[Extended version] Building user-centric security model in iOS applications

Read text and watch video on eng:
https://realm.io/news/tryswift-anastasiia-voitova-building-user-centric-security-model-ios-applications-swift/

video on ru:
https://www.youtube.com/watch?v=h4egvZ4JuvI

The extended version of my talk about user-centric trust for your mobile app layout!

- risk and threats models
- real-world app analysis
- building user-app-server interactions step by steps
- code samples
- ways to make it even more tough
- possible attacks
- "crypto is not expensive"
- "Apple cares about security, you should too!"
- key points

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If you can't tap on the link inside slides, please open as pdf (button on the right).

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I presented this talk with slight modifications on #nsspain2016 and #mobiconf conferences. September-October 2016.

In this presentation we will talk about building security, that does not fail when application keys are exposed; when servers are hacked; security that lasts as long as unique user's crypto keys (or passwords) are safe. Putting secrets known by the user to be a source of trust is the ultimate way for an app to become "thin" in relation to the security model, thus lowering the risks and developer pain. We will learn about thin transparent security layers system and its applicability in client-server systems.

Transcript

1. Building user-centric security model in iOS apps @vixentael
2. @vixentael Lead Developer at stanfy.com Core Contributor at themis/ cossacklabs.com Who am I Get in touch if you need help in building a secure mobile app
3. Security talk ahead! #courage
4. #mobiconf @vixentael Risks and threat models Trust models Analyze real app Protection methods ZKP Code samples Attack scenarios Security model future improvements
5. Why we should think more about security? #mobiconf @vixentael
6. Users trust Apple platform Users trust us Why we should think more about security? #mobiconf @vixentael
7. Most users trust sensitive data to our app regardless of how well we protect it #mobiconf @vixentael
8. #mobiconf @vixentael abstract app in a vacuum
10. security security is set of ultimatum rules abstract app in a vacuum #mobiconf @vixentael
11. security is set of ultimatum rules abstract app in a vacuum real apps, real ecosystems #mobiconf @vixentael
12. App Flow App Features Code User Problem #mobiconf @vixentael
13. Risk Threat Model Secure Methods Secure Implemen- tations Libs/ Code App Flow App Features Code User Problem #mobiconf @vixentael
14. #mobiconf @vixentael It is secure
15. It is secure It is secure against certain threat model and adversary #mobiconf @vixentael
16. https://twitter.com/mubix/status/745403991475904513 #mobiconf @vixentael
17. Risk Model & Threat Model create demands for security #mobiconf @vixentael
18. Real world risks Data leak/ data tampering Reputation risks Legal responsibility Financial damage #mobiconf @vixentael
19. Risk impact Data is used/sold by someone Data is tampered and you’re operating on adversary’s plan Identity/auth is used elsewhere DL DT data leakage data tampering identity theft #mobiconf @vixentael
20. Risk prevention data leakage data tampering identity theft confidentiality (secrecy) integrity authentication #mobiconf @vixentael
21. Risk prevention (for us) - Encryption w/ secret or PKC - Limit access - Signed encryption - Protected transport with trust and integrity - Authenticated encryption - Action authentication confidentiality (secrecy) integrity authentication #mobiconf @vixentael
22. Encryption is letting only those who know the secret to access the data, no matter how they alter the code or the system (read Kerckhoffs's desideratum) #mobiconf @vixentael
23. Trust model is whose secrets you trust in a security system #mobiconf @vixentael
24. Everything is broken Trust no one, but the user #mobiconf @vixentael
25. Risks Trust model Threat model Methods and instruments #mobiconf @vixentael
26. Now let’s apply this to the real app #mobiconf @vixentael
28. What user hero has? secret data paranoia pa55w0rd trust #mobiconf @vixentael
29. secret data paranoia pa55w0rd trust tin foil hat! #mobiconf @vixentael What user hero has?
30. for saving your important docs during trips Let’s make an app!
31. Take pictures of important documents App functionality Store them on server Lets user see them #mobiconf @vixentael
32. Architecture and flow user app network server storage #mobiconf @vixentael
33. Threats we can handle T2 T3 passive MitM active MitM T1/T4 data loss/ tampering #mobiconf @vixentael
34. More complicated.. 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 malicious dependency T19 storing keys with data T20 weak cipher random generator abuse T21 T2 T3 passive MitM active MitM T1/T4 data loss/ tampering T16 misconfigured access T17 T18 unattended backups #mobiconf @vixentael
35. Back to threats we can handle T2 T3 passive MitM active MitM T1/T4 data loss/ tampering #mobiconf @vixentael
36. #mobiconf @vixentael Threats: T1/T4 attacker steals stored data or tampers it
