The iButton is a computer chip enclosed in a 16mm thick stainless steel can. Because of this unique and durable container, up-to-date information can travel with a person or object anywhere they go. The steel iButton can be mounted virtually anywhere because it is rugged enough to withstand harsh environments, indoors or outdoors. It is small and portable enough to attach to a key fob, ring, watch, or other personal items, and be used daily for applications such as access control to buildings and computers, asset management, and various data logging tasks.
The physical device is a 16mm dime-sized metal can. There are a number of advantages to the iButton™ compared to previously used hardware token devices: • Rugged. The iButton™ is housed in a water-proof, stainless steel metal housing. Due to the housing armor, the iButton™ can withstand extreme environmental conditions and handling with no loss of data or performance. The device has been wear-tested for 10-year durability. The ruggedness of the device is an extreme advantage over smartcards and other devices that contain only minimal circuitry protection. For example, smartcard contacts are inherently fragile and any mishandling often leads to wirebond breakage and irrepairable damage. • Wearable. Unlike credit card-sized smartcards and large keychain-sized USB keys and other hardware tokens, the iButton™ is small enough to mount onto wearable accessories. • Tamper Responsive. The iButton™ has been touted as having a number of tamper proofing features which prevent the device from being physically attacked with invasive methods. A later section describes these specific features.
2.2 Ibutton and its Classification:
The family of iButtons™ is split into two sections:
• Touch Memory iButtons™ make up a large portion of the family. These devices can serve as replacements for stored-value or debit card applications, the majority of which are currently handled by smartcards. • Java™-powered Cryptographic iButtons™ consist of a microprocessor and high-speed math accelerator, the foundations for a complete cryptographic engine. The device also runs a Java Card 2.0-compliant Java Virtual Machine.
2.1.1 Touch Memory iButtons™
The first generation of the iButton™ family consist of the Touch Memory devices. These devices are often used for very specific implementations. Depending on the button type, a variety of application-specific features are provided: • Up to 64Kbit of One-Time Programmable Read-Only Memory • Up to 64Kbit of Non-Volatile RAM
• Temperature Sensor
• Real-Time Clock
Any type of digital data can be stored in these buttons. Unfortunately, none of the Touch Memory iButtons™, with the exception of the Monetary, Crypto, and Multikey iButtons™, employ any type of security protection to limit access to the data stored on the button.
2.1.2 Java™-Powered Cryptographic iButton™
Often considered the second generation of the iButton™ family is the Java™-Powered Cryptographic iButton™, also referred to as the DS1954. The device is a feature-rich iButton™ with a focus on e-commerce and secure transactions. Although the iButtons™ can be mounted in a variety of fashions, the Java™-Powered Cryptographic iButton™ is most often crafted into a ring.
The Java™-Powered Cryptographic iButton™ has a feature set that mimics, and often betters, that which is supported by smartcards and other hardware token devices: • 8051-compatible microcontroller. The Dallas Semiconductor DS83C950 security processor was specifically designed for security-concious applications. • High-speed math accelerator. Designed for 1024-bit public key cryptography. • Large ROM/RAM configuration. 6kB of Non-Volatile RAM and up to 64kB ROM allow sufficient memory space for the pre-loaded Java™ Virtual Machine (JVM) and execution of multiple Java™ applets. • Java Card™ 2.0-compliant.