Java Card


Java Card refers to a software technology that allows Java-based applications to be run securely on smart cards and similar small memory footprint devices. Java Card is the tiniest of Java platforms targeted for embedded devices. Java Card gives the user the ability to program the devices and make them application specific. It is widely used in ATM cards. The first Java Card was introduced in 1996 by Schlumberger's card division which later merged with Gemplus to form Gemalto. Java Card products are based on the Java Card Platform specifications developed by Sun Microsystems. Many Java card products also rely on the GlobalPlatform specifications for the secure management of applications on the card.
The main design goals of the Java Card technology are portability and security.

Portability

Java Card aims at defining a standard smart card computing environment allowing the same Java Card applet to run on different smart cards, much like a Java applet runs on different computers. As in Java, this is accomplished using the combination of a virtual machine, and a well-defined runtime library, which largely abstracts the applet from differences between smart cards. Portability remains mitigated by issues of memory size, performance, and runtime support.

Security

Java Card technology was originally developed for the purpose of securing sensitive information stored on smart cards. Security is determined by various aspects of this technology:
; Data encapsulation: Data is stored within the application, and Java Card applications are executed in an isolated environment, separate from the underlying operating system and hardware.
; Applet Firewall: Unlike other Java VMs, a Java Card VM usually manages several applications, each one controlling sensitive data. Different applications are therefore separated from each other by an applet firewall which restricts and checks access of data elements of one applet to another.
; Cryptography: Commonly used symmetric key algorithms like DES, Triple DES, AES, and asymmetric key algorithms such as RSA, elliptic curve cryptography are supported as well as other cryptographic services like signing, key generation and key exchange.
; Applet: The applet is a state machine which processes only incoming command requests and responds by sending data or response status words back to the interface device.

Design

At the language level, Java Card is a precise subset of Java: all language constructs of Java Card exist in Java and behave identically. This goes to the point that as part of a standard build cycle, a Java Card program is compiled into a Java class file by a Java compiler; the class file is post-processed by tools specific to the Java Card platform.
However, many Java language features are not supported by Java Card. Further, some common features of Java are not provided at runtime by many actual smart cards.

Bytecode

Java Card bytecode run by the Java Card Virtual Machine is a functional subset of Java 2 bytecode run by a standard Java Virtual Machine but with a different encoding to optimize for size. A Java Card applet thus typically uses less bytecode than the hypothetical Java applet obtained by compiling the same Java source code. This conserves memory, a necessity in resource constrained devices like smart cards. As a design tradeoff, there is no support for some Java language features, and size limitations. Techniques exist for overcoming the size limitations, such as dividing the application's code into packages below the 64 KiB limit.

Library and runtime

Standard Java Card class library and runtime support differs a lot from that in Java, and the common subset is minimal. For example, the Java Security Manager class is not supported in Java Card, where security policies are implemented by the Java Card Virtual Machine; and transients are supported via a Java Card class library, while they have native language support in Java.

Specific features

The Java Card runtime and virtual machine also support features that are specific to the Java Card platform:
; Persistence: With Java Card, objects are by default stored in persistent memory. The runtime environment as well as the bytecode have therefore been adapted to manage persistent objects.
; Atomicity: As smart cards are externally powered and rely on persistent memory, persistent updates must be atomic. The individual write operations performed by individual bytecode instructions and API methods are therefore guaranteed atomic, and the Java Card Runtime includes a limited transaction mechanism.
; Applet isolation: The Java Card firewall is a mechanism that isolates the different applets present on a card from each other. It also includes a sharing mechanism that allows an applet to explicitly make an object available to other applets.

Development

Coding techniques used in a practical Java Card program differ significantly from those used in a Java program. Still, that Java Card uses a precise subset of the Java language speeds up the learning curve, and enables using a Java environment to develop and debug a Java Card program ; further, one can run and debug both the Java Card code for the application to be embedded in a smart card, and a Java application that will be in the host using the smart card, all working jointly in the same environment.

Versions

Oracle has released several Java Card platform specifications and is providing SDK tools for application development.
Usually smart card vendors implement just a subset of algorithms specified in Java Card platform target
and the only way to discover what subset of specification is implemented is to test the card.
The version 3.0 of the Java Card specification is separated in two editions: the Classic Edition and the Connected Edition.