Certificate pinning 101

Lightning talk

Xavier Rubio Jansana

 @teknik_tdr
 https://xrubio.com
 https://github.com/xrubioj/

Summary

• What?
• Why?
• How SSL/TLS works
• MiTM Attacks
• Certificate pinning 101
• Security considerations

What?

Network security technique

Why?

Avoid MiTM attacks 😱

Implications

• Stealing app secrets
• Stealing user secrets
• Subverting communication
  (e.g. change delivery address)

How SSL/TLS works

HTTPS Connection

Certificate

Certificate

Certificate vs Signature

Subject Public Key Info

Certificate name validation

Certificate chain validation

Root CAs

MiTM Attacks

• Root CA injection 😈
• CA insuficient validation → rogue certificate 😐
• Self-signed certificates → validation disabled 🚨😅

Certificate pinning 101

OkHttp

					val hostname = "*.google.com"
					val certificatePinner = CertificatePinner.Builder()
					      .add(hostname, "sha256/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=")
					      .build()
					val client = OkHttpClient.Builder()
					      .certificatePinner(certificatePinner)
					      .build()
					

javax.net.ssl.SSLPeerUnverifiedException: Certificate pinning failure!
   Peer certificate chain:
     sha256/afwiKY3RxoMmLkuRW1l7QsPZTJPwDS2pdDROQjXw8ig=afwiKY3RxoMmLkuRW1l7QsPZTJPwDS2pdDROQjXw8ig=: CN=publicobject.com, OU=PositiveSSL
     sha256/klO23nT2ehFDXCfx3eHTDRESMz3asj1muO+4aIdjiuY=: CN=COMODO RSA Secure Server CA
     sha256/grX4Ta9HpZx6tSHkmCrvpApTQGo67CYDnvprLg5yRME=: CN=COMODO RSA Certification Authority
     sha256/lCppFqbkrlJ3EcVFAkeip0+44VaoJUymbnOaEUk7tEU=: CN=AddTrust External CA Root
   Pinned certificates for publicobject.com:
     sha256/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
   at okhttp3.CertificatePinner.check(CertificatePinner.java)
   at okhttp3.Connection.upgradeToTls(Connection.java)
   at okhttp3.Connection.connect(Connection.java)
   at okhttp3.Connection.connectAndSetOwner(Connection.java)

Android N

						<?xml version="1.0" encoding="utf-8"?>
						<network-security-config>
						    <domain-config>
						        <domain includeSubdomains="true">appmattus.com</domain>
						        <pin-set>
						            <pin digest="SHA-256">4hw5tz+scE+TW+mlai5YipDfFWn1dqvfLG+nU7tq1V8=</pin>
						            <pin digest="SHA-256">YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg=</pin>
						        </pin-set>
						    </domain-config>
						</network-security-config>
					

							<?xml version="1.0" encoding="utf-8"?>
							<manifest>
							    <application
							        android:networkSecurityConfig="@xml/network_security_config"android:networkSecurityConfig="@xml/network_security_config">
							        <!-- ... -->
							    </application>
							</manifest>
						

Backport

CWAC-NetSecurity https://github.com/commonsguy/cwac-netsecurity

"Allows the same XML configuration to be used, going back to API Level 17 (Android 4.2)"

With some manual work... 🤷‍♂️

How to react

• Hard failure
• Soft failure

Strategies

• Hardcoded pins
• Accept on first access
• Get pins from server → inception! 🙃

Security considerations

⚠️ Hide your secrets!

See "Android security basics" talk by Krzysztof Kocel https://www.meetup.com/Barcelona-Android-Developer-Group/events/244107028/

References

• "Android Security: SSL Pinning" by Matthew Dolan https://medium.com/@appmattus/android-security-ssl-pinning-1db8acb6621e
• Network Security Configuration https://developer.android.com/training/articles/security-config.html
• "CWAC-NetSecurity: Simplifying Secure Internet Access" by CommonsWare https://github.com/commonsguy/cwac-netsecurity
• CertificatePinner class OkHttp documentation https://square.github.io/okhttp/3.x/okhttp/okhttp3/CertificatePinner.html

Questions? 🤔

Thanks! 🎉

Xavier Rubio Jansana

 @teknik_tdr
 https://xrubio.com
 https://github.com/xrubioj/

This talk is available at:
https://xrubio.com/talks/talk-lightning-certificate-pinning/