For the error be like Setup.FileExtractor / SourceIsCorrupted: show the generic msgSourceIsCorrupted message and only log the detail. So a failed verification on an external file now shows the same abort/retry/ignore error as failed decompression on an internal file:

"<filename>

An error occurred while trying to copy a file:
The source file is corrupted."

Projects/Src/Setup.Install.pas

@@ -253,7 +253,7 @@ end;
 procedure ISSigVerifyError(const AReason: String);
 begin
   Log('ISSig verification error: ' + AddPeriod(AReason));
-  raise Exception.Create(AReason);
+  raise Exception.Create(SetupMessages[msgSourceIsCorrupted]);
 end;
 
 procedure CopySourceFileToDestFile(const SourceF, DestF: TFile;