Rainbow Electronics AT86RF231 - Manual (Page 130)

130
8111A–AVR–05/08
AT86RF231
A security operation can be started within one SRAM access by appending the start command
AES_REQUEST = 1 (register 0x94, AES_CON_MIRROR) to the SPI sequence. Register
AES_CON_MIRROR is a mirrored version of register 0x83 (AES_CON).
Figure 11-1. ECB Programming SPI Sequence - Encryption
Summarizing, the following steps are required to perform a security operation using only one
SPI access:
This sequence is recommended because the security operation is configured and started within
one SPI transaction.
The ECB encryption operation is illustrated in Figure 11-2 on page 130 . Figure 11-3 on page 130
shows the ECB decryption mode, which is supported in a similar way.
Figure 11-2. ECB Mode - Encryption
Figure 11-3. ECB Mode - Decryption
0 1 0 0 0 0 0 0 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 data_0[7:0]
byte 1 (address) byte 0 (cmd.) byte 2 (AES cmd) byte 3 (data)
data_15[7:0]
byte 18 (data)
1 0 0 0 0 0 0 0
byte 19 (AES cmd)
AES start ECB, encryption 0x83 SRAM write
1. Configure SPI Access a) SRAM Write, refer to Section 6.2.3
b) Start Address 0x83
2. Configure AES Operation
Address 0x83: select ECB mode, direction
3. Write 128-bit data block Addresses 0x84 - 0x93: either plain or ciphertext
4. Start AES Operation Addresses 0x94: start AES operation, ECB mode
Block Cipher
Encryption
Encryption
Key
Plaintext
Ciphertext
Block Cipher
Encryption
Plaintext
Ciphertext
Encryption
Key
Block Cipher
Decryption
Decryption
Key
Plaintext
Ciphertext
Block Cipher
Decryption
Decryption
Key
Plaintext
Ciphertext