Android Key Management

DroidCon London 2014

Transcript

1. Android Key Management Roberto Piccirillo (r.piccirillo@mseclab.com) Roberto Gassirà (r.gassira@mseclab.com) Droidcon London 2014
2. Android Key Management Droidcon London 2014 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 • GDG Rome Lab @robpicone
3. Android Key Management Droidcon London 2014 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 • GDG Rome Lab @robgas
4. Android Key Management Droidcon London 2014 Android Key Management: Agenda • Mobile Application Cryptography • Key Management and CryptoSystem • Crypto in Android • Symmetric Encryption • Symmetric Key Management • Asymmetric key: Encryption/Digital Signature • Keychain e AndroidKeyStore
5. Android Key Management Droidcon London 2014 Mobile Application Cryptography ➢ Exchange data securely: ➢ Protect Data: ◦ Sensitive Data ◦ Backups on /sdcard
6. Android Key Management Droidcon London 2014 Key Management "Key management is the management of cryptographic keys in a cryptosystem."
7. Android Key Management Droidcon London 2014 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 key for encryption/decryption ▪ AES, Blowfish, DES, Triple DES ◦ Asymmetric Key Algorithms ▪ Pair of keys (public/private) for encryption/decryption ▪ RSA, DSA, ECDSA
8. Android Key Management Droidcon London 2014 Symmetric Key Algorithms: 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 bit at a time(no padding) • Block Cipher modes of operation: ◦ ECB: each block encrypted independently ◦ CBC, CFB, OFB: (feedback mode) each block is encrypted combined with the previous encrypted block (starting from an IV) ◦ CTR: each block xored with the encrypted successive values of a counter ( starting from a nonce) ECB CBC
9. Android Key Management Droidcon London 2014 Crypto in Android • Framework based on JCA ( Java Cryptography Architecture) • Provides API for: • Encryption/Decryption • Message digests (hashes) • Key management • Secure random number generation • API implemented by Cryptographic Service "Provider" • "Dynamic" Provider: javax.crypto.* java.security.*
10. Android Key Management Droidcon London 2014 Default Providers ➢ From the beginning ◦ Bouncy Castle (Customized): ▪ Some services and API removed ▪ Varies between Android versions ▪ Fixed only in the latest versions ◦ Crypto (Apache Harmony) ▪ Few basic services ▪ Only for backward compatibility ➢ From Android 4.0 ◦ AndroidOpenSSL: ▪ OpenSSL JNI ▪ Performance Improved ▪ Vulnerable to Heartbleed in 4.1.1
11. Android Key Management Droidcon London 2014 ➢ Spongy Castle (SC) ◦ Repackage of Bouncy Castle ◦ Supports more cryptographic options ◦ Not vulnerable to the Heartbleed Bug ◦ Up-to-date ➢ GPS Dynamic Security Provider ◦ Available from Play Services 5.0 ◦ Based on OpenSSL ( No Heartbleed) ◦ Rapid delivery of security patches ◦ Vendor independent !!! Dynamic Providers
12. Android Key Management Droidcon London 2014 Cipher Benchmarks Run on Google Nexus 5 Android 4.4.4 CBC CTR
13. Android Key Management Droidcon London 2014 Cipher Class Secret Key Specification Cipher getInstance Cipher Init Cipher Final
14. Android Key Management Droidcon London 2014 SecretKey Specification javax.crypto.spec.SecretKeySpec • SecretKeySpec specifies a key for a specific algorithm SecretKeySpec skeySpec = new SecretKeySpec(key, "AES"); Encryption/Decryption Key Cryptographic Algorithm
15. Android Key Management Droidcon London 2014 Cipher GetInstance javax.crypto.Cipher • Create cryptographic cipher Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding”,“SC”); Transformation (describes set of operation to perform): • algorithm/mode/padding • algorithm Provider ( SpongyCastle )
16. Android Key Management Droidcon London 2014 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 )
17. Android Key Management Droidcon London 2014 Cipher Final javax.crypto.Cipher • Complete a multi-part transformation (encryption or decryption) byte[] encryptedText = cipher.doFinal(clearText.getBytes()); Encrypted Text in byte ClearText in bytes
18. Android Key Management Droidcon London 2014 Key Generation: 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
19. Android Key Management Droidcon London 2014 Some SecureRandom Thoughts... • Android security team discovered in August 2013 an improper PRNG initialization for default OpenSSL provider • 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() http://android-developers.blogspot.it/2013/08/some-securerandom-thoughts.html
20. Android Key Management Droidcon London 2014 KeyGenerator keyGenerator = KeyGenerator.getInstance("AES","SC"); keyGenerator.init(outputKeyLength, secureRandom); SecretKey key = keyGenerator.generateKey(); Generate Secret Key javax.crypto.KeyGenerator • Symmetric cryptographic keys generator Specify Key Size Algorithm and Provider Key to use in Cipher.init()
21. Android Key Management Droidcon London 2014 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
22. Android Key Management Droidcon London 2014 Key Management: Store on device ➢ Device rooted? ◦ Check at run-time...
23. Android Key Management Droidcon London 2014 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 • Hide with Code obfuscation REVERSING
24. Android Key Management Droidcon London 2014 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 • Available with BC
25. Android Key Management Droidcon London 2014 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
