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Consulthink @ GDG Meets U - L'Aquila2014 - Codelab: Android Security -Il key management

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This document discusses Android key management and cryptography. It covers symmetric and asymmetric encryption algorithms like AES and RSA. It describes using the Android Keystore to securely store cryptographic keys and how PBKDF2 can be used to derive keys from passwords. It also demonstrates how apps can be reversed to extract hardcoded keys and discusses more secure alternatives like storing keys on a server.

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Android Security Key Management Roberto Piccirillo (r.piccirillo@mseclab.com) Roberto Gassirà (r.gassira@mseclab.com)
Android Security Key Management Roberto Piccirillo ● Senior Security Analyst - Mobile Security Lab ○ Vulnerability Assessment (IT, Mobile Application) ○ Hijacking Mobile Data Connection ■ BlackHat Europe 2009 ■ DeepSec Vienna 2009 ■ HITB Amsterdam 2010 ○ Android Secure Development @robpicone
Android Security Key Management Roberto Gassirà ● Senior Security Analyst - Mobile Security Lab ○ Vulnerability Assessment (IT, Mobile Application) ○ Hijacking Mobile Data Connection ■ BlackHat Europe 2009 ■ DeepSec Vienna 2009 ■ HITB Amsterdam 2010 ○ Android Secure Development ● IpTrack Developer @robgas
Android Security Key Management Agenda ● Cryptography in Mobile Application ● CryptoSystem ● Crypto in Android ● Symmetric Encryption ● Symmetric Key Management ● Keychain e AndroidKeyStore ● Tipologie di AndroidKeyStore
Android Security Key Management Requirements ● A computer ● Eclipse with ADT Plugin 22.3.0 ● SDK Android 4.4 ( API 19 rev 2) ● Android SDK Build-tools 19
Android Security Key Management Cryptography in Mobile Applications ● Protect data ○ Sensitive data ○ Data on /sdcard ○ Cryptographic material ● Exchange data securely ○ Documents ○ Mail ○ SMS ○ Session Keys ● Digital Signature ○ Documents ○ Mail
Android Security Key Management Key Management "Key management is the management of cryptographic keys in a cryptosystem."
Android Security Key Management CryptoSystem "refers to a suite of algorithms needed to implement a particular form of encryption and decryption" ● ● Two types of encryption: ○ Symmetric Key Algorithms ■ Identical encryption key for encryption/decryption ■ AES, Blowfish, DES, Triple DES ○ Asymmetric Key Algorithms ■ Different key for encryption/decryption ■ RSA, DSA, ECDSA
Android Security Key Management Ciphers ● Two types of ciphers: ○ Block: Process entire blocks of fixed-length groups of bits at a time ( padding may be required) ○ Stream: Process single byte at a time ( no padding ) ● Block Cipher modes of operation ○ ECB: each block encrypted independently ○ CBC, CFB, OFB: the previous block of output is used to alter the input blocks before applying the encryption algorithm starting from a IV ( initialization vector )
Android Security Key Management Crypto in Android ● Based on JCA ( Java Cryptographic Architecture) provides API for: ● Encryption/Decryption ● Digital signatures ● Message digests (hashes) ● Key management ● Secure random number generation ● “Provider” Architecture with CSP ● Bouncy Castle is Android default CSP
Android Security Key Management Bouncy Castle Android Version ● Customized: ○ Some services and API removed ● Varies between Android versions ● Fixed only in the latest versions ● Solution: Spongy Castle ● Repackage of Bouncy Castle ● Supports more cryptographic options ● Up-to-date ● Not vulnerable to the Heartbleed Bug (CVE-2014-0160)
Android Security Key Management Set Spongy Castle ● Include Libs: ● Enable at Application Level:
Android Security Key Management GC overhead limit exceeded ● Solution: modify eclipse.ini with: -Xms256m -Xmx1024m -XX:MaxPermSize=1024m
Android Security Key Management Step 1 Enabling SpongyCastle https://github.com/mseclab/gdgmeetsu2014-symmetric-demo-step1.git
Android Security Key Management Import Project from https://github.com/mseclab 1 2 3 4
Android Security Key Management Import Project from https://github.com/mseclab 5 6 7
Android Security Key Management Import Project from https://github.com/mseclab 8 9 10 https://github.com/mseclab/droidconit2014-symmetric-demo-step3.git
Android Security Key Management The project cannot be built... 1 2 3
Android Security Key Management Cipher Object Secret Key Specification Cipher getInstance Cipher Init Cipher Final
Android Security Key Management SecretKey Specification javax.crypto.spec.SecretKeySpec ● SecretKeySpec specifies a key for a specific algorithm SecretKeySpec skeySpec = new SecretKeySpec(key, "AES"); Topic of this workshop Cryptographic Algorithm
Android Security Key Management Cipher GetInstance javax.crypto.Cipher ● Provides access to implementations of cryptographic ciphers for encryption and decryption Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding”,“SC”); Trasformation (describes set of operation to perform): • algorithm/mode/padding • algorithm Provider ( SpongyCastle )
Android Security Key Management Cipher Init javax.crypto.Cipher ● Initializes the cipher instance with the specified operational mode, key and algorithm parameters. cipher.init(Cipher.DECRYPT_MODE, keySpec, new IvParameterSpec(iv)); Operational Mode: • ENCRYPT_MODE • DECRYPT_MODE • WRAP_MODE • UNWRAP_MODE SecretKeySpec Specify Cipher Algorithm parameters ( IV for CBC )
Android Security Key Management Cipher Final javax.crypto.Cipher ● Finishes a multi-part transformation (encryption or decryption) byte[] encryptedText = cipher.doFinal(clearText.getBytes()); Encrypted Text in byte ClearText in bytes
Android Security Key Management Step 2 Encryption Example https://github.com/mseclab/gdgmeetsu2014-symmetric-demo-step2.git
Android Security Key Management SecureRandom java.security.SecureRandom ● Cryptographically secure pseudo-random number generator SecureRandom secureRandom = new SecureRandom(); Default constructor uses the most cryptographically strong provider available ● Seeding SecureRandom is dangerous: ○ Not Secure ○ Output may change
Android Security Key Management Some SecureRandom Thoughts... ● Android security team discovered a JCA improper PRNG initialization in August 2013 ● Applications invoking system-provided OpenSSL PRNG without explicit initialization are also affected ● Key Generation, Signing or Random Number Generation not receiving cryptographically strong values ● Developer must explicitly initialize the PRNG PRNGFixes.apply()
Android Security Key Management KeyGenerator keyGenerator = KeyGenerator.getInstance("AES”,“SC”); keyGenerator.init(outputKeyLength, secureRandom); SecretKey key = keyGenerator.generateKey(); Generate Secret Key javax.crypto.KeyGenerator ● Symmetric cryptographic keys generator API Specify Key Size Algorithm and Provider Key to use in Cipher.init()
Android Security Key Management Key Management: Store on device ● Protected by Android Filesystem Isolation ● Plain File ● SharedPreferences ● Keystore File (BKS, JKS) ● More secure with Phone Encryption ● Store safely ○ MODE_PRIVATE flag ○ Use only internal storage /data/data/app_package
Android Security Key Management Key Management: Store on device ● Device Rooted?
