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RSA Algorithm For Encryption and Decryption

  1. #include<stdio.h> #include<conio.h> #include<stdlib.h> #include<math.h> #include<string.h> 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() { printf("\nENTER FIRST PRIME NUMBER\n"); scanf("%d",&p); flag=prime(p); if(flag==0) { printf("\nWRONG INPUT\n"); getch(); exit(1); } printf("\nENTER ANOTHER PRIME NUMBER\n"); scanf("%d",&q); flag=prime(q); if(flag==0||p==q) { printf("\nWRONG INPUT\n"); getch(); exit(1); } printf("\nENTER MESSAGE\n"); 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("\nPOSSIBLE VALUES OF e AND d ARE\n"); for (i=0;i<j-1;i++) printf("\n%ld\t%ld",e[i],d[i]); encrypt(); decrypt(); getch(); } int prime(long int pr) { int i; j=sqrt(pr); for (i=2;i<=j;i++) { if(pr%i==0) return 0; } return 1; } void ce() { int k; k=0; for (i=2;i<t;i++) { if(t%i==0) continue; flag=prime(i); if(flag==1&&i!=p&&i!=q) { e[k]=i; flag=cd(e[k]); if(flag>0) { 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<key;j++) { k=k*pt; k=k%n; } temp[i]=k; ct=k+96; en[i]=ct; i++; } en[i]=-1; printf("\nTHE ENCRYPTED MESSAGE IS\n"); for (i=0;en[i]!=-1;i++) printf("%c",en[i]); } void decrypt() { long int pt,ct,key=d[0],k; i=0; while(en[i]!=-1) { ct=temp[i]; k=1; for (j=0;j<key;j++) { k=k*ct; k=k%n; } pt=k+96; m[i]=pt; i++; } m[i]=-1; printf("\nTHE DECRYPTED MESSAGE IS\n"); for (i=0;m[i]!=-1;i++) printf("%c",m[i]); }


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