Use ISSigFunc to check trust. Works while debugging from Delphi as well. Defining TRUSTALL would only be needed while debugging isscint.dll from VS for example.

AllowedPublicKeyText is formatted as a Delphi 12 multiline string literal since I plan to make ISSigTool embed it automatically from issig.bat to avoid complicating the build for others.

Components/TrustFunc.pas

@@ -7,9 +7,7 @@ unit TrustFunc;
   For conditions of distribution and use, see LICENSE.TXT.
 }
 
-{$IFDEF DEBUG}
+{.$DEFINE TRUSTALL}
-{$DEFINE TRUSTALL}
-{$ENDIF}
 
 interface
 
@@ -18,35 +16,56 @@ function TrustedFileExists(const FileName: String): Boolean;
 implementation
 
 uses
-  Winapi.Windows {$IFDEF TRUSTALL}, System.SysUtils {$ENDIF};
+  Winapi.Windows, System.SysUtils {$IFNDEF TRUSTALL}, System.Classes, ECDSA, SHA256, ISSigFunc {$ENDIF};
 
 function TrustedFileExists(const FileName: String): Boolean;
 begin
-{$IFNDEF TRUSTALL}
-  var FileInfo: TWinTrustFileInfo;
-  ZeroMemory(@FileInfo, SizeOf(FileInfo));
-  FileInfo.cbStruct := SizeOf(FileInfo);
-  FileInfo.pcwszFilePath := PChar(FileName);
-
-  var WinTrustData: TWinTrustData;
-  ZeroMemory(@WinTrustData, SizeOf(WinTrustData));
-  WinTrustData.cbStruct := SizeOf(WinTrustData);
-  WinTrustData.dwUIChoice := WTD_UI_NONE;
-  WinTrustData.fdwRevocationChecks := WTD_REVOKE_NONE;
-  WinTrustData.dwUnionChoice := WTD_CHOICE_FILE;
-  WinTrustData.pFile := @FileInfo;
-  WinTrustData.dwStateAction := WTD_STATEACTION_VERIFY;
-  WinTrustData.dwProvFlags := WTD_REVOCATION_CHECK_NONE;
-
-  var PolicyGUID := WINTRUST_ACTION_GENERIC_VERIFY_V2;
-
-  Result := WinVerifyTrust(0, PolicyGUID, @WinTrustData) = 0;
-
-  WinTrustData.dwStateAction := WTD_STATEACTION_CLOSE;
-  WinVerifyTrust(0, PolicyGUID, @WinTrustData);
-{$ELSE}
   var Attr := GetFileAttributes(PChar(FileName));
   Result := (Attr <> INVALID_FILE_ATTRIBUTES) and (Attr and faDirectory = 0);
+{$IFNDEF TRUSTALL}
+  if Result then begin
+    try
+      const
+        AllowedPublicKeyText = '''
+format issig-public-key
+key-id c2587f3885b12463bafdadb799f23435f26c03944c1afc1716aabc6a43f2426f
+public-x f9a30c72189077370a8846015ac3ec1e9a1cf425d2996d34dc25bd4f4923dd1b
+public-y f754897b7819da5bbbc5ac568311eee922fbea492578748e07f453dc1289c532
+
+''';
+      const Key = TECDSAKey.Create;
+      try
+        if ISSigImportKeyText(Key, AllowedPublicKeyText, False) <> ikrSuccess then
+          raise Exception.Create('ISSigImportKeyText failed');
+
+        const SigFileName = FileName + '.issig';
+        const SigText = ISSigLoadTextFromFile(SigFileName);
+
+        var ExpectedFileSize: Int64;
+        var ExpectedFileHash: TSHA256Digest;
+        if ISSigVerifySignatureText([Key], SigText, ExpectedFileSize,
+           ExpectedFileHash) <> vsrSuccess then
+          raise Exception.CreateFmt('Signature file "%s" is not valid',
+            [SigFileName]);
+
+        const F = TFileStream.Create(FileName, fmOpenRead or fmShareDenyWrite);
+        try
+          if F.Size <> ExpectedFileSize then
+            raise Exception.CreateFmt('File "%s" is not trusted (incorrect size).',
+              [FileName]);
+          if not SHA256DigestsEqual(ISSigCalcStreamHash(F), ExpectedFileHash) then
+            raise Exception.CreateFmt('File "%s" is not trusted (incorrect hash).',
+              [FileName]);
+        finally
+          F.Free;
+        end;
+      finally
+        Key.Free;
+      end;
+    except
+      Result := False;
+    end;
+  end;
 {$ENDIF}
 end;
 