Android Security Key Management Step 3 Rooted device demo https://github.com/mseclab/gdgmeetsu2014-symmetric-demo-step3.git
Android Security Key Management Key Management: Store in App ● Uses static keys or device specific information at run-time (IMEI, mac address, ANDROID_ID) ● Android app can be easily reversed ( live demo ) ● Hide with Code obfuscation ● Security by Obscurity is never a good idea...
Android Security Key Management Key Management: Store in App ● unzip: APK -> DEX ● dex2jar: DEX -> JAR ● JD-GUI: JAR -> Source
Android Security Key Management Reversing Demo
Android Security Key Management Key Management: PBKDF2 ● Password Based Key Derivation Function (PKCS#5) ● Variable length password in input ● Fixed length key in output ● User interaction required ● Params: ○ Password ○ Pseudorandom Function ○ Salt ○ Number of iteration ○ Key Size
Android Security Key Management KeySpec keySpec = new PBEKeySpec(password.toCharArray(), salt, NUM_OF_ITERATIONS, KEY_SIZE); SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance(PBE_ALGORITHM); encKey = secretKeyFactory.generateSecret(keySpec); Key Management: PBKDF2 javax.crypto.spec.PBEKeySpec ● PBE Key specification and generation A good PBE algorithm is PBKDF2WithHmacSHA1 User Password N. >= 1000
Android Security Key Management SecretKeyFactory factory; if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) // Use compatibility key factory -- only uses lower 8-bits of passphrase chars factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1And8bit"); else if (Build.VERSION.SDK_INT >= 10) // Traditional key factory. Will use lower 8-bits of passphrase chars on // older Android versions (API level 18 and lower) and all available bits // on KitKat and newer (API level 19 and higher) factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1"); else // FIX for Android 8,9 factory = SecretKeyFactory.getInstance("PBEWITHSHAAND128BITAES-CBC-BC"); SecretKeyFactory API in Android 4.4
Android Security Key Management Step 4 PBE Example https://github.com/mseclab/gdgmeetsu2014-symmetric-demo-step4.git
Android Security Key Management Key Management: Other solutions ● Store on server side ● Internet connection required ● Use trusted and protected connections (HTTPS, Certificate Pinning) ● Store on external device ○ NFC Java Card (NXP J3A081) ○ Smartcard ○ USB PenDrive ○ MicroSD with secure storage ● AndroidKeyStore???
Android Security Key Management Asymmetric Algorithms ● Public/Private Key ○ Public Key -> encrypt/verify signature ○ Private Key -> decrypt/sign ● Advantages: ○ Public Key distribution is not dangerous ● Disadvantages: ○ Computationally expensive ● Usually used with PKI (Public Key Infrastructure for digital certificates)
Android Security Key Management Public-key Applications ● Can classify uses into 3 categories: ○ Encryption/Decryption (provides confidentiality) ○ Digital Signatures (provides authentication and Integrity) ○ Key Exchange (of session keys) ● Some algorithms are suitable for all uses (RSA), others are specific to one
Android Security Key Management PKCS for Asymmetric Algorithms ● PKCS is a group of public-key cryptography standards published by RSA Security Inc ● PKCS#1 (v.2.1) ○ RSA Cryptography Standard ● PKCS#3 (v.1.4) ○ Diffie-Hellman Key Agreement Standard ● PKCS#8 (v.1.2) ○ Private-Key Information Syntax Standard ● PKCS#10 (v.1.7) ○ Certification Request Standard ● PKCS#12 (v.1.0) ○ Personal Information Exchange Syntax Standard
Android Security Key Management Android: RSA KeyPairGenerator kpg = KeyPairGenerator.getIstance(”RSA"); Java.security.KeyPairGenerator ● KeyPairGenerator is an engine capable of generating public/private keys with specified algorithms Cryptographic Algorithm
Android Security Key Management Available Providers for RSA Algorithm KeyPairGenerator.getInstance(”RSA”,”SEC_PROVIDERS”); Java.security.KeyPairGenerator ● Different security providers could be used (could change for different OS versions) “AndroidOpenSSL” “BC” “AndroidKeyStrore” Version 1.0 Version 1.49 Version 1.0
Android Security Key Management ● KeySize – 1024,2048,4096 bits KeyPairGenerator: Initialization and Randomness KeyPairGenerator kpg = KeyPairGenerator.initialize(2048); Java.security.KeyPairGenerator ● KeyPairGenerator initialization with the key size Key Size
Android Security Key Management KeyPairGenerator: Initialization and Randomness KeyPairGenerator kpg = KeyPairGenerator.initialize(2048,sr); Java.security.KeyPairGenerator, Java.security.SecureRandom ● KeyPairGenerator initialization with a SecureRandom SecureRandom sr = new SecureRandom();
Android Security Key Management Generating RSA Key Java.security.KeyPair ● KeyPair is a container for a public/private key generated by the KeyPairGenerator KeyPair keypair = kpg.genKeyPair() ● We can retrieve public/private keys from KeyPair Key public_key = kaypair.getPublic(); Key private_key = kaypair.getPrivate();
Android Security Key Management Using RSA Keys: cipher example Javax.crypto.Cipher ● Cipher provides access to implementation of cryptography ciphers for encryption and decryption Cipher cipher = Cipher.getInstance(“RSA”,”SEC_PROVIDER); Transformation “AndroidOpenSSL” “BC” “AndroidKeyStrore”
Android Security Key Management Using RSA Key: cipher example Javax.crypto.Cipher ● Encryption cipher.init(Cipher.ENCRYPT_MODE,public_key); ● Decryption byte[] encrypted_data= cipher.doFinal(“GDG-Meets-U2014”.getBytes()); cipher.init(Cipher.DECRYPT_MODE,private_key); byte[] decrypted_data= cipher.doFinal(cipherd_data);
