Android security (for developers) at jDays 2015

Slides from the 'Android Security For Developers' session at jDays 2015 in Göteborg, Sweden

Transcript

1. Android
   security
   FOR DEVELOPERS
   FILIP MAELBRANCKE
   

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2. Your host
   Filip Maelbrancke
   Consultant @ AppFoundry
   filip.maelbrancke@appfoundry.be
   @fmaelbrancke
   

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4. X
   

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5. Security = managing risk
   ASSET VULNERABILITY
   THREAT
   

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6. Security = managing risk
   ASSET VULNERABILITY
   THREAT
   

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7. All in one device
   Increases threat
   proBability
   • GPS
   • Contacts
   • Camera
   • Email (work)
   • Wallet
   

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8. Always out
   Vulnerability / Exploitability
   • Stolen
   • Forgotten
   • Lost
   

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9. Everyone uses it
   Vulnerability /
   Exploitability
   • Weak pins
   • Use of open public WiFi
   

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10. Android security MODEL
    Game X
    Game Y
    System
    Contacts Email Google Play
    Verify app signature
    App sandbox
    Permissions
    application isolation
    

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11. typical mobile app
    MOBILE APPLICATION
    UI
    LOCAL
    STORAGE
    REMOTING
    LAYER
    REMOTE
    API
    COMMUNICATION
    CHANNEL
    

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12. Security
    APP HARDENING DATA NETWORK SERVICES
    

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14. Securing the app
    JAVA
    CLASS
    DEX
    

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15. reverse engineer
    

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16. obtain apk
    adb backup -apk be.myapp
    ADB backup app
    Titanium, Astro, Helium, …
    adb shell
    pm list packages -f
    adb pull /data/app/be.myapp-1.apk
    

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17. apk structure
    apk = zip
    APK
    AndroidManifest
    classes.dex
    Resources
    

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18. reverse engineer
    TOOLS
    • Apktool
    • Dex2jar
    • JADX
    

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19. Reverse engineer
    smali / baksmali
    apktool low level
    disassembled Dex bytecode
    code
    code can be modified
    recompile / resign
    

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20. Reverse engineer
    apktool d myapp.apk
    

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21. Reverse engineer
    

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22. Reverse engineer
    

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23. Reverse engineer
    convert .dex file to a .jar with java
    bytecode
    DEX2JAR dex -> java
    java decompiler
    code
    very readable
    

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24. Reverse engineer
    

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25. Reverse engineer
    command-line / GUI tools
    JADX
    

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26. Reverse engineer
    Jeb Decompiler
    PAID dex -> java
    native dex decompiler
    

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27. reverse engineer
    

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28. Obfuscation
    

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29. Proguard
    obfuscate
    optimize
    Shrink
    

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30. proguard
    obfuscation
    

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31. proguard
    

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32. proguard
    configuration
    

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33. other techniques
    If possible, run code at server!
    server String encryption
    Hide sensitive strings eg “Secure”
    Native code
    Java Native Interface
    reflection
    Proxy
    Introduces indirection
    Class encryption
    Use DexGuard
    

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34. dexguard
    Same config
    proguard++ Commercial
    Good value for the money
    Tamper checks
    

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35. dexguard
    

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36. proguard tips
    Test!
    release build Mapping.txt
    Save!
    Crash?
    Supported on Crashlytics, Crittercism, ...
    

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37. TAMPER DETECTION
    

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38. Environment
    1.installer
    2.debugger / emulator
    3.BINARY
    Validation
    Tamper detection / protection
    

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39. INSTALLER
    PLAY STORE INSTALLER
    

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40. debugger
    Debugger check
    

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41. debugger
    Debugger check
    

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42. emulator
    EMULATOR check
    

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43. SIGNING KEY
    Valid signing key
    • SHA1 of signing cert
    • Embed
    • Check with runtime signature
    

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44. SIGNING KEY
    Valid signing key
    

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45. rooted device
    root detection
    • Check typical apps / files
    • Check keys
    • /system r/w
    

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47. Data protection
    laws that govern data protection
    Law obligation
    beyond legal obligations ➪ moral
    obligation
    

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48. local Data protection
    Avoid it if you can
    Avoid External storage
    Avoid external storage for sensitive
    information
    For critical info
    set android:saveEnabled="false"
    Backup
    set android:allowBackup=false
    proper permissions
    MODE_PRIVATE with files
    

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49. local Data protection
    getWindow().setFlags(LayoutParams.FLAG_SECURE,
    LayoutParams.FLAG_SECURE);
    avoid screen shots LOGOUT on inactivity
    if usability allows and clear the cached
    information
    

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50. keylogger
    

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51. Android not enough?
    rooted devices
    internal storage full disk crypto
    brute forcing
    

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52. CRYPTO
    

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53. crypto in Android = JCA
    APP
    JCA (Java Cryptography Architecture)
    Provider Provider
    Message Digest
    Key Generation
    Digital Signature
    ...
    

