What is the difference between learning code, rolling code and fixed code? The number of repeated codes, coding capacity and the principle of rolling code

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Learning code Rolling code Fixed code What's the difference?

Multiple code number , Coding capacity

The principle of rolling code

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Learning code Rolling code Fixed code What's the difference?

One 、 Meaning is different ：

1、 Fixed code ： The address code is fixed , Although the address code is fixed , But it's made up of 8 Bits of different address codes , Pairing can be done through different combinations , This will not happen . The fixed code of the remote control is relative to the rolling code , Generally by PT2262/2272 The system consists of hardware coding 、 Fixed code remote control system .

2、 Learning code ： Composed of millions of different codes , The receiver learns only through code matching , To recognize the remote control . It greatly increases the security of the product . Usually learn the code IC by 1527 and 2240, Decode to MCU .

3、 Rolling code ： At present, it is mainly used in RKE(Remote Keyless Entry) In the system , Authentication .

Two 、 Characteristics of different ：

1、 Both fixed code and learning code are used in civil and commercial alarm products , Home burglar alarm and home gas alarm are common at home , The rolling code is only used for RKE The system authenticates .

2、 Coding, decoding and coding combination are different ： Coding of learning code IC by 1527 and 2240, Decode to MCU ; The fixed code code is PT2262( Traditional anti-theft detector ), decode PT2272( Traditional alarm host );

3、 The security of fixed code is not high , Address coding is easy to duplicate ; The security of learning code is relatively high ,100 Ten thousand groups of codes greatly reduce the probability of code repetition in use .

Multiple code number , Coding capacity

1、 The number of duplicate yards is different ：

Rolling code ： In the use “ Duplicate code ” The probability is very small , And there will be solder joints on the back of the chip .

Fixed code ： Automatically change the code after each launch , The probability of repeated code is very high .

2、 The coding capacity is different ：

Rolling code ： The code value can be seen through the right solder joint connection .

Fixed code ： Coding capacity is only 6561 individual , Out-of-service “ Code interceptor ” Get the address code .

The principle of rolling code

The encoder detects key input , Wake up the system from the power saving state , Synchronous counting plus 1 , Together with the serial number, it is encrypted by the key to form ciphertext data , And send it out with key value and other data . Because the synchronization count value is different every time it is sent , Even if the same key is pressed many times . Sync count automatically scrolls forward , The transmitted codeword will not happen again . Therefore, it is called rolling code . The synchronous count is the same as the encoder serial number 64 Two people passed together DES encryption ,DES The key is unique to the manufacturer , It must be kept secret . The encrypted ciphertext is transmitted through the RF system .

After the receiving end receives the ciphertext , Through the manufacturer's DES Key to decrypt , After decryption, the synchronization count and encoder serial number are obtained . First, check whether the encoder serial number corresponds to the receiver serial number , If the corresponding , Check whether the synchronization count is within the synchronization window , That is, whether it is greater than the synchronization count saved locally , But not much , If it's too big , This machine will synchronize again . If in the synchronization window , Inform the actuator to execute the user command , For example, open or close the door lock .

Because the encryption algorithm can break up the plaintext , therefore , The rolling of codes will make the transmitted codes vary greatly and difficult to crack , Due to the existence of synchronous counting , Repeated sending has no effect , Therefore, to break this kind of system, we must break DES Algorithm . The synchronization count is 16 position , Can be up to 2 Of 16 Power =65536 , If you use... Every day 10 Time , Then there are 18 Years of service life .32 Bit's serial number , Capacity of 232 = 42 Billion , It can fully meet the production requirements .