Web Crypto API example

web_crypto_api_example.js

// for uint8array = new TextEncoder("utf-8").encode("¢");
// for string = new TextDecoder("utf-8").decode(uint8array);

var string = new Uint8Array([0x01, 0x02])
var data = new Uint8Array([0x03, 0x04, 0x05])

var handle_error = function (error) {
  cnosole.log("Error:",error)
}

window.crypto.subtle.digest({name: "SHA-256"}, string).then(function (hash) {
  console.log("SHA-256:",new Uint8Array(hash))

  window.crypto.subtle.importKey("raw", hash, {name: "AES-GCM"}, true, ["encrypt", "decrypt"]).then(function (key) {
    var algorithm = key.algorithm
    algorithm.iv = window.crypto.getRandomValues(new Uint8Array(16))

    window.crypto.subtle.encrypt(algorithm, key, data).then(function (ct) {
      console.log("AES-GCM encrypt:",new Uint8Array(ct))

      window.crypto.subtle.decrypt(algorithm, key, ct).then(function (pt) {
        console.log("AES-GCM decrypt:",new Uint8Array(pt))
      }, handle_error)
    }, handle_error)
  }, handle_error)
}, handle_error)

function sha256(str) {
  // We transform the string into an arraybuffer.
  var buffer = new TextEncoder("utf-8").encode(str);
  return crypto.subtle.digest("SHA-256", buffer).then(function (hash) {
    return hex(hash);
  });
}

function hex(buffer) {
  var hexCodes = [];
  var view = new DataView(buffer);
  for (var i = 0; i < view.byteLength; i += 4) {
    // Using getUint32 reduces the number of iterations needed (we process 4 bytes each time)
    var value = view.getUint32(i)
    // toString(16) will give the hex representation of the number without padding
    var stringValue = value.toString(16)
    // We use concatenation and slice for padding
    var padding = '00000000'
    var paddedValue = (padding + stringValue).slice(-padding.length)
    hexCodes.push(paddedValue);
  }

  // Join all the hex strings into one
  return hexCodes.join("");
}

sha256("foobar").then(function(digest) {
  console.log(digest);
});