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Android Security Key Management
Roberto Piccirillo ([email protected]) Roberto Gassirà ([email protected])
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
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Android Security Key Management
Import Project from https://github.com/mseclab
5 6
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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...
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2
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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&A www.mseclab.com www.consulthink.it
goo.gl/TA8EA1