hcs500 Microchip Technology Inc., hcs500 Datasheet - Page 17

• Manufacturer Part Number: hcs500
• Description: Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

6.0
The HCS500 supports three learning schemes which are selected during the initialization of the system EEPROM. The
learning schemes are:
• Normal learn using the K
• Secure learn using the K
• Secure learn using the XOR algorithm
6.1
This learning scheme uses the K
the crypt key. The 28-bit serial number is patched with predefined values as indicated below to form two 32-bit seeds.
Then, using the K
6.2
This scheme uses the secure seed transmitted by the encoder to derive the two input seeds. The decoder always uses
the lower 64 bits of the transmission to form a 60-bit seed. The upper 4 bits are always forced to zero.
For 32-bit seed encoders (HCS200, HCS201, HCS300, HCS301):
For 48-bit seed encoders (HCS360, HCS361):
For 60-bit seed encoders (HCS362, HCS365, HCS370, HCS410, HCS412, HCS473):
The K
6.3
This scheme uses the seed transmitted by the encoder to derive the two input seeds. The decoder always use the lower
64 bits of the transmission to form a 60-bit seed. The upper 4 bits are always forced to zero.
For 32-bit seed encoders (HCS200, HCS201, HCS300, HCS301):
For 48-bit seed encoders (HCS360/HCS361):
For 60-bit seed encoders (HCS362, HCS365, HCS370, HCS410, HCS412, HCS473):
Then, using the manufacturer’s code the crypt key is derived as follows:
2002 Microchip Technology Inc.
SourceH = 60000000 00000000H + Serial Number |
SourceL = 20000000 00000000H + Serial Number |
KeyH
KeyL
SourceH = Serial Number
SourceL = Seed
SourceH = Serial Number (with upper 4 bits set to zero)
SourceL = Seed
SourceH = Seed
SourceL = Seed
KeyH
KeyL
SourceH = Serial Number
SourceL = Seed
SourceH = Serial Number (with upper 4 bits set to zero)
SourceL = Seed
SourceH = Seed
SourceL = Seed
KeyH
KeyL
EE
L
KEY GENERATION
Normal (Serial Number derived) Learn using the K
Secure (Seed Derived) Learn using the K
Secure (Seed Derived) Learn using the XOR Algorithm
OQ
Lower 32 bits
Lower 32 bits
Lower 32 bits
Upper 32 bits
Upper 32 bits
Upper 32 bits
decryption algorithm and the manufacturer’s code is used to derive the crypt key as follows:
EE
L
32 bits
Lower 32 bits
Lower 32 bits
32 bits
Lower 32 bits
Lower 32 bits
= F
= Decrypt (SourceL)
= SourceL XOR 64-Bit Manufacturer’s Code
Upper 32 bits
Upper 32 bits
= F
= Decrypt (SourceH)
= SourceH XOR 64-Bit Manufacturer’s Code
OQ
K
K
decryption algorithm and the manufacturer’s code the crypt key is derived as follows:
EE
EE
EE
EE
L
L
L
L
OQ
OQ
OQ
OQ
Lower 28 bits
Lower 28 bits
Decryption
Decryption
EE
(with upper 4 bits set to zero)
with upper 4 bits set to zero
decryption algorithm
decryption algorithm
L
OQ
decryption algorithm and the 28-bit serial number of the transmitter to derive
(SourceL) |
(SourceH) |
64 Bit Manufacturer’s Code
64 Bit Manufacturer’s Code
64-Bit Manufacturer’s Code
64-Bit Manufacturer’s Code
28 Bits
28 Bits
Upper 16 bits
Upper 16 bits
EE
L
Lower 32 bits
OQ
Upper 32 bits
Decryption Algorithm
<<16 + Seed
<<16 + Seed
EE
L
OQ
Decryption Algorithm
Upper 16 bits
Upper 16 bits
HCS500
DS40153C-page 17