Cryptography & Network Security Exercise 2

Cryptography & Network SecurityExercise 2 MSc. NGUYEN CAO DAT

Goals • Learn about JCA (Java Cryptography Architecture) • Understand the JCE (Java Cryptography Extension) • How to use Java Crypto API’s • How to use Java BigInteger class

References • [1].Java Cryptography, Jonathan Knudsen, O'Reilly Media, 2010. • [2].http://download.oracle.com/javase/1.4.2/docs/guide/security/CryptoSpec.html • [3].http://download.oracle.com/javase/6/docs/technotes/guides/security/crypto/CryptoSpec.html • [4].http://download.oracle.com/javase/1.4.2/docs/api/java/math/BigInteger.html

Introduction (1/2) • JDK Security API • Core API for Java • Built around the java.security package • First release of JDK Security introduced "Java Cryptography Architecture" (JCA) • Framework for accessing and developing cryptographic functionality • JCA encompasses • Parts of JDK 1.2 Security API related to cryptography • Architecture that allows for multiple and interoperable cryptography implementations

Introduction (2/2) • The Java Cryptography Extension (JCE) • Extends JCA ->javax.crypto.* • Includes APIs for encryption, key exchange, and Message Authentication Code (MAC) • Multiple “providers” supported • Keys & certificates in “keystore” database

Design Principles • Implementation independence and interoperability • "provider“ based architecture • Set of packages implementing cryptographic services • Programs request a particular type of object • Various implementations working together, use each other's keys, or verify each other's signatures • Algorithm independence and extensibility • Cryptographic classes providing the functionality • Classes are called engine classes, example Signature • Addition of new algorithms straight forward

Architecture (1/2)

Architecture (2/2) • Cryptographic Service Providers • Sun, SunJSSE, SunJCE, SunRsaSign • SUN provider (default) • JCA provides APIs to query providers and services • Key management • “keystore” database: keys and certificates • Available to applications • Authentication • Signing

JCA Overview • Core classes and interfaces related to Java cryptography • Contains 2 provider classes that are used to manage and maintain the service providers • Provider: class that represents a cryptographic service provider • Security: class that manages the installed providers and their security properties • Contains a number of engine classes which are used to interface with cryptographic services

JCA Engine Classes • MessageDigest: used to implement one-way hash functions such as MD5 or SHA • Signature: used to implement digital signatures • KeyPairGenerator: used to create public/private key pairs for different algorithms • KeyFactory: used to convert keys into key specifications and then vice-versa • CertificateFactory: used to generate certificates • KeyStore: used to create a keystore which maintains keys and certificates in memory for later usage • AlgorithmParameters: used to maintain the security parameters for specific algorithms • AlgorithmParameterGenerator: used to create a set of parameters to be used for specific algorithms • SecureRandom: used to create random or pseudo-random numbers

Create Message Digest byte[] dataBytes = “This is test data”.getBytes(); MessageDigest md = MessageDigest.getInstance("SHA1"); md.update(dataBytes); byte[] digest = md.digest(); First, the test data is populated. Second, a concrete message digest object is created with SHA1 as the cryptographic algorithm Third, the message digest object is updated; i.e. the digest is updated using the current bytes Finally, the digest method completes the algorithm JcaMessageDigest.java JCA Examples (1/2)

Create Keystore KeyStore ks = KeyStore.getInstance("JCEKS"); ks.load(null,password.toCharArray()); java.io.FileOutputStream fos = new java.io.FileOutputStream(keyFilePath); ks.store(fos, password.toCharArray()); fos.close(); First, create the concrete KeyStore object. Second, load “ks” with a null input Third, create the output stream to save the file. Fourth, the store method saves the KeyStore to the file specified and protects it with the password Finally, close the output stream. JcaCertificateTest.java JCA Examples (2/2)

