LPC1837FET256,551 NXP Semiconductors, LPC1837FET256,551 Datasheet - Page 27

• Manufacturer Part Number: LPC1837FET256,551
• Description: Microcontrollers (MCU) 32BIT ARM CORTEX-M3 MCU 136KB SRAM
• Manufacturer: NXP Semiconductors
• Series: LPC18xxr

Specifications of LPC1837FET256,551

• Core: ARM Cortex M3
• Core Processor: ARM® Cortex-M3™
• Core Size: 32-Bit
• Speed: 150MHz
• Connectivity: CAN, EBI/EMI, Ethernet, I²C, Microwire, SD/MMC, SPI, SSI, SSP, UART/USART, USB OTG
• Peripherals: Brown-out Detect/Reset, DMA, I²S, Motor Control PWM, POR, PWM, WDT
• Number Of I /o: 80
• Program Memory Size: 1MB (1M x 8)
• Program Memory Type: FLASH
• Eeprom Size: -
• Ram Size: 136K x 8
• Voltage - Supply (vcc/vdd): 2 V ~ 3.6 V
• Data Converters: A/D 16x10b; D/A 1x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 256-LBGA
• Lead Free Status / Rohs Status: Details
• Other names: 935293795551

NXP Semiconductors
<Document ID>
User manual
3.3.4.1 CMAC
3.3.4 Boot image creation
The CMAC algorithm is used to calculate a tag which is used for image authentication.
The tag is stored in the header field HASH_VALUE.
The authentication process is as follows:
To generate an l-bit CMAC tag T of message M using a 128-bit block cipher AES and
secret key K, the CMAC tag generation process is as follows:
The first message block is the header. Since the CMAC tag is stored in the header field
HASH_VALUE, and this tag is not yet known until after CMAC calculation, a temporary
header with a dummy tag value of 0x3456789A is used during CMAC calculation. This
dummy value should be replaced by the calculated tag value in the final header field
HASH_VALUE.
For LPC18xx the chosen CMAC parameters are: encryption key K = User Key (same as
used for decryption) and tag length l = 64. Data is processed in little endian mode. This
means that the first byte read from the image is integrated into the AES codeword as least
significant byte. The 16th byte read from the image is the most significant byte of the first
AES codeword.
CMAC is calculated over the header and encrypted image.
1. Use the CMAC algorithm to generate the 128-bit tag. Truncate the tag to 64 MSB and
2. At boot time the tag is recalculated. Authentication passes when the calculated tag is
1. Generate sub key K
2. Divide message into 128-bit blocks M = M
3. The last block, M
4. Let c
5. For i = 1, ..., n, calculate c
6. Output T = msb
insert this truncated tag in the header.
equal to the received tag in the image header.
– Calculate a temporary value K
– If msb(K
complete blocks.
M
n
*.
0
= 00...0.
0
All information provided in this document is subject to legal disclaimers.
) = 0 then K
l
(c
n
n
*, should be padded to be a complete block and then M
Rev. 00.13 — 20 July 2011
).
1
:
1
= (K
i
= AES
0
<< 1) else K
0
K
(c
= AES
i-1
 M
K
1
(0).
i
|| ... || M
1
).
= (K
0
<< 1)  0x87
n-1
Chapter 3: LPC18xx Boot ROM
|| M
n
*, where M
UM10430
© NXP B.V. 2011. All rights reserved.
1
...M
n
= K
n-1
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are
1
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