MSC8144E Reference Manual, Rev. 3
26-42
Freescale
Semiconductor
Security Engine (SEC)
The use of a restore decrypt key (RDK) is completely optional, because the input time of the
preserved decrypt key may exceed the ~12 cycles required to restore the decrypt key for
processing the first block.
The following procedure is recommended if you are using an RDK:
1.
Set the AESU mode as Decrypt. The descriptor causes the SEC to write the contents of
the Context Registers and the key registers (containing the expanded decrypt key) to
memory.
2.
Use the descriptor type 0100_0- AESU Key Expand Output for the decryption of the
first portion of the message.
3.
To process the remainder of the message, use a common descriptor type (0001_0), and
set the restore decrypt key mode bit.
4.
Load the Context Registers and the expanded decrypt key with previously saved key and
context data from the first message. The key size is written as before (16, 24, or 32
bytes).
26.4.3.2 AESU Key Size Register
The AESU Key Size Register stores the number of bytes in the key (16, 24, or 32). Any key data
beyond the number of bytes in the Key Size Register is ignored. This register is cleared when the
AESU is reset or reinitialized. If you specify a key size other than 16, 24, or 32 bytes, an illegal
key size error is generated. If the Key Size Register is modified during processing, a context error
is generated.
26.4.3.3 AESU Data Size Register
The AESU Data Size Register stores the number of bits in the final message block. Acceptable
sizes vary depending on the AES mode selected. In ECB and CBC modes, the message
processed by the AESU must be a multiple of 128 bits; the AESU does not automatically pad
messages out to 128-bit blocks. In CCM and CTR modes, data size must be a multiple of 8 bits.
In XOR mode the data size must be a multiple of 256 bits (32 bytes). If an improper data size is
written, a data size error is generated. Only the lowest 3, 7, or 8 bits of the Data Size Register are
checked to determine if there is a data size error. Since all upper bits are ignored, the entire
message length (in bits) can be written to this register. This register is cleared when the AESU is
reset or reinitialized. Writing to this register signals the AESU to start processing data from the
input FIFO as soon as it is available. If the value of data size is modified during processing, a
context error is generated.
26.4.3.4 AESU Reset Control Register
This register allows three levels reset of just AESU, as defined by the three self-clearing bits:
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
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 ...