuration in the Java Platform, Standard Edition Security Developer's Guide.

Java 8 and earlier

Java 8 Update 161 and higher

Starting with Java 8 Update 161, Java 8 defaults to the Unlimited Strength Jurisdiction Policy. If you receive this error, it could indicate the configuration has been changed to limited. See instructions in the next section on Java 8 Update 151, or the previous section on Java 9, for changing this back to unlimited.

Java 8 Update 151 and higher

Starting with Java 8 Update 151, the Unlimited Strength Jurisdiction Policy is included with Java 8 but not used by default. To enable it, you need to edit the java.security file in <java_home>/jre/lib/security (for JDK) or <java_home>/lib/security (for JRE). Uncomment (or include) the line

crypto.policy=unlimited

Make sure you edit the file using an editor run as administrator.

The policy change only takes effect after restarting the JVM (this is especially important for long-running server processes like Tomcat).

For backwards compatibility, installing the policy files as documented in the next section will still work as well.

Before Java 8 Update 151

For Java 8 Update 144 and earlier, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files (available at Oracle).

To install these files (from the README.txt in the download):

1. Download the unlimited strength JCE policy files.

2. Uncompress and extract the downloaded file.

   This will create a subdirectory called jce. This directory contains the following files:

   README.txt                   This file
   local_policy.jar             Unlimited strength local policy file
   US_export_policy.jar         Unlimited strength US export policy file
   

3. Install the unlimited strength policy JAR files.

   In case you later decide to revert to the original "strong" but limited policy versions, first make a copy of the original JCE policy files (US_export_policy.jar and local_policy.jar). Then replace the strong policy files with the unlimited strength versions extracted in the previous step.

   The standard place for JCE jurisdiction policy JAR files is:

   <java-home>/lib/security           [Unix]
   <java-home>\lib\security           [Windows]
   

Note for the JDK it is in jre/lib/security.

The new policy file only takes effect after restarting the JVM (this is especially important for long-running server processes like Tomcat).

I had a similar problem, but in my case, there was a path error.

JAVA_HOME was jdk1.6.0_18, so I put the two jars into jdk1.6.0_18/lib/security, but within jdk1.6.0_18 is the jre directory. Both files should have been put in jdk1.6.0_18/jre/lib/security.

In addition to installing policy files, also make sure that CUSTOMLONGSECRETKEY...getBytes() does indeed produce 32 bytes array. I would use CUSTOMLONGSECRETKEY.getBytes(some encoding) and get first 32 bytes from that. Better yet, use whole secret key to derive keys for AES with the size that you need.