EM2420 ETC [List of Unclassifed Manufacturers], EM2420 Datasheet - Page 45

• Manufacturer Part Number: EM2420
• Description: 2.4 GHz IEEE 802.15.4 / ZigBee RF Transceiver
• Manufacturer: ETC [List of Unclassifed Manufacturers]

The EM2420 gives the user full flexibility in
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.
Figure 24. The EM2420 Security Flag Byte
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 29.
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
The
operations (encryption, decryption and
authentication)
TXFIFO and RXFIFO. These operations
are called in-line security operations.
As with other MAC hardware support
within
operation relies on the length field in the
PHY header. A correct length field must
Ember Part Number: 120-0049-000C
Res
7
7
-
EM2420
as
Res
AES
CTR Flag
6
6
bits 7:6
the
stand-alone
reading
MSB in EM2420 nonce RAM
The
5
5
0
encryption,
EM2420,
CTR mode flag byte
can
on
CBC Flag
4
4
0
bits 7:6
frames
do
out
selected
encryption.
3
3
0
in-line
MAC
with
the
2
2
within
128
previous
security
security
1
L
1
L
The
EM2420 Datasheet
key
the
bit
0
0
The frame counter part of the nonce must
be incremented for each new packet by
software.
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:
•
•
When enabled, RX in-line security is
started as follows:
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
EM2420
for
in-line
3
or
all
Page 45 of 89
2
STXONCCA
security
security
1
L
0