Override default HashAlgorithm.Create()

user_8417363 0
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I've been trying to override the default value from SHA1 to SHA256 of what System.Security.Cryptography.HashAlgorithm.Create() returns. Based off the docs, it is supposed to be override-able.

I came across this article, but it seems to only mention mapping a custom hash algorithm to override one of the existing ones. I want to just override the default of SHA1 to a default of SHA256.

Is that possible using the article above?

Something like this?

<configuration>  
   <mscorlib>  
      <cryptographySettings>  
         <cryptoNameMapping>    
            <nameEntry name="System.Security.Cryptography.HashAlgorithm"  
                       class="System.Security.Cryptography.SHA256"/>  
         </cryptoNameMapping>  
      </cryptographySettings>  
   </mscorlib>  
</configuration>
sha256 signing cryptography hash c#
2 Answers

Yes, it's possible.

If you need to apply new default hash algorithm in every running .NET Framework application on machine just write this section inside machine.config file:

<mscorlib>  
    <cryptographySettings>  
        <cryptoNameMapping>  
            <cryptoClasses>  
                <cryptoClass DefaultHashAlgorithm="System.Security.Cryptography.SHA256Managed, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>  
            </cryptoClasses>
            <nameEntry name="System.Security.Cryptography.HashAlgorithm"  
                    class="DefaultHashAlgorithm"/>  
        </cryptoNameMapping>  
    </cryptographySettings>  
</mscorlib>

Note that machine.config file placed here:

x32:

%windir%\Microsoft.NET\Framework\[version]\config\machine.config

x64:

%windir%\Microsoft.NET\Framework64\[version]\config\machine.config

Also you can change default algorithm on every built-in hash algorithm by change DefaultHashAlgorithm attribute. See list of algorithms here.

user_92625350

The drawback of changing machine.config is that it affects all applications that will use System.Security.Cryptography.HashAlgorithm.

Another approach is to use CryptoConfig class. The next code snippet registers SHA256Managed as a default hash algorithm:

using System.Security.Cryptography;

...

CryptoConfig.AddAlgorithm(
    typeof(SHA256Managed),
    "System.Security.Cryptography.HashAlgorithm");

This changes default hash algorithm only for current application.

Note that a concrete implementation SHA256Managed of an abstract class SHA256 must be used.

user_128332050
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