CC2420-RTR1 datasheet(45/92 Pages) TI

45 / 92 page

CC2420

SWRS041B

Page 45 of 89

21 MAC Security Operations (Encryption and Authentication)

CC2420 features hardware IEEE 802.15.4

MAC security operations. This includes

counter

mode

(CTR)

encryption

decryption, CBC-MAC authentication and

CCM encryption + authentication. All

security operations are based on AES

encryption [2] using 128 bit keys. Security

operations are performed within the

transmit and receive FIFOs on a frame

basis.

CC2420 also includes stand-alone AES

encryption, in which one 128 bit plaintext

is encrypted to a 128 bit ciphertext.

The

SAES

STXENC

and

SRXDEC

command strobes are used to start

security operations in

CC2420 as will be

described in the following sections. The

ENC_BUSY

status bit (see Table 5) may be

used to monitor when a security operation

has been completed. Security command

strobes issued while the security engine is

busy will be ignored, and the ongoing

operation will be completed.

Table 6 on page 31 shows the

CC2420

RAM memory map, including the security

related data located from addresses

0x100 through 0x15F. RAM access (see

the RAM access section on page 29) is

used to write or read the keys, nonces and

stand-alone buffer. All security related

data is stored little-endian, i.e. the least

significant byte is transferred first over the

SPI interface during RAM read or write

operations.

For a complete description of IEEE

802.15.4 MAC security operations, please

refer to [1].

21.1

Keys

All security operations are based on 128

bit keys. The

CC2420 RAM space has

storage space for two individual keys

(KEY0 and KEY1). Transmit, receive and

stand-alone encryption may select one of

these

two

keys

individually

the

SEC_TXKEYSEL

SEC_RXKEYSEL

and

SEC_SAKEYSEL

control bits (SECCTRL0).

As can be seen from Table 6 on page 31,

KEY0 is located from address 0x100 and

KEY1 from address 0x130.

A way of establishing the keys used for

encryption and authentication must be

decided for each particular application.

IEEE 802.15.4 does not define how this is

done, it is left to the higher layer of the

protocol.

ZigBee

uses

Elliptic

Curve

Cryptography (ECC) based approach to

establish keys. For PC based solutions,

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