密钥仍存在于密码流中？使用外部序列号的优势？

我已经阅读了Catalin Baetoniu撰写的“使用Dallas Semiconductos / Maxim DS2432安全EEPROM的FPGA IFF复制保护”，我有两个问题：
1）据我所知，为了实现本文档中描述的系统，当配置FPGA时，密钥仍然出现在从闪存到FPGA的线路上。
我对么？
2）所描述的系统提到使用外部设备的唯一序列号作为HMAC-SHA1的密钥的一部分（以及密钥和随机数）。
包含外部设备唯一的序列号（在这种情况下必须由FPGA读取）的优点是什么，而不仅仅是使用HMAC的随机数和密钥？
提前谢谢了。
回复可能引发进一步的问题！
最好的祝福，
奥利



以下为原文

I've read through "FPGA IFF Copy Protection Using Dallas Semiconductos/Maxim DS2432 Secure EEPROMs" by Catalin Baetoniu, and I have two questions:

1) As far as I can see, to implement the system described in this document, the secret key still appears on the wire from the flash memory to the FPGA when the FPGA is configured.  Am I correct?

2) The system described mentions using the unique Serial-Number of the external device as part of the key for the HMAC-SHA1 (along with the Secret Key and the Random Number).  What is the advantage of including the external device's unique Serial-Number (which has to be read by the FPGA in this case), over just using the Random Number and Secret Key for the HMAC?

Many thanks in advance.  Responses may trigger further questions!

Best regards,

Ollie