First of all, explain the meaning of ECID and ECID, that is, exclusive chip.
ID is the ID number of iPhone, and each iPhone has its own unique ECID. With this ECID, you can determine the information of an iPhone. The ECID is not the same as the serial number *#06# pressed at ordinary times, although both can recognize the mobile phone. But ECID is the unique number of the iPhone, and the serial number is only the unique number of the communication module of the iPhone.
The purpose of ECID is that Apple will generate a hash value together with the firmware file of the corresponding version and the ECID of the mobile phone. When the backup phone restores the system through itunes, iTunes will receive this hash value and send it to the user device. When the user's device receives it, it immediately checks and verifies the signature. If the signatures match, it will continue the firmware recovery operation. If there is no match, the device will report an error and the recovery operation will be suspended.