For character strings, padding is with blanks; for bit strings, it is with zeros. 对于字符串,填充的是空格字符;对于位串,填充的是零。
Although the receiver should not tell the sender that the padding is not correct, it is meaningful that non-procession of a decrypted message ultimately leaks this bit of information. 尽管解密程序不该告诉调用方填充错误,但是提供一些解密过程中的信息还是有意义的。