KeeLoq Code Hopping Encoder and Transponder
2001 Microchip Technology Inc.
Preliminary
DS40158E-page 1
FEATURES
Security
Two programmable 64-bit encoder keys
16/32-bit bi-directional challenge and response
using one of two keys
69-bit transmission length
32-bit unidirectional code hopping, 37-bit non-
encrypted portion
Encoder keys are read protected
Programmable 28/32-bit serial number
60/64-bit, read-protected seed for secure learning
Three IFF encryption algorithms
Delayed increment mechanism
Asynchronous transponder communication
Queuing information transmitted
Operating
2.0V - 6.6V operation, 13V encoder only
operation
Three switch inputs [S2, S1, S0]--seven functions
Batteryless bi-directional transponder
Selectable baud rate and code word blanking
Automatic code word completion
Battery low signal transmitted
Non-volatile synchronization
PWM or Manchester RF encoding
Combined transmitter, transponder operation
Anti-collision of multiple transponders
Passive proximity activation
Device protected against reverse battery
Intelligent damping for high Q LC-circuits
Other
37-bit nonencrypted part contains 28/32-bit serial
number, 4/0-bit function code, 1-bit battery low,
2-bit CRC, 2-bit queue
Simple programming interface
On-chip tunable RC oscillator (10%)
On-chip EEPROM
64-bit user EEPROM in transponder mode
Battery-low LED indication
SQTP serialization quick-time programming
8-pin PDIP/SOIC/TSSOP and die
PACKAGE TYPES
BLOCK DIAGRAM
Typical Applications
Automotive remote entry systems
Automotive alarm systems
Automotive immobilizers
Gate and garage openers
Electronic door locks (Home/Office/Hotel)
Burglar alarm systems
Proximity access control
HCS4
1
0
S0
S1
S2/LED
LC1
V
DD
LC0
PWM
GND
1
8
2
3
4
7
6
5
PDIP, SOIC
HCS
410
S2/LED
LC1
GND
PWM
1
2
3
4
8
7
6
5
S1
S0
V
DD
LC0
TSSOP
Oscillator
Configuration Register
Power
Control
Wake-up
Logic
Address
Decoding EEPROM
Debounce
Control
and
Queuer
LED
Control
PWM
Driver
PPM
Detector
PWM
PPM
Manch.
Encoder
T
r
ansponder Circ
u
it
r
y
Cont
rol Logi
c
and C
ount
ers
E
n
cry
p
t
i
on/
I
n
c
r
ement
Logic
R
egi
s
t
er
V
DD
S0
S1
S2
LCI0
LCI1
PWM
*Secure Learn patent pending.
HCS410
K
EE
L
OQ
Code Hopping Encoder and Transponder
HCS410
DS40158E-page 2
Preliminary
2001 Microchip Technology Inc.
DESCRIPTION
The HCS410 is a code hopping transponder device
designed for secure entry systems. The HCS410 uti-
lizes the patented K
EELOQ
code hopping system and
bi-directional challenge-and-response for logical and
physical access control. High security learning mecha-
nisms make this a turnkey solution when used with the
K
EELOQ
decoders. The encoder keys and synchroniza-
tion information are stored in protected on-chip
EEPROM.
A low cost batteryless transponder can be imple-
mented with the addition of an inductor and two capac-
itors. A packaged module including the inductor and
capacitor will also be offered.
A single HCS410 can be used as an encoder for
Remote Keyless Entry (RKE) and a transponder for
immobilization in the same circuit and thereby dramat-
ically reducing the cost of hybrid transmitter/transpon-
der circuits.
1.0
SYSTEM OVERVIEW
1.1
Key Terms
Anti-Collision Allows two transponders to be in
the files simultaneously and be verified individu-
ally.
CH Mode Code Hopping Mode. The HCS410
transmits a 69-bit transmission each time it is acti-
vated, with at least 32-bits changing each time the
encoder is activated.
