using System;
using System.IO;
using System.Security.Cryptography.X509Certificates;
using Microsoft.AspNetCore.DataProtection;

namespace ConsoleApp9
{
    class Program
    {
        static void Main(string[] args)
        {
            var dpp =
                DataProtectionProvider.Create(
                    keyDirectory:
                        new DirectoryInfo(
                            @"C:\tmp\DataProtectionTestKeyStore"),
                    setupAction:
                        cfg =>
                        {
                            cfg.ProtectKeysWithCertificate(
                                new X509Certificate2(
                                    fileName: @"C:\tmp\key.pfx",
                                    password: @"super-secret-password"));
                        });

            var dp = dpp.CreateProtector("test purpose");
            var secret = dp.Protect("test secret");
            Console.WriteLine(secret);
        }
    }
}

Unhandled Exception: System.Security.Cryptography.CryptographicException: Unable to retrieve the decryption key.
   at System.Security.Cryptography.Xml.EncryptedXml.DecryptDocument()
   at Microsoft.AspNetCore.DataProtection.XmlEncryption.EncryptedXmlDecryptor.Decrypt(XElement encryptedElement)
   at Microsoft.AspNetCore.DataProtection.XmlEncryption.XmlEncryptionExtensions.DecryptElement(XElement element, IActivator activator)
   at Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager.Microsoft.AspNetCore.DataProtection.KeyManagement.Internal.IInternalXmlKeyManager.DeserializeDescriptorFromKeyElement(XElement keyElement)
   at Microsoft.AspNetCore.DataProtection.KeyManagement.DeferredKey.<>c__DisplayClass1_0.<GetLazyDescriptorDelegate>b__0()
   at System.Lazy`1.CreateValue()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Lazy`1.get_Value()
   at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyBase.get_Descriptor()
   at Microsoft.AspNetCore.DataProtection.AuthenticatedEncryption.CngGcmAuthenticatedEncryptorFactory.CreateEncryptorInstance(IKey key)
   at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyBase.CreateEncryptor()
   at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRing.KeyHolder.GetEncryptorInstance(Boolean& isRevoked)
   at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRing.get_DefaultAuthenticatedEncryptor()
   at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingBasedDataProtector.Protect(Byte[] plaintext)
   at Microsoft.AspNetCore.DataProtection.DataProtectionCommonExtensions.Protect(IDataProtector protector, String plaintext)
   at ConsoleApp9.Program.Main(String[] args)

cd C:\Program Files\Crypto Pro\.NET
alarm info

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Security.Cryptography.Xml;
using System.Text;
using System.Threading.Tasks;
using System.Xml;

namespace CryptoProDotNetEncryptedXml
{
    class Program
    {
        static void Main(string[] args)
        {
            var xml = @"
        <EncryptedData Type='http://www.w3.org/2001/04/xmlenc#Element' xmlns='http://www.w3.org/2001/04/xmlenc#'>
          <EncryptionMethod Algorithm='http://www.w3.org/2001/04/xmlenc#aes256-cbc' />
          <KeyInfo xmlns='http://www.w3.org/2000/09/xmldsig#'>
            <EncryptedKey xmlns='http://www.w3.org/2001/04/xmlenc#'>
              <EncryptionMethod Algorithm='http://www.w3.org/2001/04/xmlenc#rsa-1_5' />
              <KeyInfo xmlns='http://www.w3.org/2000/09/xmldsig#'>
                <X509Data>
                  <X509Certificate>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</X509Certificate>
                </X509Data>
              </KeyInfo>
              <CipherData>
                <CipherValue>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</CipherValue>
              </CipherData>
            </EncryptedKey>
          </KeyInfo>
          <CipherData>
            <CipherValue>AJp357+F98MEg04+IbtCM+mF0CvxPalEHya/SVK8PynDt4wW5xr9CKtYc3AWIqKgiikQGoxe1CFR4G6cKDQwV3lF0UvLEjJWjZSiMSTY+1jbEmnk8RTMfCjlu7/FdgnXNErmWBb0bdASTlaCCXmSA/qakgBkC0KpMmBbg9HKa6Z+5NE/S2Ipb5mxZgGhwWOc/tfTg9CB0fE8NEW8CP9u7RZ+j690CoFWk7Q46LyigMtqXNgN6XqjQ886uyhKFwmjX8auE48Cep9she7NUA3asJmKPRsNbraQOCvUaOeoTHOqoWp8gtk5sd7Q5ducUaTHzBUEV53PfrtKneS69hm9XduT0AvbBQXD5M5z7nH+Sv/wWir4HBtFJOUIEh2kKZZ9Es2CKb2abkbCqLCFjsNvyg==</CipherValue>
          </CipherData>
        </EncryptedData>";

            var xmlDocument = new XmlDocument();
            xmlDocument.LoadXml(xml);

            var encryptedXml = 
                new EncryptedXml2(xmlDocument);

            encryptedXml.DecryptDocument();

        }
    }

    class EncryptedXml2
        : EncryptedXml
    {
        public EncryptedXml2(XmlDocument xmlDocument)
            : base(xmlDocument)
        { }

        public override byte[] DecryptEncryptedKey(EncryptedKey encryptedKey)
        {
            throw new Exception("OK");
        }
    }
}