Freescale Semiconductor MCF5480 - Manual (Page 695)

EU Specific Data Packet Descriptors
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 22-93
Table 22-93 lists typical AESU/HMAC multi-function descriptor header values.
Table 22-94 shows the representative descriptor used for multi-function encryption such as outbound
IPSec ESP. The descriptor header encodes to select the DEU or AESU as the primary EU, and the MDEU
for the secondary EU. Because all the data necessary to calculate the HMAC in a single dynamic descriptor
is available, initialize and autopad are set, while continue is cleared in the SMODE field.
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 loaded first, followed by the length and pointer to the data
over which the HMAC will be calculated. The DEU/AESU key is loaded next, followed by the context
(IV). The number of bytes to be ciphered and starting address will be an offset of the number of bytes being
HMAC’d. The data to be decrypted and HMAC’d is only brought in the SEC a single time, with the
DEU/AESU and MDEU only reading the portion that matches the starting address and byte length in the
length/pointer fields corresponding to their data of interest.
Plaintext is brought into the DEU/AESU input FIFO, with the MDEU out-snooping the portion of the data
it has been told to process. As the encryption continues, the ciphertext fills the DEU/AEU output FIFO,
and this data is written back to system memory as needed. When the final byte of data to be HMAC’d has
been processed through the MDEU, the descriptor will cause the MDEU to write the HMAC to the
indicated area in system memory. Software will append the most significant bytes of the HMAC generated
by the SEC to the packet as the authentication trailer. Common practice in IPSec ESP with TDES-CBC is
to use the last 8 bytes of the ciphertext as the IV for the next packet. If this is the case, software should
0x20231D22 CBC Single DES Decrypt SHA256 Yes Yes
0x20231E22 CBC Single DES Decrypt MD5 Yes Yes
0x20231C22 CBC Single DES Decrypt SHA Yes Yes
0x20631D22 CBC Triple DES Decrypt SHA256 Yes Yes
0x20631E22 CBC Triple DES Decrypt MD5 Yes Yes
0x20631C22 CBC Triple DES Decrypt SHA Yes Yes
Table 22-93. Typical Header Values for Dynamic Multi-Function AESU Descriptors
Header Value Mode E/D Algorithm HMAC Pad
0x60831D22 ECB Decrypt SHA256 Yes Yes
0x60831E22 ECB Decrypt MD5 Yes Yes
0x60831C22 ECB Decrypt SHA Yes Yes
0x60A31D22 CBC Decrypt SHA256 Yes Yes
0x60A31E22 CBC Decrypt MD5 Yes Yes
0x60A31C22 CBC Decrypt SHA Yes Yes
0x60E31D22 CTR — SHA256 Yes Yes
0x60E31E22 CTR — MD5 Yes Yes
0x60E31C22 CTR — SHA Yes Yes
Table 22-92. Typical Header Values for Dynamic Multi-Function DEU Descriptors (Continued)
Header Value E/C S/T E/D Algorithm HMAC Pad