byte[] plainData = cipher.doFinal(data, KerberosConstants.CHECKSUM_SIZE, plainDataLength);

        byte[] plainDataChecksum = getHmac(plainData, codeHmac);
        if ( plainDataChecksum.length >= KerberosConstants.CHECKSUM_SIZE )
            for ( int i = 0; i < KerberosConstants.CHECKSUM_SIZE; i++ )
                if ( plainDataChecksum[ i ] != data[ i ] )
                    throw new GeneralSecurityException("Checksum failed while decrypting.");