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SYSLIB0043 warning - ECDiffieHellmanPublicKey.ToByteArray is obsolete
Learn about the obsoletion of ECDiffieHellmanPublicKey.ToByteArray() and the associated constructor that generates compile-time warning SYSLIB0043.
04/08/2022
syslib0043

SYSLIB0043: ECDiffieHellmanPublicKey.ToByteArray is obsolete

The following methods are obsolete, starting in .NET 7. Using them in code generates warning SYSLIB0043 at compile time.

  • xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.ToByteArray?displayProperty=nameWithType
  • xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.%23ctor(System.Byte[]) (constructor)

The xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.ToByteArray?displayProperty=nameWithType method does not have an implied file format. Also, for the built-in implementations, it throws xref:System.PlatformNotSupportedException on all non-Windows operating systems. Since xref:System.Security.Cryptography.ECDiffieHellmanPublicKey also has a standard format export (via the xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.ExportSubjectPublicKeyInfo method), the older member has been obsoleted.

Workaround

If you're exporting the public key value, use the xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.ExportSubjectPublicKeyInfo method instead.

For new derived types (or existing derived types that don't currently call the xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.%23ctor(System.Byte[]) constructor), don't call the protected xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.%23ctor(System.Byte[]) constructor, and either override xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.ToByteArray to throw an exception, or accept the default behavior of returning an empty array.

For existing derived types that already call the protected xref:System.Security.Cryptography.ECDiffieHellmanPublicKey.%23ctor(System.Byte[]) constructor, continue calling the constructor and suppress the SYSLIB0043 warning.

Suppress a warning

If you must use the obsolete APIs, you can suppress the warning in code or in your project file.

To suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.

// Disable the warning.
#pragma warning disable SYSLIB0043

// Code that uses obsolete API.
// ...

// Re-enable the warning.
#pragma warning restore SYSLIB0043

To suppress all the SYSLIB0043 warnings in your project, add a <NoWarn> property to your project file.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
   ...
   <NoWarn>$(NoWarn);SYSLIB0043</NoWarn>
  </PropertyGroup>
</Project>

For more information, see Suppress warnings.