AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 8

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

Execution Unit Mode Data
Execution Unit Mode Data
4.3.1 Host-Provided Context via Prevent Permute
In the default mode of operation, the host provides the key and key size to the AFEU. The initial memory
values in the S-box are permuted with the key to create new S-box values, which are used to encrypt the
plaintext.
If the ‘prevent permute’ mode bit is set, the AFEU will not require a key. Rather, the host will write the
context to the AFEU and message processing will occur using the provided context. This mode is used to
resume processing of a message using the already permuted S-box. The context may be written through the
FIFO if the ‘context source’ mode bit is set.
4.3.2 Dump Context
This mode may be independently specified in addition to host-provided context mode. In this mode, once
message processing is complete and the output data is read, the AFEU will make the current context data
available for reads via the output FIFO.
8
Reset
Reset
Field
Field
Addr
Addr
R/W
R/W
31
31
After the initial key permute to generate a context for an AFEU encrypted
session, all subsequent messages will re-use that context, such that it is
loaded, modified during the encryption, and unloaded, similar to the use of
a CBC initialization vector in DES operations. A new context is generated
(via key permute) according to a rekeying interval specified by the security
protocol. Context should never be loaded to encrypt a message if a key is
loaded and permuted at the same time.
MPC184 Descriptor Programmer’s Guide— PCI View
Freescale Semiconductor, Inc.
Reserved
For More Information On This Product,
0
Figure 7. AFEU Mode Register
Go to: www.freescale.com
NOTE
AFEU 0x08000
AFEU 0x08004
Reserved
11
R/W
R/W
0
Burst Size
10
0
8
7
Reserved
0
3
CS
2
0
MOTOROLA
DC
0
1
PP
0
0
0