ActiveCode API & Authentication

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.MessageDigest;
import java.util.Base64;

public class Crypto {

    public static String decrypt(String data, String key) throws Exception {
        byte[] keyBytes = MessageDigest.getInstance("SHA-256").digest(key.getBytes());
        byte[] combined = Base64.getDecoder().decode(data);
        byte[] iv = new byte[16];
        byte[] ciphertext = new byte[combined.length - 16];

        System.arraycopy(combined, 0, iv, 0, 16);
        System.arraycopy(combined, 16, ciphertext, 0, ciphertext.length);

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(keyBytes, "AES"), new IvParameterSpec(iv));

        return new String(cipher.doFinal(ciphertext));
    }
}

import javax.crypto.Cipher
import javax.crypto.spec.IvParameterSpec
import javax.crypto.spec.SecretKeySpec
import java.security.MessageDigest
import java.util.Base64

object Crypto {

    fun decrypt(data: String, key: String): String {
        val keyBytes = MessageDigest.getInstance("SHA-256").digest(key.toByteArray())
        val combined = Base64.getDecoder().decode(data)
        val iv = combined.copyOfRange(0, 16)
        val ciphertext = combined.copyOfRange(16, combined.size)

        val cipher = Cipher.getInstance("AES/CBC/PKCS5Padding")
        cipher.init(Cipher.DECRYPT_MODE, SecretKeySpec(keyBytes, "AES"), IvParameterSpec(iv))

        return String(cipher.doFinal(ciphertext))
    }
}

const crypto = require('crypto');

function decrypt(data, key) {
    const keyBuf = crypto.createHash('sha256').update(key).digest();
    const combined = Buffer.from(data, 'base64');
    const iv = combined.subarray(0, 16);
    const ciphertext = combined.subarray(16);

    const decipher = crypto.createDecipheriv('aes-256-cbc', keyBuf, iv);
    let plaintext = decipher.update(ciphertext);
    plaintext = Buffer.concat([plaintext, decipher.final()]);

    return plaintext.toString('utf8');
}

/*
Add dependencies to your pubspec.yaml:
dependencies:
  encrypt: ^5.0.1
  crypto: ^3.0.1
*/

import 'dart:convert';
import 'dart:typed_data';
import 'package:crypto/crypto.dart';

String decrypt(String data, String key) {
  final keyBytes = sha256.convert(utf8.encode(key)).bytes;
  final combined = base64.decode(data);
  final iv = IV(Uint8List.fromList(combined.sublist(0, 16)));
  final ciphertext = Encrypted(Uint8List.fromList(combined.sublist(16)));

  final encrypter = Encrypter(AES(Key(Uint8List.fromList(keyBytes)), mode: AESMode.cbc));
  return encrypter.decrypt(ciphertext, iv: iv);
}