diff --git a/DIRECTORY.md b/DIRECTORY.md index 652ecbfd6..3d215855b 100644 --- a/DIRECTORY.md +++ b/DIRECTORY.md @@ -73,6 +73,7 @@ * [PlayfairCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java) * [Polybius](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Polybius.java) * [ProductCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ProductCipher.java) + * [RailFenceCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/RailFenceCipher.java) * [RSA](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/RSA.java) * [SimpleSubCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/SimpleSubCipher.java) * [Vigenere](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Vigenere.java) @@ -729,6 +730,7 @@ * [HillCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/HillCipherTest.java) * [PlayfairTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/PlayfairTest.java) * [PolybiusTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/PolybiusTest.java) + * [RailFenceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/RailFenceTest.java) * [RSATest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/RSATest.java) * [SimpleSubCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/SimpleSubCipherTest.java) * [VigenereTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/VigenereTest.java) diff --git a/src/main/java/com/thealgorithms/ciphers/RailFenceCipher.java b/src/main/java/com/thealgorithms/ciphers/RailFenceCipher.java new file mode 100644 index 000000000..f81252980 --- /dev/null +++ b/src/main/java/com/thealgorithms/ciphers/RailFenceCipher.java @@ -0,0 +1,147 @@ +package com.thealgorithms.ciphers; + +import java.util.Arrays; + +/** + * The rail fence cipher (also called a zigzag cipher) is a classical type of transposition cipher. + * It derives its name from the manner in which encryption is performed, in analogy to a fence built with horizontal rails. + * https://en.wikipedia.org/wiki/Rail_fence_cipher + * @author https://github.com/Krounosity + */ + +public class RailFenceCipher { + + // Encrypts the input string using the rail fence cipher method with the given number of rails. + public String encrypt(String str, int rails) { + + // Base case of single rail or rails are more than the number of characters in the string + if (rails == 1 || rails >= str.length()) { + return str; + } + + // Boolean flag to determine if the movement is downward or upward in the rail matrix. + boolean down = true; + // Create a 2D array to represent the rails (rows) and the length of the string (columns). + char[][] strRail = new char[rails][str.length()]; + + // Initialize all positions in the rail matrix with a placeholder character ('\n'). + for (int i = 0; i < rails; i++) { + Arrays.fill(strRail[i], '\n'); + } + + int row = 0; // Start at the first row + int col = 0; // Start at the first column + + int i = 0; + + // Fill the rail matrix with characters from the string based on the rail pattern. + while (col < str.length()) { + // Change direction to down when at the first row. + if (row == 0) { + down = true; + } + // Change direction to up when at the last row. + else if (row == rails - 1) { + down = false; + } + + // Place the character in the current position of the rail matrix. + strRail[row][col] = str.charAt(i); + col++; // Move to the next column. + // Move to the next row based on the direction. + if (down) { + row++; + } else { + row--; + } + + i++; + } + + // Construct the encrypted string by reading characters row by row. + StringBuilder encryptedString = new StringBuilder(); + for (char[] chRow : strRail) { + for (char ch : chRow) { + if (ch != '\n') { + encryptedString.append(ch); + } + } + } + return encryptedString.toString(); + } + // Decrypts the input string using the rail fence cipher method with the given number of rails. + public String decrypt(String str, int rails) { + + // Base case of single rail or rails are more than the number of characters in the string + if (rails == 1 || rails >= str.length()) { + return str; + } + // Boolean flag to determine if the movement is downward or upward in the rail matrix. + boolean down = true; + + // Create a 2D array to represent the