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Anisha Raghu

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What is SSL?

Digital signatures and SSL certificates

Introduction to HTTPS

MD5 chosen-prefix collision attack

Attack on SSL

Final Thoughts

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SSL (Secure socket Layer) is a cryptographic

protocol that provide security and data

integrity for communications over networkssuch as the internet.

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Few of the details contained in a certificate:

Web servers host name

Issue and expire time

Public key for the Web server

Steps to view the certificates in yourcomputer:

Internet Explorer: Tools | Internet Options |Contents | Certificates (view)

Firefox: Tools | Options | Advanced |Encryption | View Certificates (view)

http://ie.htm/http://firefox.htm/http://firefox.htm/http://ie.htm/

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Collisions = different messages, same hash

Chosen prefix method allows two completely

arbitrary files to have the same MD5 hash, by

appending a few thousand bytes at the end

of each file.

Example of a chosen prefix collision attack

http://collision%20attack.htm/http://collision%20attack.htm/

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Two certificates that have Different Identities

Different Public keys

But have the same digital signature

Collision of these two certificates using MD5chosen-prefix attack.

Demo of colliding certificates

http://colliding%20certificates.htm/http://colliding%20certificates.htm/

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A Certification

Authoritydistributes its CA

root certificate via

browser vendors to

browsers.

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A company that

wants its website

to be secured,

purchases a

website certificate

at the CA

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If its signature can

be verified with

the certificate of aCA in the trust list,

the website

certificate will be

accepted.

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1a. A legitimate

website

certificate is

obtained from

a commercial

CA

1b. A rogue CAcertificate is

constructed

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Hackers created a

rouge Certificationauthority using a

cluster of 200 PS3s

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2. A copy of thegenuine

website isbuilt, put onanother webserver, andequipped withthe roguewebsitecertificate.

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3. There exist"redirectionattacks", by

which thecommunicationfrom thebrowser can be

redirected tothe roguewebsite.

Demo

http://demo.htm/http://demo.htm/

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1. VeriSign Inc

2. RSA data Security

3. Entrust.net

4. Equifax5. GTE corporation

6. IPS safeguard CA

7. NetLock Halozatbiztonsagi kft

8. StartCom Ltd9. TC trust Center for security in data

networks

10. Thawte

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Users

CertificationAuthorities

Browser and

Operating Systemvendors

Website owners

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http://www.win.tue.nl/hashclash/rogue-ca/

http://www.phreedom.org/research/rogue-

ca/

http://www.win.tue.nl/hashclash/TargetColl

idingCertificates/

http://blogs.techrepublic.com.com/network

ing/?p=776

http://www.win.tue.nl/hashclash/rogue-ca/http://www.phreedom.org/research/rogue-ca/http://www.phreedom.org/research/rogue-ca/http://www.win.tue.nl/hashclash/TargetCollidingCertificates/http://www.win.tue.nl/hashclash/TargetCollidingCertificates/http://blogs.techrepublic.com.com/networking/?p=776http://blogs.techrepublic.com.com/networking/?p=776http://blogs.techrepublic.com.com/networking/?p=776http://blogs.techrepublic.com.com/networking/?p=776http://www.win.tue.nl/hashclash/TargetCollidingCertificates/http://www.win.tue.nl/hashclash/TargetCollidingCertificates/http://www.phreedom.org/research/rogue-ca/http://www.phreedom.org/research/rogue-ca/http://www.phreedom.org/research/rogue-ca/http://www.win.tue.nl/hashclash/rogue-ca/http://www.win.tue.nl/hashclash/rogue-ca/http://www.win.tue.nl/hashclash/rogue-ca/

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Colliding X.509 Certificates, Arjen Lenstra,Xiaoyun Wang, and Benne de Weger

Short chosen-prefix collisions for MD5 andthe creation of a rogue CA certificate, MarcStevens, Alex Sotirov, Jake Appelbaum, ArjenLenstra, David Molnar, Dag Arne Osvik andBenne de Weger

Target Collisions for MD5 and Colliding X.509Certificates for Different Identities, MarcStevens, Arjen Lenstra, and Benne de Weger

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