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54. JCA
    Bouncy Castle Android OpenSSL
    APP
    JCA (Java Cryptography Architecture)
    Harmony
    

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55. bouncy castle
    Android = subset of upstream release
    cut-down CONSISTENT
    Consistent crypto across Android
    versions
    MINIMAL change
    github.com/rtyley/spongycastle
    Spongy castle
    Repackage of Bouncy Castle for Android
    

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56. GPS dynamic Security provider
    Since Google Play Services 5
    google play services replacement
    for the platform’s bundled provider
    security patches
    rapid delivery
    frequently updated
    by Google
    

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57. dynamic security provider
    setup
    dependencies {
    compile 'com.google.android.gms:play-services:6.1.+'
    }
    

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58. dynamic security provider
    setup
    

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59. Android security providers
    

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60. Conscrypt
    

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61. encryption libs
    SQLCipher
    sqlcipher.net
    • Modified version of SQLite
    • AES-256 encryption
    • Drop-in replacement
    iocipher
    guardianproject.info/code/iocipher
    Virtual encrypted disk
    

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62. key management
    Store along with the data
    (file private to the app)
    Store Embed
    Embed in source code
    (obfuscated ?)
    EASY TO EXTRACT
    

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63. key management
    don’t store
    Don’t store the key on the device
    Have it entered each time necessary
    Store
    In systems service
    SOLUTIONS
    

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64. key derivation
    Long random strings of bits
    encryption keys people vs keys
    Users are familiar with passwords
    Crypto algo
    PBKDF2WithHmacSHA1
    password based encryption
    Generate strong crypto keys based on
    humanly-manageable passwords
    

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65. proper key derivation
    Using a salt protects from table-
    assisted / pre-computed dictionary
    attacks
    SALT key stretching
    Repeat the key derivation operation
    multiple times to produce the final key
    Slows down brute force attacks
    

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66. key derivation
    https://github.com/nelenkov/android-pbe
    http://nelenkov.blogspot.jp/2012/04/using-password-based-encryption-on.html
    Nikolay Elenkov
    

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67. KEYCHain?
    Keystore provider
    • Since Android 4.3
    • Can be hardware-backed
    

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68. Android keystore
    available from Android 4.3
    java security provider APP
    can generate & save private keys
    keys
    private to each app
    

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69. keystore
    

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70. keystore
    

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71. network
    

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72. Secure communication channel
    use https
    Use SSL / TLS
    • Confidentiality
    • Authentication
    VALIDATION
    Hostname verification
    Certificate pinning
    http://android-ssl.org/
    

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73. secure communication channel
    hostname verification
    

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74. SSL certificates
    CA issued, Android recognized CA issued
    behaviour change
    custom TrustManager
    self-signed certificates
    

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75. certificate authorities
    

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76. certificate authorities
    https://bluebox.com/blog/technical/questioning-the-chain-of-trust-investigations-into-
    the-root-certificates-on-mobile-devices
    

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77. Trustmanager
    StrongTrustManager
    • Validate whole certificate chain
    • Debian certificate store
    

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78. self signed cert
    

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79. anti-pattern
    don’t trust all!
    

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80. Self-signed cert
    import in your app
    certificate custom trustmanager
    no man-in-the-middle attacks
    

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81. certificate pinning
    with expected certificate /
    public key
    Associate host hashing
    anonymize certificate / public
    key
    

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82. certificate pinning
    echo | openssl s_client -connect host:443 2>&1 | sed
    -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' >
    mycertificate.pem
    get certificate (openssl) embed in application
    /res/raw
    Custom trustmanager
    Based on keystore
    Load into keystore
    SSL context
    Init SSL context with TrustManager
    https://developer.android.com/training/articles/security-ssl.html
    

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83. NOGOTOFAIL
    Test tool man in the middle server
    attempts to inject
    attacks into connections
    checks
    https://github.com/google/nogotofail
    

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85. Securing services
    Controls
    • Kill switch for specific
    functionality
    • Server downtime communication
    • Mandatory update mechanism
    

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86. securing services
    Backend
    REST and APIs can have similar
    vulnerabilities to web applications
    mitigate
    follow OWASP top 10
    

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88. Effective security
    Using CryptoLint, we performed a study on cryptographic
    implementations in 11,748 Android applications. Overall we find that
    10,327 programs – 88% in total – use cryptography inappropriately.
    The raw scale of misuse indicates a widespread misunderstanding of
    how to properly use cryptography in Android development.
    “
    ”
    

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89. effective security
    hardcoded passphrases manually seeded SecureRandom
    insufficient key generation iterations
    hardcoded salts
    non-random initialization vectors
    

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90. security testing
    Static analysis
    Manual
    code review design review
    Analysis
    Static
    Dynamic
    Penetration testing
    

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91. suggested reading
    Android Security Cookbook

    Keith Makan / Scott Alexander-Bown (9781782167167)
    Android Security Internals 

    Nikolay Elenkov (9781593275815)
    Android Hacker’s Handbook

    Joshua J. Drake et al. (9781118608647)
    Application Security for the Android platform

    Jeff Six (9781449315078)
    

    

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92. suggested reading
    developer.android.com

    https://developer.android.com/training/articles/security-tips.html 

    https://source.android.com/devices/tech/security/
    OWASP

    https://www.owasp.org/index.php/OWASP_Mobile_Security_Project
    Google+ community 

    Android security discussions
    Blogs

    http://nelenkov.blogspot.com.tr/…

    

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93. Questions?
    Filip Maelbrancke
    Consultant @ AppFoundry
    filip.maelbrancke@appfoundry.be
    @fmaelbrancke
    

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