Interesting new attack on SSL-based security - compromise the CA
infrastructure.
Begin forwarded message:
------ Forwarded Message
From: InfoSec News <ale...@infosecnews.org>
Date: Wed, 31 Dec 2008 09:08:14 +0000
To: "i...@infosecnews.org" <i...@infosecnews.org>
Subject: [ISN] Creating a rogue CA certificate
http://www.win.tue.nl/hashclash/rogue-ca/
December 30, 2008
MD5 considered harmful today
Creating a rogue CA certificate
-=-
Alexander Sotirov, Marc Stevens,
Jacob Appelbaum, Arjen Lenstra,
David Molnar, Dag Arne Osvik,
Benne de Weger
-=-
Summary
We have identified a vulnerability in the Internet Public Key
Infrastructure
(PKI) used to issue digital certificates for secure websites. As a
proof of
concept we executed a practical attack scenario and successfully
created a
rogue
Certification Authority (CA) certificate trusted by all common web
browsers.
This certificate allows us to impersonate any website on the Internet,
including
banking and e-commerce sites secured using the HTTPS protocol.
Our attack takes advantage of a weakness in the MD5 cryptographic hash
function
that allows the construction of different messages with the same MD5
hash.
This
is known as an MD5 "collision". Previous work on MD5 collisions
between 2004
and
2007 showed that the use of this hash function in digital signatures
can
lead to
theoretical attack scenarios. Our current work proves that at least
one
attack
scenario can be exploited in practice, thus exposing the security
infrastructure
of the web to realistic threats.
As a result of this successfull attack, we are currently in
possession of a
rogue Certification Authority certificate. This certificate will be
accepted
as
valid and trusted by all common browsers, because it appears to be
signed by
one
of the root CAs that browsers trust by default. In turn, any website
certificate
signed by our rogue CA will be trusted as well. If an unsuspecting
user is a
victim of a man-in- the-middle attack using such a certificate, they
will be
assured that the connection is secure through all common security
indicators: a
"https:// " url in the address bar, a closed padlock and messages
such as
"This
certificate is OK" if they chose to inspect the certificate.
This successful proof of concept shows that the certificate validation
performed
by browsers can be subverted and malicious attackers might be able to
monitor or
tamper with data sent to secure websites. Banking and e-commerce
sites are
particularly at risk because of the high value of the information
secured
with
HTTPS on those sites. With a rogue CA certificate, attackers would
be able
to
execute practically undetectable phishing attacks against such sites.
The infrastructure of Certification Authorities is meant to prevent
exactly
this
type of attack. Our work shows that known weaknesses in the MD5 hash
function
can be exploited in realistic attack, due to the fact that even
after years
of
warnings about the lack of security of MD5, some root CAs are still
using
this
broken hash function.
The vulnerability we expose is not in the SSL protocol or the web
servers
and
browsers that implement it, but in the Public Key Infrastructure. This
infrastructure has applications in other areas than the web, but we
have not
investigated all other possible attack scenarios. So other attack
scenarios
beyond the web are conceivable, such as in the areas of code
signing, e-mail
security, and in other areas that use certificates for enabling
digital
signatures or public key encryption.
The rest of this document will explain our work and its implications
in a
fair
amount of detail. In the interest of protecting the Internet against
malicious
attacks using our technique, we have omitted the critical details of
our
sophisticated and highly optimized method for computing MD5
collisions. A
scientific paper about our method is in preparation and will be
released
after a
few months, so that the affected Certification Authorities have had
some
time to
remedy this vulnerability.
[...]
http://www.win.tue.nl/hashclash/rogue-ca/