It's a Debian stretch server (Armbian to be specific). When I ran "apt-get update" the day before yesterday, it gave me an error: "The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 648ACFD622F3D138 NO_PUBKEY 0E98404D386FA1D9".

I searched the Internet and finally resolved the issue by running the following commands:
apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 648ACFD622F3D138
apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 0E98404D386FA1D9

Initially I tried to use "--keyserver keyring.debian.org" but it didn't work. Therefore, I did some further research, and I read from https://wiki.debian.org/SecureApt that "The current and the retired Debian archive "signing" keys are available from https://ftp-master.debian.org/keys.html."

The latter web page provides the key as ".asc" files, but I cannot find how should I do with these ".asc" files. Could someone point out the official recommended method to fix such NO_PUBKEY errors? It's a bit strange that I have to consult ubuntu keyserver to fix Debian signing key issues.

 

30 minutes ago, sockscap said:

It's a bit strange that I have to consult ubuntu keyserver to fix Debian signing key issues.

ubuntu's keyservers are like any other keyserver around. http://pgp.mit.edu/ for example is a well known keyserver that has been there for ages. However it depends on the key owners to spread their keys on various keyservers.

17 minutes ago, Werner said:

ubuntu's keyservers are like any other keyserver around. http://pgp.mit.edu/ for example is a well known keyserver that has been there for ages. However it depends on the key owners to spread their keys on various keyservers.

 

Thanks for the reply. A few more questions:

 

1. It sounds like the keys will not be synchronized automatically between these servers, and it relies on key owners' manual action? I'm a little worried, if I encounter the issue again, how do I know which server holds the info? For example, I initially thought keyring.debian.org should work, but actually it's not. 

 

2. If I simply use the default sources.list like the one below, what key server is considered to be the official one?

 

deb http://httpredir.debian.org/debian stretch main contrib non-free
#deb-src http://httpredir.debian.org/debian stretch main contrib non-free

deb http://httpredir.debian.org/debian stretch-updates main contrib non-free
#deb-src http://httpredir.debian.org/debian stretch-updates main contrib non-free

deb http://httpredir.debian.org/debian stretch-backports main contrib non-free
#deb-src http://httpredir.debian.org/debian stretch-backports main contrib non-free

deb http://security.debian.org/ stretch/updates main contrib non-free
#deb-src http://security.debian.org/ stretch/updates main contrib non-free

 

3. What's the purpose of https://ftp-master.debian.org/keys.html? I'm asking because it sounds like the official source which should be the most trustful. Can I use the info from it to generate the keys missing?

 

9 minutes ago, sockscap said:

It sounds like the keys will not be synchronized automatically between these servers, and it relies on key owners' manual action?

Correct. Keyservers work independent.

 

9 minutes ago, sockscap said:

2. If I simply use the default sources.list like the one below, what key server is considered to be the official one?

I don't know.

What I do know however is that httpredir has been deprecated by Debian for years now. deb.debian.org should be used instead. Can be read somewhere in Debian wiki.

 

10 minutes ago, sockscap said:

3. What's the purpose of https://ftp-master.debian.org/keys.html?

No idea

4 hours ago, sockscap said:

The latter web page provides the key as ".asc" files, but I cannot find how should I do with these ".asc" files. Could someone point out the official recommended method to fix such NO_PUBKEY errors? It's a bit strange that I have to consult ubuntu keyserver to fix Debian signing key issues.

 

You can download and add the key with

apt-key add <file.asc>

 

The keyservers are capable of synchronization and I suspect (wouldn't know for sure) the ubuntu service is.

20 minutes ago, xwiggen said:

You can download and add the key with

apt-key add <file.asc>

 

Ah yes! I double check "man apt-key", it indeed accepts ".asc" file. Thanks for pointing this out!