Android Security Key Management Parameters of RSA Keys java.security.KeyFactory, java.security.spec, ● Retrieve RSA Key parameters using KeyFactory RSAPublicKeySpec rsa_public = keyfactory.getKeySpec(keypair.getPublic(), RSAPublicKeySpec.class); RSAPrivateKeySpec rsa_private = keyfactory.getKeySpec(keypair.getPrivate(), RSAPrivateKeySpec.class);
Android Security Key Management Extract Parameters of RSA Keys Java.security.spec.RSAPublicKeySpec, java.security.spec.RSAPrivateKeySpec ● Retrieved parameters can be stored BigInteger m = rsa_public.getModulus(); BigInteger e = rsa_public.getPublicExponent(); BigInteger d = rsa_private.getPrivateExponent(); Is Private
Android Security Key Management Step 1 RSA Keys Generaration https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
Android Security Key Management AndroidKeyStore ● Custom Java Security Provider available from Android 4.3 version and beyond ● An App can generate and save private keys ● Keys are private for each App ● 2048-bit key size (4.3), 1024-2048-4096-bit key size (4.4) can be stored ● ECDSA support added from Android 4.4
Android Security Key Management Key Management Evolution API LEVEL 14 API LEVEL 18 Global Level: KeyChain ( Public API ) App Level: KeyStore ( Closed API ) Global Level Only: Default TrustStore cacerts.bks (ROOTED device) Global Level: KeyChain ( Public API ) App Level and per User Level: AndroidKeyStore ( Public API )
Android Security Key Management AndroidKeyStore Storage ● Two kinds of storage ○ Hardware-backed (Nexus 7, Nexus 4, Nexus 5 :-) with OS >= 4.3) ○ Secure Element ○ TPM ○ TrustZone ○ Software only (Other devices with OS >= 4.3)
Android Security Key Management Type of Storage import android.security.KeyChain; if (KeyChain.isBoundKeyAlgorithm("RSA")) // Hardware-Backed else // Software Only
Android Security Key Management Certificate parameters Context cx = getActivity(); String pkg = cx.getPackageName(); Calendar notBefore = Calendar.getInstance(); Calendar notAfter = Calendar.getInstance(); notAfter.add(1, Calendar.YEAR); import android.security.KeyPairGeneratorSpec.Builder; Builder builder = new KeyPairGeneratorSpec.Builder(cx); builder.setAlias(“DEVKEY1”); String infocert = String.format("CN=%s, OU=%s", “DEVKEY1”, pkg); builder.setSubject(new X500Principal(infocert)); builder.setSerialNumber(BigInteger.ONE); builder.setStartDate(notBefore.getTime()); builder.setEndDate(notAfter.getTime()); KeyPairGeneratorSpec spec = builder.build(); Times parameters Self-Signed X.509 ● Common Name (CN) ● Subject (OU) ● Serial Number Generate certificate ALIAS to index the certificate
Android Security Key Management Generating Public/Private keys KeyPairGenerator kpGenerator; kpGenerator = KeyPairGenerator .getInstance("RSA", "AndroidKeyStore"); kpGenerator.initialize(spec); KeyPair kp; kp = kpGenerator.generateKeyPair(); Engine to generate Public/Private key Init Engine with: ● RSA Algorithm ● Provider: AndroidKeyStore Init Engine with certificate parameters After generation, the keys will be stored into AndroidKeyStore and will be accessible by ALIAS ● Generating Private/Public key
Android Security Key Management AndroidKeyStore Initialization keyStore = KeyStore.getInstance("AndroidKeyStore"); keyStore.load(null); Now we have the KeyStore reference that will be used to access to the Private/Public key by the ALIAS Should be used if there is an InputStream to load (for example the name of imported KeyStore). If not used the App will crash Get a reference to the AndroidKeyStore
Android Security Key Management Step 2 AndroidKeyStore Gen Keys https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
Android Security Key Management RSA Digital Signature ● Digital Signature ○ Authentication, Non-Repudiation and Integrity ○ RSA Private key to Sign ○ RSA Public Key to Verify KeyStore.Entry entry = ks.getEntry(“DEVKEY1”, null); byte[] data = “GDG-Meets-U 2014!”.getBytes(); Signature s = Signature.getInstance(“SHA256withRSA”); s.initSign(((KeyStore.PrivateKeyEntry) entry).getPrivateKey()); s.update(data); byte[] signature = s.sign(); String result = null; result = Base64.encodeToString(signature, Base64.DEFAULT); Access to Private/Public key identified by ALIAS Algorithm choice Private key to sign Signature and Base64 encoding
Android Security Key Management Verify RSA Digital Signature byte[] data = input.getBytes(); byte[] signature; signature = Base64.decode(signatureStr, Base64.DEFAULT); KeyStore.Entry entry = ks.getEntry(“DEVKEY1”, null); Signature s = Signature.getInstance("SHA256withRSA"); s.initVerify(((KeyStore.PrivateKeyEntry) entry).getCertificate()); s.update(data); boolean valid = s.verify(signature); Base64 decoding Access to the Private/Public key identified by ALIAS==DEVKEY1 Algorithm choice Public Key in certificate to verify signature TRUE == Verified FALSE== Not Verified
Android Security Key Management Step 3 AndroidKeyStore Sign/Verify https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
Android Security Key Management RSA Encryption ● Encryption ○ Confidentiality ○ RSA Public key to Encrypt ○ RSA Private key to Decrypt PublicKey publicKeyEnc = ((KeyStore.PrivateKeyEntry) entry) .getCertificate().getPublicKey(); String textToEncrypt = new String(”GDG-Meet-U-2014"); byte[] textToEncryptToByte = textToEncrypt.getBytes(); Cipher encCipher = null; byte[] encryptedText = null; encCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding"); encCipher.init(Cipher.ENCRYPT_MODE, publicKeyEnc); encryptedText = encCipher.doFinal(textToEncryptToByte); Access to Public key to encrypt ● Algorithm ● Encryption with Public key Ciphered
