v2rayN/v2rayN/ServiceLib/Common/AesUtils.cs

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

namespace ServiceLib.Common;

public class AesUtils
{
    private const int KeySize = 256; // AES-256
    private const int IvSize = 16;   // AES block size
    private const int Iterations = 10000;
    private static readonly byte[] Salt = Encoding.ASCII.GetBytes("saltysalt".PadRight(16, ' ')); 
    private static readonly string DefaultPassword = Utils.GetMd5(Utils.GetHomePath() + "AesUtils");

    /// <summary>
    /// Encrypt
    /// </summary>
    /// <param name="text">Plain text</param>
    /// <param name="password">Password for key derivation or direct key in ASCII bytes</param>
    /// <returns>Base64 encoded cipher text with IV</returns>
    public static string Encrypt(string text, string? password = null)
    {
        if (string.IsNullOrEmpty(text))
            return string.Empty;

        var plaintext = Encoding.UTF8.GetBytes(text);
        var key = GetKey(password);
        var iv = GenerateIv();

        using var aes = Aes.Create();
        aes.Key = key;
        aes.IV = iv;

        using var ms = new MemoryStream();
        ms.Write(iv, 0, iv.Length);

        using (var cs = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write))
        {
            cs.Write(plaintext, 0, plaintext.Length);
            cs.FlushFinalBlock();
        }

        var cipherTextWithIv = ms.ToArray();
        return Convert.ToBase64String(cipherTextWithIv);
    }

    /// <summary>
    /// Decrypt
    /// </summary>
    /// <param name="cipherTextWithIv">Base64 encoded cipher text with IV</param>
    /// <param name="password">Password for key derivation or direct key in ASCII bytes</param>
    /// <returns>Plain text</returns>
    public static string Decrypt(string cipherTextWithIv, string? password = null)
    {
        if (string.IsNullOrEmpty(cipherTextWithIv))
            return string.Empty;

        var cipherTextWithIvBytes = Convert.FromBase64String(cipherTextWithIv);
        var key = GetKey(password);

        var iv = new byte[IvSize];
        Buffer.BlockCopy(cipherTextWithIvBytes, 0, iv, 0, IvSize);

        var cipherText = new byte[cipherTextWithIvBytes.Length - IvSize];
        Buffer.BlockCopy(cipherTextWithIvBytes, IvSize, cipherText, 0, cipherText.Length);

        using var aes = Aes.Create();
        aes.Key = key;
        aes.IV = iv;

        using var ms = new MemoryStream();
        using (var cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write))
        {
            cs.Write(cipherText, 0, cipherText.Length);
            cs.FlushFinalBlock();
        }

        var plainText = ms.ToArray();
        return Encoding.UTF8.GetString(plainText);
    }

    private static byte[] GetKey(string? password)
    {
        if (password.IsNullOrEmpty())
        {
            password = DefaultPassword;
        }

        using var pbkdf2 = new Rfc2898DeriveBytes(password, Salt, Iterations, HashAlgorithmName.SHA256);
        return pbkdf2.GetBytes(KeySize / 8);
    }

    private static byte[] GenerateIv()
    {
        var randomNumber = new byte[IvSize];

        using var rng = RandomNumberGenerator.Create();
        rng.GetBytes(randomNumber);
        return randomNumber;
    }
}