Vignere Cipher

[MrBeavis]

Hello Guys,

Not sure if I've advanced past beginner yet so I'll post this here, I'm having some problems with my Vignere Cipher, it is only reading the first 4 chars in my array and encoding them. The test expression MAC'S RULE with key APPLE should become MPR'D VUAT, but its only coming up as MPR'S RULE, Where have I gone wrong? Excuse all the error checking trying to get myself into a good practice of doing it.

cheers for any help

vignere.h


void vignere_encrypt(char data[], char key[]);
void vignere_decrypt(char data[], char key[]);


vignere.cpp

#include <iostream>
#include <fstream>
#include "vignere.h"
using namespace std;

void vignere_encrypt(char data[], char key[])
{

	int j = 0;
	for (int i = 0; i < sizeof data; i++)
	{
		if (isalpha(data[i]))
		{
			data[i] += key[j] - 'A';
			if (data[i] > 'Z')
			{
				data[i] += -'Z' + 'A' - 1;
			}
				
		}
		
		if(j + 1 == sizeof key)
		{
			j = 0;
		}
		else
		{
			j++;
		}

	}
}

void vignere_decrypt(char data[], char key[])
{

	int j = 0;
	for (int i = 0; i < sizeof data; i++)
	{
		if (isalpha(data[i]))
		{
			if(data[i] >= key[j])
			{
				data[i] = data[i] - key[j] + 'A';
			}
			else
			{
				data[i] = 'A' + ('Z' - key[j] + data[i] - 'A') + 1;
			}

		}

		if(j + 1 == sizeof key)
		{
			j = 0;
		}
		else
		{
			j++;
		}
	}
}


driver.cpp

#include <iostream>
#include <fstream>
#include <string>
#include "vignere.h"
using namespace std;

int main(int argc, char const *argv[])
{
	string Filein, Fileout;
	ifstream fin;

	const int KeySize = 8;
	const int DataSize = 1024;

	char key[KeySize];
	char select;
	char data[DataSize];

	cout << "Enter File to be read in: ";
	cin >> Filein;

	fin.open(Filein.c_str());

	if(!fin.good())
	{
		cout << "No File Exisits" << endl;
	}
	else
	{
		cout << "File opened" << endl;
		fin.getline(data, DataSize, '\n');
		cout << sizeof data << endl;
		ofstream fout;

		cout << "Enter File to be read out to: ";
		cin >> Fileout;

		fout.open(Fileout.c_str());

		if(!fout.good())
		{
			cout << "File could not be created" << endl;
		}
		else
		{
			cout << "File Created" << endl;

			cout << "Enter Key: ";
			cin >> key;
			cout << key << endl;	
		
			cout << "Would you like to [E]ncrypt or [D]ecrypt the file " << Filein << "?: ";
			cin >> select;
			select = toupper(select);
			cout << select << endl;

			switch(select)
			{
				case 'D':
				{
					cout << "you are decrypting" << endl;
					vignere_decrypt(data, key);
					fout << data << endl;
					break;
				}
				case 'E':
				{
					cout << "you are encrypting" << endl;
					vignere_encrypt(data, key);
					fout << data << endl;
					break;
				}
			}
		}
	}

	return 0;
}

[discofire]

You are using sizeof data as your for loop end condition. That is going to return the size of the pointer to your array which is 4 bytes. Hence the reason you are only getting 4 characters encoded. You need to determine the actual number of characters in your array.

[MrBeavis]

haha good timing I got that about an hour ago, is it possible to determine that within the function without changing its conditions?

[discofire]

This should do it: http://www.cplusplus.com/reference/cstring/strlen/
You might want to store the length values of data and key so you don't have to continually call strlen. Then just refer to those variables (like dataLenth and keyLength)

[Cody0023]

You could get rid of the for loop entirely and just use a while loop to detect the null terminator. '\0'

unsigned i=0;

while(array[i])
{
do stuff

i++;
}

[MrBeavis]

ah wonderful ive tried both, I have run into a problem with extern int though, when compiling it is coming up with:

undefined reference to 'KeyLen'
collect2.exe: error: ld returned 1 exit status

what happened? the DataLen worked fine

driver .cpp

#include <iostream>
#include <fstream>
#include <string>
#include "vignere.h"
using namespace std;

int main(int argc, char const *argv[])
{
	string Filein, Fileout;
	ifstream fin;

	const int KeySize = 8;
	const int DataSize = 1024;

	char key[KeySize];
	char select;
	char data[DataSize];

	cout << "Enter File to be read in: ";
	cin >> Filein;

	fin.open(Filein.c_str());

	if(!fin.good())
	{
		cout << "No File Exisits" << endl;
	}
	else
	{
		cout << "File opened" << endl;
		fin.getline(data, DataSize, '\n');
		int DataLen = strlen(data);
		cout << DataLen << endl;

		ofstream fout;

		cout << "Enter File to be read out to: ";
		cin >> Fileout;

		fout.open(Fileout.c_str());

		if(!fout.good())
		{
			cout << "File could not be created" << endl;
		}
		else
		{
			cout << "File Created" << endl;

			cout << "Enter Key: ";
			cin >> key;
			int KeyLen = strlen(key);
			cout << KeyLen << endl;
		
			cout << "Would you like to [E]ncrypt or [D]ecrypt the file " << Filein << "?: ";
			cin >> select;
			select = toupper(select);
			cout << select << endl;

			switch(select)
			{
				case 'D':
				{
					cout << "you are decrypting" << endl;
					vignere_decrypt(data, key);
					fout << data << endl;
					break;
				}
				case 'E':
				{
					cout << "you are encrypting" << endl;
					vignere_encrypt(data, key);
					fout << data << endl;
					break;
				}
			}
		}
	}

	return 0;
}

vignere.cpp

#include <iostream>
#include <fstream>
#include <cctype>
#include <string>
#include "vignere.h"
using namespace std;

void vignere_encrypt(char data[], char key[])
{
	//extern int DataLen;
	extern int KeyLen;

	int j = 0;
	unsigned i =0;
	//for (int i = 0; i < sizeof(data); i++)
	while(data[i])
	{
		if(data[i] != '\n')
		{
			if (isalpha(data[i]))
			{
				data[i] += key[j] - 'A';
				if (data[i] > 'Z')
				{
					data[i] += -'Z' + 'A' - 1;
				}

				if(j == '\n' || j == KeyLen)
				{
					j = 0;
				}
				else
				{
					j++;
				}		
			}
		}
		i++;
	}
}

void vignere_decrypt(char data[], char key[])
{

	int j = 0;
	unsigned i = 0;
	//for (int i = 0; i < sizeof data; i++)
	while(data[i])
	{
		if (isalpha(data[i]))
		{
			if(data[i] >= key[j])
			{
				data[i] = data[i] - key[j] + 'A';
			}
			else
			{
				data[i] = 'A' + ('Z' - key[j] + data[i] - 'A') + 1;
			}

		}

		if(j + 1 == sizeof(key))
		{
			j = 0;
		}
		else
		{
			j++;
		}
		i++;
	}
}