[cfarm-users] Is RSA really insecure?

[Arsen Arsenović]

Segher Boessenkool via cfarm-users <cfarm-users at lists.tetaneutral.net> writes:

> On Thu, Dec 14, 2023 at 01:22:28AM -0300, Alexandre Oliva via cfarm-users wrote:
>> On Dec 13, 2023, Jacob Bachmeyer <jcb62281 at gmail.com> wrote:
>> > This is a pet peeve of mine:  unless you have a citation for an actual
>> > viable attack on RSA as used in SSH, or perhaps on the protocol SSH
>> > uses for RSA-based authentication
>> 
>> AFAIK, ssh-rsa relies on SHA1 and SHA1 is weakening.  Labeling it as
>> 'insecure', like I did, was probably an exaggeration, but there seems to
>> be good reason to phase it out proactively rather than reactively.
>
> Exactly.  And this wouldn't endanger your keys, in the worst case your
> connections to these old machines could be eavesdropped, or very maybe
> even taken over.  So enabling these older protocols for machines that
> run older software and so do not support newer, better protocols should
> be fine for almost everyone.
> Maybe add a comment to your .ssh/config to that effect ;-)

Right.  I have:

  Host gcc211.fsffrance.org
       IdentityFile .ssh/id_gccfarm
       PubkeyAcceptedAlgorithms +ssh-rsa
       HostkeyAlgorithms +ssh-rsa

... in my ~/.ssh/config (which hasn't been updated in a bit).  You can
do a similar thing.

The separate key here was done because I use an EC key.

The above should let you 'locally' enable the RSA algorithms.

>
>
> Segher
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-- 
Arsen Arsenović
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