Remanent Data Readable after Memory Erase

Data remanence occurs when stored, memory content is not fully lost after a memory-clear or -erase operation. Confidential memory contents can still be readable through data remanence in the hardware. Data remanence can occur because of performance optimization or memory organization during 'clear' or 'erase' operations, like a design that allows the memory-organization metadata (e.g., file pointers) to be erased without erasing the actual memory content. To protect against this weakness, memory devices will often support different commands for optimized memory erase and explicit secure erase. Data remanence can also happen because of the physical properties of memory circuits in use. For example, static, random-access-memory (SRAM) and dynamic, random-access-memory (DRAM) data retention is based on the charge retained in the memory cell, which depends on factors such as power supply, refresh rates, and temperature. Other than explicit erase commands, self-encrypting, secure-memory devices can also support secure erase through cryptographic erase commands. In such designs, only the decryption keys for encrypted data stored on the device are erased. That is, the stored data are always remnant in the media after a cryptographic erase. However, only the encrypted data can be extracted. Thus, protection against data recovery in such designs relies on the strength of the encryption algorithm.