Jumpstart:
curl -L -o Makefile https://github.com/DiosDelRayo/MoneroSigner/releases/download/v0.9/Makefile
make image
DEVICE=<device path to microSD> make flash
make image will download the image parts, merge and verify the sha256 and the signature, CHECK!
make flash, will not flash, it will give you a line to flash via copy&paste...
Or DIY:
You need to download all the split fies, either for xz or bzip2, the you merge them together like this:
cat xmrsigner-dev-buster-16gb.img.xz.* > xmrsigner-dev-buster-16gb.img.xz
or
cat xmrsigner-dev-buster-16gb.img.bz2.* > xmrsigner-dev-buster-16gb.img.bz2
then you will verify the signature, and checksums (all at once, for that you wil need signify(-openbsd on debian based systems):
signify -C -p <path/to/xmrsigner.pub> -x SHA256.sig
Your file you unpack or the file you flash needs to be OK, all other FAILED lines you can ignore, because the absence of a fie cause that it fails, too.
Unpack the file with:
xz -d xmrsigner-dev-buster-16gb.img.xz
or
bunzip2 xmrsigner-dev-buster-16gb.img.bz2
Then flash like normal:
sudo dd if=xmrsigner-dev-buster-16gb.img of=<path/to/microSD> bs=16M status=progress conv=fsync
or however you flash normal your images...