JCE Overview • Originally created as an optional extension package for cryptographic services subject to U.S. export controls • Uses JCA’s “provider” and “security” classes to manage its service providers • Comprised of all “engine” classes

JCE Engine Classes • Cipher: provides encryption and decryption functionality • CipherInputStream & CipherOutputStream: used as a convenient way to encrypt or decrypt information using streams • Mac: used to check the integrity of messages based on a secret key • KeyGenerator: used to generate symmetric keys • SecretKeyFactory: similar to the KeyFactory of JCA which converts keys into key specifications and vice-versa • SealedObject: used to create a serialized object which is protected using cryptography • KeyAgreement: provides functionality to use a key agreement protocol • Interfaces: provides interfaces for Diffie-Hellman keys • Spec: similar to algorithmParamaters of JCA which provides key and parameter specifications for different algorithms

Generate Secret Key KeyGenerator kg = KeyGenerator.getInstance(“DES”); SecretKey sKey = kg.generateKey(); A secret key is used for symmetric encryption/decryption First, create a concrete key generator object; in this case a DES key Second, create a SecretKey object and call the generateKey method of the KeyGenerator object to retrieve the key JceSecretKeyTest.java JCE Examples (1/2)

Encrypt byte[] testdata = “Understanding Java Cryptography”.getBytes(); Cipher myCipher = Cipher.getInstance("DES/ECB/PKCS5Padding"); myCipher.init(Cipher.ENCRYPT_MODE, sKey); byte[] cipherText = myCipher.doFinal(testdata); First, load some test data. Second, create a concrete Cipher object Third, initialize the cipher with the secret key for encryption Finally, the doFinal method actually encrypts the data JCE Examples (2/2)

Examples • An application to encrypt text files • An application to decrypt text files

Provider Class • Providers are installed in a given preference order, the order in which the provider list is searched if a specific provider is not requested. • Example • PROVIDER1 • SHA1withDSA, SHA-1, MD5, DES, and DES3 • Preference order 1 • PROVIDER2 • SHA1withDSA, MD2, MD5, RC4, and RSA • Preference order 2 Signature dsa = Signature.getInstance("SHA1withDSA","PROVIDER_2");

Installing Providers • Installing the Provider Classes (two ways) • Place a zip or JAR file containing the classes anywhere in your classpath. • Supply your provider JAR file as an "installed" or "bundled" extension. • Configuring the Provider • Add the provider to your list of approved providers • Static method • Edit the java.security file in the lib/security directory of the SDK • security.provider.n=masterClassName

Security class • Manage installed providers and security-wide properties • Only static methods and never instantiated • The methods for adding or removing providers, and for setting Security properties. • Can only be executed by a trusted program, that is: • Local application not running a security manager • An applet or application with permission

Java BigInteger class (1/3) • Constructor public BigInteger(String val) throws NumberFormatException • Example BigInteger m = new BigInteger(“92387569832653429874569286898623498”)

Java BigInteger class (2/3) • Methods • public BigInteger add(BigInteger val) • public BigInteger subtract(BigInteger val) • public BigInteger multiply(BigInteger val) • public BigInteger divide(BigInteger val) throws ArithmeticException • public BigInteger remainder(BigInteger val)throws ArithmeticException

Java BigInteger class (3/3) • Others methods • public BigInteger modPow(BigInteger e, BigInteger m) : a^e (mod m) • public BigInteger modInverse(BigInteger m) throws ArithmeticException: • public BigInteger shiftLeft(int n) • public BigInteger shiftRight(int n) • Example

Exercises • 1. Run the programs above • Check if you can supply a key as user input? • What other encryption algorithms you may use? And Try them. • Write a java program to retrieve the HTML file at URL http://www.cse.hcmut.edu.vn/ , encrypt the contents and store it into a local file “index.enc”, then decrypt the file “index.enc” and store it into a local file “index.dec”. • Try to encrypt your emails sent to your friends.

Cryptography & Network Security Exercise 2