Adding assembly level UnsupportedOSPlatform("browser") System.Security.Cryptography.Primitives is not correct, HashAlgorithm supported on browser

[buyaa-n]

Adding assembly level UnsupportedOSPlatform("browser") System.Security.Cryptography.Primitives is not correct, HashAlgorithm and HashAlgorithmName supported on browser cc @jeffhandley

The issue appears to be that we are generating the attribute for all of System.Security.Cryptography.Primitives which is not correct. Originally posted by @lewing in #43363 (comment)

[ghost]

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[lewing]

HashAlgorithm and HashAlgorithmName are currently marked as unsupported on browser but are available for use. Absent a compelling reason I don't think we should annotate the other primitives that don't include any implementation as unsupported either.

/cc @steveisok @marek-safar

[kjpou1]

From my understanding of the Primitives they are there for use of the other Cryptography modules without specific implementations so can be available for use as well.

[lewing]

@kjpou1 please review the primitive classes, especially where they are base classes, and correct the platform annotations.

[kjpou1]

This should be only needed to remove the os platform not supported. The classes are abstract and implemented in the other cryptography modules.

[akoeplinger]

Shouldn't we still mark the static methods on some of these classes as unsupported that we know don't work:

namespace System.Security.Cryptography
{
    public abstract partial class AsymmetricAlgorithm : System.IDisposable
    {
        public static System.Security.Cryptography.AsymmetricAlgorithm Create() { throw null; }
        public static System.Security.Cryptography.AsymmetricAlgorithm? Create(string algName) { throw null; }
    }
    public abstract partial class HMAC : System.Security.Cryptography.KeyedHashAlgorithm
    {
        public static new System.Security.Cryptography.HMAC Create() { throw null; }
        public static new System.Security.Cryptography.HMAC? Create(string algorithmName) { throw null; }
    }
    public abstract partial class KeyedHashAlgorithm : System.Security.Cryptography.HashAlgorithm
    {
        public static new System.Security.Cryptography.KeyedHashAlgorithm Create() { throw null; }
        public static new System.Security.Cryptography.KeyedHashAlgorithm? Create(string algName) { throw null; }
    }
    public abstract partial class SymmetricAlgorithm : System.IDisposable
    {
        public static System.Security.Cryptography.SymmetricAlgorithm Create() { throw null; }
        public static System.Security.Cryptography.SymmetricAlgorithm? Create(string algName) { throw null; }
    }
}

[lewing]

@akoeplinger that is an interesting question. Create() on all those classes is marked Obsolete and throw PNSE unconditionally on all platforms already

runtime/src/libraries/System.Security.Cryptography.Primitives/src/System/Security/Cryptography/AsymmetricAlgorithm.cs

Line 17 in 2ca0b93

public static AsymmetricAlgorithm Create() =>

Create(string name) should probably be marked but the code is written such that HashAlgorithm.Create(string name) could try to create a KeyedHashAlgorithm.