早晨起床，完成菜农老师昨天晚上布置CRC32碰撞作业

只看该作者 · 2011-6-3 07:50

本帖最后由 CC2530 于 2011-6-3 13:07 编辑

https://bbs.21ic.com/icview-240248-1-1.html
作业题：
1.现有一串数据xxxxxxxx0123456789abcdef，知道其crc32结果为12345678，求xxxxxxxx是多少
2.现有一串数据01234567xxxxxxxx89abcdef，知道其crc32结果为12345678，求xxxxxxxx是多少

答案：
#include "uni_int.h"
#include <stdlib.h>

uint32 crc32l_update_byte(uint32 crc_in,uint8 data);
uint32 crc32l_update_word(uint32 crc_in,uint16 data);
uint32 crc32l_update_dword(uint32 crc_in,uint32 data);
uint32 crc32l_update_nibble(uint32 crc_in,uint8 data);
uint32 crc32l_dis_update_dword(uint32 crc_out,uint32 data);
uint32 crc32l_dis_update_word(uint32 crc_out,uint16 data);
uint32 crc32l_dis_update_byte(uint32 crc_out,uint8 data);
uint32 crc32l_dis_update_nibble(uint32 crc_out,uint8 data);
uint8 crc32l_calculate(uint32 crc_in,const uint8 *data,uint16 size);
volatile uint32 A;
volatile uint32 B;
int main(void)
{
  A=0xFFFFFFFF;
  A=crc32l_update_dword(A,0X12345678);
  A=crc32l_dis_update_dword(A,0X12345678);  //恢复初值

  A=0xFFFFFFFF;
  A=crc32l_update_word(A,0X1234);
  A=crc32l_update_word(A,0X5678);
  A=crc32l_dis_update_word(A,0X5678);
  A=crc32l_dis_update_word(A,0X1234);  //恢复初值


  A=0xFFFFFFFF;
  A=crc32l_update_byte(A,0X12);
  A=crc32l_update_byte(A,0X34);
  A=crc32l_update_byte(A,0X56);
  A=crc32l_update_byte(A,0X78);
  A=crc32l_dis_update_byte(A,0X78);
  A=crc32l_dis_update_byte(A,0X56);
  A=crc32l_dis_update_byte(A,0X34);
  A=crc32l_dis_update_byte(A,0X12); //恢复初值

  A=0xFFFFFFFF;
  A=crc32l_update_nibble(A,0X1);
  A=crc32l_update_nibble(A,0X2);
  A=crc32l_update_nibble(A,0X3);
  A=crc32l_update_nibble(A,0X4);
  A=crc32l_update_nibble(A,0X5);
  A=crc32l_update_nibble(A,0X6);
  A=crc32l_update_nibble(A,0X7);
  A=crc32l_update_nibble(A,0X8);

  A=crc32l_dis_update_nibble(A,0X8);
  A=crc32l_dis_update_nibble(A,0X7);
  A=crc32l_dis_update_nibble(A,0X6);
  A=crc32l_dis_update_nibble(A,0X5);
  A=crc32l_dis_update_nibble(A,0X4);
  A=crc32l_dis_update_nibble(A,0X3);
  A=crc32l_dis_update_nibble(A,0X2);
  A=crc32l_dis_update_nibble(A,0X1);  //恢复初值


  //作业：
  //1.现有一串数据xxxxxxxx0123456789abcdef，知道其crc32结果为12345678，求xxxxxxxx是多少
  A=0x12345678;
  A=crc32l_dis_update_dword(A,0x89abcdef);
  A=crc32l_dis_update_dword(A,0x01234567);
  A=crc32l_dis_update_dword(A,0xFFFFFFFF); //得0x0D1AD0D8
  //答xxxxxxxx是0D1AD0D8

  //检验：
  A=0xFFFFFFFF;
  A=crc32l_update_dword(A,0x0D1AD0D8);
  A=crc32l_update_dword(A,0x01234567);
  A=crc32l_update_dword(A,0x89abcdef);    //得0x12345678


//2.现有一串数据01234567xxxxxxxx89abcdef，知道其crc32结果为12345678，求xxxxxxxx是多少
  A=0xFFFFFFFF;
  A=crc32l_update_dword(A,0x01234567);
  B=A;                                  //保存结果
  A=0x12345678;
  A=crc32l_dis_update_dword(A,0x89abcdef);
  A=crc32l_dis_update_dword(A,B);          //得0x2D2F927A

  //检验：
  A=0xFFFFFFFF;
  A=crc32l_update_dword(A,0x01234567);
  A=crc32l_update_dword(A,0x2D2F927A);
  A=crc32l_update_dword(A,0x89abcdef);    //得0x12345678
  //答xxxxxxxx是2D2F927A


  while(1);
}