4KB Secure Memory with Tamper Protection for Network Server Applications

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The DS3645 is a secure supervisor with 4096 bytes of SRAM for applications requiring the secure storage of sensitive data and the physical tamper-sensing response functions required in cryptographic processors and data security equipment.

One of the DS3645's primary features is the on-chip encryption key memory, consisting of 32 128-byte banks incorporating a high-speed, direct-clearing function. The 4KB key memory is constantly complemented in the background to prevent memory imprinting. In the event of a qualified tamper event, the key memory is rapidly cleared and a negative bias is applied to clear SRAM external to the DS3645.

The device includes a real-time seconds counter, watchdog timer, CPU supervisor, nonvolatile (NV) SRAM controller, and on-chip temperature sensor. In the event of a primary power failure, an external battery source is automatically switched in to keep the key memory, seconds counter, and tamper-detection circuitry active. The DS3645 provides low-leakage tamper-detection inputs for interface to external sensors, interlocks, and antitamper meshes. The DS3645 also invokes a tamper event if the backup battery drops below a specified threshold or absolute temperature, if the temperature rate-of-change exceeds programmed limits, or if the crystal oscillator frequency falls outside a specified window. The tamper event is latched and timestamped for future debugging purposes.

Access to the seconds counter, tamper monitoring, key memory, and device configuration is conducted through an I²C-compatible interface. The DS3645 is assembled in a CSBGA package, which enhances key security because the leads are not exposed to the outer edges of the package.

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