Encoder Key A unique 64-bit key generated and
programmed into the encoder during the manu-
facturing process. The encoder key controls the
encryption algorithm and is stored in EEPROM on
the encoder device.
IFF Identify friend or foe is a means of validating
a token. A decoder sends a random challenge to
the token and checks that the response of the
token is a valid response.
K
EE
L
OQ
Encryption Algorithm The high security
level of the HCS410 is based on the patented
K
EE
L
OQ
technology. A block cipher encryption
algorithm based on a block length of 32 bits and a
key length of 64 bits is used. The algorithm
obscures the information in such a way that even
if the unencrypted/challenge information differs by
only one bit from the information in the previous
transmission/challenge, the next coded transmis-
sion/response will be totally different. Statistically,
if only one bit in the 32-bit string of information
changes, approximately 50 percent of the coded
transmission will change.
Learn The HCS product family facilitates sev-
eral learning strategies to be implemented on the
decoder. The following are examples of what can
be done.
Normal Learn The receiver uses the same infor-
mation that is transmitted during normal operation to
derive the transmitter's encoder key, decrypt the dis-
crimination value and the synchronization counter.
Secure Learn* The transmitter is activated through
a special button combination to transmit a stored
60-bit value (random seed) that can be used for key
generation or be part of the key. Transmission of the
random seed can be disabled after learning is com-
pleted.
Manufacturer's Code A 64-bit word, unique to
each manufacturer, used to produce a unique
encoder key in each transmitter (encoder).
Passive Proximity Activation When the HCS410
is brought into in a magnetic field without a
command given by the base station, the HCS410
can be programmed to give an RF transmission.
Transport Code A 32-bit transport code needs to
be given before the HCS410 can be inductively
programmed. This prevents accidental
programming of the HCS410.
HCS410
2001 Microchip Technology Inc.
Preliminary
DS40158E-page 3
1.2
K
EE
L
OQ
Code Hopping Encoders
When the HCS410 is used as a code hopping encoder
device, it is ideally suited to keyless entry systems,
primarily for vehicles and home garage door openers.
It is meant to be a cost-effective, yet secure solution to
such systems. The encoder portion of a keyless entry
system is meant to be carried by the user and operated
to gain access to a vehicle or restricted area.
Most keyless entry systems transmit the same code
from a transmitter every time a button is pushed. The
relative number of code combinations for a low end
system is also a relatively small number. These
shortcomings provide the means for a sophisticated
thief to create a device that `grabs' a transmission and
retransmits it later or a device that scans all possible
combinations until the correct one is found.
The HCS410 employs the K
EE
L
OQ
code hopping tech-
nology and an encryption algorithm to achieve a high
level of security. Code hopping is a method by which
the code transmitted from the transmitter to the
receiver is different every time a button is pushed. This
method, coupled with a transmission length of 69 bits,
virtually eliminates the use of code `grabbing' or code
`scanning'.
The HCS410 has a small EEPROM array which must
be loaded with several parameters before use. The
most important of these values are:
A 28/32-bit serial number which is meant to be
unique for every encoder
64-bit seed value
A 64-bit encoder key that is generated at the time
of production
A 16-bit synchronization counter value.
Configuration options
The 16-bit synchronization counter value is the basis
for the transmitted code changing for each transmis-
sion, and is updated each time a button is pressed.
Because of the complexity of the code hopping encryp-
tion algorithm, a change in one bit of the synchroniza-
tion counter value will result in a large change in the
actual transmitted code.
Once the encoder detects that a button has been
pressed, the encoder reads the button and updates the
synchronization counter. The synchronization counter
value, the function bits, and the discrimination value
are then combined with the encoder key in the
encryption algorithm, and the output is 32 bits of
encrypted information (Figure 1-1). The code hopping
portion provides up to four billion changing code com-
binations. This data will change with every button
press, hence, it is referred to as the code hopping
portion of the code word.
