Rail-Fence cipher encryption-decryption

#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<ctype.h>

void main()

{

            int i,j=0,d,k=0;

            char p[50],ct[50][50];

            clrscr();

            printf("Enter the plain text:\n");

            gets(p);

            printf("\nEnter the depth in the integer:");

            scanf("%d",&d);

            //declare null for empty array values

            for(i=0;i<50;i++)

            {

                        for(j=0;j<50;j++)

                        {

                                    ct[i][j]='\0';

                        }

            }

            k=0;

       //loop up to string lenght of the pliantext

            {

            for(i=0;i<strlen(p);i++)

            {

                        for(j=0;j<d;j++)

                        {

                                    if(k<=strlen(p))

                               ct[i][j]=p[k];

                                    k++;

                        }

                        ct[i][j]='\0';

                        }

            }

            for(i=0;i<d;i++)

            {

                        for(j=0;j<strlen(p);j++)

                        {

                                    if(ct[j][i]!='\0')

                                       {

                                           printf("%c",ct[j][i]);

                                       }

                        }

                        printf("\n");

            }

            // Read the text

            printf("\nThe encrypted text is:\n");

            for(i=0;i<d;i++)

            {

                        for(j=0;j<strlen(p);j++)

                        {

                                    if(ct[j][i]!='\0')

                                    printf("%c",ct[j][i]);

                        }

            }

            getch();

}

output:

columnar transposition cipher encryption-decryption.

#include<stdio.h>

#include<conio.h>

#include<string.h>

void main()

{

            char k[20]={'\0'},pt[30]={'\0'},key[30]={'\0'},mat[10][10]={'\0'},ct[30]={'\0'};

            int i=0,j=0,no[10]={0},ctr,z,c=0,a=0;

            clrscr();

            printf("Enter the plaintext:\n");

            gets(pt);

            printf("Enter the key:\n");

            gets(k);

            strcpy(key,k);

            strcat(k,pt);

            strcpy(pt,k);

            printf("Enter the ordering starting from 0 to the (keylength-1):\n");

            for(i=0;i<strlen(key);i++)

            {

                        scanf("%d",&no[i]);

            }

            j=0;

            ctr=j;

            printf("The matrix is:\n");

            for(i=0;i<strlen(pt);i++)

            {

                        for(j=j;ctr<strlen(key);j++)

                        {

                                    if(pt[j]!='\0')

                                    {

                                                mat[i][ctr]=pt[j];

                                                printf("%c",mat[i][ctr]);

                                                ctr++;

                                    }

                                    else

                                    {

                                                goto out;

                                    }

                        }

                        ctr=0;

                        if(i==0) printf("\n");

                        printf("\n");

            }

            out:

            printf("\n\nThe Encrypted  text is:\n");

            for(i=0;i<strlen(key);i++)

            {

                        for(j=0;j<strlen(key);j++)

                        {

                                    if(no[i]==j)

                                    {

                                           for(z=1;z<10;z++)

                                           {

                                                            if(isalpha(mat[z][j]))

                                                            {

                                                            printf("%c",mat[z][j]);

                                                            ct[a]=mat[z][j];

                                                            a++;

                                                            }

                                           }

                                    }

                        }

            }

            printf("\n\nDecrypted Ciphertext is:\n");

            for(a=0;a<30;a++)

            {

            if(isalpha(ct[a]) || isspace(ct[a]))

            c++;

            }

            for(i=1;i<c;i++)

            {

                        for(j=0;j<strlen(key);j++)

                        {

                                    if(isalpha(mat[i][j]))

                                    printf("%c",mat[i][j]);

                                    else

                                    goto ext;

                        }

            }

            ext:

            getch();

}

output:

Polyalphabetic cipher encryption-decryption

the source code for Polyalphabetic cipher encryption-decryption is as follows in c..

#include<stdio.h>

#include<conio.h>

#include<string.h>

char pt[40]={'\0'},key[40]={'\0'},ct[40]={'\0'},pta[40]={'\0'},k[40]={'\0'};

int i,j;      // global values

void main()

{

            clrscr();

            printf("\nEnter the keyword:\n");

            gets(k);//read the key

            printf("\nEnter the Plain text:\n");

            gets(pt);    //read the plain text

            // print the table

            printf("The convergen matrix\n");

            printf("\n   ");

            for(j=97;j<=122;j++)

            {

                        printf(" %c",j);

            }

            printf("\n--------------------------------------------------------\n");

            for(i=97;i<=122;i++)

            {

                        printf("%c |",i);

                        for(j=97;j<=122;j++)

                        {

                                    if(((i+j))>219)

                                    {

                                                printf(" %c",toupper((i+j)-123));

                                    }

                                    else

                                    {

                                                printf(" %c",toupper((i+j)-97));

                                    }

                        }

                        printf("\n");

            }

            // for keyword

            j=0;

            for(i=0;i<strlen(pt);i++)

            {

                        key[i]=k[j];