Android Security Key Management RSA Decryption Cipher decCipher = null; byte[] plainTextByte = null; decCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding"); decCipher.init(Cipher.DECRYPT_MODE, ((KeyStore.PrivateKeyEntry) entry).getPrivateKey()); plainTextByte = decCipher.doFinal(ecryptedText); String plainText = new String(plainTextByte); Algorithm Decryption with Private key Plaintext
Android Security Key Management Step 4 AndroidKeyStore Enc/Dec https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
Android Security Key Management It is observed that... ● Different screen lock ● The choice of screen lock impactsthe keys ● If you change the screen lock the keys are deleted
Android Security Key Management Expected behavior? ● The official documentation shows: ● The keys should ramain intact when the type of screen lock is changed by the user
Android Security Key Management Issue 61989 ...
Android Security Key Management Cryptographic material on devices ● Device with Storage “Hardware-backed” ● Device with Storage “Software-only”
Android Security Key Management KeyChain ● KeyChain ○ Accessible by any Application ● Typically used for corporate certificates
Android Security Key Management Example: Import Certificates ● Import .p12 certificates Intent intent = KeyChain.createInstallIntent(); byte[] p12 = readFile(“CERTIFICATE_NAME.p12”); Intent.putExtra(KeyChain.EXTRA_PKCS12,p12); Specify PKCS#12 Key to install startActivity(intent); The user will be prompted for the password
Android Security Key Management KeyChain.choosePrivateKeyAlias( Activity activity, KeyChainAliasCallBack response, String[] keyTypes, Principal[] issuers, String host, Int port, String Alias); Example: Retrieve the key ● The KeyChainAliasCallback invoked when a user chooses a certificate/private key
Android Security Key Management @Override public void alias(String alias){ . . PrivateKey private_key = KeyChain. getPrivateKey(this,alias); . . X509Certificate[] chain = KeyChain. getCertificateChain(this,”Droidcon”); . PublicKey public_key = chain[0].getPublicKey(); } Example: Retrieve and use the keys ● KeyChainAliasCallbak must implement the abstract method alias: Private Key Public Key
Android Security Key Management Step 5 KeyChain https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
Android Security Key Management References ● http://developer.android.com/about/versions/android-4.3.html#Security ● http://developer.android.com/reference/java/security/KeyStore.html ● http://en.wikipedia.org/wiki/Encryption ● http://en.wikipedia.org/wiki/Digital_signature ● http://nelenkov.blogspot.it/2013/08/credential-storage-enhancements-android-43.html ● http://nelenkov.blogspot.it/2012/05/storing-application-secrets-in-androids.html ● http://nelenkov.blogspot.it/2012/04/using-password-based-encryption-on.html ● http://nelenkov.blogspot.it/2011/11/ics-credential-storage-implementation.html ● http://developer.android.com/reference/android/security/KeyPairGeneratorSpec.html ● http://android-developers.blogspot.it/2013/02/using-cryptography-to-store- credentials.html ● http://www.bouncycastle.org/ ● http://android-developers.blogspot.it/2013/08/some-securerandom-thoughts.html ● http://nelenkov.blogspot.it/2013/10/signing-email-with-nfc-smart-card.html ● http://en.wikipedia.org/wiki/PKCS ● http://developer.android.com/reference/android/security/KeyChain.html ● http://android-developers.blogspot.it/2013/12/changes-to-secretkeyfactory-api-in.html
Android Security Key Management Thank you Q&Awww.mseclab.com www.consulthink.it research@mseclab.comgoo.gl/TA8EA1

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Consulthink @ GDG Meets U - L'Aquila2014 - Codelab: Android Security -Il key management

  • 2. Android Security Key Management Roberto Piccirillo ● Senior Security Analyst - Mobile Security Lab ○ Vulnerability Assessment (IT, Mobile Application) ○ Hijacking Mobile Data Connection ■ BlackHat Europe 2009 ■ DeepSec Vienna 2009 ■ HITB Amsterdam 2010 ○ Android Secure Development @robpicone
  • 3. Android Security Key Management Roberto Gassirà ● Senior Security Analyst - Mobile Security Lab ○ Vulnerability Assessment (IT, Mobile Application) ○ Hijacking Mobile Data Connection ■ BlackHat Europe 2009 ■ DeepSec Vienna 2009 ■ HITB Amsterdam 2010 ○ Android Secure Development ● IpTrack Developer @robgas
  • 4. Android Security Key Management Agenda ● Cryptography in Mobile Application ● CryptoSystem ● Crypto in Android ● Symmetric Encryption ● Symmetric Key Management ● Keychain e AndroidKeyStore ● Tipologie di AndroidKeyStore
  • 5. Android Security Key Management Requirements ● A computer ● Eclipse with ADT Plugin 22.3.0 ● SDK Android 4.4 ( API 19 rev 2) ● Android SDK Build-tools 19
  • 6. Android Security Key Management Cryptography in Mobile Applications ● Protect data ○ Sensitive data ○ Data on /sdcard ○ Cryptographic material ● Exchange data securely ○ Documents ○ Mail ○ SMS ○ Session Keys ● Digital Signature ○ Documents ○ Mail
  • 7. Android Security Key Management Key Management "Key management is the management of cryptographic keys in a cryptosystem."
