使用DataProtection解密时抛出「The payload was invalid」错误的解决咨询

问题场景 #

通过.NET Framework 4.8加密字符串，代码如下：

var dataProtectionProvider = DataProtectionProvider.Create(new DirectoryInfo(@"d:\SharedKeys\"), builder =>
{
  builder.SetApplicationName("myApp");
});

var dataProtector = dataProtectionProvider.CreateProtector("Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationMiddleware", "Cookies", "v2");
var text = dataProtector.Protect("abc");

得到的密文为：

CfDJ8GHt0XxGzaFBlFEwKShBTYZTKFl3jI6DiCAmTaackE0ymGCf_WeBXN2CL4RHN1i9o5kK5fms-9ZmFHV8-e-3bRd0yR5YOxBdcQoxajS9vCe5lrMNZ0gze0PZ-yfV8kqSMQ

使用.NET SDK 6.0解密时，代码如下：

var protectionProvider = DataProtectionProvider.Create(
            new DirectoryInfo(@"d:\SharedKeys\"), cfg => cfg.SetApplicationName("myApp"));
var dataProtector = protectionProvider.CreateProtector(
    "Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationMiddleware", "Cookie", "v2");
var result = dataProtector.Unprotect(
    "CfDJ8GHt0XxGzaFBlFEwKShBTYZTKFl3jI6DiCAmTaackE0ymGCf_WeBXN2CL4RHN1i9o5kK5fms-9ZmFHV8-e-3bRd0yR5YOxBdcQoxajS9vCe5lrMNZ0gze0PZ-yfV8kqSMQ");

运行后抛出错误「The payload was invalid」，错误触发代码：

if (!CryptoUtil.TimeConstantBuffersAreEqual(correctHash, 0, correctHash.Length, protectedPayload.Array!, macOffset, eofOffset - macOffset))
{
   throw Error.CryptCommon_PayloadInvalid(); // integrity check failure
}

经排查为MAC校验不正确。

解决方法 #

问题核心是加密与解密时CreateProtector的参数不匹配：

• 加密代码中第二个参数为"Cookies"（复数）
• 解密代码中对应参数写成了"Cookie"（单数）

CreateProtector的参数会参与生成加密的目的字符串，参数不一致会直接导致MAC校验失败。只需将解密代码中的第二个参数改为"Cookies"即可，修正后的解密代码如下：

var protectionProvider = DataProtectionProvider.Create(
            new DirectoryInfo(@"d:\SharedKeys\"), cfg => cfg.SetApplicationName("myApp"));
var dataProtector = protectionProvider.CreateProtector(
    "Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationMiddleware", "Cookies", "v2");
var result = dataProtector.Unprotect(
    "CfDJ8GHt0XxGzaFBlFEwKShBTYZTKFl3jI6DiCAmTaackE0ymGCf_WeBXN2CL4RHN1i9o5kK5fms-9ZmFHV8-e-3bRd0yR5YOxBdcQoxajS9vCe5lrMNZ0gze0PZ-yfV8kqSMQ");

内容的提问来源于stack exchange，提问作者user2661881