Execution Units
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
26-45
ciphertext, or with the ciphertext to recover the plaintext. The modulus exponent M can be set
between 8 and 128 in multiples of 8. The value of M is specified by writing to Context Register 3.
The only difference between SRT mode and CTR mode is that in SRT mode, the AES Context is
loaded and read via Context Registers 1–3, with no requirement to access Context Registers 4–7.
In CTR mode, Context Registers 1–4 must be loaded with zeros, with the counter and modulus
being loaded into and read from Context Registers 5–7.
26.4.3.9.4 Context for CCM Mode
The SEC AESU can performing single pass encryption and MAC generation. The core processor
is required to arrange the CCM context so that the context can be fetched as a contiguous string
into the Context Registers prior to encryption/MAC generation or decryption/MAC validation.
The Context Register contents for CCM mode is summarized in Figure 26-8.
The context for CCM encryption/MAC generation is:
Reg 1–2 are session specific and hold the 128-bit Initialization Vector (from memory)
Reg 3–4 contains 128 bits of zero padding
Reg 5–6 are a session specific counter (Initial Counter Value) (from memory)
Reg 7 has the Counter Modulus Exponent (msb to lsb). Should be fixed at 0x0000_0080.
Note:
The counter modulus for CCM mode is currently defined as 2
128
making the exponent
128. This value has been made programmable in the SEC in case the final version of
802.11i uses a different counter modulus. Because this is a programmable field, it must
be generated and stored along with other session specific information for loading into
the AESU Context Register prior to CCM encryption.
26.4.3.9.5 CCM Encryption Processing
With the session specific key and context, the AESU will perform the following operations.
Context Registers
1
2
3
4
5
6
7
Encrypt
(outbound)
Inputs
IV
0
Initial Counter
Counter
Modulus
Exponent
Outputs
MAC
0
MIC
0
Decrypt
(inbound)
Inputs
IV
MIC
0
Initial Counter
Counter
Modulus
Exponent
Outputs
Computed
MAC
0
Decrypted
MAC
0
Figure 26-8. AESU CCM Context Registers
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
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Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...