rails (rows) and the length of the string (columns). + char[][] strRail = new char[rails][str.length()]; + + int row = 0; // Start at the first row + int col = 0; // Start at the first column + + // Mark the pattern on the rail matrix using '*'. + while (col < str.length()) { + // Change direction to down when at the first row. + if (row == 0) { + down = true; + } + // Change direction to up when at the last row. + else if (row == rails - 1) { + down = false; + } + + // Mark the current position in the rail matrix. + strRail[row][col] = '*'; + col++; // Move to the next column. + // Move to the next row based on the direction. + if (down) { + row++; + } else { + row--; + } + } + + int index = 0; // Index to track characters from the input string. + // Fill the rail matrix with characters from the input string based on the marked pattern. + for (int i = 0; i < rails; i++) { + for (int j = 0; j < str.length(); j++) { + if (strRail[i][j] == '*') { + strRail[i][j] = str.charAt(index++); + } + } + } + + // Construct the decrypted string by following the zigzag pattern. + StringBuilder decryptedString = new StringBuilder(); + row = 0; // Reset to the first row + col = 0; // Reset to the first column + + while (col < str.length()) { + // Change direction to down when at the first row. + if (row == 0) { + down = true; + } + // Change direction to up when at the last row. + else if (row == rails - 1) { + down = false; + } + // Append the character from the rail matrix to the decrypted string. + decryptedString.append(strRail[row][col]); + col++; // Move to the next column. + // Move to the next row based on the direction. + if (down) { + row++; + } else { + row--; + } + } + + return decryptedString.toString(); + } +} diff --git a/src/test/java/com/thealgorithms/ciphers/RailFenceTest.java b/src/test/java/com/thealgorithms/ciphers/RailFenceTest.java new file mode 100644 index 000000000..2bfa704e3 --- /dev/null +++ b/src/test/java/com/thealgorithms/ciphers/RailFenceTest.java @@ -0,0 +1,62 @@ +package com.thealgorithms.ciphers; + +import static org.junit.jupiter.api.Assertions.assertEquals; + +import org.junit.jupiter.api.Test; + +public class RailFenceTest { + + @Test + void testEncryption() { + RailFenceCipher cipher = new RailFenceCipher(); + + String input = "We are discovered! Flee at once"; + int rails = 3; + String encrypted = cipher.encrypt(input, rails); + assertEquals("Wrivdlaneaedsoee!Fe toc cr e e", encrypted); + + String singleChar = "A"; + int singleRail = 2; + String encryptedSingleChar = cipher.encrypt(singleChar, singleRail); + assertEquals("A", encryptedSingleChar); + + String shortString = "Hello"; + int moreRails = 10; + String encryptedShortString = cipher.encrypt(shortString, moreRails); + assertEquals("Hello", encryptedShortString); + + String inputSingleRail = "Single line"; + int singleRailOnly = 1; + String encryptedSingleRail = cipher.encrypt(inputSingleRail, singleRailOnly); + assertEquals("Single line", encryptedSingleRail); + } + + @Test + void testDecryption() { + RailFenceCipher cipher = new RailFenceCipher(); + + // Scenario 1: Basic decryption with multiple rails + String encryptedInput = "Wrivdlaneaedsoee!Fe toc cr e e"; + int rails = 3; + String decrypted = cipher.decrypt(encryptedInput, rails); + assertEquals("We are discovered! Flee at once", decrypted); + + // Scenario 2: Single character string decryption + String encryptedSingleChar = "A"; + int singleRail = 2; // More than 1 rail + String decryptedSingleChar = cipher.decrypt(encryptedSingleChar, singleRail); + assertEquals("A", decryptedSingleChar); + + // Scenario 3: String length less than the number of rails + String encryptedShortString = "Hello"; + int moreRails = 10; // More rails than characters + String decryptedShortString = cipher.decrypt(encryptedShortString, moreRails); + assertEquals("Hello", decryptedShortString); + + // Scenario 4: Single rail decryption (output should be the same as input) + String encryptedSingleRail = "Single line"; + int singleRailOnly = 1; + String decryptedSingleRail = cipher.decrypt(encryptedSingleRail, singleRailOnly); + assertEquals("Single line", decryptedSingleRail); + } +}