Derive strong name key pairs deterministically from a seed instead of a static .snk

Directory.Packages.props

@@ -7,7 +7,7 @@
     <PackageVersion Include="CSharpier.MSBuild" Version="1.2.6" />
     <PackageVersion Include="Microsoft.Build.Framework" Version="17.14.28" />
     <PackageVersion Include="Microsoft.Build.Utilities.Core" Version="17.14.28" />
-    <PackageVersion Include="PolyShim" Version="2.11.0" />
+    <PackageVersion Include="PolyShim" Version="2.14.0" />
     <PackageVersion Include="System.Reflection.Metadata" Version="9.0.8" />
   </ItemGroup>
 </Project>

Readme.md

@@ -38,7 +38,7 @@ To learn more about the war and how you can help, [click here](https://tyrrrz.me
 
 ## Usage
 
-Simply install the **Snek** package as a private dependency in your project and it will automatically sign your assembly with a static key pair:
+Simply install the **Snek** package as a private dependency in your project and it will automatically sign your assembly with a strong name key pair, deterministically derived from your package ID or assembly name (whichever is set):
 
 ```xml
 <ItemGroup>
@@ -49,12 +49,19 @@ Simply install the **Snek** package as a private dependency in your project and
 You can then inspect the output assembly in **ILSpy** or a similar tool and see that it has a public key token:
 
 ```csharp
-// Snek.Demo, Version=0.0.0.0, Culture=neutral, PublicKeyToken=337a390ad141274e
+// Snek.Demo, Version=0.0.0.0, Culture=neutral, PublicKeyToken=929e72f1096e8eac
 ```
 
-> [!NOTE]
-> The public key token will be the same for all assemblies signed with **Snek**.
-> For the majority of use cases involving strong naming in modern .NET, this is sufficient.
+The public key token is derived from the seed, so it stays the same across rebuilds and machines, but differs between projects with different package IDs or assembly names.
+You can also set the seed explicitly, to control the resulting public key token independently of the package ID or assembly name:
+
+```xml
+<PropertyGroup>
+  <AssemblyOriginatorKeySeed>my-custom-seed</AssemblyOriginatorKeySeed>
+</PropertyGroup>
+```
+
+Note that the seed only affects the identity of the resulting public key token &mdash; it is not a secret, and the private key is never meant to be kept confidential (it's derived deterministically and can trivially be reproduced by anyone who knows the seed).
 
 ## Etymology
 

Snek.Demo/Snek.Demo.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <!-- Props/targets are automatically imported by NuGet, but here we need to do it manually. -->
   <!-- This needs to be done before any other props or targets, to match NuGet's behavior. -->
-  <Import Project="../Snek/Snek.props" />
+  <Import Project="../Snek/Snek.Local.props" />
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
@@ -15,4 +15,8 @@
   <ItemGroup>
     <ProjectReference Include="../Snek/Snek.csproj" />
   </ItemGroup>
+
+  <!-- Props/targets are automatically imported by NuGet, but here we need to do it manually. -->
+  <!-- This needs to be done after everything else, to match NuGet's behavior. -->
+  <Import Project="../Snek/Snek.targets" />
 </Project>

Snek/Snek.Local.props

@@ -0,0 +1,17 @@
+<Project
+  xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
+  ToolsVersion="4.0"
+  TreatAsLocalProperty="TaskAssembly"
+>
+  <Import Project="Snek.props" />
+
+  <!-- Props for local testing, used by the demo project -->
+  <PropertyGroup>
+    <TaskAssembly Condition="'$(MSBuildRuntimeType)' == 'Core'"
+      >$(MSBuildThisFileDirectory)/bin/$(Configuration)/netstandard2.0/Snek.dll</TaskAssembly
+    >
+    <TaskAssembly Condition="'$(MSBuildRuntimeType)' != 'Core'"
+      >$(MSBuildThisFileDirectory)/bin/$(Configuration)/net472/Snek.dll</TaskAssembly
+    >
+  </PropertyGroup>
+</Project>

Snek/Snek.csproj

@@ -16,7 +16,7 @@
   <ItemGroup>
     <None Include="../favicon.png" Pack="true" PackagePath="" Visible="false" />
     <Content Include="Snek.props" Pack="true" PackagePath="build" />
-    <Content Include="Snek.snk" Pack="true" PackagePath="build" />
+    <Content Include="Snek.targets" Pack="true" PackagePath="build" />
   </ItemGroup>
 
   <ItemGroup>

Snek/Snek.props

@@ -1,9 +1,21 @@
-<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="4.0">
+<Project
+  xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
+  ToolsVersion="4.0"
+  TreatAsLocalProperty="TaskAssembly"
+>
   <PropertyGroup>
     <SignAssembly>true</SignAssembly>
     <PublicSign>false</PublicSign>
-    <AssemblyOriginatorKeyFile Condition="'$(AssemblyOriginatorKeyFile)' == ''"
-      >$(MSBuildThisFileDirectory)/Snek.snk</AssemblyOriginatorKeyFile
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <TaskAssembly Condition="'$(MSBuildRuntimeType)' == 'Core'"
+      >$(MSBuildThisFileDirectory)/../tasks/netstandard2.0/Snek.dll</TaskAssembly
+    >
+    <TaskAssembly Condition="'$(MSBuildRuntimeType)' != 'Core'"
+      >$(MSBuildThisFileDirectory)/../tasks/net472/Snek.dll</TaskAssembly
     >
   </PropertyGroup>
+
+  <UsingTask TaskName="Snek.StrongNameTask" AssemblyFile="$(TaskAssembly)" />
 </Project>

Snek/Snek.targets

@@ -0,0 +1,38 @@
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="4.0">
+  <!--
+    Resolves the seed used to derive the strong name key pair (explicit value, falling back to
+    the package ID or the assembly name) and generates/caches the key pair before it's needed
+    by the `ResolveKeySource` target.
+  -->
+  <Target
+    Name="Snek_GenerateStrongNameKeyPair"
+    BeforeTargets="ResolveKeySource"
+    Condition="'$(SignAssembly)' == 'true' and '$(AssemblyKeyContainerName)' == ''"
+  >
+    <Error
+      Condition="'$(AssemblyOriginatorKeyFile)' != ''"
+      Text="Snek generates 'AssemblyOriginatorKeyFile' automatically and does not expect it to be set manually. Remove this property from your project, or remove the Snek package reference if you want to provide your own key file."
+    />
+
+    <PropertyGroup>
+      <AssemblyOriginatorKeySeed
+        Condition="'$(AssemblyOriginatorKeySeed)' == '' and '$(PackageId)' != ''"
+        >$(PackageId)</AssemblyOriginatorKeySeed
+      >
+      <AssemblyOriginatorKeySeed
+        Condition="'$(AssemblyOriginatorKeySeed)' == '' and '$(AssemblyName)' != ''"
+        >$(AssemblyName)</AssemblyOriginatorKeySeed
+      >
+      <AssemblyOriginatorKeySeed Condition="'$(AssemblyOriginatorKeySeed)' == ''"
+        >$(MSBuildProjectName)</AssemblyOriginatorKeySeed
+      >
+    </PropertyGroup>
+
+    <StrongNameTask
+      Seed="$(AssemblyOriginatorKeySeed)"
+      CacheDirectoryPath="$(BaseIntermediateOutputPath)Snek\"
+    >
+      <Output TaskParameter="KeyFilePath" PropertyName="AssemblyOriginatorKeyFile" />
+    </StrongNameTask>
+  </Target>
+</Project>