CC2420 Chipcon AS, CC2420 Datasheet - Page 42

• Manufacturer Part Number: CC2420
• Description: 2.4 GHz RF Transceiver for IEEE 802.15.4 and ZigBee
• Manufacturer: Chipcon AS

CC2420
selecting the flags for both nonces. The
flag setting is stored in the most significant
byte of the nonce. The flag byte used for
encryption and authentication is then
generated as shown in Figure 24.
Stand-alone encryption
Plain
plaintext and 128 bit keys [2], is available
using
plaintext is stored in stand-alone buffer
located at RAM location 0x120, as can be
seen from Table 6 on page 27.
A stand-alone encryption operation is
initiated by using the SAES command
strobe.
(SECCTRL0.SEC_SAKEYSEL) is then used
to encrypt the plaintext written to the
stand-alone buffer. Upon completion of the
encryption operation, the ciphertext is
written back to the stand-alone buffer,
thereby overwriting the plaintext.
Note that RAM write operations also
output data currently in RAM, so that a
new plaintext may be written at the same
time
ciphertext.
In-line security operations
CC2420
(encryption, decryption and authentication)
on
RXFIFO. These operations are called in-
line security operations.
As with other MAC hardware support
within
relies on the length field in the PHY
Chipcon AS SmartRF ® CC2420 Preliminary Datasheet (rev 1.0), 2003-11-17
Res
7
7
-
frames
as
Res
CC2420
AES
CTR Flag
6
6
can do MAC security operations
gives the user full flexibility in
bits 7:6
stand-alone
reading
MSB in CC2420 nonce RAM
The
5
5
0
encryption,
within
, in-line security operation
CTR mode flag byte
CBC Flag
4
4
0
bits 7:6
out
the
selected
encryption.
3
3
0
with
Figure 24.
the
TXFIFO
2
2
128
previous
1
L
1
L
The
CC2420
and
key
bit
0
0
Security Flag Byte
SmartRF
The frame counter part of the nonce must
be incremented for each new packet by
software.
header. A correct length field must
therefore
operations.
The key, nonce (does not apply to CBC-
MAC), and SECCTRL0 and SECCTRL1
control registers must be correctly set
before
operation.
The in-line security mode is set in
SECCTRL0.SEC_MODE to one of the
following modes:
•
•
•
•
When enabled, TX in-line security is
started in one of two ways:
•
•
Res
7
Disabled
CBC-MAC (authentication)
CTR (encryption / decryption)
CCM (authentication and encryption /
decryption)
Issue a STXENC command strobe. In-
line security will be performed within
the TXFIFO, but a RF transmission
will not be started. Ciphertext may be
read back using RAM read operations.
Issue
command strobe. In-line security will
be performed within the TXFIFO and a
RF transmission of the ciphertext is
started.
CBC-MAC flag byte
Adata
starting
6
be
a
SECCTRL0.SEC_M
5
used
STXON
®
any
M
4
CC2420
for
in-line
3
or
all
Page 42 of 85
STXONCCA
2
security
security
1
L
0