Cryptography Reference
In-Depth Information
Diagram 5.3 SSL Handshake Protocol Actions (continued)
Stage 3
Client Certificate
(
if requested
)
−−−−−−−−−−−−−−−−−−−−−−−−−−−−−→
Client-Key-Exchange
−−−−−−−−−−−−−−−−−−−−−−−−−−−−−→
Server Certificate Verify
(
if sent
)
−−−−−−−−−−−−−−−−−−−−−−−−−−−−−→
R
T
Stage 4
Client
Server
Master Secret
Master Secret
Server-Finished
←−−−−−−−−−−−−−−
−−−−−−−−−−−−−−→
Client-Finished
Session Key
Session Key
Analysis
: SSL server authentication allows a user to confirm a server's
identity, which is quite important if, for instance, the user is sending a credit
card number over a network, and needs to check the receiving server's identity.
SSL client authentication allows a server to confirm a user's identity. This is
veryimportant if, for example, a bank is sending confidential financial informa-
tion to a customer, and needs to check the recipient's identity. An enciphered
SSL session is protected bya tamper-detection mechanism, which automatically
checks to see if information has been altered in transit, a secure hybrid cryp-
tosystem, with the handshake allowing independent creation of symmetric keys
for fast enciphering, deciphering, and tamper-detection during the session.
If authentication of client and/or server is chosen, then X.509V3 certificates
are used; see page 238. This makes the use of SSL somewhat unwieldygiven the
necessityof an established PKI to manage the certificates. Yet, the certificates
render a scalable key-management scheme, which is a powerful mechanism. Of
course, a totallyanonymous SSL mode provides no authentication, and opens
the scheme up to the man-in-the-middle attack, as noted earlier. However, when
users want to take advantage of SSL on their Web site without being associated
with their host, then anonymous SSL is the way to go. Hence, the anonymous
SSL server has its place, and there are numerous vendors available to sell such
packages to the willing.
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