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The internet has trust issues
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About usThijs Alkemade
• Security Specialist
• [email protected] / @xnyhps
Christiaan Ottow
• Security Coach
• [email protected] / @cottow
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Performance Security TestAutomation
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https://www.computest.nl/blog/startencrypt-considered-harmful-today/
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Domain Validation Organization Validation
Extended Validation
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Domain Validation
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How much control do you need to get a certificate?
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• <user>.github.io/<file>
• bit.ly/<token>
• <user>.s3.amazonaws.com/<key>
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Client StartCom example.com
I want a cert for example.com
Okay, put abc on example.com
Put abc on attacker.com
Done, it’s on /?redir=attacker.com/abc
GET /?redir=attacker.com/abc
Location: attacker.com/abc
Good, here’s a cert
attacker.com
GET /abc
abc
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Timeline of events• 23/6 report of issue
• 29/6 StartSSL confirms fix
• 30/6 Computest publishes findings
• ~2/7 StartEncrypt API offline
• 2/7 Google asks for details
• ~4/7 Product suspended
• 24/8 Mozilla opens discussion
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Who should intervene if a CA misbehaves?
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Mailinglist discussion
• Long list of issues at https://wiki.mozilla.org/CA:WoSign_Issues
• WoSign improvements
• Publish everything to CT, from 2015
• Always include SCT after July 5, 2016
• Central questions:
• Which incidents are CA/Bf BR violations?
• How do we punish a CA for those?
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Sanctions
• Remove the CA
• Actively distrust the CA
• Remove the CA, whitelisting previously issued certs
• How do we ship the whitelist? Too large
• Distrust certs without CT information.
• Distrust certs without CT information. Whitelist certs before 2016
• See above, issues with whitelist
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Scenarios
• WoSign is removed
• Continues to issue certs because of cross-signing
• WoSign is distrusted
• Continues to issue certs under StartCom CA
• WoSign and StartCom are removed
• Continues to issue certs because of cross-signing
• WoSign is distrusted for C != CN
• Doesn’t solve security implications
• WoSign is distrusted for CN != *.cn
• All browsers need to be patched
• WoSign dramatically improves
• Difficult to prove
• WoSign and StartCom are distrusted
• Business goes bankrupt
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How to minimize risk
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Cheers