Starting to build the hashcash. At the point where I need to check if…

… the bits are zero.

.paket/Paket.Restore.targets

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+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <!-- Prevent dotnet template engine to parse this file -->
+  <!--/-:cnd:noEmit-->
+  <PropertyGroup>
+    <!-- Mark that this target file has been loaded.  -->
+    <IsPaketRestoreTargetsFileLoaded>true</IsPaketRestoreTargetsFileLoaded>
+    <PaketToolsPath>$(MSBuildThisFileDirectory)</PaketToolsPath>
+    <MonoPath Condition="'$(MonoPath)' == '' And Exists('/Library/Frameworks/Mono.framework/Commands/mono')">/Library/Frameworks/Mono.framework/Commands/mono</MonoPath>
+    <MonoPath Condition="'$(MonoPath)' == ''">mono</MonoPath>
+    <!-- Paket command -->
+    <PaketExePath Condition=" '$(PaketExePath)' == '' AND Exists('$(PaketRootPath)paket.exe')">$(PaketRootPath)paket.exe</PaketExePath>
+    <PaketExePath Condition=" '$(PaketExePath)' == '' ">$(PaketToolsPath)paket.exe</PaketExePath>
+    <PaketCommand Condition=" '$(OS)' == 'Windows_NT'">"$(PaketExePath)"</PaketCommand>
+    <PaketCommand Condition=" '$(OS)' != 'Windows_NT' ">$(MonoPath) --runtime=v4.0.30319 "$(PaketExePath)"</PaketCommand>
+    <PaketBootStrapperExePath Condition=" '$(PaketBootStrapperExePath)' == '' AND Exists('$(PaketRootPath)paket.bootstrapper.exe')">$(PaketRootPath)paket.bootstrapper.exe</PaketBootStrapperExePath>
+    <PaketBootStrapperExePath Condition=" '$(PaketBootStrapperExePath)' == '' ">$(PaketToolsPath)paket.bootstrapper.exe</PaketBootStrapperExePath>
+    <PaketBootStrapperCommand Condition=" '$(OS)' == 'Windows_NT'">"$(PaketBootStrapperExePath)"</PaketBootStrapperCommand>
+    <PaketBootStrapperCommand Condition=" '$(OS)' != 'Windows_NT' ">$(MonoPath) --runtime=v4.0.30319 "$(PaketBootStrapperExePath)"</PaketBootStrapperCommand>
+  </PropertyGroup>
+
+  <Target Name="PaketRestore" BeforeTargets="_GenerateDotnetCliToolReferenceSpecs;_GenerateProjectRestoreGraphPerFramework;_GenerateRestoreGraphWalkPerFramework;CollectPackageReferences" >
+
+    <Exec Command='$(PaketBootStrapperCommand) ' Condition="Exists('$(PaketBootStrapperExePath)') AND !(Exists('$(PaketExePath)'))" ContinueOnError="false" />
+    <Exec Command='$(PaketCommand) restore --project "$(MSBuildProjectFullPath)" --target-framework $(TargetFramework)' Condition="$(TargetFramework) != ''" ContinueOnError="false" />
+    <Exec Command='$(PaketCommand) restore --project "$(MSBuildProjectFullPath)" --target-framework "$(TargetFrameworks)"' Condition="$(TargetFramework) == ''" ContinueOnError="false" />
+
+    <PropertyGroup>
+      <PaketReferencesFilePath>$(MSBuildProjectDirectory)/obj/$(MSBuildProjectFile).references</PaketReferencesFilePath>
+    </PropertyGroup>
+
+    <ReadLinesFromFile File="$(PaketReferencesFilePath)" >
+      <Output TaskParameter="Lines" ItemName="PaketReferencesFileLines"/>
+    </ReadLinesFromFile>
+
+    <ItemGroup Condition=" '@(PaketReferencesFileLines)' != '' " >
+      <PaketReferencesFileLinesInfo Include="@(PaketReferencesFileLines)" >
+        <PackageName>$([System.String]::Copy('%(PaketReferencesFileLines.Identity)').Split(',')[0])</PackageName>
+        <PackageVersion>$([System.String]::Copy('%(PaketReferencesFileLines.Identity)').Split(',')[1])</PackageVersion>
+      </PaketReferencesFileLinesInfo>
+      <PackageReference Include="%(PaketReferencesFileLinesInfo.PackageName)">
