Dallas Semiconductor’s DS3600 is a battery-backup controller for data protection in point-of-sale terminals. It is the first in a family of seven secure battery-management products and provides active tamper detection and a rapid-erasure encryption-key memory. It supports FIPS-140 security levels 3 and 4, and meets the highest requirements of Common Criteria.
According to Swati Joshi, a business manager for Dallas Semiconductor, this product family was developed to thwart increasingly sophisticated methods of breaching the physical integrity of electronic devices in order to extract their data. This data can include the encryption keys stored by point-of-sale terminals for credit card transactions.
The design of the DS3600 is based on a complimentary strategy of active and passive data protection. For active protection, the DS3600 performs internal and external monitoring of physical and electrical parameters to detect potential tampering. When the DS3600 generates a tamper alarm, the entire 64-byte array that stores the encryption key is cleared within 100 ns. This rapid and active erasure of data is accomplished through the memory's high-speed direct hardwired clearing function and on-chip power source.
According to Joshi, one documented method of recovering data from protected SRAM involves the application of liquid nitrogen prior to the removal of power to the device, which extends the data retention of unpowered SRAM cells to the millisecond timescale. However, the DS3600 includes a programmable temperature monitor that can correctly interpret this action as a tampering event and erase its internal memory before the onset of this cryogenic memory retention effect.
The device also uses an internal oscillator to determine when the integrated crystal oscillator for the real-time clock is outside its programmable range. This feature is used to detect data clock variations that indicate electrical tampering on the I/O signals of the device. Other active measures include tamper-detection inputs to interface with system voltages, resistive meshes, external sensors, and digital interlocks.
The DS3600 operates from 3.3 V and consumes less that 25 μA. A lithium coin cell battery powers the device when main power is removed. Removal of the battery is registered as a tampering event.
Joshi stated passive protection is derived from continuously complimenting the device’s conventional battery-backed SRAM memory. Collectively referred to as “non-imprinting key memory”, the technology prevents memory imprinting due to oxide stresses. For further security, the DS3600 is packaged in a CSBGA, a preferred choice for certification because no pins are exposed to the outside world, so the package is resistant to tampering.
In addition to point-of-sale applications, this device can also be used in other secure applications, such as police radios. While the part is designed to be sensitive to its surroundings in order to enable the security functions, it is also robust enough for military applications. The DS3600 is scheduled to undergo military certification at third-party test houses, according to Joshi.
The part is presently offered as a stand-alone device, only. Future development will incorporate the device and the battery within a single module, providing even greater security and reducing the power design requirements for the device.
Although the device is carefully designed to keep data secret, the device itself will probably become quite familiar to designers of battery-backed memories. For more information visit http://www.maxim-ic.com/DS3600info.