class RailFence {
// function to encrypt a message
public static String encryptRailFence(String text, int key)
{
// create the matrix to cipher plain text
// key = rows , length(text) = columns
char[][] rail = new char[key][text.length()];
// filling the rail matrix to distinguish filled
// spaces from blank ones
for (int i = 0; i < key; i++)
Arrays.fill(rail[i], '\n');
boolean dirDown = false;
int row = 0, col = 0;
for (int i = 0; i < text.length(); i++) {
// check the direction of flow
// reverse the direction if we've just
// filled the top or bottom rail
if (row == 0 || row == key - 1)
dirDown = !dirDown;
// fill the corresponding alphabet
rail[row][col++] = text.charAt(i);
// find the next row using direction flag
if (dirDown)
row++;
else
row--;
}
// now we can construct the cipher using the rail
// matrix
StringBuilder result = new StringBuilder();
for (int i = 0; i < key; i++)
for (int j = 0; j < text.length(); j++)
if (rail[i][j] != '\n')
result.append(rail[i][j]);
return result.toString();
}
// This function receives cipher-text and key
// and returns the original text after decryption
public static String decryptRailFence(String cipher, int key)
{
// create the matrix to cipher plain text
// key = rows , length(text) = columns
char[][] rail = new char[key][cipher.length()];
// filling the rail matrix to distinguish filled
// spaces from blank ones
for (int i = 0; i < key; i++)
Arrays.fill(rail[i], '\n');
// to find the direction
boolean dirDown = true;
int row = 0, col = 0;
// mark the places with '*'
for (int i = 0; i < cipher.length(); i++) {
// check the direction of flow
if (row == 0)
dirDown = true;
if (row == key - 1)
dirDown = false;
// place the marker
rail[row][col++] = '*';
// find the next row using direction flag
if (dirDown)
row++;
else
row--;
}
// now we can construct the fill the rail matrix
int index = 0;
for (int i = 0; i < key; i++)
for (int j = 0; j < cipher.length(); j++)
if (rail[i][j] == '*'
&& index < cipher.length())
rail[i][j] = cipher.charAt(index++);
StringBuilder result = new StringBuilder();
row = 0;
col = 0;
for (int i = 0; i < cipher.length(); i++) {
// check the direction of flow
if (row == 0)
dirDown = true;
if (row == key - 1)
dirDown = false;
if (rail[row][col] != '*')
result.append(rail[row][col++]);
// find the next row using direction flag
if (dirDown)
row++;
else
row--;
}
return result.toString();
}
public static void main(String[] args)
{
// Encryption
System.out.println("Encrypted Message: ");
System.out.println(encryptRailFence("attack at once", 2));
System.out.println( encryptRailFence("GeeksforGeeks ", 3));
System.out.println(encryptRailFence("defend the east wall", 3));
// Now decryption of the same cipher-text
System.out.println("\nDecrypted Message: ");
System.out.println(decryptRailFence("atc toctaka ne", 2));
System.out.println(decryptRailFence("GsGsekfrek eoe", 3));
System.out.println(decryptRailFence("dnhaweedtees alf tl", 3));
}
}