UM10503
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
52 of 1269
NXP Semiconductors
UM10503
Chapter 6: LPC43xx Security API
6.5.5 Storing AES keys in Deep power-down mode
In Deep power-down mode, all AES information is lost. After wake-up, the AES keys need
to be reloaded. If you want to use the same RNG key as before entering Deep
power-down mode, then you can store the RNG key in the backup registers at 0x4004
1000. Process the AES keys in the following order:
1. Generate a random number by calling the otp_GenRand() API.
2. Store this number in the RTC REGFILE registers.
3. Load this number in the AES engine using aes_LoadKeySW.
After every wake-up, perform the following operations:
Fig 22. AES endianess
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
AES plain text - Arr ay of 16 bytes
RAM address
0C0D0EOF
08090A0B
04050607
000102 03
AES plain text – Arr ay of 4 w ords (32 bits)
0F
0E
0D
0C
0B
0A
09
08
07
06
05
04
03
02
01
00
Byte Nr
AES cypher text - Ar ray of 16 bytes
RAM address
Pr inte d text
0F
0E
0D
0C
0B
0A
09
08
07
06
05
04
03
02
01
00
Pr inte d text
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
RAM address
0F
0E
0D
0C
0B
0A
09
08
07
06
05
04
03
02
01
00
Byte Nr
C5
CC
8F
C 2
EF
34
5D
92
AB
89
7B
F 2
F F
9D
E0
F9
Pr inte d text
0
1
2
3
Word N r
00
04
08
0C
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0F
0E
0D
0C
0B
0A
09
08
07
06
05
04
03
02
01
00
0F
0E
0D
0C
0B
0A
09
08
07
06
05
04
03
02
01
00
AES key - Ar ray of 16 bytes
C28F CCC5
925D34EF
F27B89AB
F 9E09DF F
AES cypher text – Ar ray of 4 words (32 bits)
RAM addre ss
Printed text
0
1
2
3
Wor d Nr
00
04
08
0C
AES
0C0D 0EOF
0809 0A0B
04050607
00010203
0
1
2
3
00
04
08
0C
AES key - Arr ay of 4 wor ds ( 32 bits)
AES API
HW / SW
RAM address
Pr inted text
Byte Nr
R AM addr ess
Pr inted text
Word Nr