I was reinstalling my parent's laptop with Debian via netinst, and when retrieving packages from the mirror (no matter which one) the download failed and in the shell I read this error: gpgv: Can't check signature: public key not found
error: Bad signature on /tmp/net-retriever-858-Release.
Thanks to a bugreport I found a workaround, I just needed to append debian-installer/allow_unauthenticated=true
to the boot line.
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