spoof rsa fingerprint

[Mikkel]

Gordon Messmer wrote:
> On 11/17/2009 04:53 AM, Patrick O'Callaghan wrote:
>>
>> It's my understanding that the password would still be sent over an
>> encrypted channel (using the original host's public key), so I don't see
>> the problem.
>>    
> 
> There is no original host in the hypothesized scenario.  There's an
> attacker whose public key has a fingerprint that matches the original
> host.  The victim connects to the attacker instead of the original
> host.  Since the original host isn't involved, the original host's key
> won't be either.
> 
> However, as previously stated, this is extraordinarily difficult by design.
> 
From the original post:

> what happens, if someone turns off my router, then installs a pc
> with ip 192.168.1.1?
>
> And! - it spoofs _the same rsa fingerprint_, that was on my
> router.

I think what the OP was missing was that the fingerprint being sent
is telling you what public key to use. If you already have that key,
then the replacement machine is out of luck unless it also has the
matching private key.

Now, if the fingerprint sent does not match a public key in
known_hosts, and the host is not known, you will be asked to accept
the public key. But if the host is known, and the fingerprint does
not match, you will be warned about a possible man-in-the-middle
attach, and will have to authorize the connection.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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