  • 8. Android Security Key Management CryptoSystem "refers to a suite of algorithms needed to implement a particular form of encryption and decryption" ● ● Two types of encryption: ○ Symmetric Key Algorithms ■ Identical encryption key for encryption/decryption ■ AES, Blowfish, DES, Triple DES ○ Asymmetric Key Algorithms ■ Different key for encryption/decryption ■ RSA, DSA, ECDSA
  • 9. Android Security Key Management Ciphers ● Two types of ciphers: ○ Block: Process entire blocks of fixed-length groups of bits at a time ( padding may be required) ○ Stream: Process single byte at a time ( no padding ) ● Block Cipher modes of operation ○ ECB: each block encrypted independently ○ CBC, CFB, OFB: the previous block of output is used to alter the input blocks before applying the encryption algorithm starting from a IV ( initialization vector )
  • 10. Android Security Key Management Crypto in Android ● Based on JCA ( Java Cryptographic Architecture) provides API for: ● Encryption/Decryption ● Digital signatures ● Message digests (hashes) ● Key management ● Secure random number generation ● “Provider” Architecture with CSP ● Bouncy Castle is Android default CSP
  • 11. Android Security Key Management Bouncy Castle Android Version ● Customized: ○ Some services and API removed ● Varies between Android versions ● Fixed only in the latest versions ● Solution: Spongy Castle ● Repackage of Bouncy Castle ● Supports more cryptographic options ● Up-to-date ● Not vulnerable to the Heartbleed Bug (CVE-2014-0160)
  • 12. Android Security Key Management Set Spongy Castle ● Include Libs: ● Enable at Application Level:
  • 13. Android Security Key Management GC overhead limit exceeded ● Solution: modify eclipse.ini with: -Xms256m -Xmx1024m -XX:MaxPermSize=1024m
  • 14. Android Security Key Management Step 1 Enabling SpongyCastle https://github.com/mseclab/gdgmeetsu2014-symmetric-demo-step1.git
  • 15. Android Security Key Management Import Project from https://github.com/mseclab 1 2 3 4
  • 16. Android Security Key Management Import Project from https://github.com/mseclab 5 6 7
  • 17. Android Security Key Management Import Project from https://github.com/mseclab 8 9 10 https://github.com/mseclab/droidconit2014-symmetric-demo-step3.git
  • 18. Android Security Key Management The project cannot be built... 1 2 3
  • 19. Android Security Key Management Cipher Object Secret Key Specification Cipher getInstance Cipher Init Cipher Final
  • 20. Android Security Key Management SecretKey Specification javax.crypto.spec.SecretKeySpec ● SecretKeySpec specifies a key for a specific algorithm SecretKeySpec skeySpec = new SecretKeySpec(key, "AES"); Topic of this workshop Cryptographic Algorithm
  • 21. Android Security Key Management Cipher GetInstance javax.crypto.Cipher ● Provides access to implementations of cryptographic ciphers for encryption and decryption Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding”,“SC”); Trasformation (describes set of operation to perform): • algorithm/mode/padding • algorithm Provider ( SpongyCastle )
  • 22. Android Security Key Management Cipher Init javax.crypto.Cipher ● Initializes the cipher instance with the specified operational mode, key and algorithm parameters. cipher.init(Cipher.DECRYPT_MODE, keySpec, new IvParameterSpec(iv)); Operational Mode: • ENCRYPT_MODE • DECRYPT_MODE • WRAP_MODE • UNWRAP_MODE SecretKeySpec Specify Cipher Algorithm parameters ( IV for CBC )
  • 23. Android Security Key Management Cipher Final javax.crypto.Cipher ● Finishes a multi-part transformation (encryption or decryption) byte[] encryptedText = cipher.doFinal(clearText.getBytes()); Encrypted Text in byte ClearText in bytes
  • 24. Android Security Key Management Step 2 Encryption Example https://github.com/mseclab/gdgmeetsu2014-symmetric-demo-step2.git
  • 25. Android Security Key Management SecureRandom java.security.SecureRandom ● Cryptographically secure pseudo-random number generator SecureRandom secureRandom = new SecureRandom(); Default constructor uses the most cryptographically strong provider available ● Seeding SecureRandom is dangerous: ○ Not Secure ○ Output may change
  • 26. Android Security Key Management Some SecureRandom Thoughts... ● Android security team discovered a JCA improper PRNG initialization in August 2013 ● Applications invoking system-provided OpenSSL PRNG without explicit initialization are also affected ● Key Generation, Signing or Random Number Generation not receiving cryptographically strong values ● Developer must explicitly initialize the PRNG PRNGFixes.apply()
  • 27. Android Security Key Management KeyGenerator keyGenerator = KeyGenerator.getInstance("AES”,“SC”); keyGenerator.init(outputKeyLength, secureRandom); SecretKey key = keyGenerator.generateKey(); Generate Secret Key javax.crypto.KeyGenerator ● Symmetric cryptographic keys generator API Specify Key Size Algorithm and Provider Key to use in Cipher.init()
  • 28. Android Security Key Management Key Management: Store on device ● Protected by Android Filesystem Isolation ● Plain File ● SharedPreferences ● Keystore File (BKS, JKS) ● More secure with Phone Encryption ● Store safely ○ MODE_PRIVATE flag ○ Use only internal storage /data/data/app_package
  • 29. Android Security Key Management Key Management: Store on device ● Device Rooted?
