Hi Shlomi,
The challenge/response protocol you proposed is fine, as far as it goes.
The main weakness is outside the protocol, in that you need to setup the
shared secret on both sides out-of-band, and you have to worry about an
attacker getting the secret from either point, after which you can be
impersonated with ease. Aside from that, as Orr pointed out, you need to
take care not to have repeated or predictable challenges.
As others have pointed out, it's far better (in terms of security and
effort) to go with a proven and tested protocol, e.g., ssh, than to invent
one yourself.
Cheers,
Rony
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Orr Dunkelman
> Sent: Friday, June 16, 2006 5:49 PM
> To: Shlomi Fish
> Cc: Linux-il
> Subject: Re: Crypto: Securely Invoking an event remotely
>
> The security protocol is good.
>
> The main problem that still stands is - why?
>
> As people wrote before - you have better options. But in case
> you choose
> this light-weight service, please recall that this service will
> A) have high security clearances (it's a service that can do
> shutdown).
> B) will pharse input from the (untrusted) network.
>
> Most likely that you'll get some buffer overflow/malformed input
> vulnerability/anything in this class. You also will need to
> make sure that
> the challanges that Eskimo sends are random enough.
>
> To conclude - use ssh's services.
>
>
>
> --
> Orr Dunkelman,
> [EMAIL PROTECTED]
>
> "If it wasn't for C, we'd be writing programs in BASI, PASAL,
> and OBOL", anon
>
> Spammers: http://vipe.technion.ac.il/~orrd/spam.html
> GPG fingerprint: C2D5 C6D6 9A24 9A95 C5B3 2023 6CAB 4A7C B73F D0AA
> (This key will never sign Emails, only other PGP keys.)
>
> On Fri, 16 Jun 2006, Shlomi Fish wrote:
>
> > Hi all!
> >
> > The iglu.org.il server had to be rebooted several times in
> the past months,
> > because it has become unresponsive. It has some potential
> problems like a
> > lack of enough memory, etc. (we are planning a memory
> upgrade). Nevertheless,
> > this time (and as I recall others) it still answered pings
> and could initiate
> > HTTP connections.
> >
> > What I would like to have there is a lightweight network
> service that upon
> > receiving a remote signal will initiate a shutdown of all
> services except
> > sshd. I'll worry about what exactly to shutdown and how,
> but would like to
> > consult the collective wisdom of Linux-IL regarding how to
> securely transmit
> > the signal.
> >
> > The scheme I've been thinking is this:
> >
> > 1. My home machine (let's call it Redwolf) initiates the connection.
> >
> > 2. The service (let's call it Eskimo) sends Redwolf a
> random string of bits.
> >
> > 3. Redwolf receives this string and encrypts it using a
> symmetrical (= private
> > key) key algorithm, and using a key that only him and
> Eskimo knows. (Assume
> > that this key can be decided upon in advance).
> >
> > 4. Redwolf sends the encrypted string back to Eskimo.
> >
> > 5. Eskimo encrypts the string he sent Redwolf himself,
> compares it to the
> > string Redwolf sent and if they are identical initiates the
> shutdown process.
> >
> > Is this scheme cryptologically secure? (Assuming there
> isn't a weakness in the
> > encryption algorithm). Was it proven to be so? If it does
> have a weakness
> > what is a better (and hopefully proven) scheme?
> >
> > Thanks in advance and I'm sorry that I didn't use Alice and
> Bob here.
> >
> > Shlomi Fish
> >
> >
> ---------------------------------------------------------------------
> > Shlomi Fish [EMAIL PROTECTED]
> > Homepage: http://www.shlomifish.org/
> >
> > 95% of the programmers consider 95% of the code they did
> not write, in the
> > bottom 5%.
> >
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