RailfenceCipher.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * @author arthur.paixao
 * @category Rail Fence Cipher Encode/Decode
 */
public class RailfenceCipher {
	public void encrypt(String line, int rail) {
		System.out.println("Result:");
		int shift = 0, p = 0, itr;
		for (int i = 0; i < rail; i++) {
			p = i;
			if (i == 0 || i == rail - 1)
				shift = ((rail - 2) * 2) + 2;
			itr = 1;
			while (p < line.length()) {
				System.out.print(line.charAt(p));
				if (i != 0 && i != rail - 1) {
					shift = ((rail * itr - itr) - p) * 2;
				}
				p += shift;
				itr++;
			}
		}
	}

	public void decrypt(String line, int arr[]) {
		System.out.println("Result:");
		int ptr[] = new int[arr.length + 1];
		int p1 = 0, p2 = 0, p3 = 0, c = 1;
		boolean chk = true;
		System.out.print(line.charAt(ptr[p3] + p1));
		ptr[p3]++;
		while (c < line.length()) {
			if (chk) {
				p1 += arr[p2];
				p2++;
				p3++;
			} else {
				p1 -= arr[p2];
				p2--;
				p3--;
			}
			System.out.print(line.charAt(ptr[p3] + p1));
			c++;
			ptr[p3]++;
			if (p2 == arr.length) {
				p2--;
				chk = false;
			} else if (p2 == -1) {
				p2++;
				chk = true;
			}
		}
	}

	public static void main(String args[]) throws IOException {
		RailfenceCipher obj = new RailfenceCipher();
		String line;
		int rail, arr[], temp;
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		System.out.println("MENU:\n1) Encryption:\n2) Decryption:");
		int choice = Integer.parseInt(in.readLine());
		System.out.println("Enter the string:");
		line = in.readLine();
		System.out.println("Enter the no of rails:");
		rail = Integer.parseInt(in.readLine());
		switch (choice) {
		case 1:
			temp = line.length() - rail;
			int spaces;
			if (temp % (rail - 1) != 0) {
				spaces = (rail - 1) - (temp % (rail - 1));
				if ((temp / (rail - 1)) % 2 != 0) {
					spaces += rail - 1;
				}
			} else {
				spaces = temp % (rail - 1);
				if ((temp / (rail - 1)) % 2 == 0) {
					spaces += rail - 1;
				}
			}
			for (int g = 0; g < spaces; g++)
				line += ' ';
			obj.encrypt(line, rail);
			break;
		case 2:
			temp = line.length() - rail;
			arr = new int[rail - 1];
			if ((temp / (rail - 1)) % 2 == 0)
				arr[0] = 1 + (temp / (rail - 1)) / 2;
			else
				arr[0] = 1 + ((temp / (rail - 1)) + 1) / 2;
			arr[1] = arr[0] * 2 - 2;
			for (int i = 2; i < rail - 1; i++)
				arr[i] = arr[1];
			obj.decrypt(line, arr);
			break;
		}
	}
}