  • 30. Android Security Key Management Step 3 Rooted device demo https://github.com/mseclab/gdgmeetsu2014-symmetric-demo-step3.git
  • 31. Android Security Key Management Key Management: Store in App ● Uses static keys or device specific information at run-time (IMEI, mac address, ANDROID_ID) ● Android app can be easily reversed ( live demo ) ● Hide with Code obfuscation ● Security by Obscurity is never a good idea...
  • 32. Android Security Key Management Key Management: Store in App ● unzip: APK -> DEX ● dex2jar: DEX -> JAR ● JD-GUI: JAR -> Source
  • 34. Android Security Key Management Key Management: PBKDF2 ● Password Based Key Derivation Function (PKCS#5) ● Variable length password in input ● Fixed length key in output ● User interaction required ● Params: ○ Password ○ Pseudorandom Function ○ Salt ○ Number of iteration ○ Key Size
  • 35. Android Security Key Management KeySpec keySpec = new PBEKeySpec(password.toCharArray(), salt, NUM_OF_ITERATIONS, KEY_SIZE); SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance(PBE_ALGORITHM); encKey = secretKeyFactory.generateSecret(keySpec); Key Management: PBKDF2 javax.crypto.spec.PBEKeySpec ● PBE Key specification and generation A good PBE algorithm is PBKDF2WithHmacSHA1 User Password N. >= 1000
  • 36. Android Security Key Management SecretKeyFactory factory; if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) // Use compatibility key factory -- only uses lower 8-bits of passphrase chars factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1And8bit"); else if (Build.VERSION.SDK_INT >= 10) // Traditional key factory. Will use lower 8-bits of passphrase chars on // older Android versions (API level 18 and lower) and all available bits // on KitKat and newer (API level 19 and higher) factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1"); else // FIX for Android 8,9 factory = SecretKeyFactory.getInstance("PBEWITHSHAAND128BITAES-CBC-BC"); SecretKeyFactory API in Android 4.4
  • 37. Android Security Key Management Step 4 PBE Example https://github.com/mseclab/gdgmeetsu2014-symmetric-demo-step4.git
  • 38. Android Security Key Management Key Management: Other solutions ● Store on server side ● Internet connection required ● Use trusted and protected connections (HTTPS, Certificate Pinning) ● Store on external device ○ NFC Java Card (NXP J3A081) ○ Smartcard ○ USB PenDrive ○ MicroSD with secure storage ● AndroidKeyStore???
  • 39. Android Security Key Management Asymmetric Algorithms ● Public/Private Key ○ Public Key -> encrypt/verify signature ○ Private Key -> decrypt/sign ● Advantages: ○ Public Key distribution is not dangerous ● Disadvantages: ○ Computationally expensive ● Usually used with PKI (Public Key Infrastructure for digital certificates)
  • 40. Android Security Key Management Public-key Applications ● Can classify uses into 3 categories: ○ Encryption/Decryption (provides confidentiality) ○ Digital Signatures (provides authentication and Integrity) ○ Key Exchange (of session keys) ● Some algorithms are suitable for all uses (RSA), others are specific to one
  • 41. Android Security Key Management PKCS for Asymmetric Algorithms ● PKCS is a group of public-key cryptography standards published by RSA Security Inc ● PKCS#1 (v.2.1) ○ RSA Cryptography Standard ● PKCS#3 (v.1.4) ○ Diffie-Hellman Key Agreement Standard ● PKCS#8 (v.1.2) ○ Private-Key Information Syntax Standard ● PKCS#10 (v.1.7) ○ Certification Request Standard ● PKCS#12 (v.1.0) ○ Personal Information Exchange Syntax Standard
  • 42. Android Security Key Management Android: RSA KeyPairGenerator kpg = KeyPairGenerator.getIstance(”RSA"); Java.security.KeyPairGenerator ● KeyPairGenerator is an engine capable of generating public/private keys with specified algorithms Cryptographic Algorithm
  • 43. Android Security Key Management Available Providers for RSA Algorithm KeyPairGenerator.getInstance(”RSA”,”SEC_PROVIDERS”); Java.security.KeyPairGenerator ● Different security providers could be used (could change for different OS versions) “AndroidOpenSSL” “BC” “AndroidKeyStrore” Version 1.0 Version 1.49 Version 1.0
  • 44. Android Security Key Management ● KeySize – 1024,2048,4096 bits KeyPairGenerator: Initialization and Randomness KeyPairGenerator kpg = KeyPairGenerator.initialize(2048); Java.security.KeyPairGenerator ● KeyPairGenerator initialization with the key size Key Size
  • 45. Android Security Key Management KeyPairGenerator: Initialization and Randomness KeyPairGenerator kpg = KeyPairGenerator.initialize(2048,sr); Java.security.KeyPairGenerator, Java.security.SecureRandom ● KeyPairGenerator initialization with a SecureRandom SecureRandom sr = new SecureRandom();
  • 46. Android Security Key Management Generating RSA Key Java.security.KeyPair ● KeyPair is a container for a public/private key generated by the KeyPairGenerator KeyPair keypair = kpg.genKeyPair() ● We can retrieve public/private keys from KeyPair Key public_key = kaypair.getPublic(); Key private_key = kaypair.getPrivate();