+        <Version>%(PaketReferencesFileLinesInfo.PackageVersion)</Version>
+      </PackageReference>
+    </ItemGroup>
+
+    <PropertyGroup>
+      <PaketCliToolFilePath>$(MSBuildProjectDirectory)/obj/$(MSBuildProjectFile).paket.clitools</PaketCliToolFilePath>
+    </PropertyGroup>
+
+    <ReadLinesFromFile File="$(PaketCliToolFilePath)" >
+      <Output TaskParameter="Lines" ItemName="PaketCliToolFileLines"/>
+    </ReadLinesFromFile>
+
+    <ItemGroup Condition=" '@(PaketCliToolFileLines)' != '' " >
+      <PaketCliToolFileLinesInfo Include="@(PaketCliToolFileLines)" >
+        <PackageName>$([System.String]::Copy('%(PaketCliToolFileLines.Identity)').Split(',')[0])</PackageName>
+        <PackageVersion>$([System.String]::Copy('%(PaketCliToolFileLines.Identity)').Split(',')[1])</PackageVersion>
+      </PaketCliToolFileLinesInfo>
+      <DotNetCliToolReference Include="%(PaketCliToolFileLinesInfo.PackageName)">
+        <Version>%(PaketCliToolFileLinesInfo.PackageVersion)</Version>
+      </DotNetCliToolReference>
+    </ItemGroup>
+
+    <PropertyGroup>
+      <RestoreConfigFile>$(MSBuildProjectDirectory)/obj/$(MSBuildProjectFile).NuGet.Config</RestoreConfigFile>
+    </PropertyGroup>
+
+  </Target>
+
+  <Target Name="PaketDisableDirectPack" AfterTargets="_IntermediatePack" BeforeTargets="GenerateNuspec" >
+    <PropertyGroup>
+      <ContinuePackingAfterGeneratingNuspec>false</ContinuePackingAfterGeneratingNuspec>
+    </PropertyGroup>
+  </Target>
+
+  <Target Name="PaketOverrideNuspec" AfterTargets="GenerateNuspec" >
+    <PropertyGroup>
+      <PaketReferencesFilePath>$(MSBuildProjectDirectory)/obj/$(MSBuildProjectFile).references</PaketReferencesFilePath>
+      <ContinuePackingAfterGeneratingNuspec>true</ContinuePackingAfterGeneratingNuspec>
+      <UseNewPack>false</UseNewPack>
+      <UseNewPack Condition=" '$(NuGetToolVersion)' != '4.0.0' ">true</UseNewPack>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <_NuspecFiles Include="$(BaseIntermediateOutputPath)*.nuspec"/>
+    </ItemGroup>
+
+    <Exec Command='$(PaketCommand) fix-nuspecs files "@(_NuspecFiles)" references-file "$(PaketReferencesFilePath)" ' Condition="@(_NuspecFiles) != ''" />
+
+    <ConvertToAbsolutePath Condition="@(_NuspecFiles) != ''" Paths="@(_NuspecFiles)">
+      <Output TaskParameter="AbsolutePaths" PropertyName="NuspecFileAbsolutePath" />
+    </ConvertToAbsolutePath>
+
+    <!-- Call Pack -->
+    <PackTask Condition="$(UseNewPack)"
+              PackItem="$(PackProjectInputFile)"
+              PackageFiles="@(_PackageFiles)"
+              PackageFilesToExclude="@(_PackageFilesToExclude)"
+              PackageVersion="$(PackageVersion)"
+              PackageId="$(PackageId)"
+              Title="$(Title)"
+              Authors="$(Authors)"
+              Description="$(Description)"
+              Copyright="$(Copyright)"
+              RequireLicenseAcceptance="$(PackageRequireLicenseAcceptance)"
+              LicenseUrl="$(PackageLicenseUrl)"
+              ProjectUrl="$(PackageProjectUrl)"
+              IconUrl="$(PackageIconUrl)"
+              ReleaseNotes="$(PackageReleaseNotes)"
+              Tags="$(PackageTags)"
+              DevelopmentDependency="$(DevelopmentDependency)"
+              BuildOutputInPackage="@(_BuildOutputInPackage)"
+              TargetPathsToSymbols="@(_TargetPathsToSymbols)"
+              TargetFrameworks="@(_TargetFrameworks)"
