Silicon Laboratories Si4010 User Manual

Si4010-Keyfob-AES-DEMO

Si4010 KEY FOB DEMO KIT WITH AES CAPABILITY
U

SER’S GUIDE

1. Purpose

Thank you for your interest in Silicon Laboratories’ Si4010 SoC RF key fob demo kit with AES capability. The
Silicon Laboratories Si4010 key fob demo kit with AES capability contains everything you need to familiarize
yourself with and evaluate the Si4010 RF SoC. The kit has two versions, one for the 434 MHz band and one for the
868 MHz band. The key features of the developme nt pla tform are as fo llows :

 The key fob demo board has five push buttons and one LED output, a PCB antenna, and a battery in a plastic

case.

 The key fob uses hardware-accelerated 128-bit advanced encryption standard (AES) encryption and rolling

counter for RKE application.

 The receiver demo board has a graphic LCD to display received key fob commands.
 The provided software pack contains all the d ocum entation and files needed to develop a user application. Th e

kit supports the use of Silicon Laboratories’ Integrated Development Environment (IDE) for software debugging
and the use of the Keil C compiler, assembler, and linker toolchain.

 Contains demo applications using API functions and the key fob demo application.

2. Kit Contents

The kit contains the following items:

Qty Part Number Description

4010-DAAKF_434 Si4010 Key Fob Demo Kit with AES Capability 434 MHz

1 4010-DAPB_434 Si4010 Universal Key Fob 434 MHz
1 4313-DACB_ANY Si4313 LCD FSK/OOK Receiver any band
1 MSC-AT50-434 434 MHz Antenna
1 MSC-PLPB_1 Key Fob Plastic Case (translucent grey)
1 CRD2032 CR2032 3 V coin battery
1 MSC-DKSW1 Wireless Development Suite disc

4010-DAAKF_868 Si4010 Key Fob Demo Kit with AES Capability 868 MHz

1 4010-DAPB_868 Si4010 Universal Key Fob 868 MHz
1 4313-DACB_ANY Si4313 LCD FSK/OOK Receiver any band
1 MSC-AT50-868 868 MHz Antenna
1 MSC-PLPB_2 Key Fob Plastic Case (translucent red)
1 CRD2032 CR2032 3 V coin battery
1 MSC-DKSW1 Wireless Development Suite disc

Rev 1.1 4/11 Copyright © 2011 by Silicon Laboratories Si4010-Keyfob-AES-DEMO

Si4010-Keyfob-AES-DEMO



Figure 1. Si4010 Universal Key Fob and Plastic Case (P/N 4010-DAPB 868 and MSC-PLPB_1)

Figure 2. Si4313 LCD FSK/OOK Receiver Any-Band (P/N 4313-DACB ANY) with 434 MHz Antenna

(P/N MSC-AT50-434)

2 Rev 1.1

Si4010-Keyfob-AES-DEMO

3. Key Fob Demo with AES Capability

The 4010-DAPB RKE key fob transmitter and the Si4313 FSK receiver are the transmit and receive devices used
in this key fob demo. This transmit/receive pair can be used to evaluate the capabilities of the Si4010 transmitter
and the Si4313 receiver.

3.1. Operation of the Demo

The Si4313 demo receiver board uses the following RF parameters:

 9.6 kbps
 FSK modulation
 433.92 MHz or 868.3 MHz center frequency (menu selectable)
 ±70 kHz deviation

If any push button is pressed on the key fob, it sends a message to the receiver. The demo uses Silicon Labs'
general EZMacPRO protocol.

Table 1. General EZMacPRO Extended Packet Configuration Used by Demo Key Fobs

Preamble SynchWord MACHeader MACPayload CRC

Min.13 bytes 2 bytes 5 bytes 0...64 bytes 2 bytes
0xAA...0xAA 0x2DD4 CTRL CID SID DID PL NHDR NWK payload CRC

3.2. Association

To enable the receiver to react to the button presses on the key fob(s), they have to be paired (i.e., the key fob has
to be associated to the receiver by pressing the left and right buttons simultaneously on the key fob).

Table 2. The MAC Payload Field of the “Associate Request from TX only Device” Packet

MACPayload

NHDR NWK Payload

1 byte 1 bytes 1 byte 1 byte 4 byte 4 byte

0x47 0x05 0x01 AES Address Rolling Counter

3.2.1. Meanings of the Different Fields

 AES—Defines whether the transmitter is using AES-128 encryption or not. It is set to 0x01; then, the Rolling

counter field of the packets is extended to 16 bytes length (12 dummy bytes are appended) and is encoded by
AES-128. Other fields of the packet are not affected by the encryption.

 Address—4 bytes of key fob address. The four byte random number factory burned in the Si4010 is used as

the address.

 Rolling Counter—The transmitter increments a 4 byte counter after every packet transmission. This counter is

stored in the MTP memory of the Si4010.

If the receiver accepts the association, it registers the Address, Master Key, and Rolling Counter value of the
requesting key fob.

