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TD0086:  DisplayPort to HDMI Conversion Functionality

Publication Date
2016.03.10

Protection Profiles
PP_PSS_V3.0

Other References
FDP_IFF.1.5(2), Rule 10

Issue Description

FDP_IFF.1.5(2), Rule 10; Section 4.2.13, Test 4.4, Part 2, Steps 17-32.

The AUX channel is a critical component of the DisplayPort video protocol and video cannot be transmitted unless the AUX channel is functional.  Due to security reasons, the PSS PPv3.0 limits the AUX traffic to certain types (i.e. link negotiation, link training, and extended display identification data [EDID] reading). 

The test steps in the PSS PPv3.0 (Test 4.4, Part 2) related to AUX filtering depend on a DisplayPort interface on both the peripheral and computer interfaces and cannot be performed as described in the PP when the TOE converts the DisplayPort signals at the computer interface to HDMI signals at the peripheral interface.

Resolution

Test 4.4, Part 2, Steps 17-32

An alternate testing approach for TOEs that do not support the AUX channel on both the computer and peripheral interfaces is to verify that the HDMI Consumer Electronic Control (CEC - pin 13) and HDMI Ethernet Audio Control (HEAC - pin 14) cannot be used to pass signals.  The evaluators will test that the AUX channel related path through the TOE is floating (disconnected) by measuring the resistance-to-ground of the pins at the HDMI end and verify that the measured resistance-to-ground is unlimited. In addition, the absence of any signal on these pins can be verified using an oscilloscope.

Justification

The internal conversion from DisplayPort to HDMI reduces the security risks related to the AUX channel by eliminating the AUX channel risks except for two optional information flows that may be converted to HDMI – the CEC (pin 13) and HEAC (pin 14).  If the TOE does not support these HDMI pins, other similar PSS products might support the HDMI CEC and HEAC pins using messages sent and received over DisplayPort’s AUX channel.

 
 
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