26. Android Key Management Droidcon London 2014 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
27. Android Key Management Droidcon London 2014 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???
28. Android Key Management Droidcon London 2014 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)
29. Android Key Management Droidcon London 2014 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
30. Android Key Management Droidcon London 2014 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
31. Android Key Management Droidcon London 2014 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
32. Android Key Management Droidcon London 2014 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” “AndroidKeyStore” “GmsCore_OpenSSL” Version 1.0 Version 1.49 Version 1.0
33. Android Key Management Droidcon London 2014 • KeySize – 1024,2048,4096 bits KeyPairGenerator: Initialization and Randomness KeyPairGenerator kpg = KeyPairGenerator.initialize(2048); Key Size Java.security.KeyPairGenerator • KeyPairGenerator initialization with the key size
34. Android Key Management Droidcon London 2014 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();
35. Android Key Management Droidcon London 2014 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();
36. Android Key Management Droidcon London 2014 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” “AndroidKeyStore” “GmsCore_OpenSSL”
37. Android Key Management Droidcon London 2014 Using RSA Key: cipher example Javax.crypto.Cipher • Encryption cipher.init(Cipher.ENCRYPT_MODE,public_key); • Decryption byte[] encrypted_data= cipher.doFinal(“DroidconUK-2014”.getBytes()); cipher.init(Cipher.DECRYPT_MODE,private_key); byte[] decrypted_data= cipher.doFinal(cipherd_data);
38. Android Key Management Droidcon London 2014 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);
39. Android Key Management Droidcon London 2014 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
40. Android Key Management Droidcon London 2014 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
41. Android Key Management Droidcon London 2014 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 )
42. Android Key Management Droidcon London 2014 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)
43. Android Key Management Droidcon London 2014 Type of Storage import android.security.KeyChain; if (KeyChain.isBoundKeyAlgorithm("RSA")) // Hardware-Backed else // Software Only
44. Android Key Management Droidcon London 2014 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(); Time parameters Self-Signed X.509 • Common Name(CN) • Subject(OU) • Serial Number Generate certificate ALIAS to index the certificate
45. Android Key Management Droidcon London 2014 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
46. Android Key Management Droidcon London 2014 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
47. Android Key Management Droidcon London 2014 RSA Encryption • Encryption ◦ Confidentiality ◦ RSA Public key to Encrypt ◦ RSA Private key to Decrypt KeyStore.Entry entry = keyStore.getEntry(“DEVKEY1”, null); PublicKey publicKeyEnc = ((KeyStore.PrivateKeyEntry) entry) .getCertificate().getPublicKey(); String textToEncrypt = new String(”DroidconUK-2014"); Cipher encCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding"); encCipher.init(Cipher.ENCRYPT_MODE, publicKeyEnc); byte[] encryptedText = encCipher.doFinal(byteTextToEncrypt); Access to Public key to encrypt • Algorithm • Encryption with Public key Ciphered Access to keys identified by ALIAS
48. Android Key Management Droidcon London 2014 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(byteEcryptedText); String plainText = new String(plainTextByte); Algorithm Decryption with Private key Plaintext
49. Android Key Management Droidcon London 2014 s.initVerify(((KeyStore.PrivateKeyEntry) entry).getCertificate()); s.update(data); boolean valid = s.verify(signature); RSA Digital Signature • Digital Signature ◦ Authentication, Non-Repudiation and Integrity ◦ RSA Private key to Sign ◦ RSA Public Key to Verify KeyStore.Entry entry = keyStore.getEntry(“DEVKEY1”, null); s.initSign(((KeyStore.PrivateKeyEntry) entry).getPrivateKey()); Access to Private/Public key identified by ALIAS Private key to sign Public Key in certificate to verify signature
50. Android Key Management Droidcon London 2014 Issue 61989 …
51. Android Key Management Droidcon London 2014 KeyChain • KeyChain ◦ Accessible by any Application • Typically used for corporate certificates
52. Android Key Management Droidcon London 2014 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
53. Android Key Management Droidcon London 2014 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
54. Android Key Management Droidcon London 2014 @Override public void alias(String alias){ . . PrivateKey private_key = KeyChain. getPrivateKey(this,alias); . . X509Certificate[] chain = KeyChain. getCertificateChain(this,”DroidconUK-2014”); . PublicKey public_key = chain[0].getPublicKey(); } Example: Retrieve and use the keys Private Key Public Key • KeyChainAliasCallbak must implement the abstract method alias:
55. Android Key Management Droidcon London 2014 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
56. Android Key Management Droidcon London 2014 Thank you Q&A www.mseclab.com www.consulthink.it research@mseclab.com