On a new way to read data from memory

Abstract

This paper explains a new family of techniques to extract data from semiconductor memory, without using the read-out circuitry provided for the purpose. What these techniques have in common is the use of semi-invasive probing methods to induce measurable changes in the analogue characteristics of the memory cells of interest. The basic idea is that when a memory cell, or read-out amplifier, is scanned appropriately with a laser, the resulting increase in leakage current depends on its state; the same happens when we induce an eddy current in a cell. These perturbations can be carried out at a level that does not modify the stored value, but still enables it to be read out. Our techniques build on it number of recent advances in semi-invasive attack techniques, low temperature data remanence, electromagnetic analysis and eddy current induction. They can be used against a wide range of memory structures, from registers through RAM to FLASH. We have demonstrated their practicality by reading out DES keys stored in RAM without using the normal read-out circuits. This suggests that vendors of products such as smartcards and secure microcontrollers should review their memory encryption, access control and other storage security issues with care.