HCS512-ISO 查看數據表（PDF） - Microchip Technology

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HCS512-ISO

KEELOQ® Code Hopping Decoder

Microchip Technology 

HCS512

7.3 Key Generation Algorithms

There are two key generation algorithms implemented in the HCS512 decoder. The KEELOQ decryption algorithm pro-

vides a higher level of security than the XOR algorithm. Section 6.1 describes the selection of the algorithms in the con-

figuration byte.

7.3.1 KEELOQ DECRYPT ALGORITHM

This algorithm uses the KEELOQ decryption algorithm and the manufacturer’s code to derive the crypt key as follows:

Key Upper 32 bits = Decrypt (SourceH) 64 Bit Manufacturers Code

Key Lower 32 bits = Decrypt (SourceL) 64 Bit Manufacturers Code

7.3.2 XOR WITH THE MANUFACTURER’S CODE

The two 32-bits seeds are XOR with the manufacturer’s code to form the 64 bit crypt key.

Key Upper 32 bits = SourceH XOR Manufacturers Code Upper 32 bits

Key Lower 32 bits = SourceL XOR Manufacturers Code Lower 32 bits

After programming the manufacturer’s code, the HCS512 decoder will automatically activate an Erase All function,

removing all transmitters from the system.

If LRNIN is taken low momentarily during the learn status indication, the indication will be terminated. Once a successful

learning sequence is detected, the indication can be terminated, allowing quick learning in a manufacturing setup.

FIGURE 7-2: HCS512 KEY GENERATION

Padding

2

Normal Learn (SC_LRN = 0)

28-bit Serial Number

Padding

6

28-bit Serial Number

LRN0 = 0

KEELOQ®

Decryption

Algorithm

LS 32 bits of crypt key

MS 32 bits of crypt key

Secure Learn (SC_LRN = 1)

LS 32 bits of Seed Transmission

Padding

0000b

MS 28 bits of Seed Transmission

LRN0 = 0

KEELOQ

Decryption

Algorithm

LS 32 bits of crypt key

MS 32 bits of crypt key

Secure Learn XOR (SC_LRN = 1)

LS 32 bits of Seed Transmission

Padding

0000b

MS 28 bits of Seed Transmission

LRN0 = 1

XOR

LS 32 bits of crypt key

MS 32 bits of crypt key

© 2011 Microchip Technology Inc.

DS40151E-page 13

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