"Only if Eve gets in the way of the very first connection attempt, can he pass her own public key off as Alice's, without Bob detecting it."
This is exactly my concern. Isn't that scary? On Wed, 2006-08-30 at 12:52 -0600, Mark Senior wrote: > On 8/29/06, Christ, Bryan wrote: > > All, > > > > Please pardon my naivete. > > > > I was looking at the diagram on the URL listed below and > contemplating > > how host fingerprinting prevents MITM attacks. > > > > > http://www.vandyke.com/solutions/ssh_overview/ssh_overview_threats.html > > > > So my question is this... Given the illustration in the URL above, > what > > prevents Eve from *first* contacting Alice to obtain a fingerprint > which > > then gets passed to Bob on the first connection attempt? > > > > The server passes the client its public key; the client generates a > fingerprint of this public key, and verifies that it matches a known > one from previous connections. > > Eve can pass Alice's public key to Bob, but she doesn't possess > Alice's private key, so she has no way to interfere further with the > communications (beyond tampering at a network level - introducing > delay, dropping the connection, etc.) > > Only if Eve gets in the way of the very first connection attempt, can > she pass her own public key off as Alice's, without Bob detecting it. > On the first connection, he'd have to either trust what he sees, or > verify the fingerprint offline somehow. On subsequent connections, > the mismatch would be obvious.
