Blockchain Phones: Securing a New Frontier

July 9, 2019 Dan Zhang, Mouser Electronics

In a bold move for the world’s largest mobile phone vendor, Samsung is promoting support for a secure cryptocurrency wallet and blockchain-focused key store on its new flagship phones, the Galaxy S10 series. Other manufacturers are blazing the same trail – HTC’s Exodus 1 phone includes a “secure enclave” for private key transactions. This has implications for general embedded and IoT device security, because it may create demand for more advanced security features in tens of millions of low-cost mobile devices, perhaps making powerful security cheaper for all devices.

Samsung described the S10’s new currency features: “Galaxy S10 is built with defense-grade Samsung Knox, as well as a secure storage backed by hardware, which houses your private keys for blockchain-enabled mobile services.” Curiously, early reports suggested that Samsung’s first shot at a wallet app has delayed support for the best-known cryptocurrency system, Bitcoin, in favor of Ethereum and related assets – but the reasons are unclear. (By the way, “Knox” is not a new Samsung brand, although the blockchain focus is new and the hardware implementation also appears to be new.)

Why are phone manufacturers promoting these blockchain features now? Adding more features always helps to sell phones, and blockchain apps are a potentially cheap value-add for phone makers (particularly as they hit ceilings in other attractive features such as screen size and CPU speed).

Though phone makers naturally and understandably look to their own interests, we should not casually dismiss this security trend, whatever we might think about cryptocurrencies and blockchains. That’s because the tough cryptocurrency security challenges that must now be addressed by these major manufacturers could drive hardware security improvements for other devices, including general-purpose embedded and IoT devices.

Why are cryptocurrencies a special security challenge for phone makers? The task of securely storing cryptocurrencies and other blockchain-based assets is a new frontier for mobile devices. That’s mainly because it raises the potential reward for an attacker, even in targeted and small-scale attacks. For a malicious hacker, seizing control of a single phone is generally not a lucrative pursuit, but if the phone contains a cryptocurrency wallet with tens of thousands of dollars of assets inside, then it becomes a more attractive target, worthy of far more effort. A theft from a traditional bank may be reversible – but a cryptocurrency theft usually is not. This, in turn, forces vendors to up their game and make phones more secure.

Security is More Than a Label

Any Android or iOS phone can easily include a cryptocurrency wallet. In fact, there are numerous cryptocurrency and blockchain apps available free of charge in app stores. By simply including such off-the-shelf apps in the firmware of a phone, a manufacturer could claim it is “cryptocurrency ready.” However, how secure is such a product? Would we trust it with thousands of dollars in assets? Perhaps not, because even if we trust the app, a vulnerability in the phone OS might let attackers steal our money – and such vulnerabilities are not unusual.

Breaking down the security challenge: At the lowest level is a device relying on “sideloaded” blockchain apps, which are not even available through major app stores – they may not have been vetted at all. Above this level are devices relying on apps from curated app stores managed by trusted names such as Apple and Google.

But the most secure devices ideally contain a dedicated hardware security module (HSM), which is the sole arbiter of cryptographic transactions. The module is a repository for cryptographic keys – effectively an isolated computer within a computer. A phone can request that its hardware security module verifies transactions and returns the results, but otherwise the phone has limited control over the module. In no case does the hardware security module ever reveal its cryptographic keys to the phone or to its owner. Ideally, even if the phone OS is thoroughly compromised, the hardware module cannot give up its secrets. In a cellphone, the HSM implementation probably will not be a discrete chip, due to costs, but a secure area on the ARM SOC – this, apparently, is what HTC means by a “secure enclave,” for example. While the Android OS itself theoretically provides a secure key store feature, this has been demanded in typical vendor implementations.

Forty Million Blockchain-Enabled Devices Unleashed

While these are early days for built-in cryptocurrency wallets on phones, the tough security challenges that must be addressed could drive hardware security improvements for other devices. The huge economies of scale offered by the cellphone market (Samsung is predicted to ship over 40 million S10s in 2019) could reduce the cost of hardware security modules, either discrete or integrated into standard phone chips, and also help to root out potential bugs and vulnerabilities.

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