I prefer generic exceptions for the following reasons:
https://www.owasp.org/index.php/Error_Handling
https://www.owasp.org/index.php/Top_10_2007-A6
http://cwe.mitre.org/data/definitions/209.html
http://stackoverflow.com/questions/14922130/which-error-message-is-better-when-users-entered-a-wrong-password

Is "The key could not be decrypted" insufficient?