crypto-keygen-suite/keyGen/ciphers/hillciphergenerator.js

Key generation utilities for cryptographic operations. YES I RENAMED IT. SIX STATE PROTOCOL!!! See its folder for all <3

function charToNum(c) {
  return c.toUpperCase().charCodeAt(0) - 65;
}

function numToChar(n) {
  return String.fromCharCode((n % 26) + 65);
}

function padPlaintext(text) {
  text = text.toUpperCase().replace(/[^A-Z]/g, '');
  while (text.length % 3 !== 0) text += 'X';
  return text;
}

function matrixMultiplyMod26(matrix, vector) {
  let result = [];
  for (let i = 0; i < 3; i++) {
    let sum = 0;
    for (let j = 0; j < 3; j++) {
      sum += matrix[i][j] * vector[j];
    }
    result[i] = ((sum % 26) + 26) % 26;
  }
  return result;
}

function detMod26(m) {
  const det =
    m[0][0] * (m[1][1] * m[2][2] - m[1][2] * m[2][1]) -
    m[0][1] * (m[1][0] * m[2][2] - m[1][2] * m[2][0]) +
    m[0][2] * (m[1][0] * m[2][1] - m[1][1] * m[2][0]);
  return ((det % 26) + 26) % 26;
}

function modInverse(a, m = 26) {
  let m0 = m, x0 = 0, x1 = 1;
  if (m === 1) return 0;
  while (a > 1) {
    let q = Math.floor(a / m);
    [a, m] = [m, a % m];
    [x0, x1] = [x1 - q * x0, x0];
  }
  if (x1 < 0) x1 += m0;
  return x1;
}

function matrixOfMinors(m) {
  return [
    [
      (m[1][1] * m[2][2] - m[1][2] * m[2][1]) % 26,
      (m[1][0] * m[2][2] - m[1][2] * m[2][0]) % 26,
      (m[1][0] * m[2][1] - m[1][1] * m[2][0]) % 26,
    ],
    [
      (m[0][1] * m[2][2] - m[0][2] * m[2][1]) % 26,
      (m[0][0] * m[2][2] - m[0][2] * m[2][0]) % 26,
      (m[0][0] * m[2][1] - m[0][1] * m[2][0]) % 26,
    ],
    [
      (m[0][1] * m[1][2] - m[0][2] * m[1][1]) % 26,
      (m[0][0] * m[1][2] - m[0][2] * m[1][0]) % 26,
      (m[0][0] * m[1][1] - m[0][1] * m[1][0]) % 26,
    ],
  ];
}

function cofactorMatrix(m) {
  const cof = matrixOfMinors(m);
  for (let i = 0; i < 3; i++)
    for (let j = 0; j < 3; j++) {
      if ((i + j) % 2 === 1) cof[i][j] = -cof[i][j];
      cof[i][j] = ((cof[i][j] % 26) + 26) % 26;
    }
  return cof;
}

function transposeMatrix(m) {
  let t = [];
  for (let i = 0; i < 3; i++) {
    t[i] = [];
    for (let j = 0; j < 3; j++) t[i][j] = m[j][i];
  }
  return t;
}

function scalarMultiplyMatrix(m, scalar) {
  let r = [];
  for (let i = 0; i < 3; i++) {
    r[i] = [];
    for (let j = 0; j < 3; j++) r[i][j] = (m[i][j] * scalar) % 26;
  }
  return r;
}

function matrixInverseMod26(m) {
  const det = detMod26(m);
  const detInv = modInverse(det);
  if (detInv === 0) throw new Error("Matrix not invertible mod 26");
  const cof = cofactorMatrix(m);
  const adj = transposeMatrix(cof);
  const inv = scalarMultiplyMatrix(adj, detInv);
  for (let i = 0; i < 3; i++)
    for (let j = 0; j < 3; j++)
      inv[i][j] = ((inv[i][j] % 26) + 26) % 26;
  return inv;
}

function hillEncrypt(text, keyMatrix) {
  text = padPlaintext(text);
  let ciphertext = "";
  for (let i = 0; i < text.length; i += 3) {
    const block = [charToNum(text[i]), charToNum(text[i+1]), charToNum(text[i+2])];
    const encBlock = matrixMultiplyMod26(keyMatrix, block);
    ciphertext += encBlock.map(numToChar).join('');
  }
  return ciphertext;
}

function hillDecrypt(text, keyMatrix) {
  text = text.toUpperCase().replace(/[^A-Z]/g, '');
  const invKey = matrixInverseMod26(keyMatrix);
  let plaintext = "";
  for (let i = 0; i < text.length; i += 3) {
    const block = [charToNum(text[i]), charToNum(text[i+1]), charToNum(text[i+2])];
    const decBlock = matrixMultiplyMod26(invKey, block);
    plaintext += decBlock.map(numToChar).join('');
  }
  return plaintext;
}

function parseKeyMatrix(str) {
  // str example: "6,24,1;13,16,10;20,17,15"
  const rows = str.split(';');
  if (rows.length !== 3) throw new Error("Key must be 3 rows");
  const matrix = rows.map(row => {
    const nums = row.split(',').map(Number);
    if (nums.length !== 3 || nums.some(isNaN)) throw new Error("Each row must have 3 numbers");
    return nums.map(n => ((n % 26) + 26) % 26);
  });
  return matrix;
}

// --- CLI Logic ---

const args = process.argv.slice(2);
if (args.length < 3) {
  console.log("Usage:");
  console.log("  node hillcipher.js encrypt <plaintext> <key>");
  console.log("  node hillcipher.js decrypt <ciphertext> <key>");
  console.log("Key format: 3 rows separated by semicolons, each row 3 comma-separated numbers");
  console.log('Example key: "6,24,1;13,16,10;20,17,15"');
  process.exit(1);
}

const [command, text, keyStr] = args;

let keyMatrix;
try {
  keyMatrix = parseKeyMatrix(keyStr);
} catch (e) {
  console.error("Invalid key:", e.message);
  process.exit(1);
}

try {
  if (command === "encrypt") {
    const encrypted = hillEncrypt(text, keyMatrix);
    console.log("Encrypted:", encrypted);
  } else if (command === "decrypt") {
    const decrypted = hillDecrypt(text, keyMatrix);
    console.log("Decrypted:", decrypted);
  } else {
    console.error("Unknown command. Use encrypt or decrypt.");
    process.exit(1);
  }
} catch (e) {
  console.error("Error:", e.message);
  process.exit(1);
}