Early on in the development of cryptography, it became clear that off-the-shelf hardware intended for general purpose computing was not well suited to safely managing secrets. Smart-cards were the answer. A miniature computer with its own modest CPU, modest amount of RAM and persistent storage, packaged into the shape an ordinary identity card. Unlike an ordinary PCs, these devices were not meant to be generic computers, with end-user choice of applications. Instead they were preprogrammed for a specific security application, such as credit-card payments in the case of chip & PIN or identity verification in the case of the US government identification programs.

Smart-cards solved a vexing problem in securing sensitive information such as credentials and secret keys: bits are inherently copyable. Smart-cards created an “oracle” abstraction for using secrets while making it difficult for attackers to extricate that secret out of the card. The point-of-sale terminal at the checkout counter can ask this oracle to authorize a payment or the badge-reader mounted next to a door could ask for proof that it was in possession of a specific credential. But they can not ask the card to cough up the underlying secret used in those protocols. Not even the legitimate owner of the card can do that, at least not by design. Tamper-resistance features are built into the hardware design to frustrate attempts to extract any information from the card beyond what the intended interface exposes.

“Insert or swipe card”

The original card form-factor proved convenient in many scenarios when credentials were already carried on passive media in the shape of cards. Consider the ubiquitous credit card. Digits of the card number, expiration date and identity of the cardholder are embossed on the card in raised lettering for the ultimate low-tech payment solution, where a mechanical reader presses the card imprint through carbon paper on a receipt. Magnetic stripes were added later for automated reading and slightly more discrete encoding of the same information. We can view these as two different “interfaces” to the card. Both involve retrieving information from a passive storage medium on the card. Both are easy targets for perpetrating fraud at scale. So when it came time for card networks to switch to a better cryptographic protocol to authorize payments, it made sense to keep the form factor constant while introducing a third interface to the card: the chip. By standardizing protocols for chip & PIN and incentivizing/strong-arming participants in the ecosystem to adopt newer mart-cards, payment industry opened up new market for secure IC manufacturers.

In fact EMV ended up introducing two additional interfaces, contact and contactless. As the name implies, first one used direct contact with a brass plate mounted on the card to communicate with the embedded chip. The latter used a wireless communication protocol, called NFC or Near Frequency Communication for shuttling the same bits back and forth. (The important point however is that in both cases those bits typically arrive at the same piece of hardware: while there exist some stacked designs where the card has two different chips operating independently, in most cases a single “dual-interface” IC handles traffic from both interfaces.)

Identity & access management

Identity badges followed a similar evolution. Federal employees in the US always had to wear and display their badges for access to controlled areas. When presidential directive HSPD-12 called for raising the bar on authentication in the early 2000s, the logical next step was upgrading the vanilla plastic cards to smart-cards that supported public-key authentication protocols. This is what the Common Access Card (CAC) and its later incarnation Personal Identity Validation (PIV) systems achieved.

With NFC, smart-cards can open doors at the swipe of a badge. But they can do a lot more when it comes to access control online. In fact the most common use of smart-cards prior to CAC/PIV programs were in the enterprise space. Companies operating in high-security environments issues smart-cards systems to employees for accessing information resources. Cards could be used to login to a PC, access websites through a browser and even encrypt email messages.  In many ways the US government was behind the curve in adoption of smart-cards for logical access. Several European countries have already deployed large-scale electronic ID or eID systems for all citizens and offer government services online accessed using those cards.

Can you hear me now?

Another early application of smart-card technology for authentication appeared in wireless communication, with the ubiquitous SIM card. These cards hold the cryptographic secrets for authenticating the “handset”— in other words, a cell phone— to the wireless carrier providing service. Early SIM cards had the same dimensions as identity cards, called ID1. As cell-phones miniaturized to the point where some flip-phones were smaller than the card itself, SIM cards followed suit. The second generation of “mini-SIM” looked very much like a smart-card with the plastic surrounding the brass contract-plate trimmed. In fact many SIM cards are still delivered this way, as a full size card with a SIM-sized section that can be removed. Over time standards were developed for even smaller form-factors designated “micro” and “nano” SIM, chipping away at the empty space surrounding the contact plate.

This underscores the point that most of the space taken up by the card is wasted; it is inert plastic. All of the functionality is concentrated in a tiny area where the contact plate and secure IC are located. The rest of the card can be etched, punched or otherwise cut with no effect on functionality. (Incidentally this statement is not true of contactless cards because the NFC antenna runs along the circumference of the card. This is in order to maximize the surface area covered by antenna in order to maximize NFC performance: recall that these cards have no battery or other internal source of power. When operating in contactless mode, the chip relies on induction to draw power from the electromagnetic field generated by the reader. Antenna size is a major limiting factor, which is why most NFC tags and cards have a loop antenna that closely follows the external contours of its physical shape.)

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CP