The Master accepts the association if it is in pairing mode and there is a free slot for a key fob (i.e., if there are
fewer than four key fobs associated to the receiver).

After power up, the Receiver board is in pairing mode automatically. After pairing, it goes to normal packet
reception mode. The Pairing mode can be invoked by pressing the push button, PB3, on the Receiver Board. This
button needs to be pressed before the second and any subsequent pairing. If the PB is pressed for more than one
second, the receiver disassociates all key fobs.

Rev 1.1 3

Si4010-Keyfob-AES-DEMO

3.3. Button is Pressed on the Key Fob

If any single button or button combination (except association combination) is pressed on the key fob, then it
transmits a key fob data packet showing the button number in the button field.

Table 3. The MAC Payload Field of the “Key Fob Data” Packet

MAC Payload

NHDR NWK payload

1byte 1byte 4bytes 1byte 2bytes 1byte 4byte

0x04 AES Address Button TEMP Battery Rolling Counter

3.3.1. Meaning of the Different Fields

 AES—Defines whether the transmitter is using AES-128 encryption. It is set to 0x01, then Button, Temp,

Battery, and Rolling counter fields of the packets are extended to 16 bytes length all together and are encoded
by AES-128. Other fields of the packet are not affected by the encryption.

 Address—4 bytes of key fob address. The four-byte random number factory burned in the Si4010 is used as

the address.

 Button—Each bit of this byte corresponds to the status of a push button on the key fob. If the bit is set, the

given button is pressed. If the bit is cleared, the button is released.

 TEMP—The temperature is encoded as a signed 16-bit integer. Each incremental bit of temperature reading

represents 0.1 °C. If the temperature function is not implemented in the key fob, this field is set to 0xFFFF.

 Battery—1 byte unsigned char showing the actual power supply status of the key fob. It must be interpreted as

follows:

1bit 1bit 1bit 5bits

Lbd Available LBD Status Battery Voltage Available Battery Voltage[4:0]

 LBD Available Bit—If set, the LBD status bit shows the actual status of the batter y.
 LBD Status—Shows whether the actual battery voltage is above the LBD limit (set if the actual voltage is below

the threshold). The LBD limit is configurable in the key fob program.

 Battery Voltage Available—If set, the battery voltage information is available.
 Battery Voltage—It shows the actual battery voltage of the key fob. Each increment of the battery voltage bit

corresponds to 50 mV. However, 0 represents 1.7 V.

 Rolling Counter—The transmitter increments a 4 byte counter after every packet transmission. This counter is

stored in the MTP memory of the Si4010.

Since AES is used by the key fob, the receiver board decrypts the encrypted portion of the packet and discards the
dummy bytes. Then, the receiver board checks the sync counte r value agains t it s own copy of the sender key fob's
counter. If the key fob sync counter value minus the copy counter value is more than zero and less than a
configurable window value (default value is 10), the master increments the copy.

4 Rev 1.1

3.4. Key Handling

Application

Level

MK: Master Key
SK: Session Key

RKE_MK

Function

Level

AES_128AES_128 AES_128Node_Association Node_ButtonPress Functionzzzzzzzz

Btn_K

Session

Level

FuncX_K

Assoc_K

AES_128

12byte padding(0) +

Node Addr

Assoc_SK

AES_128

12byte padding(0) +

Node Addr

Btn_SK

Si4010-Keyfob-AES-DEMO

Figure 3. SRW AES128 Applications Key Hierarchy

AES keys used in the demos are generated according to the hierarchy shown in Figure 3. Only the Application
level keys are stored on the receiver board. The function level keys are calculated at power-up. The Session level
keys are calculated at their first use.

In the key fobs Function level, keys are not generated but only stored to save power. The Session level keys are
calculated at each power up.

The Assoc_SK is used for association packets, and the Btn_SK is used for encrypting the messages generated by
a button press.

3.5. Key Fob Firmware Description

The complete project of the program used in the demo key fob can be fo und in the Si4 010 documentation kit in the
“rke_demo” folder.

The key fob wakes up for button push or battery insert. If the battery was inserted, the vSys_FirstPowerUp() API
function is called, which shuts down the chip after 600 ms. This is for safe startup in case of battery contact
bouncing. Upon button push wakeup, the system variables and hardware control registers are initialized first, and
the session keys used in the AES encoding are generated from the function keys and the device address. Then,
button debouncing is made.

If a valid button push is detected, first a packet is assembled and transmitted six times for the LED receiver demo
board used in the Si4010 Simplified Key Fob Demo Kit (see details in “AN516: Si4010 Simplified Key Fob Demo
Quick Start Guide”). Then, a packet is assembled according to the description in the previous chapters. It is
transmitted in FSK modulation for the Si4313 receiver board (part of this kit), and then also in OOK modulation.
The next step is to increment the sync counter stored in the MTP memory.

If there is no valid button push detected for 3.2 s, the program shuts down the chip.

Rev 1.1 5