Java Card Technology Ch04: Java Card Object

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Java Card TechnologyCh04 Java Card Object

• Instructors
• Fu-Chiung Cheng
• (???)
• Associate Professor
• Computer Science Engineering
• Tatung University

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Objects in the Java Card

• JCRE and applets create objects to represent,
  store and manipulate data
• Object in in the Java Card
• All the objects on the Java Card platform are
  instances of classes or array types, which have
  the same root class java.lang.Object.
• Fields in a new object or components in a new
  array are set to their default values (zero,
  null, or false) unless they are initialized to
  some other values in the constructor.

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Java Card Memory Model

• Three kinds of memory ROM, RAM, and EEPROM.
• ROM
• read only memory where program and data were
  burned.
• The least expensive
• RAM and EEPROM can be read and written.
• RAM is used for temporary storage EEPROM is used
  for longer-lived data.

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Persistent Objects (?)

• A persistent object is created by the new
  operator.
• A persistent object holds states and values
  across CAD sessions.
• Any update to single field in a persistent object
  is atomic.
• A persistent object can be referenced by a field
  in a transient object.
• A field in a persistent object can reference a
  transient object.

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Persistent Objects (?)

• If a persistent object is not referenced by other
  objects, it becomes unreachable or can be garbage
  collected.

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Transient Object

• The term transient object is somewhat of
  misnomer.
• It can be incorrectly interpreted to mean that
  the object itself is temporary when the power is
  removed, the transient object is destroyed
• In fact, the term transient object means that the
  contents of the fields of the object have a
  temporary nature
• As with persistent objects, the space allocated
  for transient objects is reserved and cannot be
  reclaimed unless a garbage collector is
  implemented.

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Transient Object

• An applet should create a transient object only
  once during its lifetime and should save the
  object reference in a persistent field (see
  Figure 4.1 on page 51)
• The next time the card is powered on, the applet
  use the same object reference to access the
  transient object (variable)

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Transient objects

• In Java Card 2.1, only arrays with primitive
  types or arrays with references to Object can be
  declared transient
• The primitive type in Java Card platform are
  byte, short, int and boolean
• Transient object transient array

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Properties of transient objects(?)

• A transient object is created by invoking the
  Java Card APIs.
• A transient object does not hold states and
  values across CAD sessions. The fields of a
  transient object are cleared to their default
  value (zero,false, or null) at the occurrence of
  certain events.
• Any update to a single field in a transient
  object is not atomic.

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Properties of Transient
Objects (?)

• A transient object can be referenced by a field
  in persistent objects.
• A field in a transient object can reference a
  persistent object.
• If a transient object is not referenced by other
  objects, it becomes unreachable or can be garbage
  collected.
• Writes to the fields of a transient object do not
  have a performance penalty, because RAM has a
  much faster write cycle time than EEPROM

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Transient Object Types

• CLEAR_ON_RESET Transient objects are used for
  maintaining data that need to be preserved across
  applet selections but not across card resets.
• Card master session key
• CLEAR_ON_DESELECT transient objects are used for
  maintaining data that must be preserved as long
  as an applet is selected but not across applet
  selections or card resets.
• Applet-owned session key

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Creating Transient Objects

• In Java Card technology, transient objects are
  created by using one of the factory methods in
  the JCSystem class.
• Table 4.1 on page 53
• public static boolean makeTransientBooleanArray(
  short length, byte event)
• makeTransientByteArray
• makeTransientShortArray
• makeTransientObjectArray

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Creating Transient Objects

• Length specifies the requested transient array
  length
• Event indicates which kind of event clear the
  object (CLEAR_ON_RESET and CLEAR_ON_DESELECT)
• Example
• byte buffer JCSystem.makeTransientByteArray(B
  UFFER_LENGTH, JCSystem.CLEAR_ON_DESELECT)

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Querying Transient Objects

• An applet may need to access an object that is
  created by different applet.
• JCSystem class provides a convenient query method
  for an applet to determine whether an object
  being accessed is transient
• public static byte isTransient(Object theObject)
• The method isTansient returns a constant (either
  CLEAR_ON_RESET or CLEAR_ON_DESELECT) or the
  constant JCSystem.NOT_A_TRANSIENT_OBJECT to
  indicate that the object is null or is a
  persistent object.

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A Few Words about Objects Creation and Deletion

• If there isnt sufficient nonvolatile space
  available when an applet tries to create a
  persistent object using the new operator, the
  JCRE will throw a SystemException with the reason
  code JCSystem.NO_RESOURCE.
• When an applet calls one of the
  make-transient-object and there is insuffient RAM
  space available, JCRE throws a SystemException
  with the reason code JCSystem.NO_TRANSIENT_SPACE