|Semiconductor chips are used
today not only to control systems, but also to protect them against
security threats. A continuous battle is waged between manufacturers
who invent new security solutions, learning their lessons from
previous mistakes, and the hacker community, constantly trying to
break implemented protections. Some chip manufacturers do not pay
enough attention to the proper design and testing of protection
mechanisms. Even where they claim their products are highly secure,
they do not guarantee this and do not take any responsibility if a
device is compromised. In this situation, it is crucial for the design
engineer to have a convenient and reliable method of testing secure
This article presents a wide range of attacks on hardware security in microcontrollers and smartcards. This includes already known non-invasive attacks, such as power analysis and glitching, and invasive attacks, such as reverse engineering and microprobing. A new class of attacks 'semi-invasive attacks' is introduced. Like invasive attacks, they require depackaging the chip to get access to its surface. But the passivation layer remains intact, as these methods do not require electrical contact to internal lines. Semi-invasive attacks stand between non-invasive and invasive attacks. They represent a greater threat to hardware security, as they are almost as effective as invasive attacks but can be low-cost like non-invasive attacks.
This article's contribution includes practical fault-injection attacks to modify SRAM and EEPROM content, or change the state of any individual CMOS transistor on a chip. This leads to almost unlimited capabilities to control chip operation and circumvent protection mechanisms. A second contribution consist of experiments on data remanence, which show that it is feasible to extract information from powered-off SRAM and erased EPROM, EEPROM and Flash memory devices.
A brief introduction to copy protection in microcontrollers is given. Hardware security evaluation techniques using semi-invasive methods are introduced. They should help developers to make a proper selection of components according to the required level of security. Various defence technologies are discussed, from low-cost obscurity methods to new approaches in silicon design.
<Sergei.Skorobogatov (at) cl.cam.ac.uk>
<Sergei.Skorobogatov (at) hushmail.com>
created 16-05-2005 -- last modified 24-11-2011 -- http://www.cl.cam.ac.uk/~sps32/