1. Java Assignment Related

2. Message digest MessageDigest class Producing byte array
getInstance(“SHA”)
update(byte [])
dijest(); digest(byte [])
Producing byte array
DataOutputStream to ByteOutputStream
Write data types: writeLong(l)
toByteArray in ByteOutputStream

3. Key, KeyGenerator Key: KeyGenerator:
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.

4. Cipher, 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.
Field Detail
public static final int ENCRYPT_MODE
Constant used to initialize cipher to encryption mode.
public static final int DECRYPT_MODE
Constant used to initialize cipher to decryption mode.

5. 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.

6. 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