Blank username?

[Alexander Lamaison]

A user has asked us to support public-key login without a username.
Does the spec allow a blank username for SSH auth?

I can't find anything expressly forbidding it, but neither can I find
mention anywhere of anyone actually doing it.

Thanks,

Alex

--
Swish - Easy SFTP for Windows Explorer (http://www.swish-sftp.org)

[Wolfgang Meiners]

Am 02.04.13 02:56, schrieb Alexander Lamaison:

> A user has asked us to support public-key login without a username.
> Does the spec allow a blank username for SSH auth?
>
> I can't find anything expressly forbidding it, but neither can I find
> mention anywhere of anyone actually doing it.
>
> Thanks,
>
> Alex
>

The simplest case is you are user1 at local and type
ssh remote
then ssh tries to connect you to user1@remote. And if there is a public
key in the remote /home/user1/.ssh/authorized_keys file corresponding to
the private key of user1 at local then this key will be used in a
default configuration of sshd.

In a more complicated setup user1 at local migth have a section

Host myHost
Hostname a_valid_host
User me
IdentityFile ~/.ssh/my_secret_key

in his ~/.ssh/config.
Then

ssh myHost

will be the same as
ssh -i ~/.ssh/my_secret_key me@a_valid_host

Maybe you should read man ssh_config for more information.

Hope this helps
Wolfgang

[Alexander Lamaison]

Wolfgang Meiners <Wolfgang...@web.de> writes:

> Am 02.04.13 02:56, schrieb Alexander Lamaison:
>> A user has asked us to support public-key login without a username.
>> Does the spec allow a blank username for SSH auth?
>>
>> I can't find anything expressly forbidding it, but neither can I find
>> mention anywhere of anyone actually doing it.
>>
>> Thanks,
>>
>> Alex
>>
>
> The simplest case is you are user1 at local and type
> ssh remote
> then ssh tries to connect you to user1@remote. And if there is a public
> key in the remote /home/user1/.ssh/authorized_keys file corresponding to
> the private key of user1 at local then this key will be used in a
> default configuration of sshd.

snip

> Maybe you should read man ssh_config for more information.

Sorry, I should have been more clear. I'm not asking what the OpenSSH
client does if you don't specify a username. Swish *is* an SSH (SFTP)
client and our user is asking us to make it support pubkey auth without
a username.

I wasn't aware that was possible, though I can't find anything expressly
forbidding it in the spec. I'm double-checking I'm not missing
something.

[Richard E. Silverman]

Alexander Lamaison <aw...@doc.ic.ac.uk> writes:

> A user has asked us to support public-key login without a username.
> Does the spec allow a blank username for SSH auth?
>
> I can't find anything expressly forbidding it, but neither can I find
> mention anywhere of anyone actually doing it.
>
> Thanks,
>
> Alex

The userauth spec (RFC 4252) for publickey authentication requires there
to be a "user name" field in the request; however, there is nothing
preventing a client from sending an empty or otherwise meaningless
string, if the server can be configured to map the public key to a
particular remote account in some way. Normally the client specifies
which account it wants to access with the username field.

- Richard