Implementing PKI
© 2002 Editions Eyrolles, ISBN 2-212-11045-6
PKI enables confidentiality, integrity, authenticity and non-repudation of data exchanges, by:
© 2002 Editions Eyrolles, ISBN 2-212-11045-6
© 2002 Editions Eyrolles, ISBN 2-212-11045-6
IPsec security services are provided through:
The protocol is composed of two layers:
An SSL client-server session is established via the following mechanisms:
The S/MIME protocol (Secure Multi-purpose Internet Mail Extension), enables digital signatures and encryption of MIME formated messages (e.g. e-mail). Similar to SSL, S/MIME uses a hybrid crypto system. The message is encrypted with a symmetric session key, that itself is secured by using the destination's public key. With multiple recipients the session key has to be encrypted several times using the different public keys.
To enable secure B-to-B transactions or document exchanges over the Internet, the W3C and IETF started the XML-Signature project, defining non-repudiation mechanisms for signing XML (eXtensible Markup Language) documents.
The following example is a detached signature of the content of the HTML4 in XML specification:
<Signature Id="MyFirstSignature" xmlns="http://www.w3.org/2000/09/xmldsig#">
<SignedInfo>
<CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
<SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#dsa-sha1"/>
<Reference URI="http://www.w3.org/TR/2000/REC-xhtml1-20000126/">
<Transforms>
<Transform Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
</Transforms>
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<DigestValue>j6lwx3rvEPO0vKtMup4NbeVu8nk=</DigestValue>
</Reference>
</SignedInfo>
<SignatureValue>MC0CFFrVLtRlk=...</SignatureValue>
<KeyInfo>
<KeyValue>
<DSAKeyValue>
<P>...</P><Q>...</Q><G>...</G><Y>...</Y>
</DSAKeyValue>
</KeyValue>
</KeyInfo>
</Signature>
Beyond using SSL/TLS, S/MINE or XML-Dsig, securing your own applications using PKI means integration. This can be done via 3 approaches:
Using more than one factor is called strong authentication.
© 1999 Department of Computer Science and Information Systems, The University of Hong Kong
March 15, 2005
Two-factor authentication isn't our saviour. It won't defend against phishing.
It's not going to prevent identity theft. It's not going to secure on-line
accounts from fraudulent transactions. It solves the security problems we had
ten years ago, not the security problems we have today.
The problem with passwords is that they're too easy to lose control of. People
give them to other people. People write them down, and other people read them.
People send them in e-mail, and that e-mail is intercepted. People use them to
log into remote servers, and their communications are eavesdropped on. They're
also easy to guess. And once any of that happens, the password no longer works
as an authentication token because you can't be sure who is typing that password
in.
Two-factor authentication mitigates this problem. If your password includes a
number that changes every minute, or a unique reply to a random challenge, then
it's harder for someone else to intercept. You can't write down the ever-changing
part. An intercepted password won't be good the next time it's needed. And a
two-factor password is harder to guess. Sure, someone can always give his password
and token to his secretary, but no solution is foolproof.
These tokens have been around for at least two decades, but it's only recently
that they have gotten mass-market attention. AOL is rolling them out. Some banks
are issuing them to customers, and even more are talking about doing it. It seems
that corporations are finally waking up to the fact that passwords don't provide
adequate security, and are hoping that two-factor authentication will fix their
problems.
Unfortunately, the nature of attacks has changed over those two decades. Back
then, the threats were all passive: eavesdropping and off-line password guessing.
Today, the threats are more active: phishing and Trojan horses.
Here are two new active attacks we're starting to see:
* Man-in-the-Middle attack. An attacker puts up a fake bank website and
entices user to that website. User types in his password, and the attacker in
turn uses it to access the bank's real website. Done right, the user will never
realize that he isn't at the bank's website. Then the attacker either disconnects
the user and makes any fraudulent transactions he wants, or passes along the
user's banking transactions while making his own transactions at the same time.
* Trojan attack. Attacker gets Trojan installed on user's computer. When user
logs into his bank's website, the attacker piggybacks on that session via the
Trojan to make any fraudulent transaction he wants.
See how two-factor authentication doesn't solve anything? In the first case, the
attacker can pass the ever-changing part of the password to the bank along with
the never-changing part. And in the second case, the attacker is relying on the
user to log in.
The real threat is fraud due to impersonation, and the tactics of impersonation
will change in response to the defences. Two-factor authentication will force
criminals to modify their tactics, that's all.
Recently I've seen examples of two-factor authentication using two different
communications paths: call it "two-channel authentication." One bank sends a
challenge to the user's cell phone via SMS and expects a reply via SMS. If you
assume that all your customers have cell phones, then this results in a two-factor
authentication process without extra hardware. And even better, the second
authentication piece goes over a different communications channel than the first;
eavesdropping is much, much harder.
But in this new world of active attacks, no one cares. An attacker using a
man-in-the-middle attack is happy to have the user deal with the SMS portion of
the log-in, since he can't do it himself. And a Trojan attacker doesn't care,
because he's relying on the user to log in anyway.
Two-factor authentication is not useless. It works for local login, and it works
within some corporate networks. But it won't work for remote authentication over
the Internet. I predict that banks and other financial institutions will spend
millions outfitting their users with two-factor authentication tokens. Early
adopters of this technology may very well experience a significant drop in fraud
for a while as attackers move to easier targets, but in the end there will be a
negligible drop in the amount of fraud and identity theft.
© 2005 Bruce Schneier
The 4-As:
A specialized form of authentication that enables a user to authenticate once and gain access to the multiple resources.
Legacy Approach to User Sign-on to Multiple Systems - © 1995-2005 The OpenGroup
Single User Sign-On To Multiple Services - © 1995-2005 The OpenGroup
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© 2003 Microsoft
© 2006 Microsoft
© 2005 OASIS
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© Kim Cameron