Java IO.pdf - Nguyen Dang Binh

}
}
Java I/O
}
catch (InvalidKeySpecException e) {System.err.println(e);}
catch (InvalidKeyException e) {System.err.println(e);}
catch (InvalidAlgorithmParameterException e) {System.err.println(e);}
catch (NoSuchAlgorithmException e) {
System.err.println(e);
e.printStackTrace();
}
catch (NoSuchPaddingException e) {System.err.println(e);}
catch (BadPaddingException e) {System.err.println(e);}
catch (IllegalBlockSizeException e) {System.err.println(e);}
catch (IOException e) {System.err.println(e);}
Let's investigate some of the methods used in Examples Example 10.6 and Example 10.7 in
more detail.
10.5.1 init( )
Before a Cipher object can encrypt or decrypt data, it requires four things:
• The mode to operate in [8]
• A key
• Algorithm parameters, e.g., an initialization vector
• A source of randomness
The init() method prepares the cipher by providing these four quantities or reasonable
defaults. There are six overloaded variants:
public final void init(int opmode, Key key) throws InvalidKeyException
public final void init(int opmode, Key key, SecureRandom random)
throws InvalidKeyException
public final void init(int opmode, Key key, AlgorithmParameterSpec params)
throws InvalidKeyException, InvalidAlgorithmParameterException
public final void init(int opmode, Key key, AlgorithmParameterSpec params,
SecureRandom random) throws InvalidKeyException,
InvalidAlgorithmParameterException
public final void init(int opmode, Key key, AlgorithmParameters params)
throws InvalidKeyException, InvalidAlgorithmParameterException
public final void init(int opmode, Key key, AlgorithmParameters params,
SecureRandom random) throws InvalidKeyException,
InvalidAlgorithmParameterException
You can reuse a cipher object by invoking its init() method a second time. If you do, all
previous information in the object is lost.
10.5.1.1 Mode
The mode determines whether this cipher is used for encryption or decryption. The mode
argument has two possible values, which are both mnemonic constants defined by the Cipher
class: Cipher.ENCRYPT_MODE and Cipher.DECRYPT_MODE .
8 This is the mode the cipher should operate in; that is, encryption or decryption; this is not a block cipher mode.
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