Consider deprecating or annotating a few S.S.C.X509Certificates members

[vcsjones]

There are a few APIs in System.Security.Cryptography.X509Certificates that might be worth obsoleting, or some variation of {Un}SupportedOSPlatformAttribute on them.

• X509Certificate2.FriendlyName - Consider marking this [SupportedOSPlatformAttribute("windows")]. This API returns an empty string on non-Windows, and throws when being set on non-Windows.
• X509Certificate2.Archived - Consider marking this [SupportedOSPlatformAttribute("windows")]. This API returns false on non-Windows, and throws when being set on non-Windows.
• X509Certificate.Import - Consider deprecating or obsoleting this. All overloads for this API are going to throw.

[ghost]

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Issue Details

---

There are a few APIs in System.Security.Cryptography.X509Certificates that it might be worth obsoleting, or some variation of {Un}SupportedOSPlatformAttribute on them.

• X509Certificate2.FriendlyName - Consider marking this [SupportedOSPlatformAttribute("windows")]. This API returns an empty string on non-Windows, and throws when being set on non-Windows.
• X509Certificate2.Archived - Consider marking this [SupportedOSPlatformAttribute("windows")]. This API returns false on non-Windows, and throws when being set on non-Windows.
• X509Certificate.Import - Consider deprecating or obsoleting this. All overloads for this API are going to throw.

Author:	vcsjones
Assignees:	-
Labels:	area-System.Security, untriaged
Milestone:	-

[vcsjones]

I guess to "proposalify" this:

public class X509Certificate2
{
+   [SupportedOSPlatform("windows")]
    public bool Archived { get; set; }

+   [SupportedOSPlatform("windows")]
    public string FriendlyName { get; set; }

+   [Obsolete("This is no longer the recommended way of retrieving the private key. Use the appropriate GetPrivateKey or CopyWithPrivateKey method instead.")]
    public AsymmetricAlgorithm PrivateKey { get; set; }

+   [Obsolete("X509Certificate2 is immutable on this platform. Use a different constructor overload instead.")]
    public X509Certificate2();

+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(byte[] rawData);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(byte[] rawData, SecureString? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(byte[] rawData, string? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(string fileName);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(string fileName, System.Security.SecureString? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(string fileName, string? password, X509KeyStorageFlags keyStorageFlags);
}

public class X509Certificate
{
+   [Obsolete("X509Certificate is immutable on this platform. Use a different constructor overload instead.")]
    public X509Certificate();

+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor instead.")]
    public void Import(byte[] rawData);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor instead.")]
    public void Import(byte[] rawData, SecureString? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor instead.")]
    public void Import(byte[] rawData, string? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor instead.")]
    public void Import(string fileName);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor instead.")]
    public void Import(string fileName, System.Security.SecureString? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor instead.")]
    public void Import(string fileName, string? password, X509KeyStorageFlags keyStorageFlags);
}

public class PublicKey
{
+   [Obsolete("The key property is no longer recommended for use. Use the appropriate GetPublicKey method instead.")]
    public AsymmetricAlgorithm Key { get; }
}

[bartonjs]

Have we put Obsolete on X509Certificate2.PrivateKey and PublicKey.Key yet? Though to fully obsolete PublicKey we would probably want to put GetRSAPublicKey/etc on it. (Or just feel we got far enough there by adding SPKI export)

[vcsjones]

Have we put Obsolete on

Not yet.

X509Certificate2.PrivateKey

That one makes sense to me since there are good APIs to success it, so I added it.

PublicKey.Key

I'm less convinced there is a good replacement for that. The SPKI APIs work, but feel a little clunky

using X509Certificate2 cert = new X509Certificate2();
using RSA rsa = RSA.Create();
byte[] spki = cert.PublicKey.ExportSubjectPublicKeyInfo();
rsa.ImportSubjectPublicKeyInfo(spki, out _);

Perhaps we can open a separate proposal for that (opened #48510)

---

Another one that strikes me as a bit weird is the parameterless constructor for X509Certificate{2}. Since Import doesn't work does it have any valid use cases? Should it get deprecated too?

[bartonjs]

the parameterless constructor(s) for X509Certificate{2}... Should [they] get deprecated too?

Yeah, it just produces a certificate in the same state as one gets in after Dispose(), so it's probably not all that useful. Obsolete away!

[vcsjones]

@bartonjs Since #53127 is merged now, I added the PublicKey.Key property to the proposal for deprecation.

[bartonjs]

How accidentally convenient that I skipped over this one to get the new methods in.

Thanks 😄.

[bartonjs]

Video

• The obsoletions should use the next available SYSLIB number
• The SupportedOSPlatform attributes were moved from the property to just the property setter (so the getters are still allowed on all platforms, since they don't throw).

public class X509Certificate2
{
    public bool Archived {
       get;
+   [SupportedOSPlatform("windows")]
       set;
 }

    public string FriendlyName
     {
         get;
+   [SupportedOSPlatform("windows")]
         set;
     }

+   [Obsolete("This is no longer the recommended way of retrieving the private key. Use the appropriate GetPrivateKey or CopyWithPrivateKey method instead.")]
    public AsymmetricAlgorithm PrivateKey { get; set; }

+   [Obsolete("X509Certificate2 is immutable on this platform. Use a different constructor overload instead.")]
    public X509Certificate2();

+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(byte[] rawData);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(byte[] rawData, SecureString? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(byte[] rawData, string? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(string fileName);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(string fileName, System.Security.SecureString? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate2 is immutable on this platform. Use the equivalent constructor instead.")]
    public override void Import(string fileName, string? password, X509KeyStorageFlags keyStorageFlags);
}

public class X509Certificate
{
+   [Obsolete("X509Certificate is immutable on this platform. Use a different constructor overload instead.")]
    public X509Certificate();

+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor on X509Certificate2 instead.")]
    public void Import(byte[] rawData);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor on X509Certificate2 instead.")]
    public void Import(byte[] rawData, SecureString? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor on X509Certificate2 instead.")]
    public void Import(byte[] rawData, string? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor on X509Certificate2 instead.")]
    public void Import(string fileName);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor on X509Certificate2 instead.")]
    public void Import(string fileName, System.Security.SecureString? password, X509KeyStorageFlags keyStorageFlags);
+   [Obsolete("X509Certificate is immutable on this platform. Use the equivalent constructor on X509Certificate2 instead.")]
    public void Import(string fileName, string? password, X509KeyStorageFlags keyStorageFlags);
}

public class PublicKey
{
+   [Obsolete("The key property is no longer recommended for use. Use the appropriate GetPublicKey method instead.")]
    public AsymmetricAlgorithm Key { get; }
}