AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 13

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

Table 8 describes the AESU mode register signals.
MOTOROLA
31:11
10:8
Bits
Reset
7:4
2-1
Field
Addr
3
0
R/W
Encrypt/Decrypt If set, AESU operates the encryption algorithm; if not set, AESU operates the decryption
31
Burst size
Signal
RDK
CM
—
—
In most networking applications, the decryption of an AES protected
packet will be performed as a single operation. However, if circumstances
dictate that the decryption of a message should be split across multiple
descriptors, the AESU allows the user to save the decrypt key, and the
active AES context, to memory for later re-use. This saves the internal
AESU processing overhead associated with regenerating the decryption
key schedule (approximately 12 AESU clock cycles for the first block of
data to be decrypted).
The use of RDK is completely optional, as the input time of the preserved
decrypt key may exceed the approximate 12 cycles required to restore the
decrypt key for processing the first block.
Reserved
MPC184 Descriptor Programmer’s Guide— PCI View
Reserved
processed with a single key/context. The AESU signals to the crypto-channel that a ’burst
size’ amount of data is available to be pushed to or pulled from the FIFO.
Note: The inclusion of this field in the AESU mode register is to avoid confusing a user who
may read this register in debug mode. Burst size should not be written directly to the AESU.
Reserved
Restore Decrypt Key (RDK)—Specifies that key data write will contain pre-expanded key
(decrypt mode only). See note on use of RDK bit.
0 Expand the user key prior to decrypting the first block
1 Do not expand the key. The expanded decryption key will be written following the
Cipher Mode: Controls which cipher mode the AESU will use in processing:
00 ECB—Electronic codebook mode
01 CBC—Cipher block chaining mode
10 Reserved
11 CTR—Counter mode
algorithm.
0 Perform decryption
1 Perform encryption
The MPC184 implements flow control to allow larger than FIFO sized blocks of data to be
context switch.
Freescale Semiconductor, Inc.
For More Information On This Product,
Table 8. AESU Mode Register Signals
NOTE: Restore Decrypt Key
11
Figure 10. AESU Mode Register
Go to: www.freescale.com
10
Burst Size
AESU 0x12000
8
R/W
0
7
Description
Reserved
Execution Unit Mode Data
4
RDK
3
2
CM
1
ED
0
13