CC2430 Datasheet, PDF (137/234 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
• (3a) If l(a)=0, (that is A_Data =0),
then L(a) is the empty string. We
note l(a) the length of a in octets.
• (3b) If 0 < l(a) < 2¹⁶ - 2⁸ , then L(a)
is the 2-octets encoding of l(a).
The Additional Authentication Data is
appended to the A_Data length field L(a).
The Additional Authentication Blocks is
padded with zeros until the last Additional
Authentication Block is full. There is no
restriction on the length of a.
AUTH-DATA = L(a) + Authentication Data
+ (zero padding)
(4) The last block of the message is
padded with zeros until full (that is if its
length is not a multiple of 128).
(5) The software concatenates the block
B0, the Additional Authentication Blocks if
any, and the message;
Input message = B0 + AUTH-DATA +
Message + (zero padding of message)
(6) Once the input message authentication
by CBC-MAC is finished, the software
leaves the uploaded buffer contents
unchanged (M=16), or keeps only the
buffer’s higher M bytes unchanged, while
setting the lower bits to 0 (M != 16).
The result is called T.
Message Encryption
(7) The software creates the key stream
block A0. Note that L=6, with the current
example of the CTR generation. The
content is shown in Figure 30.
Note that any value but zero works for the
CTR value.
The content of the Encryption Flag byte is
described in Figure 31.
Name
Designation
A0
First CTR value for CCM mode
Byte 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Name Flag
NONCE
CTR
Figure 30: Message Encryption Phase Block 0
Bit
Name
Value
Name
FLAG/A0
7
6
Reserved
0
0
Designation
Encryption Flag Field for CCM mode
5
4
3
2
-
0
0
0
1
1
L-1
0
0
1
Figure 31: Encryption Flag Byte
Message Encryption (cont.)
(8) The software loads A0 by selecting a
Load IV/Nonce command. To do so, it sets
Mode to CFB or OFB at the same time it
selects the Load IV/Nonce command.
CC2430 PRELIMINARY Data Sheet (rev. 1.03) SWRS036A
Page 137 of 232