Freescale Semiconductor MCF5480 - Manual (Page 666)

MCF548x Reference Manual, Rev. 3
22-64 Freescale Semiconductor
22.13.4 Descriptor Classes
The SEC has two general classes of descriptors: dynamic, which refers to a continually changing usage
model, and static, which refers to a relatively unchanging usage of the SEC resources.
22.13.4.1 Dynamic Descriptors
In a typical networking environment, packets from innumerable sessions can arrive randomly. The host
must determine which security association applies to the current packet and encrypt or decrypt without any
knowledge of the security association of the previous or next packet. This situation calls for the use of
dynamic descriptors.
When under dynamic assignment, an EU must be used under the assumption that a different
crypto-channel (with a different context) may have just used the EU and that another crypto-channel (with
yet another context) may use that EU immediately after the current crypto-channel has released the EU.
Therefore, for dynamic-assignment use, there is a set of data packet descriptors defined that sets up the
appropriate context, performs the cipher function, and then saves the context to system memory.
Table 22-45 shows the format for a dynamic descriptor. Since TYPE 0001 and 0010 are the most
commonly used, TYPE 0001 is used for the following examples. The descriptor loads context (IV) and
keys into the EU. Then the input data is read and ciphered and the output is written to system memory.
Finally, the new context is optionally written to system memory so that it can be used as the starting context
for a new descriptor.
1110 HMAC Key HMAC Data Key Data In Data Out IV Out via FIFO HMAC/Context Out
1111 HMAC Key HMAC Data IV Data In Data Out IV Out via FIFO HMAC/Context Out
Table 22-45. Dynamic Descriptor Example
Field Name Value/Type Description
Header 0xXXXX_XX1X TYPE 0001
LEN_1 Length (not used) NULL
PTR_1 Pointer (not used) NULL
LEN_2 IV Length Number of bytes of IV to be written to EU
PTR_2 IV Pointer Address of IV
LEN_3 Key Length Number of bytes of Key to be written to EU
PTR_3 Key Pointer Address of Key
LEN_4 Data In Length Number of bytes to be encrypted/decrypted
PTR_4 Data In Pointer Address of data to be encrypted/decrypted
LEN_5 Data Out Length Bytes to be written (should be equal to length of data in)
PTR_5 Data Out Pointer Address where final data is written
LEN_6 IV Out Length Number of bytes of IV to be written to memory (optional)
Table 22-44. Descriptor Length/Pointer Mapping (Continued)
Descriptor
Type
L/P 1 L/P 2 L/P 3 L/P 4 L/P 5 L/P 6 L/P 7