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High-Bandwidth Digital Content
Protection (HDCP)
Note:
The explanation of HDCP operation in this data
sheet is pr
ovided as a guide for general understanding.
Implementation of HDCP in a product must meet the
requirements given in the HDCP System v1.3 Amendment
for GMSL, which is available from DCP.
HDCP has two main phases of operation: authentication
and the link integrity check. The µC starts authentication
by writing to the START_AUTHENTICATION bit in the
GMSL serializer. The GMSL serializer generates a 64-bit
random number. The host
F
C first reads the 64-bit ran
-
dom number from the GMSL serializer and writes it to
the deserializer. The µC then reads the GMSL serializer
public key selection vector (AKSV) and writes it to the
deserializer. The µC then reads the deserializer KSV
(BKSV) and writes it to the GMSL serializer. The µC
begins checking BKSV against the revocation list. Using
the cipher, the GMSL serializer and deserializer calculate
a 16-bit response value, R0 and R0’, respectively. The
GMSL amendment for HDCP reduces the 100ms mini
-
mum wait time allowed for the receiver to generate R0’
(specified in HDCP rev 1.3) to 128 pixel clock cycles in
the GMSL amendment.
There are two response-value comparison modes: internal
comparison and µC comparison. Set EN_INT_COMP = 1
to select internal comparison mode. Set EN_INT_COMP
= 0 to select µC comparison mode. In internal compari
-
son mode, the
µC reads the deserializer response R0’
and writes it to the GMSL serializer. The GMSL serializer
compares R0’ to its internally generated response value
R0, and sets R0_RI_MATCHED. In µC comparison mode,
the
µC reads and compares the R0/R0’ values from the
GMSL serializer/deserializer.
During response-value generation and comparison, the
host µC checks for a valid BKSV (having 20 1s and 20
0s is also reported in BKSV_INVALID) and checks BKSV
against the revocation list. If BKSV is not on the list and the
response values match, the host authenticates the link. If
the response values do not match, the µC resamples the
response values (as described in HDCP rev 1.3, Appendix
C). If resampling fails, the µC restarts authentication by
setting the RESET_HDCP bit in the GMSL serializer. If
BKSV appears on the revocation list, the host cannot
transmit data that requires protection. The host knows
when the link is authenticated and decides when to output
data requiring protection. The µC performs a link integrity
check every 128 frames or every 2s ±0.5s. The GMSL
serializer/deserializer generate response values every 128
frames. These values are compared internally (internal
comparison mode) or can be compared in the host µC.
In addition, the GMSL serializer/deserializer provide
response values for the enhanced link verification.
Enhanced link verification is an optional method of link
verification for faster detection of loss-of-synchronization.
For this option, the GMSL serializer and deserializer
generate 8-bit enhanced link-verification response values
(PJ and PJ’) every 16 frames. The host must detect three
consecutive PJ/PJ’ mismatches before resampling.
Encryption Enable
The GMSL link transfers either encrypted or nonen
-
crypted data. To encrypt data, the host µC sets the
encryption enable (ENCRYPTION_ENABLE) bit in both
the GMSL serializer and deserializer. The µC must set
ENCRYPTION_ENABLE in the same VSYNC cycle in
both the GMSL serializer and deserializer (no internal
VSYNC falling edges between the two writes). The same
timing applies when clearing ENCRYPTION_ENABLE to
disable encryption.
Note:
ENCRYPTION_ENABLE enables/disables encryp
-
tion on the GMSL irrespective of the content. To comply
with HDCP, the µC must not allow content requiring
encryption to cross the GMSL unencrypted.
The µC must complete the authentication process before
enabling encryption. In addition, encryption must be disa
-
bled before starting a new authentication session.
Synchronization of Encryption
The video vertical sync (VSYNC) synchronizes the start
of encryption. Once encryption has started, the GMSL
generates a new encryption key for each frame and each
line, with the internal falling edge of VSYNC and HSYNC.
Rekeying is transparent to data and does not disrupt the
encryption of video or audio data.
Repeater Support
The GMSL serializer/deserializer include features to build
an HDCP repeater. An HDCP repeater receives and
decrypts HDCP content and then encrypts and transmits
on one or more downstream links. A repeater can also use
decrypted HDCP content (e.g., to display on a screen).
To support HDCP repeater-authentication protocol, the
deserializer has a REPEATER register bit. This register
bit must be set to 1 by a µC (most likely on the repeater
module). Both the GMSL serializer and deserializer use
SHA-1 hash-value calculation over the assembled KSV
lists. HDCP GMSL links support a maximum of 15 receiv
-
ers (total number including the ones in repeater modules).
If the total number of downstream receivers exceeds 14,
the
F
C must set the MAX_DEVS_EXCEEDED register bit
when it assembles the KSV list.
MAX9277/MAX9281
3.12Gbps GMSL Serializers for Coax or
STP Output Drive and LVDS Input
www.maximintegrated.com
Maxim Integrated │
48