This chip is used inside AT88SC0104/0204/0404/0808/1616C CryptoMemory devices. AT29657 code is die marking. The chip is a serial 18KB (2KB configuration zone and 16KB user zones) EEPROM that supports plain text or secure encrypted communication mode between a host (typically an MCU) and the device. Secure communication mode may be enabled in configuration zone. Same chip is used in all devices, low memory versions simply do not access all of memory.
Access to the user zones occurs only through the device's control logic. This logic is configurable through proper programming of access, passwords and keys registers in the configuration memory during device personalization. Same logic also implements the cryptographic engine for performing various higher-level security functions of the device.
Control logic defines access permissions to the configuration memory as well as to the user zones. After configuration is set, user may not alter the permissions. Access permissions include the ability to program certain portions of the configuration memory and then lock the data written through the use of Security Fuses.
Our research revealed that UV light does not reset the Security Fuses but conversely set fuses to locked state.
Atmel however did not introduced any countermeasures against Differential Power Analysis (DPA) attack in the chip design. We have successfully accessed data in the user zones by using the following steps: extraction of the secret seed by DPA attack; analysis of the communication data between a host and cryptomemory device to reveal passwords; successful authentication and reading of data.
Application of Atmel AT29657 chip in printer/fax cartridges
Atmel AT88SC0204C CryptoMemory chip is used in series of Samsung and some Xerox and Dell printers but the security features of AT88SC are not enabled in full range.
The ID number is left blank (FF bytes) in all chips of Samsung printer chartridges. So, in some cases, it is enough to only know one secret seed and password to read the programming data for different printer models and regional settings.
This is customer but not Atmel's problem because AT88SC design allows personalization of each chip (see red arrow in the picture below) at programming stage by setting individual ID number (Nc) and secret seed (Gc) derived by function F1. It provides the following security advantage – if Gc is extracted from one AT88SC sample in some application it can be used to authenticate and read data from user zones of that chip sample but it is useless to read data from other chips of the same application, because each chip has different Gc.
Most secure application of the AT88SC we found is used in some versions of Philips faxes. In addition to each chip personalization, lot history code configuration field is also used to lock sample to application. This enhances security of all system because lot history code is written and locked by chip manufacturer (Atmel) and cannot be altered in non invasive way. Fact is that faxes based on this system recognize and reject the cloned devices. This is possible because lot history code differs between original and cloned chips. It is possible that lot history code of original chip is somehow reflected in the ID number or Card Manufacturer Code. To make working clones, chip verification algorithm needs to be extracted from the fax software but it is time consuming and expensive task.