最近有个需求，要求把日志加密，因为系统一直用的是NLog，所以也只能在这个基础上加密了。本文的用法NLog很早就有了，记录下来，以作后用。
NLog加密相对好处理，只需要定义一个TargetWithLayout的子类，重写它的Write方法即可，至于加密算法，可以自己行决定，这样就可以把灵活放成最大化，有途径，不干涉。下面代码中的EncryptedFileTarget就是自定义的TargetWithLayout子类。而[Target("MyEncryptedFile")]特性，是为了在nlog.config中配置使用这个加密类。除此以外，不需要任务引用。
using NLog.Targets;using NLog;using NLog.Web;using System.Security.Cryptography;using System.Text;using System.Reflection;var builder = WebApplication.CreateBuilder(args);builder.Logging.ClearProviders();builder.Host.UseNLog();var app = builder.Build();var summaries = new[]{"Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"};app.MapGet("/weatherforecast", () =>{app.Logger.LogInformation("完成测试");var forecast = Enumerable.Range(1, 5).Select(index =>new WeatherForecast(DateOnly.FromDateTime(DateTime.Now.AddDays(index)),Random.Shared.Next(-20, 55),summaries[Random.Shared.Next(summaries.Length)])).ToArray();return forecast;});app.Run();internal record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary){public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);}[]public sealed class EncryptedFileTarget : TargetWithLayout{public string FileName { get; set; }private string key = "bb45f81e2db4a7668d98638402e2461991785f98a89520051149c271652514ba";protected override void Write(LogEventInfo logEvent){var logMessage = this.Layout.Render(logEvent);var encryptedMessage = Encrypt(logMessage, key);FileName = FileName.Replace("${basedir}", Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)).Replace("${shortdate}", DateTime.Now.ToString("yyyy-MM-dd"));System.IO.File.AppendAllText(FileName, encryptedMessage + Environment.NewLine);}private string Encrypt(string clearText, string key){var clearBytes = Encoding.Unicode.GetBytes(clearText);using (var encryptor = Aes.Create()){var saltBytes = new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 };var pdb = new Rfc2898DeriveBytes(key, saltBytes, 1000, HashAlgorithmName.SHA256);encryptor.Key = pdb.GetBytes(32);encryptor.IV = pdb.GetBytes(16);using (MemoryStream ms = new MemoryStream()){using (var cs = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write)){cs.Write(clearBytes, 0, clearBytes.Length);cs.Close();}clearText = Convert.ToBase64String(ms.ToArray());}}return clearText;}}
下面是使用MyEncryptedFile的NLog配置文件，需要引用EncryptedFileTarget所在的命名空间，放在extensions节点中即可。
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"autoReload="true"internalLogLevel="Info"><extensions><add assembly="NLogDemo" /></extensions><targets><target xsi:type="MyEncryptedFile" name="allfile" fileName="${basedir}\logs\nlog-AspNetCore-all-${shortdate}.log"layout="${longdate}|${event-properties:item=EventId:whenEmpty=0}|${level:uppercase=true}|${logger}|${message} ${exception:format=tostring}" /><target xsi:type="File" name="ownFile-web" fileName="${basedir}\logs\nlog-AspNetCore-own-${shortdate}.log"layout="${longdate}|${event-properties:item=EventId:whenEmpty=0}|${level:uppercase=true}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}" /><target xsi:type="Console" name="lifetimeConsole" layout="${MicrosoftConsoleLayout}" /> </targets><rules><logger name="*" minlevel="Trace" writeTo="allfile" /><logger name="Microsoft.Hosting.Lifetime" minlevel="Info" writeTo="lifetimeConsole, ownFile-web" final="true" /><logger name="Microsoft.*" maxlevel="Info" final="true" /><logger name="System.Net.Http.*" maxlevel="Info" final="true" /><logger name="*" minlevel="Trace" writeTo="ownFile-web" /></rules></nlog>
