CC2420 Chipcon AS, CC2420 Datasheet - Page 43

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

When enabled, RX in-line security is
started as follows:
•
RX in-line security operations are always
performed on the first frame currently
inside the RXFIFO, even if parts of this
has already been read out over the SPI
interface. This allows the receiver to first
read the source address out to decide
which
authentication of the complete frame. In
CTR or CCM mode it is of course
important that bytes to be decrypted are
not read out before the security operation
is started.
When the SRXDEC command strobe is
issued, the FIFO and FIFOP pins will go
low.
microcontroller that no further data may be
read out before the next byte to be read
has undergone the requested security
operation.
The frame in the RXFIFO may be received
over RF or it may be written into the
RXFIFO
debugging
operations.
CTR mode encryption / decryption
CTR mode encryption / decryption is
performed by
within the TXFIFO / RXFIFO respectively.
SECCTRL1.SEC_TXL / SEC_RXL sets the
number of bytes between the length field
and the first byte to be encrypted /
decrypted respectively. This controls the
number of plaintext bytes in the current
frame.
encryption, only the MAC payload (see
Figure 15 on page 32) should be
encrypted, so SEC_TXL / SEC_RXL is set
to 3 + (0 to 20) depending on the address
information in the current frame.
When encryption is initiated, the plaintext
in the TXFIFO is then encrypted as
specified by [1]. The encryption module
will encrypt all the plaintext currently
available, and wait if not everything is
Chipcon AS SmartRF ® CC2420 Preliminary Datasheet (rev 1.0), 2003-11-17
Issue a SRXDEC command strobe. The
first frame in the RXFIFO is then
decrypted / authenticated as set by
the current security mode.
This
key
For
over
or
is
to
CC2420
IEEE
the
higher
to
use
SPI
indicate
on MAC frames
802.15.4
layer
before
interface
to
security
doing
MAC
the
for
SmartRF
prebuffered. The encryption operation may
also be started without any data in the
TXFIFO at all, and data will be encrypted
as it is written to the TXFIFO.
When decryption is initiated with a
SRXDEC command strobe, the ciphertext
of the RXFIFO is then decrypted as
specified by [1].
CBC-MAC
CBC-MAC
provided by
SECCTRL0.SEC_M sets the MIC length M,
encoded as (M-2)/2.
When enabling CBC-MAC in-line TXFIFO
authentication, the generated MIC is
written to the TXFIFO for transmission.
The frame length must include the MIC.
SECCTRL1.SEC_TXL / SEC_RXL sets the
number of bytes between the length field
and the first byte to be authenticated,
normally set to 0 for MAC authentication.
SECCTRL0.SEC_CBC_HEAD defines if the
authentication length is used as the first
byte of data to be authenticated or not.
This bit should be set for compliance with
[1].
When enabling CBC-MAC in-line RXFIFO
authentication, the generated MIC is
compared to the MIC in the RXFIFO. The
last byte of the MIC is replaced in the
RXFIFO with:
The other bytes in the MIC are left
unchanged in the RXFIFO.
CCM
CCM combines CTR mode encryption and
CBC-MAC authentication in one operation.
CCM is described in [3].
SECCTRL1.SEC_TXL / SEC_RXL sets the
number of bytes after the length field to be
authenticated but not encrytpted.
•
•
0x00 if the MIC is correct
0xFF if the MIC is incorrect
CC2420
in-line
®
hardware.
authentication
CC2420
Page 43 of 85
is