AES-256-CBC encryption / decryption with secret key and IV string with additional C# decrypt-only method

CypherUtils.cs

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

public class CypherUtils {
    public static string Decrypt (string cipherData, string keyString, string ivString) {
        byte[] key = Encoding.UTF8.GetBytes (keyString);
        byte[] iv = Convert.FromBase64String (ivString);

        try {
            using (var rijndaelManaged = new RijndaelManaged { Key = key, IV = iv, Mode = CipherMode.CBC })
            using (var memoryStream = new MemoryStream (Convert.FromBase64String (cipherData)))
            using (var cryptoStream = new CryptoStream (memoryStream, rijndaelManaged.CreateDecryptor (key, iv), CryptoStreamMode.Read)) {
                return new StreamReader (cryptoStream).ReadToEnd ();
            }
        } catch (CryptographicException e) {
            Console.WriteLine ("A Cryptographic error occurred: {0}", e.Message);
            return null;
        }
        // You may want to catch more exceptions here...
    }
}

CypherUtils.ts

import * as crypto from "crypto";

export function encrypt(secret: string, utfText: string): string {
  const key = Buffer.from(secret);
  const iv = crypto.randomBytes(16);
  const cipher = crypto.createCipheriv("aes-256-cbc", key, iv);
  const encrypted = cipher.update(utfText, "utf8", "base64") + cipher.final("base64");
  return iv.toString("base64") + ":" + encrypted;
}

export function decrypt(secret: string, base64Input: string) {
  const key = Buffer.from(secret);
  const textParts = base64Input.split(":");
  const iv = Buffer.from(textParts.shift(), "base64");
  const encryptedText = Buffer.from(textParts.join(":"), "base64");
  const decipher = crypto.createDecipheriv("aes-256-cbc", key, iv);
  const decrypted = decipher.update(encryptedText);
  return Buffer.concat([decrypted, decipher.final()]).toString();
}

// ---- test ----

export function testEncryptDecrypt() {
  const key = crypto.randomBytes(32).toString();

  const data = {
    serverUrl: "wss://my-game-server.com",
    playerId: "my-playerId"
  };

  const encrypted = this.encrypt(key, JSON.stringify(data));
  console.log("encrypted:", encrypted);

  const decrypted = this.decrypt(key, encrypted);
  console.log("decrypted:", decrypted);
}