security - What value for length field for Freescale PowerPC Security Engine 2.0, when using Link Tables?

Question

I am working on the code to use the security engine of my MPC83XX with Openssl. I can already encrypt/decrypt AES up to 64KByte of data. The problem comes with data greater than 64KByte since the maximum value of the length-bits is 65535.

I can assume the data is always in one piece on the Ram. So now I am collecting all the data in a Link Table and use the pointer to the table instead of the pointer to the data and set the J bit to 1. Now I am not sure what a value I should use for the length-bits since 0 would mean the Dword will be ignored. The real length of the data is too also big for 16 bit.

http://cache.freescale.com/files/32bit/doc/app_note/AN2755.pdf?fpsp=1 Possible Informations can be found in Chapter 8.

Answer 1

您将 LENGTH 设置为数据的长度。见第 19 页：

对于链接表或链接表链访问的任何数据宗地序列，宗地的组合长度（它们的 LENGTH 和/或 EXTENT 字段的总和）必须等于链接表内存段的组合长度（SEGLEN 字段） . 否则，通道会在通道指针状态寄存器中设置相应的错误位...

我不确定您使用的是什么模式（并且文档似乎不必要地令人困惑！）但是对于通常的密码模式（CBC/CTR/CFB/OFB），通常的方法是简单地链接 AES 调用，重用相同的上下文. 您可以通过简单地将“Pointer Dword1”和“Pointer Dword5”设置为相同的东西来做到这一点。但是，文档很少；我不知道它从哪里得到静脉注射。