Encrypt in php and decrypt in Dart(flutter)

Question

Does anyone have an idea about encrypting response from my php api and decrypting data in local using dart. I'm using flutter for my mobile application.

Thank You!

Answer 1

Here is a method for encrypting/decrypting in Flutter, PHP and C# using AES-256-CBC algorithm.

AES-256 is considered quantum-safe.

Flutter:

Include the package https://pub.dev/packages/encrypt

import 'dart:convert';

import 'package:encrypt/encrypt.dart';
import 'package:crypto/crypto.dart';

class Encryption {
  static final Encryption instance = Encryption._();
  
  late IV _iv;
  late Encrypter _encrypter;

  Encryption._() {
    const mykey = 'ThisIsASecuredKey';
    const myiv = 'ThisIsASecuredBlock';
    final keyUtf8 = utf8.encode(mykey);
    final ivUtf8 = utf8.encode(myiv);
    final key = sha256.convert(keyUtf8).toString().substring(0, 32);
    final iv = sha256.convert(ivUtf8).toString().substring(0, 16);
    _iv = IV.fromUtf8(iv);

    _encrypter = Encrypter(AES(Key.fromUtf8(key), mode: AESMode.cbc));
  }

  String encrypt(String value) {
    return _encrypter.encrypt(value, iv: _iv).base64;
  }

  String decrypt(String base64value) {
    final encrypted = Encrypted.fromBase64(base64value);
    return _encrypter.decrypt(encrypted, iv: _iv);
  }
}

Usage (Singleton Class):

var encrypted = Encryption.instance.encrypt('my value to be encrypted');
var decrypted = Encryption.instance.decrypt(encrypted);

PHP:

<?php

class Encryption
{
    private string $encryptMethod = 'AES-256-CBC';
    private string $key;
    private string $iv;

    public function __construct()
    {
        $mykey = 'ThisIsASecuredKey';
        $myiv = 'ThisIsASecuredBlock';
        $this->key = substr(hash('sha256', $mykey), 0, 32);
        $this->iv = substr(hash('sha256', $myiv), 0, 16);
    }

    public function encrypt(string $value): string
    {
        return openssl_encrypt(
            $value,
            $this->encryptMethod,
            $this->key,
            0,
            $this->iv
        );
    }

    public function decrypt(string $base64Value): string
    {
        return openssl_decrypt(
            $base64Value,
            $this->encryptMethod,
            $this->key,
            0,
            $this->iv
        );
    }
}

Usage:

$encryption = new Encryption();
$encrypted = $encryption->encrypt('my value to be encrypted');
$decrypted = $encryption->decrypt($encrypted);

C#:

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

public class Encryption
{
    byte[] key;
    byte[] iv;

    private Encryption instance;
    public Encryption Instance
    {
        get
        {
            if (instance == null)
                instance = new Encryption();
            return instance;
        }
    }

    private Encryption()
    {
        var Key = "ThisIsASecuredKey";
        var Iv = "ThisIsASecuredBlock";

        using (var sha256 = SHA256.Create())
        {
            key = Encoding.UTF8.GetBytes(
                 ToHex(sha256.ComputeHash(Encoding.UTF8.GetBytes(Key)))
                    .Substring(0, 32)
            );
            iv = Encoding.UTF8.GetBytes(
                 ToHex(sha256.ComputeHash(Encoding.UTF8.GetBytes(Iv)))
                    .Substring(0, 16)
            );
        }
    }
    
    public string Encrypt(string input)
    {
        using (var aesManaged = new AesManaged())
        using (var ms = new MemoryStream())
        {
            using (var cs = new CryptoStream(
                ms,
                aesManaged.CreateEncryptor(key, iv),
                CryptoStreamMode.Write
            ))
            {
                var inputBytes = Encoding.UTF8.GetBytes(input);
                cs.Write(inputBytes, 0, inputBytes.Length);
            }

            return Convert.ToBase64String(ms.ToArray());
        }
    }

    public string Decrypt(string base64value)
    {
        using (var aesManaged = new AesManaged())
        using (var decryptor = aesManaged.CreateDecryptor(key, iv))
        using (var ms = new MemoryStream(Convert.FromBase64String(base64value)))
        using (var cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read))
        using (var sr = new StreamReader(cs))
        {
            return sr.ReadToEnd();
        }
    }

    private string ToHex(byte[] bytes, bool upperCase = false)
    {
        var result = new StringBuilder(bytes.Length * 2);
        for (int i = 0; i < bytes.Length; i++)
            result.Append(bytes[i].ToString(upperCase ? "X2" : "x2"));
        return result.ToString();
    }
}

Usage (Singleton Class):

var encrypted = Encryption.Instance.Encrypt("my value to be encrypted");
var decrypted = Encryption.Instance.Decrypt(encrypted);