/*	slant.c

	This is an implementation of a simple transposition cipher.
	See "Cryptography and Secure Communications" pp. 2, 3.

	The basic premise behind this cipher is to take a phrase
	like:

	CRYPTOGRAPHY AND DATA SECURITY

	and rearrange it in the following form:

	C  P  G  P  A  D  A  C  I
	 R  T  R  H  N  A  S  U  T
	  Y  O  A  Y  D  T  E  R  Y

	The top row is then put at the beginning of the enciphered
	text, the next row follows, and so forth:

	CPGPADACI RTRHNASUT YOAYDTERY -> CPGPADACIRTRHNASUTYOAYDTERY

	This program will take a line of clear-text and output the
	enciphered result.

	FYI - This is one of the oldest cryptosystems. It was used 
	by the Greeks as early as 400 BC.

*/

/* This is the main part of the program */

#include <iostream.h>

void getCleartext(char[]);
void encrypt(char[], char[], int);
void printString(char[]);

int main (void)
{
	char cleartext[41];	/* This is where we store the 
				   clear-text that the user inputs.
				   It is an array of characters 
				   that will store a string forty
				   characters long. (Don't forget
				   about the '\0'!) */

	char ciphertext[41];	/* This is where we will store
			  	    our enciphered text. */

	int key;		/* This is the key to use to 
				   encrypt the text. */


	for (int i = 0; i < 40; i++)
		ciphertext[i] = '!';
	ciphertext[40] = '\0';

	getCleartext(cleartext);	/* This function will
					   get the cleartext
					   and store it in 
					   our array. */

	cout << "Enter the key to encrypt [integer less than the length of the message]: ";
	cin >> key;

	encrypt(cleartext, ciphertext, key);	/* This will take the 
					  	   text in cleartext, 
					    	   encipher it, and 
						   store the results in 
						   ciphertext. */

	printString(ciphertext);	/* This will output the
					   text stored in 
					   ciphertext. */

	cout << "\n";	/* Output newline. */

	return 0;	/* Signal to the operating system that this 
		   progam has finished running. */
}


/* This function will get the cleartext and store it in 
   our array. */

void getCleartext(char text[])	
{
	/* This prompts the user to enter information. */

	cout << "Please enter some cleartext to encipher\n"
	     << "(40 characters or less): ";

	/* This gets the text and stores it in the text array... */

	cin.getline(text, 40);

	/* Signal that this function is finished. */

	return;
}


/* This will take the text in cleartext, encipher it, and 
   store the results in ciphertext. */

void encrypt(char cleartext[], char ciphertext[], int slant)
{
	/* In this example, we are going to only use a 
	   slanting pattern three characters high. */

	int j;

	int length;	/* Length of cleartext */
	int level; 	/* Length of the largest row */

	/*

	<---------level--------->
	C  P  G  P  A  D  A  C  I
	 R  T  R  H  N  A  S  U  T
	  Y  O  A  Y  D  T  E  R  Y

	*/



	int i; 	/* Used for various counting tasks */

	/* This will go through the string and count until
	   it reaches the string terminator. */

	for (length = 0; cleartext[length] != '\0'; length++);	

	/* If all rows will be the same length.... */

	if (( (length)  % slant) == 0) 
		level = (length) / slant;

	/* If not, add one extra to level. */
	else
		level = ( (length) / slant ) + 1;  

	


	/* Now we do the bulk of the work. This part will
	   take the cleartext and encipher it by placing
	   it in the ciphertext array. */

	for (i = 0; cleartext[i] != '\0'; i++)
	{
		ciphertext[ ((i % slant) * level) + (i / slant) ] 
			= cleartext[i];
	}


	ciphertext[i+slant] = '\0';

	/* Removing empty spots in the code. */

	for (i = 0; ciphertext[i] != '\0'; i++)
	{
		if (ciphertext[i] == '!')
		{
			ciphertext[i] = ' ';
		}
	}
	ciphertext[i] = '\0';

	/* Signal that function is complete. */

	return;
}


/* This function outputs the string contained in ciphertext. */

void printString(char ciphertext[])	
{
	for (int i = 0; ciphertext[i] != '\0'; i++)
		cout << ciphertext[i];

	return;
}