Transpositions cipher

Ok så jeg sad herr forleden og skulle forklare en ven epå nettet hvad et transpositions cipher er, det udviklede sig til dette program.

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <iostream>
#include <cstdlib>

using namespace std;

int main(int argc, char *argv[])
{

	char plaintext1[255];
	char plaintext2[255];
	char ciphertext[255];
	int caesarkey = 0;
	int stringlength = 0;
	int i = 0;
	cout<<"Next we are going to try a flip cipher, this is a little more complicated, so bear with 	me."<<endl;
		cout<<endl<<"First off, enter a new plaintext: ";
		cin.getline(plaintext2, 255, '\\n');
		while(plaintext2[i] != '\\0'){i++;stringlength++;}
	
		char flipcipher[stringlength+1];
		int permuter[stringlength];
		cout<<"Now we know that our ciphertext is "<<stringlength<<" Characters long. We are now going to move the characters around a little, for that we need to enter a key for them."<<endl;

		cout<<"Please enter the numbers 0 - "<<stringlength-1<<" In a random order! Don't repeat yourself!"<<endl;
		
		i = 0;
		
		while(i < stringlength){
			int n = 0;
			int u = 0;
			cout<<"Enter number: ";	
			cin>>n;
			if(n>stringlength){
				cout<<"Number too high! Try again!";
				cin>>n;
				i--;}
	
			permuter[i] = n;
			i++;}
		i = 0;
		cout<<"Ok now we have a permutor, let put it to use!"<<endl;
		while(plaintext2[i] != '\\0'){
			flipcipher[i] = plaintext2[permuter[i]];
			i++;}
		flipcipher[i+1]  = '\\0';
		i = 0;
	
		cout<<"Ok now we have flipped the plaintext, let's look at it: "<<endl;
	
		while(flipcipher[i] !='\\0'){
			cout<<flipcipher[i];
			i++;}
	
		cout<<endl<<"OK! Now let us see if we can decode the text as well!"<<endl<<endl;
		
		i = 0;	
		while(flipcipher[i] !='\\0'){
		plaintext1[permuter[i]] = flipcipher[i];
		i++;}
		
		cout<<"If what comes next is your real text then we've won!"<<endl;
		
		i = 0 ;
		while(plaintext1[i] !='\\0'){
			cout<<plaintext1[i];
			i++;}
	cout<<endl;
	return 0;
}

Jeg er ikke ligefrem nogen haj til c++ så det er ikke så kønt, men det virker.
Problemet med det er at jeg mangler en eller anden smart måde at lave en permuter (eller key, eller nøgle forhåbenligt ved I hvad jeg mener). Som i kan se er den metode jeg bruger nu ikke lige frem strømlignet, så har i nogle idér? Både til hvordan jeg generer en nøgle og til programmet generelt.
Kunne rigtigt godt tænke mig en (relativ) simpel måde at generere en bare lidt random key.