an Apple Developer ID for Signing Kexts certificate, but this code signing requirement is not enforced strictly. Unsigned kernel extensions can still be installed into /System/Library/ Extensions, which is where kernel extensions have been installed up until OS X Mavericks. However, signed kernel extensions must be installed into /Library/Extensions. OS X Yosemite Kernel extensions must be digitally signed using an Apple Developer ID for Signing Kexts certificate and installed into /Library/Extensions. However, it is still possible on OS X Yosemite to enable a kernel extension developer mode which disables the code signing requirement.