On further review, no need to throw an exception. The same encryption/decryption method that works with xlsx works with xlsb. I added a unit test with test file to confirm this.
r1787846
Broke the build with the new unit test. :( The test file requires unlimited jce. I added an if clause that tests for unlimited JCE; if no unlimited JCE, skip the test. r1787890
Use org.junut.Assume.assumeTrue(condition) so that the test is marked as skipped rather than passed.
r1788133 Thank you, Javen.