iButton 1Kb EEPROM with SHA-1 Engine
World-Class Security in Stainless Steel Case for Access Control and eCash Applications
DescriptionThe DS1961S combines 1024 bits of EEPROM, a 64-bit secret, an 8-byte register/control page with up to five user read/write bytes, a 512-bit SHA-1 engine and a fully featured 1-Wire® interface in a rugged iButton® device. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return. The DS1961S has an additional memory area called the scratchpad that acts as a buffer when writing to the main memory, the register page or when installing a new secret. Data is first written to the scratchpad from where it can be read back. After the data has been verified, a copy scratchpad command will transfer the data to its final memory location, provided that the DS1961S receives a matching 160-Bit message authentication code (MAC). The computation of the MAC involves the secret and additional data stored in the DS1961S including the device's Identity Register. Only a new secret can be loaded without providing a MAC. The SHA-1 engine can also be activated to compute 160-bit MAC when reading a memory page or to compute a new secret, instead of loading it.
The DS1961S understands a unique command "Refresh Scratchpad." Proper use of a refresh sequence (see Writing with Verification section) after a copy scratchpad operation reduces the number of weak bit failures in a touch environment. The refresh sequence also provides a means to restore functionality in a device with bits in a weak state.
Each DS1961S has its own 64-bit ROM registration number that is factory lasered into the chip to provide a guaranteed unique identity for absolute traceability. The durable stainless steel package is highly resistant to environmental hazards such as dirt, moisture, and shock. Its compact coin-shaped profile is self-aligning with mating receptacles, allowing the DS1961S to be easily used by human operators. Accessories permit the DS1961S to be mounted on almost any surface including plastic key fobs and photo-ID badges.
- 1128 bits of 5V EEPROM memory partitioned into four pages of 256 bits, a 64-bit write-only secret and up to five general purpose read/write registers
- Write access requires knowledge of the secret and the capability of computing and transmitting a 160-bit MAC as authorization
- Secret and data memory can be write-protected (all or page 0 only) or put in EPROM-emulation mode ("write to 0", page 1)
- On-chip 512-bit SHA-1 engine to compute 160-bit MAC and to generate secrets
- Reads and writes over a wide voltage range of 2.8V to 5.25V from -40°C to +85°C
- Communicates to host with a single digital signal at 14.1kb per second using 1-Wire protocol
- On-chip 16-bit CRC generator for safeguarding data transfers
- Overdrive mode boosts communication speed to 125kbps
- Operating temperature range from -40°C to +85°C
- Minimum 10 years of data retention at 85°C
- Unique, factory-lasered and tested 64-bit registration number (8-bit family code + 48-bit serial number + 8-bit CRC tester) assures absolute traceability because no two parts are alike
- Multidrop controller for 1-Wire net
- Digital identification and information by momentary contact
- Chip-based data carrier compactly stores information
- Data can be accessed while affixed to object
- Button shape is self-aligning with cup-shaped probes
- Durable stainless steel case engraved with registration number withstands harsh environments
- Easily affixed with self-stick adhesive backing, latched by its flange, or locked with a ring pressed onto its rim
- Presence detector acknowledges when reader first applies voltage
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Technical DocumentsBrochure 7011 iButton Data Loggers
App Note 5507 Understanding the DS1WM Synthesizable 1-Wire Bus Master
App Note 5485 Understanding the DSSHA1 Synthesizable SHA-1 Coprocessor
App Note 4784 Secure Access Control Through Challenge and Response Authentication
Reference Schematic 4477 Reference Design of a 1-Wire® Bidirectional Voltage-Level Translator for 1.8V to 5V
App Note 4421 Alternatives to the DS1991L MultiKey iButton®
App Note 3808 What Is an iButton Device?
App Note 3675 Protect Your R&D Investment with Secure Authentication
App Note 3522 White Paper 9: Are SHA-1 Devices Still Secure Enough?
App Note 1820 White Paper 1: SHA Devices Used in Small Cash Systems
App Note 1770 Securing Electronic Transactions Using SHA-1 Secure Hash Algorithm
Tutorial 1201 White Paper 8: 1-Wire® SHA-1 Overview
App Note 1099 White Paper 4: Glossary of 1-Wire SHA-1 Terms
App Note 1098 White Paper 3: Why are 1-Wire SHA-1 Devices Secure?
Reference Schematic 244 Advanced 1-Wire Network Driver
App Note 190 Challenge and Response with 1-Wire® SHA Devices
App Note 159 Software Methods to Achieve Robust 1-Wire® Communication in iButton® Applications
App Note 154 Passwords in SHA Authentication
App Note 151 Maxim Digital Monetary Certificates
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