ADFGVX cipher: Difference between revisions

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 (Technically, we do not need the Polybius square to recover the spaces, but it's passed as an argument here for symmetry.)
+=={{header|Java}}==
+<syntaxhighlight lang="java">
+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("Plaintext: " + 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 "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";
+}
+</syntaxhighlight>
+{{ out }}
+<pre>
+The 6 x 6 Polybius square:
+ | A D F G V X
+--------------
+A| 2 K 4 Q 9 8
+D| W C I M V A
+F| 5 S 0 Y B D
+G| F T O U J E
+V| 6 1 R X 3 G
+X| H L Z P 7 N
+The key is DISHWATER
+Plaintext: ATTACKAT1200AM
+Encrypted: DDAG XAA GDF DDF GXF DGF DDD XVX DDD
+Decrypted: ATTACKAT1200AM
+</pre>
 =={{header|Julia}}==