Getting javax.crypto.IllegalBlockSizeException: Input length must be multiple of 16 when decrypting with padded cipher?

Works on my machine. Does it help if you use `UNICODE_FORMAT' in every instance where you transform bytes to Strings and vice versa? This line could be a problem:

byte[] encValue = c.doFinal(valueToEnc.getBytes()); 

should be

byte[] encValue = c.doFinal(valueToEnc.getBytes(UNICODE_FORMAT));

Anyway, if you use "AES" as the algorithm and you use the JCE, the algorithm actually being used will be "AES/ECB/PKCS5Padding". Unless you are 100% sure about what you are doing, ECB shouldn't be used for anything. I'd recommend to always specify the algorithm explicitly in order to avoid such confusion. "AES/CBC/PKCS5Padding" would be a good choice. But watch out, with any reasonable algorithm you will also have to provide and manage an IV.

Using an ECB cipher is even less desirable in the context of encrypting passwords, which is what you seem to be doing with your encryption if I interpret your example correctly. You should use password-based encryption as specified in PKCS#5 for that purpose, in Java this is provided for you in SecretKeyFactory. Be sure to use "PBKDF2WithHmacSHA1" with a high enough iteration count (anything ranging from ~ 5-20 000, depends on your target machine) for using passwords to derive symmetric keys from them.

The same technique can be used if it is actually password storage instead of password encryption what you are trying to achieve.