The document describes a C program that implements a simple encryption algorithm using an 8-bit shared key. The program prompts the user to enter a string of up to 10 characters and the hexadecimal value of the 8-bit key. It then encrypts the string according to the key by determining the parity bits based on the number of 1s in subsets of the data bits.

1. Write a C program that implements a simple encryption
algorithm built using an 8-bit shared key. The key will be
known by the sender and receiver prior to transmission and must
have six 1-bits and two 0-bits. Suppose that every 8-bit frame
contains 6 data bits and 2 parity bits. The encryption algorithm
will build frames according to the 8-bit shared key where the 6
1-bits correspond to the 6 data bits from left to right and the 2
0-bits are determined by the data bits. The first 0-bit location
in the shared key is 1 if there are an odd number of 1-bits in the
first 3 of 6 data bits and 0 if there are an even number of 1-bits.
(from left to right) The second 0-bit location in the shared key
is 1 if there are an even number of 1-bits in the remaining 3
data bits and 0 if there are an odd number of 1-bits. (from left
to right) Your program must prompt the user to enter a string
with at most 10 characters and the hexadecimal value of the 8-
bit shared key. The characters are the
Solution
#include #include #include #include #include long int
p,q,n,t,flag,e[100],d[100],temp[100],j,m[100],en[100],i; char
msg[100]; int prime(long int); void ce(); long int cd(long int);
void encrypt(); void decrypt(); void main() { clrscr();
printf(" ENTER FIRST PRIME NUMBER ");
scanf("%d",&p); flag=prime(p); if(flag==0) { printf("
WRONG INPUT "); getch(); exit(1); } printf("
ENTER ANOTHER PRIME NUMBER "); scanf("%d",&q);
flag=prime(q); if(flag==0||p==q) { printf(" WRONG

2. INPUT "); getch(); exit(1); } printf(" ENTER
MESSAGE "); fflush(stdin); scanf("%s",msg);
for(i=0;msg[i]!=NULL;i++) m[i]=msg[i]; n=p*q; t=(p-1)*(q-
1); ce(); printf(" POSSIBLE VALUES OF e AND d ARE ");
for(i=0;i0) { d[k]=flag; k++; }
if(k==99) break; } } } long int cd(long int x) {
long int k=1; while(1) { k=k+t; if(k%x==0)
return(k/x); } } void encrypt() { long int
pt,ct,key=e[0],k,len; i=0; len=strlen(msg); while(i!=len) {
pt=m[i]; pt=pt-96; k=1; for(j=0;j