Update / repository not signed anymore?

Hello i’m running a rpi with a 3 apps in total. I usually putty into my machine and do yunohost tools update && yunohost tools upgrade. But this time i cannot update anymore :(. If i do a sudo apt update this is what i get:

What does it mean and can i get it working again?

thanks in advance.

W: GPG error: http://deb.debian.org/debian stretch Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010 NO_PUBKEY EF0F382A1A7B6500
E: The repository ‘http://deb.debian.org/debian stretch Release’ is not signed.
N: Updating from such a repository can’t be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Hello,

This topic should helps you :

ppr

i did as you asked :slight_smile: and i got this problem
E: Failed to fetch http://deb.debian.org/debian/dists/stretch/non-free/i18n/Translation-en BZ2_bzread: /var/lib/apt/lists/partial/deb.debian.org_debian_dists_stretch_non-free_i18n_Translation-en.bz2 Read error (-5: DATA_ERROR_MAGIC)

but then i did this http://forums.debian.net/viewtopic.php?f=5&t=136666

and it seems to do the trick. No idea what i did exactly but it’s working again :slight_smile: