[Python-modules-team] Bug#935038: duplicity: fails with Invalid key but ssh works, and pexpect+scp: works

[Phil Diacono]

Package: python-paramiko
Version: 2.6.0-1
Severity: important

Dear Maintainer,

   * What led up to the situation?
I made a backup from duplicity 0.6.24-1 on Debian Jessie with
python-paramiko 1.15.1-1+deb8u1.
The backup target is running openssh-sftp-server 1:6.7p1-5+deb8u8 on
Raspbian Jessie.
I'm testing restore using duplicity 0.7.18.2-1 on Debian Buster (kvm)
with python-paramiko 2.6.0-1.

   * What exactly did you do (or not do) that was effective (or
     ineffective)?
fails: duplicity restore --force --no-encryption --verbosity 5
--ssh-options=-oIdentityFile=/etc/ssh/ssh_host_rsa_key
scp://backups@192.168.115.211/foo /

works: duplicity restore --force --no-encryption --verbosity 5
--ssh-options=-oIdentityFile=/etc/ssh/ssh_host_rsa_key
pexpect+scp://backups@192.168.115.211/foo /

works: ssh -i /etc/ssh/ssh_host_rsa_key backups at 192.168.115.211 date

   * What was the outcome of this action?
duplicity fails with message:
 BackendException: ssh connection to backups at 192.168.115.211:22 failed:
Invalid key

   * What outcome did you expect instead?
I expected the paramiko (scp:) based restore to work.
Bug may be related to #896056

-- System Information:
Debian Release: 10.0
  APT prefers stable
  APT policy: (990, 'stable'), (500, 'unstable'), (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 4.19.0-5-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_AU.UTF-8, LC_CTYPE=en_AU.UTF-8 (charmap=UTF-8),
LANGUAGE=en_AU:en (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages python-paramiko depends on:
ii  python               2.7.16-1
ii  python-bcrypt        3.1.6-1
ii  python-cryptography  2.6.1-3
ii  python-nacl          1.3.0-2

python-paramiko recommends no packages.

Versions of packages python-paramiko suggests:
pn  python-gssapi  <none>

-- debconf-show failed