Bug#932373: proftpd error reading passphrase for SFTPHostKey

[Markus Raps]

Package: proftpd-basic
Version: 1.3.6-4

I think there is something wrong with the sftp module in buster
because proftpd cant read ssh Host keys

i also tried to recreate the keys with dpkg-reconfigure openssh-server
or manually by ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key
and i tried to create keys on a Debian 9 machine and copied them on the 
Debian 10 machine.
so i think it isn't the key its the module.

How to reproduce

Install Debian 10 minimal

apt install proftpd-basic

create minimal sftp config
echo '<VirtualHost 192.168.1.15>
         DefaultRoot             ~
         RequireValidShell       off

         SFTPEngine              on
         Port                    2222
         SFTPLog                 /var/log/proftpd/sftp.log

         SFTPHostKey             /etc/ssh/ssh_host_rsa_key

         SFTPAuthMethods         publickey keyboard-interactive

         #SFTPAuthorizedUserKeys file:/etc/proftpd/authorized_keys/%u

         # Enable compression
         SFTPCompression delayed

</VirtualHost>' > /etc/proftpd/conf.d/sftp.conf

Restart Service

systemctl restart proftpd

get broken service

root at proftpd-test:/etc/proftpd/conf.d# systemctl status proftpd
● proftpd.service - LSB: Starts ProFTPD daemon
    Loaded: loaded (/etc/init.d/proftpd; generated)
    Active: active (exited) since Thu 2019-07-18 15:29:38 CEST; 42min ago
      Docs: man:systemd-sysv-generator(8)
   Process: 817 ExecStart=/etc/init.d/proftpd start (code=exited, 
status=0/SUCCESS)

Jul 18 15:29:38 proftpd-test systemd[1]: Starting LSB: Starts ProFTPD 
daemon...
Jul 18 15:29:38 proftpd-test proftpd[817]: Starting ftp server: 
proftpd2019-07-18 15:29:38,355 proftpd-test proftpd[825]: processing 
configuration directory '/etc/proftpd/conf.d/'
Jul 18 15:29:38 proftpd-test proftpd[817]: Wrong passphrase for this 
key.  Please try again.
Jul 18 15:29:38 proftpd-test proftpd[817]: Wrong passphrase for this 
key.  Please try again.
Jul 18 15:29:38 proftpd-test proftpd[817]: Wrong passphrase for this 
key.  Please try again.
Jul 18 15:29:38 proftpd-test proftpd[817]: 2019-07-18 15:29:38,362 
proftpd-test proftpd[825] proftpd-test.mm-com.de: mod_sftp/1.0.0: error 
reading passphrase for SFTPHostKey '/etc/ssh/ssh_host_rsa_key': 
(unknown)
Jul 18 15:29:38 proftpd-test proftpd[817]: 2019-07-18 15:29:38,362 
proftpd-test proftpd[825] proftpd-test.mm-com.de: mod_sftp/1.0.0: unable 
to use key in SFTPHostKey '/etc/ssh/ssh_host_rsa_key', exiting
Jul 18 15:29:38 proftpd-test proftpd[817]: .
Jul 18 15:29:38 proftpd-test systemd[1]: Started LSB: Starts ProFTPD 
daemon.


-- 
Mit freundlichen Grüßen / best regards
Markus Raps