CC2510FX Datasheet, PDF (136/253 Pages) List of Unclassifed Manufacturers – True System-on-Chip with Low Power RF Transceiver and 8051 MCU

CC2510Fx / CC2511Fx
CCM is a combination of CBC-MAC and
CTR. Parts of the CCM must therefore be
done in software. The following section
gives a short explanation of the necessary
steps to be done.
13.9.5.1 CBC-MAC
When performing CBC-MAC encryption,
data is only downloaded to the
coprocessor in CBC-MAC mode except for
the last block, one block at a time. Before
the last block is loaded, the mode is
changed to CBC. The last block is
downloaded and the block uploaded is the
message MAC.
CBC-MAC decryption is similar to
encryption. The message MAC uploaded
must be compared with the MAC to be
verified.
13.9.5.2 CCM mode
To encrypt a message under CCM mode,
the following sequence can be conducted
(key is already loaded):
Message Authentication Phase
This phase takes place during steps 1-6
shown in the following.
(1) The software loads the IV with zeros.
(2) The software creates the block B0.
The layout of block B0 is shown in Figure
27.
.
Name
Designation
B0
First block for authentication in CCM mode
Byte 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Name Flag
NONCE
L_M
Figure 27: Message Authentication Phase Block 0
There is no restriction on the NONCE
value. L_M is the message length in bytes.
The content of the Authentication Flag
byte is described in Figure 28.
L is set to 6 in this example. So, L-1 is set
to 5. M and A_Data can be set to any
value.
Bit
Name
Value
Name
FLAG/B0
7
6
Reserved A_Data
0
x
Designation
Authentication Flag Field for CCM mode
5
4
3
2
1
(M-2)/2
L-1
x
x
x
1
0
0
1
Figure 28: Authentication Flag Byte
(3) If some Additional Authentication Data
(called a later) is needed (that is A_Data
=1), the software creates the A_Data
length field, called L(a) by :
• (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).
CC2510Fx/CC2511Fx PRELIMINARY Data Sheet (Rev. 1.2) SWRS055A Page 136 of
252