Re: SSH question

From: Brian Hatch (
Date: 07/17/03

  • Next message: Armin M. Safarians: "Re: SSH question"
    Date: Wed, 16 Jul 2003 17:00:15 -0700
    To: "Armin M. Safarians" <>

    > I hope someone can help with this finding.
    > We are investigating centralized control of the authorized_keys file in
    > a root owned directory with world readable permission so we can control
    > key usage. we have added user1@hosta's key into this file.

    You haven't really defined this well.

    authorized_keys files go into the .ssh directory of a specific
    user. So if I wanted the key '' to be allowed to
    ssh into my account (jdoe) on host 'host-a', I'd do the following

       me@home$ cd ~/.ssh
       me@home$ ls

       me@home$ scp
       me@home$ ssh jdoe@host-a
       (type password, since the key isn't trusted yet.)

       jdoe@host-a$ mkdir .ssh ; chmod 700 .ssh . ; cd .ssh
       jdoe@host-a$ cat ../ >> authorized_keys
       jdoe@host-a$ chmod 600 authorized_keys

       me@home$ ssh jdoe@host-a
       (no password required now.)

    Now, if I take my id_rsa key and copy it to some other
    machine (say my ISP, or my work machine, etc) then yes,
    I can use it to log into host-a with pubkey authentication.

    If I want to allow this key only from one host, then edit
    the authorized_keys file and add a 'from=' option, ala

       jdoe@host-a$ head -1 authorized_keys
       from= AAAAB3NzaC1yc2EAAAABIwAAAIEAp8Z4Efr8...

    > It seems that so long as user1 has a key on any machine, and it exists
    > in the authorized_keys file, user1 can ssh to those remote hosts as
    > anyone else.

    The user should only be able to log into an account that has included
    user1's public key in their authorized_keys file. This user couldn't
    log in as me if I don't have his pubkey in my authorized_keys file,
    for example.

    If I'm missunderstanding your situation, let me know.

    Brian Hatch                  Never test the depth
       Systems and                of the water with
       Security Engineer          both feet.
    Every message PGP signed

  • Next message: Armin M. Safarians: "Re: SSH question"

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