I encountered the following exception when deploying a JDBC configuration to Weblogic Server:
com.rsa.jsafe.JSAFE_PaddingException: Could not perform unpadding: invalid pad byte.
After some analysis this error occurs when you encrypted the password for the JDBC connection in another domain as where you deploy the JDBC configuration.
Conclusion: You should always encrypt on the same Domain as you deploy the configuration !
PS The password is encrypted within the password-encrypted element.