مشکل gpg در apt روی دبیان ۹

سلام . چند وقته هی سعی میکنم دبیان مخازنش رو بروز کنم با دستور زیر :
sudo apt updateکه هی ارور زیر رو میده :Ign:1 http://debian.asis.io/debian stretch InRelease                           
Get:2 http://debian.asis.io/debian stretch-updates InRelease [91.0 kB]
Err:2 http://debian.asis.io/debian stretch-updates InRelease                   
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
Hit:3 http://debian.asis.io/debian stretch Release                             
Err:4 http://debian.asis.io/debian stretch Release.gpg                         
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010 NO_PUBKEY EF0F382A1A7B6500
Get:5 http://security.debian.org/debian-security stretch/updates InRelease [94.3 kB]
Err:5 http://security.debian.org/debian-security stretch/updates InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9D6D8F6BC857C906 NO_PUBKEY 8B48AD6246925553
Reading package lists... Done
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://debian.asis.io/debian stretch-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://debian.asis.io/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
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://security.debian.org/debian-security stretch/updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9D6D8F6BC857C906 NO_PUBKEY 8B48AD6246925553
W: Failed to fetch http://security.debian.org/debian-security/dists/stretch/updates/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9D6D8F6BC857C906 NO_PUBKEY 8B48AD6246925553
W: Failed to fetch http://debian.asis.io/debian/dists/stretch-updates/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
W: Failed to fetch http://debian.asis.io/debian/dists/stretch/Release.gpg  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010 NO_PUBKEY EF0F382A1A7B6500
W: Some index files failed to download. They have been ignored, or old ones used instead.
تاحالا این مشکل رخ نداده برای همین نمیدونستم باید چیکار کنم .
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