Problem - Kevin Tafuro

maintenance. Adding or removing services becomes an issue of turning the service
on or off—no changes to firewalls or tunneling configurations are required. Once
the VPN is up and running, it essentially takes care of itself.
Although we do suggest the possibility of using a VPN when the other solutions
we’ve provided here aren’t feasible for your situation, a complete discussion of VPN
solutions is well beyond the scope of this book. Entire volumes have been dedicated
to the topic, and we recommend that you consult one or more of those books if you
want to pursue the use of VPNs. A good launch point for VPN information is Building
& Managing Virtual Private Networks by Dave Kosiur (John Wiley & Sons).
9.12 Building an Authenticated Secure Channel
Without SSL
Problem
You want to encrypt communications between two peers without using SSLand the
overhead that it incurs. Because it is normally a bad idea to encrypt without integrity
checking (to avoid attacks such as man-in-the-middle, capture replay, and bit-flipping
in stream ciphers), you also want to employ some kind of integrity checking so
you’ll be able to determine whether the data has been tampered with in transit.
We also assume here that you’d like to stay away from a full-fledged PKI, instead
using a more traditional model of user accounts managed on a per-machine basis.
Solution
Use an authenticating key exchange mechanism from Chapter 8, and use the resulting
session key with a solution for authenticated encryption, while performing
proper key and nonce management.
In this recipe, we provide an infrastructure for the simple secure channel, for use
once authentication and key exchange is performed.
Discussion
Given the tools we’ve discussed in previous recipes for authentication, key exchange,
and the creation of secure channels, producing an end-to-end solution isn’t drastically
difficult. Nonetheless, there are some potential “gotchas” that we still need to
address.
In protocols such as SSL/TLS, connection establishment is a bit more complex than
simply authenticating and exchanging a key. In particular, such protocols tend to
Building an Authenticated Secure Channel Without SSL | 491
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