Freescale Semiconductor MCF5480 - Manual (Page 691)

EU Specific Data Packet Descriptors
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 22-89
Table 22-87 shows the format used for the context output for AES-CCM.
Table 22-88 shows a the descriptor format used for AES-CCM in encryption mode. The descriptor loads
a key and context (IV) into the AESU, performs the cipher on data, and writes the result and context to
memory.
Table 22-86. AES-CCM Encryption Context Input Format
Offset from
Input Context
Base Address
Field Length Description
0x0 IV 16 bytes This is the session specific IV parameter
0x10 NULL 16 bytes These 16 bytes are loaded with zeroes to serve as a
placeholder
0x20 Counter 16 bytes The counter is a second session specific parameter
similar to the IV.
0x30 Counter
modulus 8 bytes Always 8 for 802.11, but can very in other protocols.
Table 22-87. AES-CCM Encryption Context Output Format
Offset from
Output Context
Base Address
Field Length Description
0x0 — 16 bytes This can be discarded
0x10 Encrypted MAC 8 bytes This is the encrypted MAC to be appended to the
frame prior to transmission.
0x18 Encrypted MAC
(cont.) 8 bytes If the MAC is larger than 8 bytes, this is the
continuation of the encrypted MAC.
Table 22-88. Descriptor for a AES-CCM Decryption
Field Name Value/Type Description
Header 0x6B000010 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 IV (always 56 bytes)
PTR_2 IV Pointer Address of IV
LEN_3 Key Length Number of bytes in Key (16 bytes)
PTR_3 Key Pointer Address of Key
LEN_4 Data In Length Number of bytes of data to be ciphered (39 bytes)
PTR_4 Data In Pointer Address of data to be ciphered
LEN_5 Data Out Length Bytes of output data (24 bytes)
PTR_5 Data Out Pointer Address to write output data