  • 47. Android Security Key Management Using RSA Keys: cipher example Javax.crypto.Cipher ● Cipher provides access to implementation of cryptography ciphers for encryption and decryption Cipher cipher = Cipher.getInstance(“RSA”,”SEC_PROVIDER); Transformation “AndroidOpenSSL” “BC” “AndroidKeyStrore”
  • 48. Android Security Key Management Using RSA Key: cipher example Javax.crypto.Cipher ● Encryption cipher.init(Cipher.ENCRYPT_MODE,public_key); ● Decryption byte[] encrypted_data= cipher.doFinal(“GDG-Meets-U2014”.getBytes()); cipher.init(Cipher.DECRYPT_MODE,private_key); byte[] decrypted_data= cipher.doFinal(cipherd_data);
  • 49. Android Security Key Management Parameters of RSA Keys java.security.KeyFactory, java.security.spec, ● Retrieve RSA Key parameters using KeyFactory RSAPublicKeySpec rsa_public = keyfactory.getKeySpec(keypair.getPublic(), RSAPublicKeySpec.class); RSAPrivateKeySpec rsa_private = keyfactory.getKeySpec(keypair.getPrivate(), RSAPrivateKeySpec.class);
  • 50. Android Security Key Management Extract Parameters of RSA Keys Java.security.spec.RSAPublicKeySpec, java.security.spec.RSAPrivateKeySpec ● Retrieved parameters can be stored BigInteger m = rsa_public.getModulus(); BigInteger e = rsa_public.getPublicExponent(); BigInteger d = rsa_private.getPrivateExponent(); Is Private
  • 51. Android Security Key Management Step 1 RSA Keys Generaration https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
  • 52. Android Security Key Management AndroidKeyStore ● Custom Java Security Provider available from Android 4.3 version and beyond ● An App can generate and save private keys ● Keys are private for each App ● 2048-bit key size (4.3), 1024-2048-4096-bit key size (4.4) can be stored ● ECDSA support added from Android 4.4
  • 53. Android Security Key Management Key Management Evolution API LEVEL 14 API LEVEL 18 Global Level: KeyChain ( Public API ) App Level: KeyStore ( Closed API ) Global Level Only: Default TrustStore cacerts.bks (ROOTED device) Global Level: KeyChain ( Public API ) App Level and per User Level: AndroidKeyStore ( Public API )
  • 54. Android Security Key Management AndroidKeyStore Storage ● Two kinds of storage ○ Hardware-backed (Nexus 7, Nexus 4, Nexus 5 :-) with OS >= 4.3) ○ Secure Element ○ TPM ○ TrustZone ○ Software only (Other devices with OS >= 4.3)
  • 55. Android Security Key Management Type of Storage import android.security.KeyChain; if (KeyChain.isBoundKeyAlgorithm("RSA")) // Hardware-Backed else // Software Only
  • 56. Android Security Key Management Certificate parameters Context cx = getActivity(); String pkg = cx.getPackageName(); Calendar notBefore = Calendar.getInstance(); Calendar notAfter = Calendar.getInstance(); notAfter.add(1, Calendar.YEAR); import android.security.KeyPairGeneratorSpec.Builder; Builder builder = new KeyPairGeneratorSpec.Builder(cx); builder.setAlias(“DEVKEY1”); String infocert = String.format("CN=%s, OU=%s", “DEVKEY1”, pkg); builder.setSubject(new X500Principal(infocert)); builder.setSerialNumber(BigInteger.ONE); builder.setStartDate(notBefore.getTime()); builder.setEndDate(notAfter.getTime()); KeyPairGeneratorSpec spec = builder.build(); Times parameters Self-Signed X.509 ● Common Name (CN) ● Subject (OU) ● Serial Number Generate certificate ALIAS to index the certificate
  • 57. Android Security Key Management Generating Public/Private keys KeyPairGenerator kpGenerator; kpGenerator = KeyPairGenerator .getInstance("RSA", "AndroidKeyStore"); kpGenerator.initialize(spec); KeyPair kp; kp = kpGenerator.generateKeyPair(); Engine to generate Public/Private key Init Engine with: ● RSA Algorithm ● Provider: AndroidKeyStore Init Engine with certificate parameters After generation, the keys will be stored into AndroidKeyStore and will be accessible by ALIAS ● Generating Private/Public key
  • 58. Android Security Key Management AndroidKeyStore Initialization keyStore = KeyStore.getInstance("AndroidKeyStore"); keyStore.load(null); Now we have the KeyStore reference that will be used to access to the Private/Public key by the ALIAS Should be used if there is an InputStream to load (for example the name of imported KeyStore). If not used the App will crash Get a reference to the AndroidKeyStore
  • 59. Android Security Key Management Step 2 AndroidKeyStore Gen Keys https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
  • 60. Android Security Key Management RSA Digital Signature ● Digital Signature ○ Authentication, Non-Repudiation and Integrity ○ RSA Private key to Sign ○ RSA Public Key to Verify KeyStore.Entry entry = ks.getEntry(“DEVKEY1”, null); byte[] data = “GDG-Meets-U 2014!”.getBytes(); Signature s = Signature.getInstance(“SHA256withRSA”); s.initSign(((KeyStore.PrivateKeyEntry) entry).getPrivateKey()); s.update(data); byte[] signature = s.sign(); String result = null; result = Base64.encodeToString(signature, Base64.DEFAULT); Access to Private/Public key identified by ALIAS Algorithm choice Private key to sign Signature and Base64 encoding
