Cyclic Redundancy Check

CRC :

A cyclic redundancy check (CRC) is an error detecting code commonly used in digital network and storage devices to detect accidental changes to raw data. Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents. On retrieval, the calculation is repeated and, in the event the check values do not match, corrective action can be taken against data corruption. CRCs can be used for Error Detection.

Program :

#include <stdio.h>
 #include <string.h>
 int main() {
	int i,j,keylen,msglen;
	char input[100], key[30],temp[30],quot[100],rem[30],key1[30],nmsg[20];
	printf("Enter Data: ");
	scanf("%s",input);
		printf("Enter Key: ");
	scanf("%s",key);
	keylen=strlen(key);
	msglen=strlen(input);
	strcpy(key1,key);
	for (i=0;i<keylen-1;i++) {
		input[msglen+i]='0';
	}
	for (i=0;i<keylen;i++)
	 temp[i]=input[i];        //Dividend Part
	for (i=0;i<msglen;i++) {
		quot[i]=temp[0];
		if(quot[i]=='0')
		 for (j=0;j<keylen;j++)
		 key[j]='0'; else
		 for (j=0;j<keylen;j++)
		 key[j]=key1[j];
		for (j=keylen-1;j>0;j--) {
			if(temp[j]==key[j])//exOR opration perform
			 rem[j-1]='0'; else
			 rem[j-1]='1';
		}
		rem[keylen-1]=input[i+keylen];
		strcpy(temp,rem);
	}
	strcpy(rem,temp);
	printf("\nQuotient is ");
	for (i=0;i<msglen;i++)
	 printf("%c",quot[i]);
	printf("\nRemainder is ");
	for (i=0;i<keylen-1;i++)
	 printf("%c",rem[i]);
	printf("\nFinal data is: ");
	int newmsglen;
		newmsglen=msglen+keylen-1;
	 for(i=msglen;i<(msglen+keylen-1);i++)
	 	input[i]=rem[i-msglen];
	for (i=0;i<newmsglen;i++)
	 printf("%c",input[i]);
	 
	 
//----------------------receiver side code--------------------------------------	
	printf("\nENTER THE RECEIEVED DATA : ");
		scanf("%s",input);
		for (i=0;i<keylen;i++)
	 temp[i]=input[i];
	for (i=0;i<msglen;i++) 
	{
		quot[i]=temp[0];
		
		if(quot[i]=='0')
		 for (j=0;j<keylen;j++)
		 key[j]='0'; 
		 else
		 for (j=0;j<keylen;j++)
		 key[j]=key1[j];
		for (j=keylen-1;j>0;j--) 
		{
			if(temp[j]==key[j])
			 rem[j-1]='0'; else
			 rem[j-1]='1';
		}
		rem[keylen-1]=input[i+keylen];
		strcpy(temp,rem);
	}
	int flag=0;
	strcpy(rem,temp);
	for(i=0;i<keylen-1;i++)
	{
		if(rem[i]=='0')
	 		continue;
		else
			flag=1;
	}
	if(flag==1)
		printf("\n\tSince Remainder Is Not 0 Hence Message Transmitted From Sender To Receriver Contains Error");
	
	else
		printf("\n\tSince Remainder Is 0 Hence Message Transmitted From Sender To Receriver Is Correct\n");
	
	 return 0;
}