Bug#888205: openssh-client: ssh-keygen -t rsa1 fails very late

[Ian Jackson <ijackson@chiark.greenend.org.uk>]

Package: openssh-client
Version: 1:7.4p1-10+deb9u2
Severity: normal

$ ssh-keygen -t rsa1 -b 2048 -f t
Generating public/private rsa1 key pair.
t already exists.
Overwrite (y/n)? y
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Saving key "t" failed: unknown or unsupported key type
$

I guess this is a consequence of dropping SSH v1 protocol support.

This is inconvenient for me as I have a program which uses RSA, relies
on an external key generator, and understands the ssh v1 key format.
So ideally I would like this facility to be restored.

Failing that, I would like ssh-keygen to say "never heard of that key
type" rather than going ahead and generating a perfectly good RSA key
before failing to marshal it up into a key file.

Thanks,
Ian.

-- System Information:
Debian Release: 9.3
  APT prefers stable-debug
  APT policy: (500, 'stable-debug'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.9.0-5-amd64 (SMP w/4 CPU cores)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE=C.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)

Versions of packages openssh-client depends on:
ii  adduser           3.115
ii  dpkg              1.18.24
ii  libc6             2.24-11+deb9u1
ii  libedit2          3.1-20160903-3
ii  libgssapi-krb5-2  1.15-1+deb9u1
ii  libselinux1       2.6-3+b3
ii  libssl1.0.2       1.0.2l-2+deb9u2
ii  passwd            1:4.4-4.1
ii  zlib1g            1:1.2.8.dfsg-5

Versions of packages openssh-client recommends:
ii  xauth  1:1.0.9-1+b2

Versions of packages openssh-client suggests:
pn  keychain      <none>
pn  libpam-ssh    <none>
pn  monkeysphere  <none>
pn  ssh-askpass   <none>

-- no debconf information