HCS365 Datasheet, PDF (2/34 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS365
The crypt key, serial number, and configuration data
are stored in an EEPROM array which is not accessible
via any external connection. The EEPROM data is pro-
grammable but read protected. The data can be veri-
fied only after an automatic erase and programming
operation. This protects against attempts to gain
access to keys or manipulate synchronization values.
In addition, the HCS365 supports a dual encoder. This
allows two manufacturers to use the same device with-
out having to use the same manufacturer’s code in
each of the encoders. The HCS365 provides an easy
to use serial interface for programming the necessary
keys, system parameters, and configuration data.
1.0 SYSTEM OVERVIEW
Key Terms
The following is a list of key terms used throughout this
data sheet. For additional information on KEELOQ and
code hopping, refer to Technical Brief (TB003).
• RKE - Remote Keyless Entry
• Button Status - Indicates what button input(s)
activated the transmission. Encompasses the 4
button status bits S3, S2, S1 and S0 (Figure 3-2).
• Code Hopping - A method by which a code,
viewed externally to the system, appears to
change unpredictably each time it is transmitted.
• Code Word - A block of data that is repeatedly
transmitted upon button activation (Figure 3-2).
• Transmission - A data stream consisting of
repeating code words (Figure 4-1).
• Crypt Key - A unique and secret 64-bit number
used to encrypt and decrypt data. In a symmetri-
cal block cipher such as the KEELOQ algorithm,
the encryption and decryption keys are equal and
will therefore be referred to generally as the crypt
key.
• Encoder - A device that generates and encodes
data.
• Encryption Algorithm - A recipe whereby data is
scrambled using a crypt key. The data can only be
interpreted by the respective decryption algorithm
using the same crypt key.
• Decoder - A device that decodes data received
from an encoder (i.e., HCS5XX).
• Decryption Algorithm - A recipe whereby data
scrambled by an encryption algorithm can be
unscrambled using the same crypt key.
• Learn – Learning involves the receiver calculating
the transmitter’s appropriate crypt key, decrypting
the received hopping code and storing the serial
number, synchronization counter value, and crypt
key in EEPROM. The KEELOQ product family facil-
itates several learning strategies to be imple-
mented on the decoder. The following are
examples of what can be done.
- Simple Learning
The receiver uses a fixed crypt key. The crypt
key is common to every component used by
the same manufacturer.
- Normal Learning
The receiver derives a crypt key from the
encoder serial number. Every transmitter has
a unique crypt key.
- Secure Learning
The receiver derives a crypt key from the
encoder seed value. Every encoder has a
unique seed value that is only transmitted by
a special button combination.
• Manufacturer’s Code – A unique and secret 64-
bit number used to derive crypt keys. Each
encoder is programmed with a crypt key that is a
function of the manufacturer’s code. Each
decoder is programmed with the manufacturer
code itself.
The HCS365 code hopping encoder is designed specif-
ically for keyless entry systems. In particular, typical
applications include vehicles and home garage door
openers. The encoder portion of a keyless entry sys-
tem is integrated into a transmitter carried by the user.
The transmitter is operated to gain access to a vehicle
or restricted area. The HCS365 is meant to be a cost-
effective yet secure solution to such systems requiring
very few external components (Figure 2-1).
Most low end keyless entry transmitters are given a
fixed identification code that is transmitted every time a
button is pushed. The number of unique identification
codes in a low end system is usually a relatively small
number. These shortcomings provide an opportunity
for a sophisticated thief to create a device that ‘grabs’
a transmission and retransmits it later or a device that
quickly ‘scans’ all possible identification codes until the
correct one is found.
The HCS365, on the other hand, employs the KEELOQ
code hopping technology coupled with a transmission
length of 67 bits to virtually eliminate the use of code
‘grabbing’ or code ‘scanning’. The high security level of
the HCS365 is based on the patented KEELOQ technol-
ogy. A block cipher 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 if a single
hopping code data bit changes (before encryption), sta-
tistically more than 50% of the encrypted data bits will
change.
DS41109D-page 2
Preliminary
© 2002 Microchip Technology Inc.