  • 61. Android Security Key Management Verify RSA Digital Signature byte[] data = input.getBytes(); byte[] signature; signature = Base64.decode(signatureStr, Base64.DEFAULT); KeyStore.Entry entry = ks.getEntry(“DEVKEY1”, null); Signature s = Signature.getInstance("SHA256withRSA"); s.initVerify(((KeyStore.PrivateKeyEntry) entry).getCertificate()); s.update(data); boolean valid = s.verify(signature); Base64 decoding Access to the Private/Public key identified by ALIAS==DEVKEY1 Algorithm choice Public Key in certificate to verify signature TRUE == Verified FALSE== Not Verified
  • 62. Android Security Key Management Step 3 AndroidKeyStore Sign/Verify https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
  • 63. Android Security Key Management RSA Encryption ● Encryption ○ Confidentiality ○ RSA Public key to Encrypt ○ RSA Private key to Decrypt PublicKey publicKeyEnc = ((KeyStore.PrivateKeyEntry) entry) .getCertificate().getPublicKey(); String textToEncrypt = new String(”GDG-Meet-U-2014"); byte[] textToEncryptToByte = textToEncrypt.getBytes(); Cipher encCipher = null; byte[] encryptedText = null; encCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding"); encCipher.init(Cipher.ENCRYPT_MODE, publicKeyEnc); encryptedText = encCipher.doFinal(textToEncryptToByte); Access to Public key to encrypt ● Algorithm ● Encryption with Public key Ciphered
  • 64. Android Security Key Management RSA Decryption Cipher decCipher = null; byte[] plainTextByte = null; decCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding"); decCipher.init(Cipher.DECRYPT_MODE, ((KeyStore.PrivateKeyEntry) entry).getPrivateKey()); plainTextByte = decCipher.doFinal(ecryptedText); String plainText = new String(plainTextByte); Algorithm Decryption with Private key Plaintext
  • 65. Android Security Key Management Step 4 AndroidKeyStore Enc/Dec https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
  • 66. Android Security Key Management It is observed that... ● Different screen lock ● The choice of screen lock impactsthe keys ● If you change the screen lock the keys are deleted
  • 67. Android Security Key Management Expected behavior? ● The official documentation shows: ● The keys should ramain intact when the type of screen lock is changed by the user
  • 69. Android Security Key Management Cryptographic material on devices ● Device with Storage “Hardware-backed” ● Device with Storage “Software-only”
  • 70. Android Security Key Management KeyChain ● KeyChain ○ Accessible by any Application ● Typically used for corporate certificates
  • 71. Android Security Key Management Example: Import Certificates ● Import .p12 certificates Intent intent = KeyChain.createInstallIntent(); byte[] p12 = readFile(“CERTIFICATE_NAME.p12”); Intent.putExtra(KeyChain.EXTRA_PKCS12,p12); Specify PKCS#12 Key to install startActivity(intent); The user will be prompted for the password
  • 72. Android Security Key Management KeyChain.choosePrivateKeyAlias( Activity activity, KeyChainAliasCallBack response, String[] keyTypes, Principal[] issuers, String host, Int port, String Alias); Example: Retrieve the key ● The KeyChainAliasCallback invoked when a user chooses a certificate/private key
  • 73. Android Security Key Management @Override public void alias(String alias){ . . PrivateKey private_key = KeyChain. getPrivateKey(this,alias); . . X509Certificate[] chain = KeyChain. getCertificateChain(this,”Droidcon”); . PublicKey public_key = chain[0].getPublicKey(); } Example: Retrieve and use the keys ● KeyChainAliasCallbak must implement the abstract method alias: Private Key Public Key
  • 74. Android Security Key Management Step 5 KeyChain https://github.com/mseclab/gdgmeetsu2014_asymmetric_demo.git
  • 75. Android Security Key Management References ● http://developer.android.com/about/versions/android-4.3.html#Security ● http://developer.android.com/reference/java/security/KeyStore.html ● http://en.wikipedia.org/wiki/Encryption ● http://en.wikipedia.org/wiki/Digital_signature ● http://nelenkov.blogspot.it/2013/08/credential-storage-enhancements-android-43.html ● http://nelenkov.blogspot.it/2012/05/storing-application-secrets-in-androids.html ● http://nelenkov.blogspot.it/2012/04/using-password-based-encryption-on.html ● http://nelenkov.blogspot.it/2011/11/ics-credential-storage-implementation.html ● http://developer.android.com/reference/android/security/KeyPairGeneratorSpec.html ● http://android-developers.blogspot.it/2013/02/using-cryptography-to-store- credentials.html ● http://www.bouncycastle.org/ ● http://android-developers.blogspot.it/2013/08/some-securerandom-thoughts.html ● http://nelenkov.blogspot.it/2013/10/signing-email-with-nfc-smart-card.html ● http://en.wikipedia.org/wiki/PKCS ● http://developer.android.com/reference/android/security/KeyChain.html ● http://android-developers.blogspot.it/2013/12/changes-to-secretkeyfactory-api-in.html
  • 76. Android Security Key Management Thank you Q&Awww.mseclab.com www.consulthink.it [email protected]/TA8EA1