Re: SSL/TLS - am I doing it right?

Frank Millman enlightened us with:
If I understand correctly, a 'man-in-the-middle' attack would
involve someone setting up a 'pseudo server', which gives the
correct responses to the client's attempt to log in

That's right. Usually it's done by proxying the data between the
client and the real server.

and would also involve someone manipulating the client parameter so
that it points to the pseudo server instead of the real server.

Yup. This can be done in various ways, like ARP poisoning of the
network. Then the IP address will not change, but the network card
that the traffic is sent to will. The fraudulent server, having the
correct ARP table, can then forward the captured data to the real
server.

What I have not understood is how to prevent this. How can the
client distinguish between a valid server and a fraudulent one?

By checking the certificates. The CA mustn't sign server certificates
except for the real server. The fraudulent server thus has no valid
server certificate.

If it obtains the server credentials dynamically, the fraudulent
server can supply fraudulent credentials. If somehow the client must
know in advance what the credentials are, then these can only be as
secure as the parameter that tells the client how to connect in the
first place.

True, but as you can see above, making the client talk to another
computer doesn't have to involve accessing and changing the client's
filesystem.

I more or less understand the concept of setting up a secure server,
with a signed key that can be validated via a trusted authority, but
surely it is not necessary for every user of my software to register
with such an authority before they can get protected communication
between their own clients and their own server.

If you want to be secure, that *is* necessary. Every client should
have a valid, signed certificate, and every server should too.

Sybren
--
The problem with the world is stupidity. Not saying there should be a
capital punishment for stupidity, but why don't we just take the
safety labels off of everything and let the problem solve itself?
Frank Zappa
.

Relevant Pages

  • Re: What doesnt lend itself to OO?
    ... >> proxy and instructs the server to constuct the real object. ... rather than client code. ... If 'clock' is instantiated in the server, ... > for the server interface at the OOA level. ...
    (comp.object)
  • This is going straight to the pool room
    ... or not the client has privilege to do what they're trying to do, ... The server environment is this: ... 3GL User action Routines that Tier3 will execute on your behalf during the ... Routine Name: USER_INIT ...
    (comp.os.vms)
  • [Full-Disclosure] R: Full-Disclosure Digest, Vol 3, Issue 42
    ... Full-Disclosure Digest, Vol 3, Issue 42 ... SD Server 4.0.70 Directory Traversal Bug ... Arkeia Network Backup Client Remote Access ...
    (Full-Disclosure)
  • Re: What doesnt lend itself to OO?
    ... > rather than client code. ... no way to do that without also touching the object with clock semantics ... will not encapsulate both clock semantics and network semantics. ... The server can do whatever it wants ...
    (comp.object)
  • RE: Fax monitor incoming + outgoing calls?
    ... problem between the client computer and the SBS server. ... Client is using the internal IP address of the SBS server as the ... To the folder redirection GPO issue: ...
    (microsoft.public.windows.server.sbs)