[Ach] SSH improvements

Aaron Zauner azet at azet.org
Sun Nov 17 17:44:20 CET 2013


I’ve modified those settings accordingly.


On 17 Nov 2013, at 17:06, Aaron Zauner <azet at azet.org> wrote:

> On 17 Nov 2013, at 16:51, christian mock <cm at coretec.at> wrote:
>> On Sun, Nov 17, 2013 at 03:30:18PM +0100, Aaron Zauner wrote:
>>> On a second thought:
>>> We should not exclude Rhosts/RhostsRSAauthentication. A lot of people use pre-shared keys.
>> I'm not sure we should go into that type of question anyways, I think
>> it's out of scope for this paper.
> I agree.
>> What we could go into: remind admins that their ssh server and user
>> keys are probably rather old and only 1024 bits long... Shall we
>> recommend to not use DSA server keys at all?
> This is why I only set an RSA key, usually you specify DSA and RSA host keys with the `HostKey` option.
> We could get rid of RSAAuthentication since it only applies to SSH v. 1.
>> Another issue section: why is “diffie-hellman-group14-sha1” excluded?
>> that is a 2048 bit exchange…
> My mistake, I was trying to avoid EC groups. Feel free to add it.
>> Also, how does one specify the DH key size for
>> diffie-hellman-group-exchange- sha256 and
>> diffie-hellman-group-exchange-sha1?
> Not sure.
>> And what is the algorithm to actually negotiate a cipher? Because it
>> doesn't seem to depend on the order that you give in the "Cipher"
>> option.
> http://tools.ietf.org/html/rfc4253#section-7.1
> ```
>      encryption_algorithms
>         A name-list of acceptable symmetric encryption algorithms (also
>         known as ciphers) in order of preference.  The chosen
>         encryption algorithm to each direction MUST be the first
>         algorithm on the client's name-list that is also on the
>         server's name-list.  If there is no such algorithm, both sides
>         MUST disconnect.
> ```
> BTW, the RFC also specifies OpenPGP:
> ```
>   The following public key and/or certificate formats are currently
>   defined:
>   ssh-dss           REQUIRED     sign   Raw DSS Key
>   ssh-rsa           RECOMMENDED  sign   Raw RSA Key
>   pgp-sign-rsa      OPTIONAL     sign   OpenPGP certificates (RSA key)
>   pgp-sign-dss      OPTIONAL     sign   OpenPGP certificates (DSS key)
> ```
> Aaron

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