1. Java Assignment Related

2. Message digest MessageDigest class getInstance(“SHA”) to feed in
update(byte [])
update(byte)
digest(); digest(byte [])
Returned as byte array

3. Digesting stream Example Producing byte array
DigestInputStream in = new DigestInputStream( new FileInputStream(args[0]), md);
Producing byte array
DataOutputStream to ByteOutputStream
ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
DataOutputStream dataOut = new DataOutputStream(byteOut);
You can do
dataOut.writeLong(l)
byteOut.toByteArray()

4. Key, KeyGenerator
Key: top-level interface for all keys. defines the functionality of all key objects.
KeyGenerator:
This class provides the functionality of a (symmetric) key generator.
static KeyGenerator getInstance(String algorithm)
Generates a KeyGenerator object for the specified algorithm.
void init(SecureRandom random)
Initializes this key generator.
SecretKey generateKey()
Generates a secret key.
KeyGenerator kg = KeyGenerator.getInstance("DES");
kg.init(new SecureRandom());
SecretKey key = kg.generateKey();

5. KeyPairGenerator Examples:
KeyPairGenerator kpg = KeyPairGenerator.getInstance("ElGamal")
KeyPairGenerator kpg = KeyPairGenerator.getInstance("DSA"); kpg.initialize(1024);
KeyPair pair = kpg.genKeyPair();
public PublicKey getPublic() - This method returns the public key.
public PrivateKey getPrivate() - This method returns the private key.

6. Cipher, For encryptio/decryption
Assymtric and symmentric key systems
static Cipher getInstance(String transformation)
Generates a Cipher object that implements the specified transformation. You can use “DES/ECB/PKCS5Padding”
void init(int opmode, Key key)
Initializes this cipher with a key.
public static final int ENCRYPT_MODE
public static final int DECRYPT_MODE
public final byte[] update (byte [])
public final byte[] doFinal()

7. CipherOutputstream CipherInputstream
CipherOutputStream(OutputStream os, Cipher c)
Constructs a CipherOutputStream from an OutputStream and a Cipher.
void write(byte[] b)
Writes b.length bytes from the specified byte array to this output stream.
CipherInputStream(InputStream is, Cipher c)
Constructs a CipherInputStream from an InputStream and a Cipher.
int read(byte[] b)
Reads up to b.length bytes of data from this input stream into an array of bytes.
void close()
Closes this output/input stream and releases any system resources associated with this stream.

8. Big Integer BeigInteger(1, messagebytes) x/y mod z
BigInteger.valueOf(1)
x/y mod z
x.multiply(y.modPow(kOne.negate(), z)).mod(z)
k relatively prime to z
k.gcd(z).equals(kOne) == true

9. Java Security API packages
Java.security.cert
Java.security.interfaces
Java.security.spec
Javax.crypto
Javax.crypto.interfaces
Javax.crypto.spec
Some Abbreviations
JCA – java cryptographic architecture
JCE – java cryptographic extensions
Access Control

10. Class or Interface
Description
java.security.cert.Certificate
A cryptographic certificate
javax.crypto.Cipher
A cipher
java.security.Key , java.security.PrivateKey , java.security.PublicKey , javax.crypto.SecretKey
A key, used for signing or encryption
javax.crypto.KeyAgreement
A secret key exchange protocol
java.security.KeyFactory
Translates public and private keys from one format to another
javax.crypto.KeyGenerator
Creates keys for symmetric ciphers
java.security.KeyPairGenerator
Creates pairs of public and private keys for signing or encryption
javax.crypto.Mac
A Message Authentication Code (MAC)
java.security.MessageDigest
A cryptographic hash function
javax.crypto.SecretKeyFactory
Translates secret keys from one format to another
java.security.SecureRandom
A cryptographically strong random number engine
java.security.Signature
A digital signature

11. Factory Methods JCA extensively use factory methods
MessageDigest md5; md5 = MessageDigest.getInstance("MD5");
Overloaded version accepts
Algorithm & Provider
KeyPairGenerator kpg = KeyPairGenerator("ElGamal", "Jonathan");
Cipher, keyGenerator, KeyPairGenerator,
MessageDigest, Signature