Microchip’s new 23K256 is a serially interfaced 32 kilobyte SRAM memory chip, available in 8 pin DIP and 8 pin SO packages. SRAM, like EEPROM, is a data storage medium. Data stored in SRAM is lost without constant power, but it’s really fast and there’s no limits to the number of write cycles. EERPOM stores data even without power, but it’s slow and usually limited to around a million write cycles.
32K SRAM chips typically have 15 address lines and 8 data lines, like the IS61LV256AL we used on our CPLD development board. The 23K256 requires just four signal lines, but sacrifices the speed of a parallel memory interface. It’s a great way to add extra memory to a low-pin count microcontroller without routing 23 signal traces. We’ll show you how to interface this chip below.
Continue reading “Parts: 32KB SPI SRAM memory (23K256)”
[les robots] had a defective Eye-Fi card on his hands and when a replacement was sent, he was told to destroy the original. What better way to ‘destroy’ something than opening the case? The Eye-Fi is an SD card with a builtin WiFi radio so it can upload images while remaining in camera. One version uses Skyhook’s location service to geotag photos. You can see a few photos of the dismantled card on Flickr. The board is manufactured by Wintec. The wireless side is handled by Atheros’ ROCm, the same low power Radio-on-Chip module you would find in a mobile phone. The flash memory comes from Samsung and the antenna is along the back edge, where it has the best chance of getting signal.
Frozen Cache is a blog dedicated to a novel way to prevent cold boot attacks. Last year the cold boot team demonstrated that they could extract encryption keys from a machine’s RAM by placing it in another system (or the same machine by doing a quick reboot). Frozen Cache aims to prevent this by storing the encryption key in the CPU’s cache. It copies the key out of RAM into the CPU’s registers and then zeroes it in RAM. It then freezes the cache and attempts to write the key back to RAM. The key is pushed into the cache, but isn’t written back to RAM.
The first major issue with this is the performance hit. You end up kneecapping the processor when you freeze the cache and the author suggests that you’d only do this when the screen is locked. We asked cold boot team member [Jacob Appelbaum] what he thought of the approach. He pointed out that the current cold boot attack reconstructs the key from the full keyschedule, which according to the Frozen Cache blog, still remains in RAM. They aren’t grabbing the specific key bits, but recreating it from all this redundant information in memory. At best, Frozen Cache is attempting to build a ‘ghetto crypto co-processor’.
We stand by our initial response to the cold boot attacks: It’s going to take a fundamental redesign of RAM before this is solved.
The Maxim DS2431 1K EEPROM is 1-Wire device that adds storage to a project using a single microcontroller pin. We previously interfaced a 1-wire thermometer, but this EEPROM is slightly different because it draws power directly from the 1-Wire bus. Grab the datasheet (PDF) and follow along while we read and write this simple 1-Wire memory.
Continue reading “Parts: 1K 1-Wire EEPROM (DS2431)”
The team from Princeton has released their cold boot attack tools at The Last HOPE. Earlier this year they showed how to recover crypto keys from the memory of a machine that had been powered off. Now they’ve provided the tools necessary to acquire and play around with your own memory dumps. The bios_memimage tool is written in C and uses PXE to boot the machine and copy the memory. The package also has a disk boot dumper with instructions for how to run it on an iPod. There’s also efi_memimage which implements the BSD TCP/IP stack in EFI, but it can be problematic. aeskeyfind can recover 128 and 256bit AES keys from the memory dumps and rsakeyfind does the same for RSA. They’ve also provided aesfix to correct up to 15% of a key. In testing, they only ever saw 0.1% error in there memory dumps and 0.01% if they cooled the chips first.
Continue reading “HOPE 2008: Cold boot attack tools released”
An article in EETimes suggests that we may see a memristor-based memory prototype in development as soon as 2009. The memristor is claimed by many to be the theorized fourth passive circuit element, linking the fundamental circuit variables of charge and flux. This news may not sound that exciting to most computer geeks, but this new component could usher in a new era of computer memory by forming the basis of RRAM (resistive random-access memory).
Scientists at HP labs have finally confirmed that the memristor behaves as their theories predicted. The reason that the component will work so well for memory is that the process is nonvolatile and the bits themselves will only change after the CPU tells them to. The bits in current DRAM systems slowly fade out and require a refreshment every 50 nanoseconds.
[Rich] over at Securosis takes us through some of his browser paranoia exercises. He uses different browser profiles for different types of web activities. Based on potential risk, various tasks are separated to protect from CSRF attacks and more. Everyday browsing with low risk passwords is done in one. RSS reading with no passwords is done in another. He runs his personal blog in a browser dedicated just to that.
For high risk research, he uses virtual machines to further minimize any potential nasty code getting through. Very high risk sites are browsed through a non-persistent read-only Linux virtual machine. While these techniques can be less effective if the entire OS is comprised, they can still provide a few layers of additional security.
Fellow browser paranoia sufferers may want to consider Firefox plug-ins like NoScript and memory protection from Diehard.