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Add a rant to the FAQ about host key checking. I'm _sick_ of people
implementing a command line option to disable it and expecting us to cheerfully accept the patch. [originally from svn r1382]
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doc/faq.but
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doc/faq.but
@ -101,6 +101,41 @@ authentication, which is more flexible and more secure. See
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\k{pubkey} in the documentation for a full discussion of public key
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authentication.
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\S{faq-hostkeys} Is there an option to turn off the annoying host
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key prompts?
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No, there isn't. And there won't be. Even if you write it yourself
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and send us the patch, we won't accept it.
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Those annoying host key prompts are the \e{whole point} of SSH.
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Without them, all the cryptographic technology SSH uses to secure
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your session is doing nothing more than making an attacker's job
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slightly harder; instead of sitting between you and the server with
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a packet sniffer, the attacker must actually subvert a router and
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start modifying the packets going back and forth. But that's not all
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that much harder than just sniffing; and without host key checking,
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it will go completely undetected by client or server.
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Host key checking is your guarantee that the encryption you put on
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your data at the client end is the \e{same} encryption taken off the
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data at the server end; it's your guarantee that it hasn't been
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removed and replaced somewhere on the way. Host key checking makes
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the attacker's job \e{astronomically} hard, compared to packet
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sniffing, and even compared to subverting a router. Instead of
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applying a little intelligence and keeping an eye on Bugtraq, the
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attacker must now perform a brute-force attack against at least one
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military-strength cipher. That insignificant host key prompt really
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does make \e{that} much difference.
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If you're having a specific problem with host key checking - perhaps
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you want an automated batch job to make use of PSCP or Plink, and
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the interactive host key prompt is hanging the batch process - then
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the right way to fix it is to add the correct host key to the
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Registry in advance. That way, you retain the \e{important} feature
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of host key checking: the right key will be accepted and the wrong
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ones will not. Adding an option to turn host key checking off
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completely is the wrong solution and we will not do it.
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\S{faq-server} Will you write an SSH server for the PuTTY suite, to
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go with the client?
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