Data update

Task/ADFGVX-cipher/C-sharp/adfgvx-cipher.cs

@@ -0,0 +1,117 @@
+using System.Diagnostics;
+
+const string cypher = "ADFGVX";
+var N = cypher.Length;
+var size = N * N;
+const string symbols = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+Debug.Assert(size == symbols.Length);
+var square = new int[size];
+
+for (var i = 0; i < size; i++)
+{
+    var j = Random.Shared.Next(i + 1);
+    square[i] = square[j];
+    square[j] = i;
+}
+
+Console.WriteLine($"{N} x {N} Polybius square:");
+Console.WriteLine();
+Console.WriteLine($"  | {string.Join(' ', cypher.AsEnumerable())}");
+Console.WriteLine(new string('-', 2 * N + 3));
+
+for (var row = 0; row < N; row++)
+{
+    Console.Write($"{cypher[row]} |");
+
+    for (var col = 0; col < N; col++)
+    {
+        Console.Write($" {symbols[square[col + row * N]]}");
+    }
+
+    Console.WriteLine();
+}
+
+static bool IsSuitableTranspositionKey(string s) =>
+    s.Length >= 7 && s.Length <= 12 && s.Length == s.Distinct().Count() && s.All(symbols.ToLowerInvariant().Contains);
+
+var keys = File.ReadAllLines("unixdict.txt").Where(IsSuitableTranspositionKey).ToArray();
+var key = keys[Random.Shared.Next(keys.Length)].ToUpperInvariant();
+Console.WriteLine();
+Console.WriteLine($"The key is {key}");
+var plaintext = "ATTACKAT1200AM";
+Console.WriteLine($"Plaintext: {plaintext}");
+
+string Encrypt(string plaintext, string key, int[] square)
+{
+    // Create a lookup table from symbol to fragment
+    var map = (from i in Enumerable.Range(0, size)
+               let k = square[i]
+               let code = cypher[i / N] + "" + cypher[i % N]
+               select (k, code))
+               .ToDictionary(kc => symbols[kc.k], kc => kc.code);
+
+    // Map the plaintext to fragments
+    var e = string.Join("", plaintext.Select(c => map[c]));
+
+    // Determine number of rows
+    var K = key.Length;
+    var rows = (e.Length + K - 1) / K;
+
+    // Pad with spaces
+    e += new string(' ', rows * K - e.Length);
+
+    // Sort the key
+    var order = string.Join("", key.OrderBy(c => c)).Select(c => key.IndexOf(c)).ToArray();
+
+    // Reorder the fragments.
+    e = string.Join("", Enumerable.Range(0, K * rows).Select(i => e[(i / K) * K + order[i % K]]));
+
+    // Transpose
+    e = new([.. from col in Enumerable.Range(0, K)
+                from row in Enumerable.Range(0, rows)
+                select e[row * K + col]]);
+
+    // Read off each column.
+    return string.Join(" ", Enumerable.Range(0, K).Select(col => e.Substring(col * rows, rows).Trim()));
+}
+
+var encrypted = Encrypt(plaintext, key, square);
+Console.WriteLine($"Encrypted: {encrypted}");
+
+string Decrypt(string encrypted, string key, int[] square)
+{
+    // Create a lookup table from fragment to symbol
+    var map = (from i in Enumerable.Range(0, size)
+               let k = square[i]
+               let code = cypher[i / N] + "" + cypher[i % N]
+               select (k, code))
+               .ToDictionary(kc => kc.code, kc => symbols[kc.k]);
+
+    // Split into columns
+    var cols = encrypted.Split(' ');
+
+    // Determine number of rows
+    var K = key.Length;
+    var rows = cols.Max(c => c.Length);
+
+    // Pad each column
+    cols = [.. cols.Select(c => c.PadRight(rows))];
+
+    // Transpose
+    string e = new([.. from row in Enumerable.Range(0, rows)
+                       from col in Enumerable.Range(0, K)
+                       select cols[col][row]]);
+
+    // Sort the key
+    var sorted = string.Join("", key.OrderBy(c => c));
+    var order = key.Select(c => sorted.IndexOf(c)).ToArray();
+
+    // Reorder the fragments
+    e = string.Join("", Enumerable.Range(0, K * rows).Select(i => e[(i / K) * K + order[i % K]])).Trim();
+
+    // Map the fragments to plaintext
+    return string.Join("", Enumerable.Range(0, e.Length / 2).Select(i => map[e.Substring(2 * i, 2)]));
+}
+
+var decrypted = Decrypt(encrypted, key, square);
+Console.WriteLine($"Decrypted: {decrypted}");