JAVA DEVELOPER
`By Stephen M. Curry
`
`About | !
`
`HOW-TO
`An introduction to the Java Ring
`Learn about the inner workings of this secure, durable, wearable Java-powered electronic
`token
`
`JavaWorld | Apr 1, 1998 12:00 AM
`
`This month's column is split into two parts. The first part, embodied in this article, offers the history
`of the Java Ring and the technology used to build it, as well as a brief discussion of the suitability of
`the iButton for security applications and other applications. The second part, demonstrates how to
`use the Java Card 2.0 API with the Java iButton and provides the reader with a very early look at
`how to design an application, download it, and then communicate with an application running on a
`Java Card.
`
`It's in the details
`
`The Java Ring is an extremely secure Java-powered electronic token with a continuously running,
`unalterable realtime clock and rugged packaging, suitable for many applications. The jewel of the
`Java Ring is the Java iButton -- a one-million transistor, single-chip trusted microcomputer with a
`powerful Java virtual machine (JVM) housed in a rugged and secure stainless-steel case. Designed
`to be fully compatible with the Java Card 2.0 standard (for more on Java Card 2.0, see last month's
`Java Developer column, "Understanding Java Card 2.0 ") the processor features a high-speed 1024-
`bit modular exponentiator for RSA encryption, large RAM and ROM memory capacity, and an
`unalterable realtime clock. The packaged module has only a single electrical contact and a ground
`return, conforming to the specifications of the Dallas Semiconductor 1-Wire bus. Lithium-backed
`non-volatile SRAM offers high read/write speed and unparalleled tamper resistance through near-
`instantaneous clearing of all memory when tempering is detected, a feature known as rapid
`zeroization. Data integrity and clock function are maintained for more than 10 years. The 16-
`millimeter diameter stainless steel enclosure accommodates the larger chip sizes needed for up to
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`128 kilobytes of high-speed nonvolatile static RAM. The small and extremely rugged packaging of
`the module allows it to attach to the accessory of your choice to match individual lifestyles, such as
`a key fob, wallet, watch, necklace, bracelet, or finger ring.
`
`Historical background
`
`In the summer of 1989, Dallas Semiconductor Corp. produced the first stainless-steel-encapsulated
`memory devices utilizing the Dallas Semiconductor 1-Wire communication protocol. By 1990, this
`protocol had been refined and employed in a variety of self-contained memory devices. Originally
`called "touch memory" devices, they were later renamed "iButtons." Packaged like batteries, iButtons
`have only a single active electrical contact on the top surface, with the stainless steel shell serving
`as ground.
`
`Data can be read from or written to the memory serially through a simple and inexpensive RS232C
`serial port adapter, which also supplies the power required to perform the I/O. The iButton memory
`can be read or written with a momentary contact to the "Blue Dot" receptor provided by the adapter.
`When not connected to the serial port adapter, memory data is maintained in non-volatile random
`access memory (NVRAM) by a lifetime lithium energy supply that will maintain the memory content
`for at least 10 years. Unlike electrically erasable programmable read-only memory (EEPROM), the
`NVRAM iButton memory can be erased and rewritten as often as necessary without wearing out. It
`can also be erased or rewritten at the high speeds typical of complementary metal oxide
`semiconductor (CMOS) memory, without requiring the time-consuming programming of EEPROM.
`
`Since their introduction, iButton memory devices have been deployed in vast quantities as rugged
`portable data carriers, often in harsh environmental conditions. Among the large-scale uses are as
`transit fare carriers in Istanbul, Turkey; as maintenance record carriers on the sides of Ryder trucks;
`and as mailbox identifiers inside the mail compartments of the U.S. Postal Service's outdoor
`mailboxes. They are worn as earrings by cows in Canada to hold vaccination records, and they are
`used by agricultural workers in many areas as rugged substitutes for timecards.
`
`The iButton product line and its many applications are described at Dallas Semiconductor's iButton
`Web site, which is listed in the Resources section. Every iButton product is manufactured with a
`unique 8-byte serial number and carries a guarantee that no two parts will ever have the same
`number. Among the simplest iButtons are memory devices that can hold files and subdirectories
`and can be read and written like small floppy disks. In addition to these, there are iButtons with
`password-protected file areas for security applications, iButtons that count the number of times
`they have been rewritten for securing financial transactions, iButtons with temperature sensors,
`iButtons with continuously running date/time clocks, and even iButtons containing powerful
`microprocessors.
`
`The postal security device
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`For over 10 years, Dallas Semiconductor also has been designing, making, and selling a line of
`highly secure microprocessors that are used in satellite TV descramblers, automatic teller machines,
`point-of-sale terminals, and other similar applications requiring cryptographic security and high
`resistance to attack by hackers. The U.S. Postal Service's (USPS) Information Based Indicia Program
`Postal Security Device Specification, intended to permit printing of valid U.S. postage on any PC,
`provided the first opportunity to combine two areas of expertise when a secure microprocessor was
`designed into an iButton.
`
`The resulting product, named the Crypto iButton, combines high processor performance, high-speed
`cryptographic primitives, and exceptional protection against physical and cryptographic attack. For
`example, the large integer modular exponentiation engine can perform 1024-bit modular
`exponentiations with a 1024-bit exponent in significantly less than a second. The ability to perform
`large integer modular exponentiations at high speed is central to RSA encryption, Diffie-Hellman
`key exchange, Digital Signature Standard (FIPS 186), and many other modern cryptographic
`operations.
