int i;
        int len;
        if (buf.length < TOK_ID_SIZE + MECH_OID_LEN_SIZE) {
            throw new IllegalArgumentException();
        }
        // TOK_ID
        for (i = 0; i < TOK_ID.length; i++) {
            if (TOK_ID[i] != buf[i]) {
                throw new IllegalArgumentException();
            }
        }
        // MECH_OID_LEN
        len = 0xff00 & buf[i] << 8;
        i++;

        int len = 2 + 2 + der.length + 4 + nb.length;
        byte[] out = new byte[len];
        int i = 0;
        out[i++] = 0x04; // TOK_ID[0]
        out[i++] = 0x01; // TOK_ID[1]
        out[i++] = (byte) ((der.length >> 8) & 0xFF);
        out[i++] = (byte) (der.length & 0xFF);
        System.arraycopy(der, 0, out, i, der.length);
        i += der.length;
        out[i++] = (byte) ((nb.length >> 24) & 0xFF);