Hi, That is why CAs (certification authorities) exists ! ! they are trusted third parties ! They mantain a database with the public keys of the entities they are confident of. The CA isues certificates signed by itself granting identities !
Cheers Christian 2006/8/30, Mark Senior <[EMAIL PROTECTED]>:
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.