                        if(j==(strlen(k)-1))

                        {

                                    j=0;

                        }

                        else

                        {

                                    j++;

                        }

            }

            for(i=0;i<(strlen(pt)-1);i++);

            k[i]='\0';

            printf("\nThe encrypted text is:\n");

            // encryption

            for(i=0;i<strlen(pt);i++)

            {

                        if(97<=(int)pt[i] && (int)pt[i]<=122)

                        {

                                    if(((int)pt[i]+(int)key[i])>219)

                                    {

                                                ct[i]=(int)pt[i]+(int)key[i]-123;

                                    }

                                    else

                                    {

                                                ct[i]=(int)pt[i]+(int)key[i]-97;

                                    }

                                    printf("%c",toupper(ct[i]));

                        }

                        else

                        {

                                    ct[i]=pt[i];

                                    printf("%c",pt[i]);

                        }

            }

            // decryption

            printf("\n\nDecrypted text is:\n");

            for(i=0;i<strlen(ct);i++)

            {

                        if(97<=(int)ct[i] && (int)ct[i]<=122)

                        {

                                    if(((int)ct[i]-(int)key[i])<0)

                                    {

                                                pta[i]=((int)ct[i]-(int)key[i])+123;

                                    }

                                    else

                                    {

                                                pta[i]=(int)ct[i]-(int)key[i]+97;

                                    }

                                    printf("%c",pta[i]);

                        }

                        else

                        {

                                    pta[i]=ct[i];

                                    printf("%c",pta[i]);

                        }

            }

            getch();

}

output:

Playfair cipher encryption-decryption

To implement Playfair cipher encryption-decryption you should see the following c code...

#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<ctype.h>

#define MX 5

void playfair(char ch1,char ch2, char key[MX][MX])

{

 int i,j,w,x,y,z;

 FILE *out;

 if((out=fopen("cipher.txt","a+"))==NULL)

  {

   printf("File Currupted.");

  }

 for(i=0;i<MX;i++)

 {

  for(j=0;j<MX;j++)

  {

   if(ch1==key[i][j])

   {

    w=i;

    x=j;

   }

   else if(ch2==key[i][j])

   {

    y=i;

    z=j;

   }

  }

 }

 //printf("%d%d %d%d",w,x,y,z);

 if(w==y)

 {

  x=(x+1)%5;z=(z+1)%5;

  printf("%c%c",key[w][x],key[y][z]);

  fprintf(out, "%c%c",key[w][x],key[y][z]);

 }

 else if(x==z)

 {

  w=(w+1)%5;y=(y+1)%5;

  printf("%c%c",key[w][x],key[y][z]);

  fprintf(out, "%c%c",key[w][x],key[y][z]);

 }

 else

 {

  printf("%c%c",key[w][z],key[y][x]);

  fprintf(out, "%c%c",key[w][z],key[y][x]);

  }

  fclose(out);

}

void main()

 {

  int i,j,k=0,l,m=0,n;

  char key[MX][MX],keyminus[25],keystr[10],str[25]={0};

char

alpa[26]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};

  clrscr();

  printf("\nEnter key:");

   gets(keystr);

  printf("\nEnter the plain text:");

    gets(str);

  n=strlen(keystr);

  //convert the characters to uppertext

  for (i=0; i<n; i++)

   {

    if(keystr[i]=='j')keystr[i]='i';

    else if(keystr[i]=='J')keystr[i]='I';

    keystr[i] = toupper(keystr[i]);

   }

  //convert all the characters of plaintext  to uppertext

  for (i=0; i<strlen(str); i++)

   {

    if(str[i]=='j')str[i]='i';

    else if(str[i]=='J')str[i]='I';

    str[i] = toupper(str[i]);

   }

  // store all characters except key

  j=0;

  for(i=0;i<26;i++)

  {

   for(k=0;k<n;k++)

   {

    if(keystr[k]==alpa[i])

    break;

    else if(alpa[i]=='J')

    break;

   }

   if(k==n)

   {

    keyminus[j]=alpa[i];j++;

   }

  }

  //construct key keymatrix

  k=0;

  for(i=0;i<MX;i++)

  {

   for(j=0;j<MX;j++)

    {

     if(k<n)

     {

     key[i][j]=keystr[k];

     k++;}

     else

     {

      key[i][j]=keyminus[m];m++;

      }

      printf("%c  ",key[i][j]);

    }

    printf("\n");

  }

 

  // construct diagram and convert to cipher text

  printf("\n\nEntered text :%s\nCipher Text :",str);

  for(i=0;i<strlen(str);i++)

  {

   if(str[i]=='J')str[i]='I';

   if(str[i+1]=='\0')

    playfair(str[i],'X',key);

   else

   {

    if(str[i+1]=='J')str[i+1]='I';

    if(str[i]==str[i+1])

     playfair(str[i],'X',key);

    else

    {

     playfair(str[i],str[i+1],key);i++;

    }

   }

  }

  getch();

 }

output: