I have figured out the format of the signature header and created a python script to sign DTB files and possibly others. I have uploaded the code at [url]https://github.com/kmartin36/nv-tegra-sign/[/url]. It currently generates identical signed files to those made by flash.sh but without needing any x86 binaries. I cannot guarantee that it will not be broken by a future update, but it works with jetpack 4.2 and the TX2. I have not tried the Nano or TX1.