SYSLIB0045: Some cryptographic factory methods are obsolete

The following System.Security.Cryptography methods are obsolete, starting in .NET 7. Using them in code generates warning SYSLIB0045 at compile time. Each of these factory methods accepts a string argument that represents the algorithm name. These methods call into CryptoConfig.CreateFromName and cast the result to the return type.

• Aes.Create(String)
• AsymmetricAlgorithm.Create(String)
• DES.Create(String)
• ECDiffieHellman.Create(String)
• ECDsa.Create(String)
• HashAlgorithm.Create(String)
• KeyedHashAlgorithm.Create(String)
• RandomNumberGenerator.Create(String)
• RC2.Create(String)
• Rijndael.Create(String)
• RSA.Create(String)
• SHA1.Create(String)
• SHA256.Create(String)
• SHA384.Create(String)
• SHA512.Create(String)
• SymmetricAlgorithm.Create(String)
• TripleDES.Create(String)

These methods were marked [Obsolete] because in trimmed applications, they can return null when they wouldn't in non-trimmed applications. Also, in non-trimmed applications, the exception-based behaviors of these methods occasionally surprises callers, and many of the well-known identifiers are associated with types that are themselves marked [Obsolete].

Workaround

Calls that pass a constant string should be changed to either the parameterless factory method or a strong call to create the appropriate type. For example, a call to Aes.Create("AES") can be replaced with either Aes.Create() or new AesCryptoServiceProvider(). Since the AesCryptoServiceProvider type is also marked [Obsolete], Aes.Create() is the preferred replacement.

Calls that pass a non-constant string can either use their own lookup table or be changed to call CryptoConfig.CreateFromName directly.

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 SYSLIB0045

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

// Re-enable the warning.
#pragma warning restore SYSLIB0045

To suppress all the SYSLIB0045 warnings in your project, add a <NoWarn> property to your project file.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
   ...
   <NoWarn>$(NoWarn);SYSLIB0045</NoWarn>
  </PropertyGroup>
</Project>

For more information, see Suppress warnings.