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

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
5
6
7

Android Security
Key Management
Import Project from
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

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

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

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”);
● 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.initialize(2048);
● KeyPairGenerator initialization with the key size
Key Size

Android Security
Key Management
KeyPairGenerator: Initialization
and Randomness
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

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

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

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

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

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

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