AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 31

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

The middle descriptor header encodes the information required to select the DEU for Op_0, and the MDEU
for Op_1. The Op_0 mode data configured the DEU to operate in 3DES, CBC, decrypt mode. The Op_1
mode data configured the MDEU to operate in SHA-1 mode. Because all the data necessary to calculate the
HMAC is still not present, the middle static descriptor is set to continue, while initialize, HMAC, and
autopad are off.
The descriptor header also encodes the descriptor type 0010, which defines the input and output ordering
for ‘hmac_snoop_no_afeu.’ The HMAC key is already loaded, and does not need to be reloaded. The length
and pointer to the data over which the initial hash will be calculated must be provided for this descriptor.
The 3DES key and IV are already loaded, and need not be reloaded.
Ciphertext is brought into the DEU input FIFO, with the MDEU snooping the portion of the data it has been
told to process. As the decryption continues, the plaintext fills the DEU output FIFO, and this data is written
back to system memory as needed. Because it has been told to expect more data (HMAC off, continue on),
the descriptor must not attempt to output the contents of the MDEU message digest register.
The next descriptor pointer should point to the descriptor shown in Table 26.
MOTOROLA
Header
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
PTR_NEXT
PTR_7
Field
Field
Table 25. Representative Middle Descriptor DPD_Type
0010_3DES_CBC_HMAC_SHA-1 Decrypt (continued)
MPC184 Descriptor Programmer’s Guide— PCI View
Table 26. Representative Final Descriptor DPD_Type
Freescale Semiconductor, Inc.
0x2063_8C22
Value/Type
Value/Type
For More Information On This Product,
Pointer
Pointer
Pointer
Pointer
Length
Length
Length
0010_3DES_CBC_HMAC_SHA-1 Decrypt
Nul
Nul
Nul
Nul
Nul
Nul
Nul
Nul
Nul
Nul
Go to: www.freescale.com
Null
Pointer to next descriptor
DPD_Type 0010_3DES_CBC_HMAC_SHA-1 decrypt
Null
Null
Number of bytes to be hashed
PCI address of data to be hashed
Null
Null
Null
Null
Number of bytes to be ciphered
PCI address of data to be ciphered
Bytes to be written (should be equal to length of data-in)
PCI address where ciphered data is to be written
Null
Null
Null
Description
Description
Additional Examples
31