Freescale Semiconductor MCF5480 - Manual (Page 670)

MCF548x Reference Manual, Rev. 3
22-68 Freescale Semiconductor
The AFEU mode bits do not control cryptographic modes, only operational modes. Therefore, the AFEU
only uses actual descriptors, i.e. there is not a representative format that is used with multiple header
values.
22.14.1.1 Dynamically Assigned AFEU
Table 22-50 shows the descriptor format to load a key into the AFEU and perform the initial
context-permutation. Then the input data is ciphered and the context is unloaded.
Table 22-49. AFEU Mode Register Field Descriptions
Bits Name Description
7–3 — Reserved
2 CS Context Source. If set, this causes the context to be moved from the input FIFO into the
S-box prior to starting encryption/decryption. Otherwise, context should be directly written
to the context registers. Context Source is only checked if the prevent permute bit is set.
0 Context not from FIFO
1 Context from input FIFO
1 DC Dump Context. If set, this causes the context to be moved from the S-box to the output
FIFO following assertion AFEU’s done interrupt.
0 Do not dump context
1 After cipher, dump context
0 PP Prevent Permute. Normally, AFEU receives a key and uses that information to randomize
the S-box. If reusing a context from a previous descriptor or if in static assignment mode,
this bit should be set to prevent AFEU from re-performing this permutation step.
0 Perform S-Box permutation
1 Do not permute
Table 22-50. Descriptor for a Dynamically Assigned AFEU Using a Key
Field Name Value/Type Description
Header 0x10200050 Perform permute and dumpt context (TYPE 0101)
LEN_1 Length (not used) NULL
PTR_1 Pointer (not used) NULL
LEN_2 IV Length NULL
PTR_2 IV Pointer NULL
LEN_3 Key Length Number of bytes in key (5–16 bytes)
PTR_3 Key Pointer Address of key to be written into AFEU
LEN_4 Data In Length Number of bytes of data to be ciphered
PTR_4 Data In Pointer Pointer to data to perform cipher upon
LEN_5 Data Out Length Number of bytes of data after ciphering
PTR_5 Data Out Pointer Pointer to location where cipher output is to be written
LEN_6 IV Out Length Number of bytes in context (259 bytes)
PTR_6 IV Out Pointer Location where AFEU context output is to be written