`
`An agreement between Dallas Semiconductor and RSA Data Security Inc. provides a paid-up license
`for anyone using the Crypto iButton to perform RSA encryption and digital signatures so that no
`further licensing of the RSA encryption technology is required. High security is afforded by the
`ability to erase the contents of NVRAM extremely quickly. This feature, rapid zeroization, is a
`requirement for high security devices that may be subjected to attacks by hackers. As a result of its
`high security, the Crypto iButton is expected to win the FIPS 140-1 security certification by the
`National Institute of Standards and Technology (NIST).
`
`A special operating system was designed and stored in the ROM of the Crypto iButton to support
`cryptography and general-purpose financial transactions -- such as those required by the Postal
`Service program. While not a Java virtual machine, the E-Commerce firmware designed for this
`application had several points of similarity with Java, including an object-oriented design and a
`bytecode interpreter to interpret and execute Dallas Semiconductor's custom-designed E-
`Commerce Script Language. A compiler was also written to compile the high-level language
`representation of the Script Language to a bytecode form that could be interpreted by the E-
`Commerce VM. Although the E-Commerce firmware was intended primarily for the USPS
`application, the firmware supports a variety of general electronic commerce models that are
`suitable for many different applications. The E-Commerce firmware also supports cryptographic
`protocols for secure information exchange such as the Simple Key-Management for Internet
`Protocol (SKIP) developed by Sun Microsystems Inc. The E-Commerce iButton and the SDK for
`programming it are described in detail on the Crypto iButton home page (see Resources).
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`The Java connection
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`With experience designing the E-Commerce operating system and VM for the Crypto iButton
`hardware platform, the firmware design team at Dallas Semiconductor could readily appreciate the
`advantages of a new operating system for the Crypto iButton based on Java. With a Java iButton, a
`vast number of existing Java programmers could easily learn to write applets that could be
`compiled with the standard tools available from Sun Microsystems, loaded into the Java iButton,
`and run on demand to support a wide variety of financial applications. The Java Card 2.0
`specification provided the opportunity to implement a useful version of the JVM and runtime
`environment with the limited resources available to a small processor.
`
`Java Ring
`
`The Crypto iButton also provides an excellent hardware platform for executing Java because it
`utilizes NVRAM for program and data storage. With 6 kilobytes of existing NVRAM and the potential
`to expand the NVRAM capacity to as much as 128 kilobytes in the existing iButton form factor, the
`Crypto iButton can execute Java with a relatively large Java stack situated in NVRAM. This memory
`acts as conventional high-speed RAM when the processor is executing, and the lithium energy
`preserves the complete state of the machine while the Java Ring is disconnected from the reader.
`There is therefore no requirement to deal with persistent objects in a special way -- objects persist
`or not depending on their scope so the programmer has complete control over object persistence.
`As in standard Java, the Java iButton contains a garbage collector that collects any objects that are
`out of scope and recycles the memory for future use. Applets can be loaded and unloaded from the
`Java iButton as often as needed. All the applets currently loaded in a Java iButton are effectively
`executing at zero speed any time the iButton is not in contact with a Blue Dot receptor.
`
`As the Java Card 2.0 specification was proposed, Dallas Semiconductor became a JavaSoft licensee.
`The agreement called for the development of a Java Card 2.0 implementation and also for the
`design of "plus portions" that take advantage of the unique capabilities afforded by the Crypto
`iButtons NVRAM, such as the ability to support a true Java stack and garbage collection. With the
`addition of the continuously running lithium-powered time-of-day clock and the high-speed, large-
`integer modular exponentiation engine, the Java iButton implementation of Java Card 2.0 with plus
`portions promises an exciting new feature set for advanced Java Card applications.
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`Keeping your money safe
`
`The Crypto iButton hardware platform offers a unique set of special features expressly designed to
`prevent private keys and other confidential information from becoming available to hackers. Figure
`1 shows a detail of the internal construction of the Crypto iButton. The silicon die containing the
`processor, ROM, and NVRAM memory is metallurgically bonded to the barrier substrate through
`which all electrical contacts are made. This barrier substrate and the triple-layer metal construction
`techniques employed in the silicon fabrication effectively deny access to the data stored in the
`NVRAM. If any attempt is made to penetrate these barriers, the NVRAM data is immediately erased.
`This construction technique and the use of NVRAM for the storage of private keys and other
`confidential data provides a much higher degree of data security than that afforded by EEPROM
`memory. The fact that the communication path between the Crypto iButton and the outside world
`is limited to a single data line provides additional security against hardware attacks by limiting the
`range of signals accessible to the hacker.
`
`In addition, the processor itself is driven by an unstabilized ring oscillator operating over a range of
`10 to 20 megahertz, so that the clock frequency of the processor is not constant and cannot be
`determined by external means. This differs from the design of alternative devices in which the
`processor clock signal is injected by the reader and is therefore exactly determined by the host
`processor. External control of the clock provides a valuable tool to hackers, since they can
`repetitively cycle such a processor to the same point in its execution simply by applying the same
`number of clock cycles. Control of the clock also affords a means to induce a calculation error and
`thereby obtain information that can ultimately reveal secret encryption keys. A 32-kilohertz crystal
`oscillator is used in the Java iButton to operate the time-of-day clock at a constant and well-
`controlled frequency that is independent of the processor clock.
`
`Conclusion
`
`Dallas Semiconductor has produced more than 20 million physically-secure memories and
`computers with hard-shell packaging optimized for personal possession. The Java iButton,
`therefore, is simply the latest and most complex descendant of a long line of products that have
`proven themselves to be highly successful in the marketplace. With its stainless steel armor, it
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`offers the most durable packaging for a class of products that likely will suffer heavy use and abuse
`as personal possessions. The iButton form factor permits attachment to a wide variety of personal
`accessories that includes rings, watchbands, keyfobs, wallets, bracelets, and necklaces, so the user
`can select a variation that suits his or her lifestyle.
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