+              AssemblyName="$(AssemblyName)"
+              PackageOutputPath="$(PackageOutputAbsolutePath)"
+              IncludeSymbols="$(IncludeSymbols)"
+              IncludeSource="$(IncludeSource)"
+              PackageTypes="$(PackageType)"
+              IsTool="$(IsTool)"
+              RepositoryUrl="$(RepositoryUrl)"
+              RepositoryType="$(RepositoryType)"
+              SourceFiles="@(_SourceFiles->Distinct())"
+              NoPackageAnalysis="$(NoPackageAnalysis)"
+              MinClientVersion="$(MinClientVersion)"
+              Serviceable="$(Serviceable)"
+              FrameworkAssemblyReferences="@(_FrameworkAssemblyReferences)"
+              ContinuePackingAfterGeneratingNuspec="$(ContinuePackingAfterGeneratingNuspec)"
+              NuspecOutputPath="$(BaseIntermediateOutputPath)"
+              IncludeBuildOutput="$(IncludeBuildOutput)"
+              BuildOutputFolder="$(BuildOutputTargetFolder)"
+              ContentTargetFolders="$(ContentTargetFolders)"
+              RestoreOutputPath="$(RestoreOutputAbsolutePath)"
+              NuspecFile="$(NuspecFileAbsolutePath)"
+              NuspecBasePath="$(NuspecBasePath)"
+              NuspecProperties="$(NuspecProperties)"/>
+
+    <PackTask Condition="! $(UseNewPack)"
+              PackItem="$(PackProjectInputFile)"
+              PackageFiles="@(_PackageFiles)"
+              PackageFilesToExclude="@(_PackageFilesToExclude)"
+              PackageVersion="$(PackageVersion)"
+              PackageId="$(PackageId)"
+              Title="$(Title)"
+              Authors="$(Authors)"
+              Description="$(Description)"
+              Copyright="$(Copyright)"
+              RequireLicenseAcceptance="$(PackageRequireLicenseAcceptance)"
+              LicenseUrl="$(PackageLicenseUrl)"
+              ProjectUrl="$(PackageProjectUrl)"
+              IconUrl="$(PackageIconUrl)"
+              ReleaseNotes="$(PackageReleaseNotes)"
+              Tags="$(PackageTags)"
+              TargetPathsToAssemblies="@(_TargetPathsToAssemblies->'%(FinalOutputPath)')"
+              TargetPathsToSymbols="@(_TargetPathsToSymbols)"
+              TargetFrameworks="@(_TargetFrameworks)"
+              AssemblyName="$(AssemblyName)"
+              PackageOutputPath="$(PackageOutputAbsolutePath)"
+              IncludeSymbols="$(IncludeSymbols)"
+              IncludeSource="$(IncludeSource)"
+              PackageTypes="$(PackageType)"
+              IsTool="$(IsTool)"
+              RepositoryUrl="$(RepositoryUrl)"
+              RepositoryType="$(RepositoryType)"
+              SourceFiles="@(_SourceFiles->Distinct())"
+              NoPackageAnalysis="$(NoPackageAnalysis)"
+              MinClientVersion="$(MinClientVersion)"
+              Serviceable="$(Serviceable)"
+              AssemblyReferences="@(_References)"
+              ContinuePackingAfterGeneratingNuspec="$(ContinuePackingAfterGeneratingNuspec)"
+              NuspecOutputPath="$(BaseIntermediateOutputPath)"
+              IncludeBuildOutput="$(IncludeBuildOutput)"
+              BuildOutputFolder="$(BuildOutputTargetFolder)"
+              ContentTargetFolders="$(ContentTargetFolders)"
+              RestoreOutputPath="$(RestoreOutputAbsolutePath)"
+              NuspecFile="$(NuspecFileAbsolutePath)"
+              NuspecBasePath="$(NuspecBasePath)"
+              NuspecProperties="$(NuspecProperties)"/>
+  </Target>
+  <!--/+:cnd:noEmit-->
+</Project>

