AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 32

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

Additional Examples
Additional Examples
The final 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 the final data necessary to calculate
the HMAC is now present, the final static descriptor is set to HMAC and autopad, while continue and
initialize 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 doesn’t 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 it has the final data for HMAC calculation
(HMAC on, continue off), the descriptor must output the contents of the MDEU message digest register to
the indicated address in system memory. The MPC184 will write the entire 20-byte HMAC-SHA-1 to PCI
memory, and depending on the security protocol in question, the host will compare the most significant
x bytes of the HMAC generated by the MPC184 with the HMAC sent with the packet.
The next descriptor pointer should be null, as the channel should not fetch another descriptor until the EUs
have been reset. The static assignment of the current EUs need not end, if the channel is expected to need
the same EUs to operate on a similar static chain belonging to a difference secure session.
Table 27 shows today’s most commonly used IPSec descriptor headers. In all the descriptor headers shown,
the MDEU performs auto padding for the final data block, as needed.
32
0x2003_9A22
0x2003_8E22
0x2013_9A22
0x2013_8E20
0x2003_8C22
0x2013_8C20
0x2043_9A22
0x2043_8E22
0x2003_8222
0x2013_8220
0x2003_9822
0x2003_8022
0x2013_9820
0x2013_8020
0x2043_8222
Value/Type
MPC184 Descriptor Programmer’s Guide— PCI View
Table 27. Common IPSec Static Descriptor Headers
Freescale Semiconductor, Inc.
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DPD_Type 0010_DES_ECB_HMAC_MD-5 Decrypt First
DPD_Type 0010_DES_ECB_HMAC_MD-5 Decrypt Middle
DPD_Type 0010_DES_ECB_HMAC_MD-5 Decrypt Last
DPD_Type 0010_DES_ECB_HMAC_MD-5 Encrypt First
DPD_Type 0010_DES_ECB_HMAC_MD-5 Encrypt Middle
DPD_Type 0010_DES_ECB_HMAC_MD-5 Encrypt Last
DPD_Type 0010_DES_ECB_HMAC_SHA-1 Decrypt First
DPD_Type 0010_DES_ECB_HMAC_SHA-1 Decrypt Middle
DPD_Type 0010_DES_ECB_HMAC_SHA-1 Decrypt Last
DPD_Type 0010_DES_ECB_HMAC_SHA-1 Encrypt First
DPD_Type 0010_DES_ECB_HMAC_SHA-1 Encrypt Middle
DPD_Type 0010_DES_ECB_HMAC_SHA-1 Encrypt Last
DPD_Type 0010_3DES_ECB_HMAC_MD-5 Decrypt First
DPD_Type 0010_3DES_ECB_HMAC_MD-5 Decrypt Middle
DPD_Type 0010_3DES_ECB_HMAC_MD-5 Decrypt Last
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Description
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