Data update

Task/ADFGVX-cipher/Java/adfgvx-cipher.java

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+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public final class ADFGVXCipher {
+
+	public static void main(String[] args) throws IOException {	
+		final char[][] polybius = initialisePolybiusSquare();
+		System.out.println("The 6 x 6 Polybius square:");
+		System.out.println(" | A D F G V X");
+		System.out.println("--------------");
+		for ( int row = 0; row < 6; row++ ) {
+			System.out.print(ADFGVX.charAt(row) + "|");
+			for ( int column = 0; column < 6; column++ ) {
+				System.out.print(" " + polybius[row][column]);
+			}
+			System.out.println();
+		}
+		System.out.println();
+
+		final String key = createKey(9);
+		System.out.println("The key is " + key);
+		System.out.println();
+		final String plainText = "ATTACKAT1200AM";
+		System.out.println("Plain text: " + plainText);
+		System.out.println();
+		final String encryptedText = encrypt(plainText, polybius, key);
+		System.out.println("Encrypted: " + encryptedText);
+		System.out.println();
+		final String decryptedText = decrypt(encryptedText, polybius, key);
+		System.out.println("Decrypted: " + decryptedText);		
+	}
+	
+	private static String encrypt(String plainText, char[][] polybius, String key) {
+		String code = "";
+		for ( char ch : plainText.toCharArray() ) {
+			for ( int row = 0; row < 6; row++ ) {
+				for ( int column = 0; column < 6; column++ ) {
+					if ( polybius[row][column] == ch ) {						
+						code += ADFGVX.charAt(row) + "" + ADFGVX.charAt(column);
+					}
+				}
+			}
+		}
+		
+		String encrypted = "";
+		for ( char ch : key.toCharArray() ) {
+			for ( int i = key.indexOf(ch); i < code.length(); i += key.length() ) {
+				encrypted += code.charAt(i);
+			}
+			encrypted += " ";
+		}
+		return encrypted;
+	}
+	
+	private static String decrypt(String encryptedText, char[][] polybius, String key) {
+		final int codeSize = encryptedText.replace(" ", "").length();		
+		String code = "";
+		for ( int i = 0; code.length() < codeSize; i++ ) {
+			for ( String block : encryptedText.split(" ") ) {
+				if ( code.length() < codeSize ) {
+					code += block.charAt(i);
+				}
+			}
+		}
+		
+		String plainText = "";
+		for ( int i = 0; i < codeSize - 1; i += 2 ) {
+		    int row = ADFGVX.indexOf(code.substring(i, i + 1));
+		    int column = ADFGVX.indexOf(code.substring(i + 1, i + 2));
+		    plainText += polybius[row][column];
+		}		
+		return plainText;	
+	}
+	
+	// Create a key using a word from the dictionary 'unixdict.txt'
+	private static String createKey(int size) throws IOException {
+		if ( size < 7 || size > 12 ) {
+			throw new AssertionError("Key should contain between 7 and 12 letters, both inclusive.");
+		}
+			
+		List<String> candidates = Files.lines(Path.of("unixdict.txt"))
+			.filter( word -> word.length() == size )
+			.filter( word -> word.chars().distinct().count() == word.length() )
+			.filter( word -> word.chars().allMatch(Character::isLetterOrDigit) )
+			.collect(Collectors.toList());
+		Collections.shuffle(candidates);
+		return candidates.get(0).toUpperCase();		
+	}
+	
+	private static char[][] initialisePolybiusSquare() {
+		List<String> letters = Arrays.asList("ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".split(""));
+		Collections.shuffle(letters);
+	
+		char[][] result = new char[6][6];
+		for ( int row = 0; row < 6; row++ ) {
+		    for ( int column = 0; column < 6; column++ ) {
+		        result[row][column] = letters.get(6 * row + column).charAt(0);
+		    }
+		}
+		return result;
+	}
+	
+	private static final String ADFGVX = "ADFGVX";	
+
+}