There are two main techniques when it comes to mobile phone data recovery and flash recoveries. When querying the NAND memory chip, both techniques give data retrieval engineers access to a low-level image of the data, although both are very different. Mobile phones, flash storage, and solid-state drives rely on memory chips to store information as opposed to hard drives, which use rotating trays and read/write heads.
When it comes to hard drives, everyone tends to use a common approach to data storage, which means that data retrieval tools can be generic. Flash devices, on the other hand, vary much more by having a lot of different data formats, file structures, algorithms, memory types and configurations, data extractors are often ‘device-specific’. This means that the only way to get some bits of the raw data is to directly query the memory chips, effectively bypassing the operating system. This is where chip-off technology and JTAG comes in.
The first method is the chip-off approach. This technique requires the memory chip to be disqualified from the circuit. In order to remove the chip from the device without causing any damage that requires microscope precision skills such as making any small mistakes you risk losing all data permanently. After removing the chip it can be read with data extractors. NAND chips are often much easier to read than other types of chips and are usually what SD cards and iPhones use. This is because the memory architecture and pin configuration are standardized. The pins are located outside, which means you don’t need to rebuild the connectors. Other common types of chips like the BGA have multiple connectors on the bottom that are welded directly to the motherboard with thousands of different configurations making them much harder to remove.
The second method is JTAG which does not require the chip to be removed. A data retrieval engineer can sometimes access memory through JTAG ports. This is a much longer process and does not harm the media. This means that it can be maintained in a working state that is sometimes a critical requirement in forensic investigations. One drawback of this method is that it is not always so effective and can be a riskier option.