What is JTAG, Chip-off and ISP?

9 December 2015, Comments: Comments Off on What is JTAG, Chip-off and ISP?
Joint Test Action Group (JTAG) is an industry standard devised for testing printed circuit boards (PCBs) using boundary scan and was designed to quickly and easily test PCBs coming off a manufacturing assembly line. JTAG Forensics is a process that uses that same process and involves connecting the the Test Access Ports (TAPs) on a PCB via solder, molex or jig and then uses a supported JTAG Box (Riff, Z3X, ATF, etc.) to instruct the processor to acquire the raw data stored on the connected memory chip to get a full physical image from the device. This process is non-destructive to the phone. Chip-off Forensics is the process in which a BGA memory chip is removed from a device and prepared so that a chip reader can acquire the raw data to obtain a physical data dump. A chip reader, like the UP 828P Programmer or a SIREDA test socket, is required to perform the read and in the case of the UP 828P, a specific adapter will be required depending on the specific chip. Unlike JTAG, chip-off is a destructive process, and the device will no longer function. Many examiners start with a non-destructive technique like JTAG or ISP before submitting to a Chip-off. In-System Programming (ISP) applied to forensics, is the practice of connecting to an eMMC or eMCP flash memory chip for the purpose of downloading a device’s complete memory contents. eMMC and eMCP memory are the standard in today’s smartphones, and the ISP practice enables examiners to directly recover a complete data dump without removing the chip or destroying the device. Identifying the taps that connect to the memory chip using a multimeter is required in in ISP technique. Thus, for each evidence phone, a second identical phone that can be destroyed will be needed.

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