37. 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. #mobiconf @vixentael
38. #mobiconf @vixentael Threats: T2 attacker captures network traffic (passive MitM)
39. attacker captures network traffic (passive MitM) Public Key Cryptography, ephemeral keys Asymmetric crypto for sending data. Ephemeral keys to avoid decrypting accumulated traffic if keys are leaked/cracked. Threats: T2 Protection #mobiconf @vixentael
40. Threats: T3 attacker redirects traffic and pretends to be remote party (active MitM) #mobiconf @vixentael
41. attacker redirects traffic and pretends to be remote party (active MitM) Public Key Cryptography, certificate pinning Asymmetric crypto for sending data. Check server certificate to make sure it matches with pinned one. Threats: T3 Protection #mobiconf @vixentael
42. Protection methods Secret Key Crypto PKC + ephem. keys T2 T3 passive MitM active MitM T1/T4 data loss/ tampering PKC + cert. pinning #mobiconf @vixentael
43. Public Key Crypto Perfect Forward Secrecy Secret Key Crypto Authenticated Encryption Certificate Pinning Trust model Trust the user only #mobiconf @vixentael
44. Relationship model plain data symmetric encryption PKC + eph. keys symmetric encryption PKC + eph. keys ZKP ZKP #mobiconf @vixentael
45. #mobiconf @vixentael …what if trapdoor function fails? …what if key exchange is flawed? add more paranoia! …what if we suspect that server is fraudulent?
46. …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! #mobiconf @vixentael
47. 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 #mobiconf @vixentael
48. #mobiconf @vixentael So, data model: Secret key (SK) = KDF(user password)
49. #mobiconf @vixentael Sensitive Data (SD) — passport photo Metadata (M1) — timestamp+CRC of photo Metadata (M2) — name of photo (user input) Secret key (SK) = KDF(user password) So, data model:
50. So, data model: Secret key (SK) = KDF(user password) Sensitive Data (SD) — passport photo Metadata (M1) — timestamp+CRC of photo Metadata (M2) — name of photo (user input) 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. #mobiconf @vixentael
51. Pwd Key + Data model SD M1 M2 MKP SKP SK #mobiconf @vixentael
52. User-centric trust Pwd MKP SKP SK symmetric encryption PKC + eph. keys KDF() Rand PKC + eph. keys Rand #mobiconf @vixentael
53. App Flows
54. 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 #mobiconf @vixentael
55. #mobiconf @vixentael 1. Encrypt photo EncData = SCell_wrap(SD, SK, Context=M2) 2. Store EncData, M1, M2 in Local Store 3. Drop SD, SK from memory prepare data Send photo to server
56. 1. Encrypt photo EncData = SCell_wrap(SD, SK, Context=M2) 2. Store EncData, M1, M2 in Local Store 3. Drop SD, SK from memory prepare data 4. Connect to Server: Session = SSession(Priv(MKP), Pub(SKP)) 5. Send EncData, M1, M2 via Session transfer data Send photo to server #mobiconf @vixentael
57. 6. Receive OK 7. Terminate Session 8. Mark EncData in Local Store as Synced 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) 2. Store EncData, M1, M2 in Local Store 3. Drop SD, SK from memory prepare data transfer data terminate session Send photo to server
58. Send photo to server 6. Receive OK 7. Terminate Session 8. Mark EncData in Local Store as Synced 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) 2. Store EncData, M1, M2 in Local Store 3. Drop SD, SK from memory prepare data transfer data terminate session
59. Read photo from server 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 #mobiconf @vixentael
60. 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) initialize connection transfer data #mobiconf @vixentael
61. 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 Read photo from server
62. 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
63. Code samples
64. Generate keys // Generating EC keys guard let keyGeneratorEC: TSKeyGen = TSKeyGen(algorithm: .EC) else { print("Error occurred while initializing object keyGeneratorEC”) return } let privateKeyEC: NSData = keyGeneratorEC.privateKey let publicKeyEC: NSData = keyGeneratorEC.publicKey https://github.com/cossacklabs/themis/wiki/Swift-Howto https://github.com/cossacklabs/themis/tree/master/docs/examples/Themis-server/swift #mobiconf @vixentael
65. let masterKeyData: NSData = self.generateMasterKey() guard let cellSeal: TSCellSeal = TSCellSeal(key: masterKeyData) else { print("Error occurred while initializing object cellSeal", #function) return } let message: String = "All your base are belong to us!" let context: String = "For great justice" var encryptedMessage: NSData = NSData() do { // context is optional parameter and may be ignored encryptedMessage = try cellSeal.wrapData(message.dataUsingEncoding(NSUTF8StringEncoding), context: context.dataUsingEncoding(NSUTF8StringEncoding)) print("encryptedMessages = \(encryptedMessage)") } catch let error as NSError { print("Error occurred while encrypting \(error)", #function) return } Symmetric encryption https://github.com/cossacklabs/themis/wiki/Swift-Howto https://github.com/cossacklabs/themis/tree/master/docs/examples/Themis-server/swift #mobiconf @vixentael
