AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 37

• Manufacturer Part Number: AN2492
• Description: MPC184 Descriptor Programmers Guide--PCI View
• Manufacturer: Freescale Semiconductor / Motorola

10.4 Inbound TLS Descriptor 2
The second descriptor performs the HMAC of the record header and the record payload. In the example
shown in Table 31, the HMAC is generated using the MD-5 algorithm.
The primary EU is the MDEU, with its mode bits set to cause the MDEU to initialize its context registers,
perform autopadding if the data size is not evenly divisible by 512 bits, and calculate an HMAC-MD-5.
The descriptor header does not designate a secondary EU, so the setting of the snoop type bit is ignored.
At the conclusion of inbound TLS Descriptor 2, the crypto-channel has calculated the HMAC, placed it in
memory, and has reset and released the MDEU. The host can compare the HMAC generated by inbound
TLS descriptor 2 with the HMAC that came as part of the record. If the HMACs match, the record is known
to have arrived unmodified, and can be passed to the application layer.
The next descriptor pointer field can also be null, or point to an unrelated dynamic descriptor.
11 Conclusion
The MPC184 device driver will generate most of the descriptors described in this application note; however,
the drivers are general purpose in structure, and may provide more options than certain applications require.
By providing the user with greater detail and specific examples of descriptor programming, the user may
choose to implement an application-specific minimal driver with higher performance and a smaller memory
footprint.
MOTOROLA
Type 0001 common_nonsnoop_non_ afeu
LEN_1
PTR_1
LEN_2
PTR_2
LEN_3
PTR_3
LEN_4
PTR_4
LEN_5
PTR_5
LEN_6
PTR_6
LEN_7
PTR_7
PTR_NEXT
Field
MPC184 Descriptor Programmer’s Guide— PCI View
Freescale Semiconductor, Inc.
For More Information On This Product,
Table 31. Inbound TLS Descriptor 2
Go to: www.freescale.com
0x31E0_0010
Value/Type
Length
Pointer
Length
Pointer
Length
Pointer
Length
Pointer
Length
Pointer
Length
Pointer
Length
Pointer
Pointer
MDEU, HMAC, MD-5, autopad
Null
Null
Null
Null
Length of MD-5 key
Pointer to MD-5 key
Length of data to be read and permuted
Pointer to data in memory
Null
Null
Length of HMAC to be written to memory (16 bytes for
MD-5)
Pointer to memory location for HMAC write (must be
modulo-8)
Null
Null
Null or pointer to unrelated next descriptor
Description
Conclusion
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