System Security : C code for Transposition Cipher (should be executed in linux with gcc)

In cryptography, a transposition cipher is a method of encryption by which the positions held by units of plaintext (which are commonly characters or groups of characters) are shifted according to a regular system, so that the ciphertext constitutes a permutation of the plaintext. That is, the order of the units is changed. Mathematically a bijective function is used on the characters' positions to encrypt and an inverse function to decrypt.
//Aim:To implement Transposition Cipher in C. //Program: #include<stdio.h> int check(int x,int y) { int a,b,c; if(x%y==0) return 0; a=x/y; b=y*(a+1); c=b-x; return c; } void main() { int l1,i,d,j; printf("\nEnter the length of the key. "); scanf("%d",&l1); int sequence[l1]; printf("\nEnter the sequence key. "); for(i=0;i<l1;++i) { scanf("%d",&sequence[i]); } int order[l1]; for(i=1;i<=l1;++i) { for(j=0;j<l1;++j) { if(sequence[j]==i) order[i-1]=j; } } printf("\nEnter the depth. "); scanf("%d",&d); int l2; printf("\nEnter the length of String without spaces . "); scanf("%d",&l2); int temp1=check(l2,l1); int r=(l2+temp1)/l1; char p[l2+temp1]; char p1[r][l1]; //char p2[r][l1]; if(temp1>0) printf("\nYou need to enter %d bogus characters.So enter total %d characters. ",temp1,(l2+temp1)); else printf("\nEnter the string. "); for(i=-1;i<(l2+temp1);++i) { scanf("%c",&p[i]); } int count=0; while(d>0) { count=0; for(i=0;i<r;++i) { for(j=0;j<l1;++j) { p1[i][j]=p[count]; count=count+1; } } printf("\n\n\n"); for(i=0;i<r;++i) { for(j=0;j<l1;++j) { printf("%c ",p1[i][j]); } printf("\n"); } count=0; for(i=0;i<l1;++i) { for(j=0;j<r;++j) { p[count]=p1[j][order[i]]; count=count+1; } } for(i=0;i<(l2+temp1);++i) printf("%c ",p[i]); d=d-1; } } /* OUTPUT [aditya@localhost Desktop]$ gcc transposition.c [aditya@localhost Desktop]$ ./a.out Enter the length of the key. 7 Enter the sequence key. 4 3 1 2 5 6 7 Enter the depth. 2 Enter the length of String without spaces . 23 You need to enter 5 bogus characters.So enter total 28 characters. attackpostponeduntiltwoamxyz a t t a c k p o s t p o n e d u n t i l t w o a m x y z t t n a a p t m t s u o a o d w c o i x k n l y p e t z t t n a a p t m t s u o a o d w c o i x k n l y p e t z n s c y a u o p t t w l t m d n a o i e p a x t t o k z */

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