Building user-centric security model in iOS applications

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Building user-centric security model in iOS apps #tryswiftnyc @vixentael

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Security talk ahead!

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#tryswiftnyc @vixentael Why we should think more about security?

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Users trust Apple platform Users trust us Why we should think more about security? #tryswiftnyc @vixentael

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Most users trust sensitive data to our app regardless of how well we protect it #tryswiftnyc @vixentael

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abstract app in a vacuum #tryswiftnyc @vixentael

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security is set of ultimatum rules security abstract app in a vacuum #tryswiftnyc @vixentael

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security is set of ultimatum rules abstract app in a vacuum real apps, real ecosystems #tryswiftnyc @vixentael

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App Flow App Features Code User Problem #tryswiftnyc @vixentael

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Risk Threat Model Secure Methods Secure Implemen- tations Libs/ Code App Flow App Features Code User Problem #tryswiftnyc @vixentael

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It is secure #tryswiftnyc @vixentael

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It is secure against certain threat model and adversary It is secure #tryswiftnyc @vixentael

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Trust model is whose secrets you trust in a security system #tryswiftnyc @vixentael

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Everything is broken Trust no one, but the user #tryswiftnyc @vixentael

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Now let’s apply this to the real app #tryswiftnyc @vixentael

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secret data paranoia pa55w0rd trust What user hero has? #tryswiftnyc @vixentael

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for saving your important docs during trips Let’s make an app!

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Architecture and flow user app network server storage #tryswiftnyc @vixentael

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T2 T3 passive MitM active MitM T1/T4 data loss/ tampering Threats we can handle #tryswiftnyc @vixentael

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More complicated.. T2 T3 passive MitM active MitM T1/T4 data loss/ tampering T5 verbal key leak T6 phishing / social engineering T7 rubber-hose cryptanalysis T8 satellite imaging of sensitive input T9 EM emissions T10 sandbox escaping T11 misconfiguration T12 random generator abuse T13 random generator abuse T14 EM emissions and physical side channel T15 physical access T16 malicious dependency T17 misconfigured access T18 unattended backups T19 storing keys with data T20 weak cipher random generator abuse T21 #tryswiftnyc @vixentael

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Back to threats we can handle T2 T3 passive MitM active MitM T1/T4 data loss/ tampering #tryswiftnyc @vixentael

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Threats: T1/T4 attacker steals stored data or tampers it #tryswiftnyc @vixentael

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attacker steals stored data or tampers it Threats: T1/T4 Secret Key Crypto Protection Symmetric crypto for storing data. If user has no secret, he can’t read or change data. #tryswiftnyc @vixentael

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Threats: T2 attacker captures network traﬃc (passive MitM) #tryswiftnyc @vixentael

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Threats: T2 attacker captures network traﬃc (passive MitM) Public Key Cryptography, ephemeral keys Protection Asymmetric crypto for sending data. Ephemeral keys to avoid decrypting accumulated traffic if keys are leaked/cracked. #tryswiftnyc @vixentael

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Threats: T3 attacker redirects traﬃc and pretends to be remote party (active MitM) #tryswiftnyc @vixentael

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Threats: T3 attacker redirects traﬃc and pretends to be remote party (active MitM) Public Key Cryptography, certiﬁcate pinning Protection Asymmetric crypto for sending data. Check server certificate to make sure it matches with pinned one. #tryswiftnyc @vixentael

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Protection methods T2 T3 passive MitM active MitM T1/T4 data loss/ tampering Secret Key Crypto PKC + ephem. keys PKC + cert. pinning #tryswiftnyc @vixentael

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Public Key Crypto Perfect Forward Secrecy Secret Key Crypto Authenticated Encryption Certificate Pinning Trust model Trust the user only #tryswiftnyc @vixentael

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Relationship model plain data symmetric encryption PKC + eph. keys symmetric encryption PKC + eph. keys ZKP ZKP #tryswiftnyc @vixentael

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…what if trapdoor function fails? …what if key exchange is flawed? …what if we suspect that server is fraudulent? add more paranoia! #tryswiftnyc @vixentael

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…what if trapdoor function fails? …what if key exchange is flawed? add more paranoia! …what if we suspect that server is fraudulent? Zero Knowledge Proof for the rescue! #tryswiftnyc @vixentael

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ZKP is comparing shared secret without transmitting it does not require the key exchange, does not leak password https://www.cossacklabs.com/zero-knowledge-protocols-without-magic.html #tryswiftnyc @vixentael

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So, data model: Secret key (SK) = KDF(user password) #tryswiftnyc @vixentael

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Secret key (SK) = KDF(user password) Sensitive Data (SD) — passport photo Metadata (M1) — timestamp+CRC of photo Metadata (M2) — name of photo (user inputs) So, data model: #tryswiftnyc @vixentael

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Secret key (SK) = KDF(user password) Sensitive Data (SD) — passport photo Metadata (M1) — timestamp+CRC of photo Metadata (M2) — name of photo (user inputs) Mobile Key Pair (MKP) — private+public keys gen. inside app. Server Key Pair (SKP) — private+public keys gen. on server. App pins Server Public Key. So, data model: #tryswiftnyc @vixentael

