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@fmaelbrancke @tegbird Android Application Security Filip Maelbrancke Tegbir Dhillon

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Application security ANDROID FOR DEVELOPERS

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WE Filip Maelbrancke Consultant @ iDA MediaFoundry ! ! ! Tegbir Dhillon Team lead @ ING Bank Belgium

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demo app http://git.io/devoxx-2013-android-app-sec CODE

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Security The only system that is truly secure is one that is switched off and unplugged, locked in a titanium-lined safe, buried in a concrete bunker, and surrounded by nerve gas and very highly-paid armed guards. Even then, I wouldn't stake my life on it. “ ” Gene Spafford

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Security = managing risk Cri$cality/Impact High  Risk Low  Risk Asset Medium  Risk Exploitability Low  Risk Vulnerability Medium  Risk M edium  Risk Probability Low  Risk   Threat

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

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Always out Vulnerability / Exploitability ! • Stolen • Forgotten • Lost • Weak pins • Use of open public WiFi

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Everyone uses it

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Everyone uses it

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Android security application sandbox Each app runs with its own userID

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traditional System resources File system Network System resource App 1 App 2 App ... UID = 1 2 3 4 5 starts permissions UID = 1 2 3 4 5

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Android sandbox App1$$ Linux$UID:$ 12345$ Resources$ UID:12345$ DB$ Network$ File$ resources$ Permissions$$ UID:12345$ Sandbox$ App2$$ Linux$UID:$ 56789$ Resources$ UID:56789$ DB$ Network$ Files$ resources$ Permissions$ UID:56789$ $ Sandbox$ App1$$ App2$$

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shared user id App1$$ App2$$ App1$$ Linux$UID:$ 10160$ Resources$ UID:10160$ DB$ Network$ File$ Resources$ DB$ Network$ File$ resources$ Permissions$$ UID:10160$ App1$$ Linux$UID:$ 10160$ Sandbox$

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Permission types Permission) Permission)Level) Normal) Permission)Level) dangerous) Permission)Level) Signature) Permission)Level) SignatureOrSystem)

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Signing tips Secure your private key Strong passwords Four eyes principle Keep key-store in safe place Provide geographic redundancy

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

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Security APP HARDENING DATA NETWORK SERVICES

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Securing the app JAVA CLASS DEX

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Obfuscation

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Proguard obfuscate optimize Shrink

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proguard obfuscation

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proguard configuration

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proguard Beware!

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proguard loggingwrapper

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proguard configuration

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proguard BEtter

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reverse engineer

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reverse engineer TOOLS ! • Apktool • Dex2jar • Apk to Java !

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reverse engineer code

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

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

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TAMPER DETECTION

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

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INSTALLER PLAY STORE INSTALLER

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debugger Debugger check

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debugger Debugger check

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emulator EMULATOR check

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

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SIGNING KEY Valid signing key

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rooted device root detection ! • Check typical apps / files • Check keys • … !

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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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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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keylogger

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encryption

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

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KEYCHain? Keystore provider ! • Since Android 4.3 • Can be hardware-backed https://github.com/nelenkov/android-keystore Nikolay Elenkov

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network

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Secure communication channel use https Use SSL / TLS ! • Confidentiality • Authentication ! VALIDATION Hostname verification ! Certificate pinning

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secure communication channel hostname verification

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Trustmanager StrongTrustManager ! • Validate whole certificate chain • Debian certificate store !

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self-signed cert

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self-signed cert don’t trust all!

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

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

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

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

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HOW TO CONTACT TWITTER: @fmaelbrancke EMAIL: [email protected] THANK YOU TWITTER: @tegbird EMAIL: [email protected]