5.1.9. HDCP 1.4 TX Architecture

HDMI Intel® FPGA IP User Guide

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Date 6/26/2023

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5.1.9. HDCP 1.4 TX Architecture

The HDCP 1.4 transmitter block encrypts video and auxiliary data prior to the transmission over serial link that has HDCP 1.4 device connected.

The HDCP 1.4 TX core consists of the following entities:

Control and Status Registers Layer
Authentication Layer
Video Stream and Auxiliary Layer

Figure 27. Architecture Block Diagram of HDCP 1.4 TX IP

The Nios II processor typically drives the HDCP 1.4 TX core. The processor implements the authentication protocol. The processor accesses the IP through the Control and Status Port using Avalon Memory Mapped (Avalon-MM) interface.

The HDCP specifications requires the HDCP 1.4 TX core to be programmed with the DCP-issued production keys – Device Private Keys (Akeys) and Key Selection Vector (Aksv). The IP retrieves the key from the on-chip memory externally to the core through the HDCP Key Port. The on-chip memory must store the key data in the arrangement in the table below.

Table 32. HDCP 1.4 TX Key Port Addressing
Address	Content
6'h28	{16’d0, Aksv[39:0]}
6'h27	Akeys39[55:0]
6'h26	Akeys38[55:0]
...	...
6'h01	Akeys01[55:0]
6'h00	Akeys00[55:0]

When authenticating with the HDCP 1.4 repeater device, the HDCP 1.4 TX core must perform the second part of the authentication protocol. This second part corresponds to the computation of the SHA-1 hash digest for all downstream device KSVs which are written to the registers in Control and Status Register Layer using the Control and Status Port (Avalon-MM).

The Video Stream and Auxiliary layer receives audio and video content over its Video and Aux Data Input Port, and performs the encryption operation. The Video Stream and Auxiliary Layer detects the Encryption Status Signaling (ESS) provided by the HDMI TX core to determine when to encrypt frames.

You can use the HDCP 1.4 registers to customize your design configurations. The HDCP 1.4 TX core supports full handshaking mechanism for authentication. Every issued command should be followed by polling of the assertion of its corresponding status bit before proceeding to issuing the next command. The value of AUTH_CMD must be in one-hot format that only one bit can be set at a time.

Table 33. HDCP 1.4 TX Registers Mapping
Address	Register	R/W	Reset	Bit	Bit Name	Description
0x00	`AUTH_CMD` (one-hot)	WO	0x00000000	31:6	Reserved	Reserved.
				5	`GO_V`	Set to 1 to compute V and compare against V’ during authentication with repeater. Self-cleared.
				4	Reserved	Reserved.
				3	`GEN_RI`	Set to 1 to generate and receive R0 during authentication exchange or Ri during link integrity verification. Ri-Ri’ comparison should be performed by Nios® II processor. Self-cleared.
				2	`GO_KM`	Set to 1 to compute master key (km). Self-cleared.
				1	`GEN_AKSV`	Set to 1 to request and receive Aksv. Self-cleared.
				0	`GEN_AN`	Set to 1 to generate and receive new true random An. Self-cleared.
0x01	`AUTH_MSGDATAIN`	WO	0x00000000	31:8	Reserved	Reserved.
0x01	`AUTH_MSGDATAIN`	WO	0x00000000	7:0	`MSGDATAIN`	Write messages (in byte) from receiver in burst mode. Master key computation: Prior to setting `GO_KM` to 1, the `BCAPS`.`REPEATER` bit had to be set and the following messages had to be written in this sequence: 5 bytes of Bksv with least significant byte (lsb) first. V generation: Prior to setting `GO_V` to 1, the following messages had to be written in this sequence: 20 bytes of V’ with lsb first Variable length of KSV list with lsb first 2 bytes of Bstatus with lsb first
0x02	`AUTH_STATUS`	RO	0x00000000	31	`KM_OK`	Asserted by the core to indicate the received Bksv is valid. Poll `KM_DONE` until it is set before reading `KM_OK`.
				30	`V_OK`	Asserted by the core to indicate V-V’ comparison is passed. Poll `V_DONE` until it is set before reading `V_OK`.
				29:6	Reserved	Reserved.
				5	`V_DONE`	Asserted by the core when V is generated. Self-cleared upon next `GO_V` is set.
				4	Reserved	Reserved
				3	`RI_DONE`	Asserted by the core when Ri is generated. Self-cleared upon next `GEN_RI` is set.
				2	`KM_DONE`	Asserted by the core when Km is generated. Self-cleared upon next `GO_KM` is set.
				1	`AKSV_DONE`	Asserted by the core when Aksv is ready to be read from `MSGDATAOUT`. Self-cleared upon next `GEN_AKSV` is set.
				0	`AN_DONE`	Asserted by the core when new random An is generated and ready to be read from `MSGDATAOUT`. Self-cleared upon next `GEN_AN` is set.
0x03	`AUTH_MSGDATAOUT`	RO	0x00000000	31:8	Reserved	Reserved.
0x03	`AUTH_MSGDATAOUT`	RO	0x00000000	7:0	`MSGDATAOUT`	Read messages (in byte) from the IP in burst mode. An generation: When `AN_DONE` is set to 1, reading this offset 8 times to obtain An with lsb first. Aksv request: When `AKSV_DONE` is set to 1, reading this offset 5 times to obtain Aksv with lsb first. Ri request: When `RI_DONE` is set to 1, reading this offset 2 times to obtain Ri with lsb first.
0x04	`VID_CTL`	RW	0x00000000	31:1	Reserved	Reserved.
0x04	`VID_CTL`	RW	0x00000000	0	`HDCP_ENABLE`	Set to 1 to enable HDCP 1.4 encryption. Set to 0 if HDCP 1.4 encryption is not required especially when it is in unauthenticated state.
0x05	`BCAPS`	RW	0x00000000	31:2	Reserved	Reserved.
				1	`REPEATER`	Downstream repeater capability. Write bit 6 (REPEATER) of `Bcaps` received from downstream to this offset.
				0	Reserved	Reserved.

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5.1.9. HDCP 1.4 TX Architecture