Here are some example of data:7B 5A C9 1F 1B 14 2B 28 39 D0 73 80 00 00   34 827B 5A CB 1F 1B 14 2B 28 39 D0 73 80 00 00   F6 CD00 00 00 00 00 80 00 00 30 00 00 00 00 00   0E 5900 00 00 00 00 C7 E0 00 30 00 00 00 00 00   45 C700 00 00 00 00 89 60 00 10 00 00 00 00 00   62 2300 00 00 00 00 89 60 00 20 00 00 00 00 00   EE 0C00 00 00 00 00 8E 10 00 10 00 00 00 00 00   C5 2200 00 00 00 00 00 00 00 00 00 00 00 00 00   F1 03It's a data validation on an mifare 1k card.I want to make a copy of the card but i want to change a value from it (like an id) so in the logs i will see who was using itI used reveng but it doesn't found any models.From 00 00 00 00 00 00 00 00 00 00 00 00 00 00   F1 03 seem to be a custom algorithm.Maybe someone have an ideea how could i find the polinomial function.EDIT:I tried to bruteforce:#include <iostream>using namespace std;typedef unsigned char byte;unsigned short crc16(byte* b,int len,unsigned short poli,unsigned short crc){    for (int j=0;j<len;j++){        crc ^= ((unsigned short)(b[j] << 8));        for (int i = 0; i < 8; i++){            if ((crc & 0x8000) != 0){                crc = ((unsigned short)((crc << 1) ^ poli));            }else{                crc <<= 1;            }        }    }    return crc;}int main(){    unsigned short start=0x0;    unsigned short poly=0x0;    byte data0[]={0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x00,0x0,0x0,0x0,0x0,0x0};    byte data1[]={0x0,0x0,0x0,0x0,0x0,0x8E,0x10,0x0,0x10,0x0,0x0,0x0,0x0,0x0};    byte data2[]={0x0,0x0,0x0,0x0,0x0,0x89,0x60,0x0,0x10,0x0,0x0,0x0,0x0,0x0};    for(int i=0;i<=65535;i++){        start=0x0;        for(int j=0;j<=65535;j++){            if(crc16(data0,14,poly,start)==0xF103){                 if(crc16(data1,14,poly,start)==0xC522){                    if(crc16(data2,14,poly,start)==0x6223){                        cout<<\npoli:<<poly<< - start:<<start<<\n;                    }                 }            }            start+=0x1;        }        poly+=0x1;        if(i%655==0)            cout<<.<<i/655<<.;    }    return 0;}No result ..
Finding out crc16 algorithm
crc