AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 14

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

Descriptor Type Field
Descriptor Type Field
5 Descriptor Type Field
The MPC184 accepts 13 fixed format descriptors. The descriptor type field in the descriptor header informs
the crypto-channel of the ordering of the inputs and outputs defined by the length/pointer pairs in the
descriptor body. The MPC190 (a previous Motorola security co-processor with mastering capability)
allowed the user to define (within limits) the order in which keys, context, and data were fetched by the
MPC190 prior to processing. The MPC184 descriptor type field advises the crypto-channel of the
predetermined ordering of keys, context, and null fields. The ordering of inputs and outputs in the
length/pointer pairs (as defined by descriptor type) is shown in Table 10.
Table 9 shows the permissible values for the descriptor type field in the descriptor header. Note that not all
descriptor types are operationally useful, some exist for test and debug reasons, and to provide flexibility in
dealing with evolving security standards. The cryptographic transforms required by most security protocols
use types 0001 and 0010.
14
Value
0000
0001
0010
0011
0100
0101
0110
1000
1001
1010
0111
To use RDK, the following procedure is recommended:
•
•
The descriptor type used in decryption of the first portion of the
message is ‘0100—AESU Key Expand Output.’ The description mode
must be ‘Decrypt.’ See Chapter 4 in the MPC184 Security
Co-Processor User’s Manual, PCI Interface, for more information.
The descriptor will cause the MPC184 to write the contents of the
context and key registers (containing the expanded decrypt key) to
memory.
To process the remainder of the message, use a ‘normal’ descriptor
type (descriptor type selected based on the need for simultaneous
HMAC generation, etc.), and set the ‘restore decrypt key’ mode bit.
Load the context registers and the expanded decrypt key with
previously saved key and context data from the first message. The key
size is written as before (16, 24, or 32 bytes).
common_nonsnoop_no_afeu
non_hmac_snoop_no_afeu
common_nonsnoop_afeu
aseu_key expand_output
non_hmac_snoop_afeu
MPC184 Descriptor Programmer’s Guide— PCI View
hmac_snoop_no_afeu
pkeu_static_ec_point
hmac_snoop_afeu
Descriptor Type
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pkeu_mm
Reserved
pkeu_ec
Table 9. Descriptor Types
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—
Common, nonsnooping, non-PKEU, non-AFEU
Snooping, HMAC, non-AFEU
Snooping, non-HMAC, non-AFEU
Non-snooping, non HMAC, AESU, expanded key out
Common, nonsnooping, AFEU
Snooping, HMAC, AFEU (no context out)
Snooping, non-HMAC, AFEU
PKEU-MM
PKEU-EC
PKEU static-EC point (completes operand loading
and executes)
Notes
MOTOROLA