.paket/paket.targets

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+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+  <PropertyGroup>
+    <!-- Enable the restore command to run before builds -->
+    <RestorePackages Condition=" '$(RestorePackages)' == '' ">true</RestorePackages>
+    <PaketToolsPath>$(MSBuildThisFileDirectory)</PaketToolsPath>
+    <PaketRootPath>$(MSBuildThisFileDirectory)..\</PaketRootPath>
+    <MonoPath Condition="'$(MonoPath)' == '' And Exists('/Library/Frameworks/Mono.framework/Commands/mono')">/Library/Frameworks/Mono.framework/Commands/mono</MonoPath>
+    <MonoPath Condition="'$(MonoPath)' == ''">mono</MonoPath>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <!-- Paket command -->
+    <PaketExePath Condition=" '$(PaketExePath)' == '' AND Exists('$(PaketRootPath)paket.exe')">$(PaketRootPath)paket.exe</PaketExePath>
+    <PaketExePath Condition=" '$(PaketExePath)' == '' ">$(PaketToolsPath)paket.exe</PaketExePath>
+    <PaketCommand Condition=" '$(OS)' == 'Windows_NT'">"$(PaketExePath)"</PaketCommand>
+    <PaketCommand Condition=" '$(OS)' != 'Windows_NT' ">$(MonoPath) --runtime=v4.0.30319 "$(PaketExePath)"</PaketCommand>
+  </PropertyGroup>
+
+  <Choose> <!-- MyProject.fsproj.paket.references has the highest precedence -->
+    <When Condition="Exists('$(MSBuildProjectFullPath).paket.references')">
+      <PropertyGroup>
+        <PaketReferences>$(MSBuildProjectFullPath).paket.references</PaketReferences>
+      </PropertyGroup>
+    </When> <!-- MyProject.paket.references -->
+    <When Condition="Exists('$(MSBuildProjectDirectory)\$(MSBuildProjectName).paket.references')">
+      <PropertyGroup>
+        <PaketReferences>$(MSBuildProjectDirectory)\$(MSBuildProjectName).paket.references</PaketReferences>
+      </PropertyGroup>
+    </When> <!-- paket.references -->
+    <When Condition="Exists('$(MSBuildProjectDirectory)\paket.references')">
+      <PropertyGroup>
+        <PaketReferences>$(MSBuildProjectDirectory)\paket.references</PaketReferences>
+      </PropertyGroup>
+    </When> <!-- Set to empty if a reference file isn't found matching one of the 3 format options -->
+    <Otherwise>
+      <PropertyGroup>
+        <PaketReferences></PaketReferences>
+      </PropertyGroup>
+    </Otherwise>
+  </Choose>
+
+  <PropertyGroup>
+  <!-- Commands -->
+    <RestoreCommand>$(PaketCommand) restore --references-files "$(PaketReferences)"</RestoreCommand>
+    <!-- We need to ensure packages are restored prior to assembly resolve -->
+    <BuildDependsOn Condition="$(RestorePackages) == 'true'">RestorePackages; $(BuildDependsOn);</BuildDependsOn>
+  </PropertyGroup>
+  <Target Name="RestorePackages">
+    <Exec Command="$(RestoreCommand)" 
+          IgnoreStandardErrorWarningFormat="true" 
+          WorkingDirectory="$(PaketRootPath)" 
+          ContinueOnError="false" 
+          Condition=" Exists('$(PaketReferences)') AND '$(PaketReferences)' != '' " 
+    />
+  </Target>
+</Project>

Program.fs

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+// Learn more about F# at http://fsharp.org
+
+open System
+open System.Security.Cryptography
+open System.Threading
+open System.Text
+
+let seed = 
+    ()
+
+let compute header zeroBytes =
+    printfn "SEED %s " header
+    let sha = System.Security.Cryptography.SHA1.Create()
+    let hash = sha.ComputeHash(Encoding.UTF8.GetBytes(header))
+    printfn "HASH %A " hash
+    let checkBytes = hash |> Seq.take zeroBytes
+    printfn "BYTES CHECK %A " checkBytes
+    let zeroArray = Array.fill (Array.zeroCreate zeroBytes) zeroBytes 0 0
+    printfn "ZERO ARRAY %A " zeroArray
+
+let verify =
+    ()
+
+let randomChars len = 
+    //"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
+    let rand = System.Random() //RandomNumberGenerator.Create()
+    let chars = String(Array.concat [ [|'A'..'Z'|]; [|'0'..'9'|]; [|'a'..'b'|] ])
+    String(Array.init len (fun _ -> chars.[rand.Next(chars.Length)]))
+
+type headerParts =
+    {
+        version: string
+        bits: string
+        timestamp: string
+        resource: string
+        extension: string
+        seed: string
+        counter: string
+    }
+
+[<EntryPoint>]
+let main argv =
+    printfn "START HASHCASH F#!"
+    let dateStamp = DateTime.Now.ToString("yyMMddmmss")
+    compute (randomChars 8) 1
+    0 // return an integer exit code

hashcash-fsharp.fsproj

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+<Project Sdk="FSharp.NET.Sdk;Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp1.1</TargetFramework>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="Program.fs" />
+  </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="FSharp.Core" Version="4.1.*" />
+    <PackageReference Include="FSharp.NET.Sdk" Version="1.0.*" PrivateAssets="All" />
+  </ItemGroup>
+  <Import Project=".paket\Paket.Restore.targets" />
+</Project>

paket.dependencies

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+source https://www.nuget.org/api/v2
+nuget System.Security.Cryptography.Algorithms