Freescale Semiconductor MCF5480 - Manual (Page 686)

MCF548x Reference Manual, Rev. 3
22-84 Freescale Semiconductor
22.14.5.1 Dynamically Assigned AESU
Table 22-77 shows a descriptor for a dynamically assigned AESU. The descriptor loads a key into the
AESU, performs the cipher on data, and writes the result and optional context (IV) to memory.
5 FM Final MAC. Processes final message block and generates final MAC tag at end of message
processing (OCB and CCM mode only)
0 Do not generate final MAC tag
1 Generate final MAC tag after CCM processing is complete.
4 IM Initialize MAC. Initializes AESU for new message (CCM mode only)
0 Do not initialize (context will be loaded by host)
1 Initialize new message with nonce
3 — Reserved, should be cleared.
2–1 CM Cipher Mode. Controls which cipher mode the AESU will use in processing:
00 ECB -Electronic Codebook mode.
01 CBC- Cipher Block Chaining mode.
10 Reserved
11 CTR- Counter Mode.
Note: CM must be set to 00 when Extend Cipher Mode (Bit 0) is set, otherwise an error will be
generated.
0 ED Encrypt/Decrypt. If set, AESU operates the encryption algorithm; if not set, AESU operates the
decryption algorithm.
Note: This bit is ignored if CM is set to “11” - CTR Mode.
0 Perform decryption
1 Perform encryption
Table 22-77. Descriptor for a Dynamically Assigned AESU
Field Name Value/Type Description
Header Table 22-61 Header common to several descriptors (TYPE 0001)
LEN_1 Length (not used) NULL
PTR_1 Pointer (not used) NULL
LEN_2 IV Length Number of bytes in input IV (56 bytes) (optional)
PTR_2 IV Pointer Address of input IV (optional)
LEN_3 Key Length Number of bytes in Key (16, 24, or 32 bytes)
PTR_3 Key Pointer Address of Key
LEN_4 Data In Length Number of bytes of data to be ciphered (multiple of 16)
PTR_4 Data In Pointer Address of data to be ciphered
LEN_5 Data Out Length Bytes of output data (should be equal to length of data in)
PTR_5 Data Out Pointer Address to write output data
LEN_6 IV Out Length Number of bytes of output IV to be written (56 bytes) (optional)
Table 22-76. AESU Mode Register Field Descriptions (Continued)
Bits Name Description