The 32-bit code hopping portion is combined with the
button information and the serial number to form the
code word transmitted to the receiver. The code word
format is explained in detail in Section 2.2.
FIGURE 1-1:
BASIC OPERATION OF A CODE HOPPING TRANSMITTER (ENCODER)
K
EE
L
OQ
Algorithm
Button Press
Information
Encryption
EEPROM Array
32 Bits of
Encrypted Data
Serial Number
Transmitted Information
Encoder Key
Sync Counter
Serial Number
HCS410
DS40158E-page 4
Preliminary
2001 Microchip Technology Inc.
1.3
K
EE
L
OQ
IFF
The HCS410 can be used as an IFF transponder for
verification of a token. In IFF mode the HCS410 is ide-
ally suited for authentication of a key before disarming
a vehicle immobilizer. Once the key has been inserted
in the car's ignition the decoder would inductively poll
the key validating it before disarming the immobilizer.
IFF validation of the token involves a random challenge
being sent by a decoder to a token. The token then
generates a response to the challenge and sends this
response to the decoder (Figure 1-2). The decoder cal-
culates an expected response using the same chal-
lenge. The expected response is compared to the
response received from the token. If the responses
match, the token is identified as a valid token and the
decoder can take appropriate action.
The HCS410 can do either 16 or 32-bit IFF. The
HCS410 has two encryption algorithms that can be
used to generate a response to a challenge. In addition
there are up to two encoder keys that can be used by
the HCS410. Typically each HCS410 will be pro-
grammed with a unique encoder key(s).
In IFF mode, the HCS410 will wait for a command from
the base station and respond to the command. The
command can either request a read/write from user
EEPROM or an IFF challenge response. A given 16 or
32-bit challenge will produce a unique 16/32-bit
response, based on the IFF key and IFF algorithm
used.
FIGURE 1-2:
BASIC OPERATION OF AN IFF TOKEN
IFF Key
Serial Number
K
EE
L
OQ
IFF
Algorithm
Serial Number
EEPROM Array
Challenge Received from Decoder
Response
Read by Decoder
HCS410
2001 Microchip Technology Inc.
Preliminary
DS40158E-page 5
2.0
DEVICE OPERATION
The HCS410 can either operate as a normal code hop-
ping transmitter with one or two IFF keys (Figure 2-1)
or as purely an IFF token with two IFF keys (Figure 2-2
and Figure 2-3). When used as a code hopping trans-
mitter the HCS410 only needs the addition of buttons
and RF circuitry for use as a transmitter. Adding the
transponder function to the transmitter requires the
addition of an inductor and two capacitors as shown in
Figure 2-1 and Figure 2-2. A description of each pin is
given in Table 2-1. Table 2-2 shows the function codes
for using the HCS410.
FIGURE 2-1:
COMBINED TRANSMITTER/
TRANSPONDER CIRCUIT
FIGURE 2-2:
TRANSPONDER CIRCUIT
FIGURE 2-3:
2-WIRE, 1 OR 2-KEY IFF
TOKEN
Figure 2-4 shows how to use the HCS410 with a 12V
battery as a code hopping transmitter. The circuit uses
the internal regulator, normally used for charging a
capacitor/battery in LC mode, to generate a 6V supply
for the HCS410.
FIGURE 2-4:
HCS410 ENCODER WITH 12V
BATTERY
FIGURE 2-5:
LED CONNECTION TO
S2/LED OUTPUT
FIGURE 2-6:
LC PIN BLOCK DIAGRAM
1
8
RF
2
3
4
7
6
5
1 F
1
8
2
3
4
7
6
5
1 F
1
8
2
3
4
7
6
5
1 F
Data I/O
1
8
RF
2
3
4
7
6
5
6.3V
12V
Pulse
V
DD
S2/LED
220
220
60k
30
V
DD
6.3V
Damp
Out
MOD
Detector
Rectifier,
Damping,
Clamping
15V
15V
100
100
LC1
LC0
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