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Pwd Key + Data model SD M1 M2 MKP SKP SK #tryswiftnyc @vixentael

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Pwd MKP SKP SK symmetric encryption PKC + eph. keys PKC + eph. keys Rand KDF() Rand User-centric trust #tryswiftnyc @vixentael

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App Flows

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Crypto primitives* Symmetric crypto SCell Asymmetric crypto based on ephemeral keys SSession SComparator ZKP implementation *based on Themis crypto lib https://github.com/cossacklabs/themis #tryswiftnyc @vixentael

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2. Store EncData, M1, M2 in Local Store 3. Drop SD, SK from memory prepare data 1. Encrypt photo EncData = SCell_wrap(SD, SK, Context=M2) Send photo to server #tryswiftnyc @vixentael

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2. Store EncData, M1, M2 in Local Store 3. Drop SD, SK from memory prepare data transfer data 4. Connect to Server: Session = SSession(Priv(MKP), Pub(SKP)) 5. Send EncData, M1, M2 via Session 1. Encrypt photo EncData = SCell_wrap(SD, SK, Context=M2) Send photo to server #tryswiftnyc @vixentael

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Send photo to server 1. Encrypt photo EncData = SCell_wrap(SD, SK, Context=M2) 6. Receive OK 7. Terminate Session 8. Mark EncData in Local Store as Synced 2. Store EncData, M1, M2 in Local Store 3. Drop SD, SK from memory 4. Connect to Server: Session = SSession(Priv(MKP), Pub(SKP)) 5. Send EncData, M1, M2 via Session prepare data transfer data terminate session

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1. Connect to Server: Session = SSession(Priv(MKP), Pub(SKP)) 2. Request EncData proof via ZKP: 2.1 Send M1 2.2 Request Server to prove he has M2 by performing SComparator(M2) initialize connection Read photo from server #tryswiftnyc @vixentael

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1. Connect to Server: Session = SSession(Priv(MKP), Pub(SKP)) 3. Receive EncData 2. Request EncData proof via ZKP: 2.1 Send M1 2.2 Request Server to prove he has M2 by performing SComparator(M2) initialize connection transfer data Read photo from server #tryswiftnyc @vixentael

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Read photo from server 1. Connect to Server: Session = SSession(Priv(MKP), Pub(SKP)) 3. Receive EncData 2. Request EncData proof via ZKP: 2.1 Send M1 2.2 Request Server to prove he has M2 by performing SComparator(M2) 4. Request password from user 5. Decrypt data: SD = SCell_unwrap(EncData, SK, Context=M2) initialize connection transfer data decrypt data

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Make it tough even more

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Apple enforces good security practices iOS 10 use HTTPS everywhere! https://developer.apple.com/videos/play/wwdc2016/706/ http://useyourloaf.com/blog/privacy-settings-in-ios-10/ add purpose strings for accessing private data https://nabla-c0d3.github.io/blog/2016/08/14/ats-enforced-2017/ read more about Apple security care in Additional reading section drop TLS < 1.2 #tryswiftnyc @vixentael

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https://www.blackhat.com/docs/us-16/materials/us-16-Krstic.pdf Apple enforces good security practices

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̣ Security is a system, not a set of methods ̣ You may need to re-read this slides when you will plan your next app ̣ User-centric trust is simple to implement, yet almost impossible to hack Key points! #tryswiftnyc @vixentael

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My other security talks https://medium.com/@vixentael/upgrading-approaches-to-the-secure-mobile- architectures-7a8fcb10d28a#.ffbsjwqx6 Upgrading Approaches to the Secure Mobile Architectures https://medium.com/stanfy-engineering-practices/data-protection-for-mobile-client- server-architectures-6e6dcabd871a Data Protection For Mobile Client-Server Architectures https://speakerdeck.com/vixentael/users-data-security-in-ios-applications Users' data security in iOS applications #tryswiftnyc @vixentael

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Additional reading by Apple https://developer.apple.com/videos/play/wwdc2016/705/ How iOS Security Really Works https://developer.apple.com/videos/play/wwdc2016/706/ What's New in Security https://www.blackhat.com/docs/us-16/materials/us-16-Krstic.pdf Behind the Scenes with iOS Security https://developer.apple.com/videos/play/wwdc2016/709/ Engineering Privacy for Your Users #tryswiftnyc @vixentael

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Additional reading by smarties https://nabla-c0d3.github.io/blog/2016/08/14/ats-enforced-2017/ Getting Ready for ATS Enforcement in 2017 http://useyourloaf.com/blog/privacy-settings-in-ios-10/ Privacy Settings in iOS 10 https://www.cossacklabs.com/zero-knowledge-protocols-without-magic.html Zero Knowledge Protocols Without Magic https://info.lookout.com/rs/051-ESQ-475/images/lookout-pegasus-technical-analysis.pdf Technical Analysis of Pegasus Spyware #tryswiftnyc @vixentael https://medium.com/@9gunpi/side-effects-of-pegasus-malware-32c9a112ec1c Side effect of Pegasus malware

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The last slide Need help? Talk to me :) @vixentael Lead Developer at stanfy.com Core Contributor at themis/ cossacklabs.com