New Apple Watch and the future of eSIM

Sep 15, 2017
Written for

September 12th event was all about the new iPhones. Despite this, Apple introduced a few other major updates in their product line. One of them was Apple Watch Series 3 with cellular support.

Having a watch, a phone and an iPod with unlimited songs on your wrist is really impressive, however one important detail in particular slipped from most of the reviews. Apple Watch Series 3 can become the driver of electronic SIM (eSIM) in telecom industry. One of the first eSIM devices — Samsung Gear S3, even after almost a year on the market, supports LTE only in US, Korea and Singapore. While Apple announced LTE support for Apple Watch Series 3 in 10 countries with more countries to follow in 2018. This is a start of eSIM era in mobile. I have spent 9 years developing software for SIM cards and I can be biased but I truly believe — that is something really remarkable.

Intro to SIM

Disclosure: this chapter has a lot of technical details. If you wonder about the future of SIM-less iPhones — just skip to the next one.

So, what SIM card is exactly and why do we still have them, taking space in our iPhones, while Apple is removing mini-jack to increase space inside our iPhones?

A lot of people think about SIM as just a simple memory card, like microSD, with your subscription data. However it is a tiny and a very secure computer with CPU, RAM, optional ROM, NVRAM (like hard drive in computers). It has OS, filesystem and even applications often run on (drumroll…) Java! (well, javacard, to be completely honest, but it is still a subset of Java). Here is a typical SIM-card architecture:

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Your phone subscription consist of several important parts.

  • Pair of IMSI and Ki — id and a secret key used for identification and authentication in the network. This data is stored during card personalisation on the factory and only your operator’s Authentication Centre (AuC) knows this key.
  • OTA (Over The Air) keys. OTA — is the way for the operator to update data on the SIM card remotely using a sequence of encrypted SMS messages. OTA is optional but very common nowadays.
  • There is a number of network related files too, with settings such as which networks have priorities in what countries and which networks are blocked, what iSMS gateway should be used, and so on. Basically a lot of settings files.

All those components called Electronic Profile should reside on a very secure chip. Modern SIM cards even have protections against attacks that use electronic microscopes to read their content.

Below is an example of network authentication and session generation key procedure.

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RAND - random sequence generated on the operator’s side
A8 and A3 - crypto algorithms used for authentication and session key generation respectively
Kc - session key
SRES (signed response) - authentication response

The Future of SIM cards

Telecom standards industry is a very slow in general. For example MicroSIM (3FF) standard was proposed in 1998 and standardised in 2003! It took another 7 years for this standard to be adopted by Apple in its first iPad.
eSIM standard was introduced in 2013 but it is not something that is currently used in mass market. First mass market device with eSIM support, Samsung Gear S3, was launched in late 2016. And Apple Watch can promote this standard among operators.

To install profile to Apple Watch eSIM user will need to use an iPhone. iPhone will download network operator’s profile in encrypted form, cut it into small chunks and feed to the Apple Watch. Apple Watch will store this profile in secure part of the modem chip.

It seems like very soon (very likely next year) we will see an iPhone with eSIM. We will be able to change our network operator via App Store or a special app from Apple. Yes, there is a possibility that Apple will introduce “Mobile Plans” in the list of its App Store categories! This can fundamentally change the way we use mobile plans. You will no longer need to go to a mobile operator shop to subscribe to or to change your mobile plan. Few taps in the app and the new SIM is ready to use on your phone. According new version of Remote SIM Provisioning specification your phone will be able to store more than one mobile plan and provide an easy way to switch between plans. This can be especially handy if you travel abroad.

In fairness, there are a lot of Android smartphones around with hardware support for eSIM already. Technically XMMTM 7260 and XMM 7360 modems from Intel and Qualcomm Snapdragon 835 are able to host an eSIM.

In order to install eSIM profile smartphone should have Local Profile Assistant (LPA) app. In iPhone an LPA will be app from Apple. Apple doesn’t provide developers access to SIM card and there is no chance they will do that in future. But a lot of Android devices have an API to send commands to their SIM card. This means that LPA for Android phones could be developed by mobile operators in the near future. There is no extra work requred from Google required to start that process.

The question here is: who will launch the first fully functional eSIM in a smarphone faster — Apple in next iPhone or various mobile operators on Android.

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Alexey Rashevskiy

Founder @ Appuchino