The Trusted Connectivity Alliance (TCA) is celebrating the maturing of the integrated SIM (iSIM) in a paper just published, asserting that the technology is now ready to underpin new IoT use cases. The document advocates global and open standards developed by the GSMA among others, ensuring that iSIM technologies are both interoperable and at least as secure as either removable or embedded SIM (eSIM).
The paper, entitled ‘Integrated SIM functionality: drivers, approaches to standardization and use cases’, defines an iSIM as an implementation of SIM functionality on a hardware tamper-resistant element (TRE), integrated into a host system-on-chip (SoC). It is an extension of the eSIM), which is a programmable SIM card incorporated in a device but still occupying a dedicated slot distinct from the SoC.
The eSIM was developed primarily for machine-to-machine (M2M) applications where remote provisioning was desirable and there was no requirement to change the SIM card during the lifetime of the device. The main saving in footprint was in shrinking the SIM a little further and avoiding need for a connector. The iSIM took this remote provisioning further by moving the SIM functionality from a dedicated chip into a secure enclave within either the application or modem SoC.
The TCA argues that this development opens up new cases with potential for the technology to advance further still with benefits in both enterprise and consumer sectors. “The standardized integrated SIM is now recognized by the TCA as an innovative, new SIM form factor, which sits alongside the established embedded SIM and which can bring numerous benefits to a broad range of secure connectivity use cases which require small SIM dimensions, low energy consumption, or high levels of accessible memory and/or advanced computing power for example,” said Claus Dietze, TCA chair.
He continued: “The publication of this paper is significant as it presents a unified, industry view that global efforts to standardize nascent integrated SIM technology have been successful and that solutions which align with open standards can now be recognized for their high levels of security assurance and global interoperability. Security is a critical consideration which must not be compromised if any ecosystem is to fully realize the performance and memory advantages of integration.”
TCA evolved from the SIM Alliance in February 2020, reflecting the continued expansion of the global SIM industry and need for broader industry collaboration among all ecosystem participants beyond traditional SIM manufacturers. It now acts as a bridgehead uniting parallel standardization efforts, with GSMA and ETSI spearheading developments there as the two principal players.
GSMA led the field with its iSIM first launched in early 2015 to address emerging market expectations and demand for deeper integration of secure network access functionality. An initial proof of concept was then demonstrated in 2017, promoting integration of SIM technology within SoCs.
The GSMA then finalized standardization of the integrated SIM with agreed security requirements added to both GSMA Remote SIM provisioning consumer and M2M specifications. This platform is often referred to rather confusingly as eUICC (embedded universal integrated circuit card), even though it describes an integrated rather than embedded SIM. UICC itself is just a synonym for SIM.
Meanwhile, ETSI was in parallel specifying its Smart Secure Platform (SSP) as one possible evolution of GSMA’s UICC platform, with various physical interfaces, including an option for an integrated form factor called integrated SSP or iSSP. It is clear that commercial deployment of these iSSP specifications will come later than the GSMA’s integrated eUICC, and indeed the timeframe is still uncertain due to greater underlying complexity. The TCA is playing a role aligning these initiatives and in its paper hints that the ETSI SSP could well represent the end of the mobile SIM as we know it, as the functionality dissolves into secure zones within chips more generally.
Currently, the iSIM is an extension of the TRE as a standalone secure element or a secure enclave, comprising hardware and low-level software providing resistance against logical and physical attacks, able to host secure applications along with associated confidential or cryptographic data. TREs as we know are now available in removeable, embedded and then most recently, the integrated form factors (that is SIM, eSIM and integrated SIM).
However, as that TCA paper noted, ETSI’s iSSP offers a potential integrated component that could extend beyond pure secure connectivity to bring benefits to other sectors including transport, payment and secure ID. This could enable the security of iSIM to be certified across devices that incorporate hardware IP blocks, that is reusable units of an integrated circuit layout that are the intellectual property of a given party.
This also dovetails with the trusted execution environments (TEEs) already deployed in many mobile devices as secure, protected environments within a chip, including processing, memory and storage. The TEE is isolated from the ‘normal’ processing environment, sometimes called the rich execution environment (REE), where the device operating system and applications run. This partitioning could be extended to enable remote provisioning of secure functions, under the more general heading of integrated secure elements (ISEs).
For now though, there is a growing number of iSIM packages to choose from. Among these is theTelit simWISE cellular LPWA module, designed for sensors and other devices connected by low power WAN wireless protocols.
Then Synopsys offers several iSIM options for designers to choose from when implementing an iSIM secure module, including a bootstrap profile with out-of-the-box global connectivity that can be used for initial provisioning of devices where there is an operator subscription. The Synopsys Hardware Secure Modules (HSMs) for iSIM integrate software from London-based remote mobile provisioning specialist Truphone, whose Io3 Platform was designed to support the GSMA’s Embedded SIM Specification.
This combination provides the standardized provisioning TCA is talking about in that paper, for secure connection and management of devices remotely over global cellular networks.