[Proftpd-user] Problem with ed25519 pubkeys in database with mod_sftp_sql

Hello,

Is it possible that mod_sftp_sql hasn't been updated to support ed25519
keys loaded from a db?

Here is the situation and what I've tried:

I have compiled version 1.3.7a as an Ubuntu package
(using dpkg-buildpackage and with sodium installed).

I'm using mod_sftp_sql and mod_pgsql. My configuration stores the username,
public key, etc. in the db and that works fine with RSA keys in SSH2
format. I have an ed25519 key in SSH2 format that I installed and it isn't
working.

The logs on the server just show the connection open and then close:

2020-07-23 20:08:19,150 jenkins proftpd[961] 0.0.0.0
> (localhost[127.0.0.1]): SSH2 session opened.
> 2020-07-23 20:09:23,730 jenkins proftpd[961] 0.0.0.0
> (localhost[127.0.0.1]): SSH2 session closed.


(They used to show an issue with an unsupported key type until I upgraded
to 1.3.7a and compiled with sodium.)

If I use verbose debugging on the client side, I see the following as part
of the log:

debug3: authmethod_is_enabled publickey
> debug1: Next authentication method: publickey
> debug1: Offering public key: ED25519
> SHA256:u+1dMagfZ1iuB5Bp1sgoKX2ryC+zfwxjk55nR2DoF4w /tmp/id_ed25519.sftp.test
> debug3: send_pubkey_test
> debug3: send packet: type 50
> debug2: we sent a publickey packet, wait for reply
> debug3: receive packet: type 60
> debug1: Server accepts key: pkalg ssh-ed25519 blen 51
> key_from_blob: unknown or unsupported key type
> debug1: no key from blob. pkalg ssh-ed25519
> debug2: we did not send a packet, disable method
> debug3: authmethod_lookup password
> debug3: remaining preferred: ,password
> debug3: authmethod_is_enabled password
> debug1: Next authentication method: password


and then it prompts for a password.  This doesn't happen with an RSA key -
which works fine.

The part that is concerning me is:

key_from_blob: unknown or unsupported key type
debug1: no key from blob. pkalg ssh-ed25519

So is it mod_sftp_sql or another module not recognizing the key type and
failing it, or am I barking up the wrong tree? Did I miss something in the
compile?  I've used ed25519 keys as my mainstay for years, but not on sftp.
. .

Some additional information:
The client supports them - it is the latest stable client from
openssh-client on Ubuntu and handles scp and ssh with ed25519 keys
constantly. I also tried scp and received the same result - it works with
password and RSA key but not with ed25519 keys - same error in the debug
output.

Thoughts? What can I try next?

Matt

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