Encrypt and decrypt from Javascript (nodeJS) to dart (Flutter) and from dart to Javascript

Keygen (NodeJS)

Docs: https://nodejs.org/api/crypto.html#crypto_crypto_generatekeypair_type_options_callback

const { generateKeyPair } = require('crypto');

generateKeyPair('rsa', {
    modulusLength: 4096,    // key size in bits
    publicKeyEncoding: {
        type: 'spki',
        format: 'pem',
    },
    privateKeyEncoding: {   
        type: 'pkcs8',      
        format: 'pem',
    },
}, (err, publicKey, privateKey) => {
    // Handle errors and use the generated key pair.
});

NodeJS encryption via JSEncrypt library

node-jsencrypt: https://www.npmjs.com/package/node-jsencrypt
JSEncrypt: https://travistidwell.com/jsencrypt/#

const JSEncrypt = require('node-jsencrypt');  

function encrypt(text, key) {
    const crypt = new JSEncrypt();
    crypt.setKey(key);
    return crypt.encrypt(text);
}

function decrypt(encrypted, privateKey) {
    const crypt = new JSEncrypt();
    crypt.setPrivateKey(privateKey);
    return crypt.decrypt(encrypted);
}

Dart encryption via crypton

GitHub: https://github.com/konstantinullrich/crypton

import 'package:crypton/crypton.dart';

import 'encryption.dart';

class AsymmetricCrypt implements Encryption {
  final String _key;
  RSAPublicKey _publicKey;
  RSAPrivateKey _privateKey;

  AsymmetricCrypt._(this._key);

  @override
  String encrypt(String plain) {
    _publicKey ??= RSAPublicKey.fromPEM(_key);
    return _publicKey.encrypt(plain);
  }

  @override
  String decrypt(String data) {
    _privateKey ??= RSAPrivateKey.fromPEM(_key);
    return _privateKey.decrypt(data);
  }
}

Check out this package for your crypto needs including RSA keys/ciphers.

Symmetric Javascript - Flutter/Dart compatible encryption package.

This was a beneficial post & helped me with Asymmetric as above.

I am creating a hybrid crypto system, here is what I played around with to get the symmetric version working:

Package

Docs

Implementation help I got

Flutter Package- SteelCrypt

The code is rough but it basically shows all the encoding required on the JS end to get proper output on the Flutter end. Flutter end is a piece of cake AS LONG AS YOU GET THE ENCODING RIGHT IN JS ;)

Implementation encryption in Javascript:

var CryptoJS = require("crypto-js");
  try {
    var JsonFormatter = {
  stringify: function(cipherParams) {
    // create json object with ciphertext
    var jsonObj = { ct: cipherParams.ciphertext.toString(CryptoJS.enc.Base64) };

    // optionally add iv or salt
    if (cipherParams.iv) {
      jsonObj.iv = cipherParams.iv.toString();
    }

    // stringify json object
    return JSON.stringify(jsonObj);
  },
  parse: function(jsonStr) {
    // parse json string
    var jsonObj = JSON.parse(jsonStr);

    // extract ciphertext from json object, and create cipher params object
    var cipherParams = CryptoJS.lib.CipherParams.create({
      ciphertext: CryptoJS.enc.Base64.parse(jsonObj.ct)
    });

    // optionally extract iv or salt

    if (jsonObj.iv) {
      cipherParams.iv = CryptoJS.enc.Hex.parse(jsonObj.iv);
    }

    return cipherParams;
  }
};

var encrypted = CryptoJS.AES.encrypt("Message", "Secret Passphrase", {
  format: JsonFormatter
});
var decrypted = CryptoJS.AES.decrypt(encrypted, "Secret Passphrase", {
  format: JsonFormatter
});
decrypted.toString(CryptoJS.enc.Utf8);

    return {
    "key": CryptoJS.enc.Base64.stringify(encrypted.key),
    "iv": CryptoJS.enc.Base64.stringify(encrypted.iv),
    "encrypted": CryptoJS.enc.Base64.stringify(encrypted.ciphertext),
    "decrypted": decrypted.toString(CryptoJS.enc.Utf8),
  }
  } catch (error) {
    throw new Error(error);
  }

Returns

{
key: Y4GKaFmHD9fPBh/LI04nooA3WVoBWSIkd0GzqJkX7fA=,
iv: DlNlgIv+Vboxq8MSrIFtVA==,
encrypted: NduRQJ7CB40r18w4meeIoQ==,
decrypted: Message
}

Flutter/Dart implementation:

//AES CBC decryption from Parse CryptoJS
  var iv = 'DlNlgIv+Vboxq8MSrIFtVA==';
  var key = 'Y4GKaFmHD9fPBh/LI04nooA3WVoBWSIkd0GzqJkX7fA=';
  var cypher = AesCrypt(key: key, padding: PaddingAES.pkcs7);
  var encryptedData = 'NduRQJ7CB40r18w4meeIoQ==';
  print(cypher.cbc.decrypt(enc: encryptedData, iv: iv)); //decrypt

Prints

Message

You can use the 'aescryptojs' package on the flutter side and 'crypto-js' on the node.js side. This way the AES algorithms will work consistently on both client and sever side.

Flutter:

class DataEncrypt {
  static wrappingEncrypted(dynamic data) {
    // Todo: datanin sifrelenmesi islemi
    final unencryptedData = data;
    final key = '${dotenv.env['ENCRYPT_KEY']}';
    final encryptedData = encryptAESCryptoJS(unencryptedData, key);
    print("Encrypted data :" + encryptedData);
    return encryptedData;
  }

  static wrappingDescrypted(dynamic data) {
    // Todo: sifrenin cozumlenmesi islemi
    final key = '${dotenv.env['ENCRYPT_KEY']}';
    final descryptedData = decryptAESCryptoJS(data, key);
    print("Descrypted data :" + descryptedData);
    return descryptedData;
  }
}

Node.js:

function funcDecryptedData(data) {
    // Todo: AES Decrypted
    var bytes = CryptoJS.AES.decrypt(data, process.env.ENCRYPT_KEY);
    var descryptedData = bytes.toString(CryptoJS.enc.Utf8);
    return descryptedData;
}
function funcEncryptedData(data) {
    //Todo: AES Encrypted
    var encryptedData = CryptoJS.AES.encrypt(data, process.env.ENCRYPT_KEY).toString();
    return encryptedData;
}