Projects/Compil32.dpr

@@ -69,7 +69,10 @@ uses
   SHA256 in '..\Components\SHA256.pas',
   Shared.DotNetVersion in 'Src\Shared.DotNetVersion.pas',
   isxclasses_wordlists_generated in '..\ISHelp\isxclasses_wordlists_generated.pas',
-  IDE.ImagesModule in 'Src\IDE.ImagesModule.pas' {ImagesModule: TDataModule};
+  IDE.ImagesModule in 'Src\IDE.ImagesModule.pas' {ImagesModule: TDataModule},
+  ECDSA in '..\Components\ECDSA.pas',
+  ISSigFunc in '..\Components\ISSigFunc.pas',
+  StringScanner in '..\Components\StringScanner.pas';
 
 {$SETPEOSVERSION 6.1}
 {$SETPESUBSYSVERSION 6.1}

Projects/Compil32.dproj

@@ -155,6 +155,9 @@
             <FormType>dfm</FormType>
             <DesignClass>TDataModule</DesignClass>
         </DCCReference>
+        <DCCReference Include="..\Components\ECDSA.pas"/>
+        <DCCReference Include="..\Components\ISSigFunc.pas"/>
+        <DCCReference Include="..\Components\StringScanner.pas"/>
         <BuildConfiguration Include="Base">
             <Key>Base</Key>
         </BuildConfiguration>

Projects/ISCC.dpr

@@ -30,7 +30,11 @@ uses
   Shared.FileClass in 'Src\Shared.FileClass.pas',
   Shared.ConfigIniFile in 'Src\Shared.ConfigIniFile.pas',
   Shared.SignToolsFunc in 'Src\Shared.SignToolsFunc.pas',
-  Shared.Int64Em in 'Src\Shared.Int64Em.pas';
+  Shared.Int64Em in 'Src\Shared.Int64Em.pas',
+  SHA256 in '..\Components\SHA256.pas',
+  ECDSA in '..\Components\ECDSA.pas',
+  ISSigFunc in '..\Components\ISSigFunc.pas',
+  StringScanner in '..\Components\StringScanner.pas';
 
 {$SETPEOSVERSION 6.1}
 {$SETPESUBSYSVERSION 6.1}

Projects/ISCC.dproj

@@ -85,6 +85,10 @@
         <DCCReference Include="Src\Shared.ConfigIniFile.pas"/>
         <DCCReference Include="Src\Shared.SignToolsFunc.pas"/>
         <DCCReference Include="Src\Shared.Int64Em.pas"/>
+        <DCCReference Include="..\Components\SHA256.pas"/>
+        <DCCReference Include="..\Components\ECDSA.pas"/>
+        <DCCReference Include="..\Components\ISSigFunc.pas"/>
+        <DCCReference Include="..\Components\StringScanner.pas"/>
         <BuildConfiguration Include="Base">
             <Key>Base</Key>
         </BuildConfiguration>

Projects/ISCmplr.dpr

@@ -49,7 +49,10 @@ uses
   Shared.SetupSteps in 'Src\Shared.SetupSteps.pas',
   SimpleExpression in '..\Components\SimpleExpression.pas',
   Shared.DotNetVersion in 'Src\Shared.DotNetVersion.pas',
-  PBKDF2 in '..\Components\PBKDF2.pas';
+  PBKDF2 in '..\Components\PBKDF2.pas',
+  ECDSA in '..\Components\ECDSA.pas',
+  ISSigFunc in '..\Components\ISSigFunc.pas',
+  StringScanner in '..\Components\StringScanner.pas';
 
 {$IMAGEBASE $00800000}
 {$SETPEOSVERSION 6.1}

Projects/ISCmplr.dproj

@@ -119,6 +119,9 @@ $(PostBuildEvent)]]></PostBuildEvent>
         <DCCReference Include="..\Components\SimpleExpression.pas"/>
         <DCCReference Include="Src\Shared.DotNetVersion.pas"/>
         <DCCReference Include="..\Components\PBKDF2.pas"/>
+        <DCCReference Include="..\Components\ECDSA.pas"/>
+        <DCCReference Include="..\Components\ISSigFunc.pas"/>
+        <DCCReference Include="..\Components\StringScanner.pas"/>
         <BuildConfiguration Include="Base">
             <Key>Base</Key>
         </BuildConfiguration>