[Bug 3279] New: UpdateHostKeys triggers "client_global_hostkeys_private_confirm: server gave bad signature for RSA key 0" error message

[bugzilla-daemon at mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=3279

            Bug ID: 3279
           Summary: UpdateHostKeys triggers
                    "client_global_hostkeys_private_confirm: server gave
                    bad signature for RSA key 0" error message
           Product: Portable OpenSSH
           Version: 8.5p1
          Hardware: Other
                OS: Windows 10
            Status: NEW
          Severity: normal
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: thomas.braun at byte-physics.de

Upstream issue: https://github.com/git-for-windows/git/issues/3108

$ ssh -V
OpenSSH_8.5p1, OpenSSL 1.1.1j  16 Feb 2021

Platform:
Windows 10

The following recipe requires a gitlab.com account with ssh key
attached.

```
$ ssh git at gitlab.com -i ~/.ssh/XXX
client_global_hostkeys_private_confirm: server gave bad signature for
RSA key 0
PTY allocation request failed on channel 0
Welcome to GitLab, @XXX!
Connection to gitlab.com closed.
```

As found on the internet disabling UpdateHostKeys turns the error
message off:

```
$ ssh -o UpdateHostKeys=no git at gitlab.com -i ~/.ssh/github_ed255519
PTY allocation request failed on channel 0
Welcome to GitLab, @t-b!
Connection to gitlab.com closed.
```

The ssh server:

```
debug1: Remote protocol version 2.0, remote software version
OpenSSH_7.9p1 Debian-10+deb10u2
debug1: compat_banner: match: OpenSSH_7.9p1 Debian-10+deb10u2 pat
OpenSSH* compat 0x04000000
````

Host Key of the server:

```
gitlab.com ssh-ed25519
AAAAC3NzaC1lZDI1NTE5AAAAIAfuCHKVTjquxvt6CM6tdG4SLp1Btn/nOeHHE5UOzRdf
```

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