66. Symmetric decryption let masterKeyData: NSData = self.generateMasterKey() guard let cellSeal: TSCellSeal = TSCellSeal(key: masterKeyData) else { print("Error occurred while initializing object cellSeal", #function) return } let message: String = "All your base are belong to us!" let context: String = "For great justice" do { let decryptedMessage: NSData = try cellSeal.unwrapData(encryptedMessage, context: context.dataUsingEncoding(NSUTF8StringEncoding)) let resultString: String = String(data: decryptedMessage, encoding: NSUTF8StringEncoding)! print("decryptedMessage = \(resultString)") } catch let error as NSError { print("Error occurred while decrypting \(error)", #function) return } https://github.com/cossacklabs/themis/wiki/Swift-Howto https://github.com/cossacklabs/themis/tree/master/docs/examples/Themis-server/swift #mobiconf @vixentael
67. Initialize Session guard let clientIdData: NSData = kClientId.dataUsingEncoding(NSUTF8StringEncoding), let clientPrivateKey: NSData = NSData(base64EncodedString: kClientPrivateKey, options: .IgnoreUnknownCharacters) else { print("Error occurred during base64 encoding", #function) return } self.transport = Transport() self.transport?.setupKeys(kServerId, serverPublicKey: kServerPublicKey) self.session = TSSession(userId: clientIdData, privateKey: clientPrivateKey, callbacks: self.transport) https://github.com/cossacklabs/themis/wiki/Swift-Howto https://github.com/cossacklabs/themis/tree/master/docs/examples/Themis-server/swift #mobiconf @vixentael
68. Encrypt/Decrypt Session messages var encryptedMessage: NSData do { guard let wrappedMessage: NSData = try self.session?.wrapData(message.dataUsingEncoding(NSUTF8StringEncoding)) else { print("Error occurred during wrapping message ", #function) return } encryptedMessage = wrappedMessage } catch let error as NSError { print("Error occurred while wrapping message \(error)", #function) completion(data: nil, error: error) return } //... do { guard let decryptedMessage: NSData = try self.session?.unwrapData(data), let resultString: String = String(data: decryptedMessage, encoding: NSUTF8StringEncoding) else { throw NSError(domain: "com.example", code: -3, userInfo: nil) } completion(data: resultString, error: nil) } catch let error as NSError { print("Error occurred while decrypting message \(error)", #function) completion(data: nil, error: error) return } https://github.com/cossacklabs/themis/tree/master/docs/examples/Themis-server/swift #mobiconf @vixentael
69. Make it tough even more
70. one password per photo Enforce app security user inputs password every time on photo access #mobiconf @vixentael
71. Use ZKP to prove that Server has M2 from any previous transfer Repeated auth #mobiconf @vixentael Received items Synced items D1 D2 Dn ... D1 D2 Dn ...
72. Repeated auth request ZKP(M1i) select any Di, where Di = (EncData, M1, M2) prove M2i transfer Dn+1 compare M2i, on success Received items Synced items D1 D2 Dn ... D1 D2 Dn ... #mobiconf @vixentael
73. The worst case scenario attacks
74. Active MitM without hacking the server: The worst scenario attacks Attacker does not have SKP. SecureSession initialization fails. App doesn’t start transfer data to server at all. Results: #mobiconf @vixentael
75. Best active MitM + hack server: The worst scenario attacks Attacker seizes SKP from Server and pretends to be normal server by DNS spoofing or routing redirection. Results: Accumulates useless M1, M2 and lousy EncData. #mobiconf @vixentael
76. The worst scenario attacks Denial of Service: Attacker floods server with requests / tons of data. Results: Server may be flooded. Monitor all the things! #mobiconf @vixentael
77. Finalizing…
78. * hardware support (AES) Crypto is very expensive!!11 https://www.cossacklabs.com/benchmarking-secure-comparator.html * scripted language and questionable frameworks affect performance as much as running the expensive math, if not more * endorse crypto everywhere to make it more cheap :) (it is not) #mobiconf @vixentael
79. 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 #mobiconf @vixentael
80. https://www.blackhat.com/docs/us-16/materials/us-16-Krstic.pdf Apple enforces good security practices
81. ̣ 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! #mobiconf @vixentael
82. My other security talks https://medium.com/@vixentael/upgrading-approaches-to-the-secure- mobile-architectures-7a8fcb10d28a#.ffbsjwqx6 Upgrading Approaches to the Secure Mobile Architectures Data Protection For Mobile Client-Server Architectures https://medium.com/stanfy-engineering-practices/data-protection-for- mobile-client-server-architectures-6e6dcabd871a https://speakerdeck.com/vixentael/users-data-security-in-ios-applications Users' data security in iOS applications #mobiconf @vixentael
83. 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 #mobiconf @vixentael
84. 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 https://medium.com/@9gunpi/side-effects-of-pegasus-malware-32c9a112ec1c Side effect of Pegasus malware #mobiconf @vixentael
85. @vixentael The last slide Lead Developer at stanfy.com Core Contributor at themis/ cossacklabs.com Need help? Talk to me :)