Instead of risking your digital security on torrents or shady file-sharing sites, you can grab the installer directly from Apple. Method 1: The App Store (Recommended)

It's a common point of confusion, but Apple has not "removed" macOS High Sierra from existence. It simply no longer promotes it on the main front page of the Mac App Store, which is reserved for the latest operating system.

sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/[YourUSBDriveName]