Intel® Software Guard Extensions (Intel® SGX)
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Problem with 'sgx_ra_msg3_t' mac field

Fabio_S_2
Beginner
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On the latest version of developer reference (2.8 - p368), the 'mac' field is described as:

"AES-CMAC of g_a, ps_sec_prop, GID, and quote[], using SMK."

But the CMAC function returns a different value. If I remove the GID, the CMAC function result matches the mac field value. Someone else had the same problem?

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JesusG_Intel
Moderator
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Hello Fabio, you are correct. The developer reference has a typo, it should not include the GID in the mac calculation. It should read: "AES-CMAC of g_a, ps_sec_prop, and quote[], using SMK.” The correct CMAC calculation for msg3 can be seen in Figure 3, which shows the full Remote Attestation Flow, on this page.

We will fix this error in the next revision of the document. Thank you for pointing it out.

Regards,

Jesus

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JesusG_Intel
Moderator
372 Views

Hello Fabio, you are correct. The developer reference has a typo, it should not include the GID in the mac calculation. It should read: "AES-CMAC of g_a, ps_sec_prop, and quote[], using SMK.” The correct CMAC calculation for msg3 can be seen in Figure 3, which shows the full Remote Attestation Flow, on this page.

We will fix this error in the next revision of the document. Thank you for pointing it out.

Regards,

Jesus

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