A sensitive information protection scheme in wearable devices based on quantum entanglement

Abstract

At present, wearable devices are in the ascendant in the field of personal smart communication terminals across the globe, but their information security issues deserve attention. We hereby propose a secure transmission solution that addresses the special requirements of wearable devices in information security. It is based on the principle of quantum secure communication and works well to protect sensitive information on wearable devices. The solution utilizes the coherence properties of quantum entanglement and uses quantum information security techniques such as quantum key distribution and non-orthogonal base measurement to realize secure transmission of sensitive information on wearable devices. Unlike traditional encryption methods based on the complexity of the mathematical algorithm, the solution has unconditional security.

Introduction

The wearable device refers to a category of small-scale portable electronic devices that can be directly worn on the user’s body or integrated into the user’s clothes, such as smart glasses, smart watches, smart wristbands, and smart shoes. In addition to these wearable devices for daily life and sports and health care, medical wearable devices such as insulin pumps and cardiac pacemakers are very common in daily life. The latter has higher requirements for information security. In 2012, the launch of “Google Glasses” marked the actual entry of wearable devices into people’s daily lives from the laboratory. Subsequently, wearable devices have flourished in the field of global communications electronics and personal smart terminals. Academia has reached a consensus that wearable devices will certainly be the future of electronic products^1,2 and gradually replace existing mainstream information terminal devices like smartphones and tablets. In addition, wearable devices are further associated with the rising Internet of Things, and people can use their own devices to implement real-world manipulations such as smart offices, smart homes, and smart cars. Our working life will become more convenient and comfortable.

However, the information security issues of wearable devices should be taken into consideration seriously. If information security of wearable devices is not equipped with reliable protection, it can cause the leakage of life habits, health information, and personal privacy. It has become a security risk that induces various criminal activities such as telecommunications fraud. In particular, it is used by hackers to hijack medical devices such as pacemakers. Wearable devices directly endanger the lives of patients. With the rapid development of smart wearable devices, their information security problems will gradually become prominent, and in the future it may become a fatal short board that restricts further development and wide application of wearable devices.^3,4 Therefore, the information security of wearable devices cannot be ignored.

Given the importance of information security for wearable devices, we need to consider appropriate information security technologies to protect information security of the wearable device. However, the mature classical security technology adopted by the Internet ⁵ belongs to the classical cryptosystem based on the intractability of the complexity problem of mathematical calculations. It has two inherent defects: from a mathematical point of view, it is based on mathematical computational complexity theory, with the continuous improvement of network computing capabilities, which will be compromised or gradually become insecure; from a physical point of view, the classical cryptosystems use electronic or photon classical attribute load information. Even simple eavesdropping attacks cannot be detected, and this is the inherent major flaw. Fortunately, quantum cryptography is now developing and improving in practice. The quantum cryptosystem can just make up for the above deficiencies of classic passwords. The security of quantum cryptography is guaranteed by the physics of the quantum state, rather than the computational complexity of mathematics. Therefore, it is independent of the computational conditions (computational power or computational resource size) possessed by the attacker. This is the “Unconditional security of quantum cryptography.” In addition, the attacker’s behavior will be discovered by perturbing the quantum state of the information carrier, which is the detectability of quantum cryptography for eavesdropping attacks. ⁶ The author believes that the use of quantum information security technology to protect the wearable device information security is a good idea.

Recently, combined with the special requirements of wearable devices for information security technology, Wen et al. ⁷ used quantum information technology such as quantum key distribution (QKD) and quantum teleportation, and proposed a secure transmission scheme for protecting sensitive messages in wearable devices. This scheme adopts the quantum teleportation technology and requires a classical channel communication. The receiver needs to carry out the corresponding quantum transformation operation on the photons of his or her own hand according to the information of the classical communication. In this article, based on the quantum entanglement coherence property, a quantum non-orthogonal basis measurement method is used, and another quantum scheme for protecting the secure transmission of sensitive messages in wearable devices is proposed. Our solution eliminates the classical channels and receiver’s quantum unitary transform operations, which are used for quantum teleportation in the Wen’s program. This makes our scheme simpler and more reliable.

Fundamental principle

Quantum measurement base

This article will use two measurement bases: base $B_Z$ and base $B_X$ . Among them $\{|0〉,|1〉\}$ are a set of standard orthogonal bases, called bases $B_Z$ , and $\{|+\mathrm{〉},|-〉\}$ construct another set of orthogonal bases, called bases $B_X$ . The relationship between the two is

$$|+〉=\frac{1}{\sqrt{2}}(|0〉+|1〉),|-〉=\frac{1}{\sqrt{2}}(|0〉-|1〉)$$

(1)

or

$$|0〉=\frac{1}{\sqrt{2}}(|+〉+|-〉),|1〉=\frac{1}{\sqrt{2}}(|+〉-|-〉)$$

(2)

It is easy to know that the two sets of measurement bases $B_Z$ and $B_X$ are non-orthogonal; $B_Z$ and $B_X$ satisfy

$$〈e_Z|e_X〉=\pm \frac{1}{\sqrt{2}}$$

(3)

where $|e_Z〉\in \{|0〉,|1〉\}$ and $|e_X〉\in \{|+〉,|-〉\}$ are the unit base vector of the bases $B_Z$ and $B_X$ , respectively, and the inner product units of the base vector are as follows

$$〈0|+〉=\frac{1}{\sqrt{2}}(〈0|0〉+〈0|1〉)=\frac{1}{\sqrt{2}}$$

(4)

$$〈0|-〉=\frac{1}{\sqrt{2}}(〈0|0〉-〈0|1〉)=\frac{1}{\sqrt{2}}$$

(5)

$$〈1|+〉=\frac{1}{\sqrt{2}}(〈1|0〉+〈1|1〉)=\frac{1}{\sqrt{2}}$$

(6)

$$〈1|-〉=\frac{1}{\sqrt{2}}(〈1|0〉-〈1|1〉)=-\frac{1}{\sqrt{2}}$$

(7)

Quantum entanglement coherence: non-orthogonal basis measurement

Quantum entanglement is a phenomenon unique to quantum mechanics and is the strangest and most inconceivable feature of quantum mechanics, setting it apart from classical mechanics. Entanglement makes quantum information possess many new features that classical information does not have, and the entangled state also provides new physical resources for information transmission and information processing. Assume that two photons A and B are in the Einstein–Podolsky–Rosen (EPR) entangled state

$$\begin{array}{c}\multicolumn{1}{c}{{|\psi 〉}_{\mathrm{AB}}={|{\Phi }^{+}〉}_{\mathrm{AB}}=\frac{1}{\sqrt{2}}(|0_A{0}_B〉+|1_A{1}_B〉)}\\ \multicolumn{1}{c}{=\frac{1}{\sqrt{2}}(|{+}_A{+}_B〉+|{-}_A{-}_B〉)}\end{array}$$

(8)

We agree that Alice owns photon A and Bob owns photon B. Due to the entanglement of EPR pairs, Alice’s measurement of photon A momentarily determines the state of photon B entangled with it, regardless of how far apart the two photons are. From equation (8), we can see that when Alice measures photon A, photon B will inevitably collapse to the same state as photon A.

Let us now consider the correlation of quantum measurement results of the base $B_Z$ or $B_X$ based on two photons A and B in the entangled state shown in equation (8). From equation (8), if Alice and Bob use the same basis between the bases $B_Z$ and $B_X$ to measure their photons, they must obtain the same result; however, if Bob chooses a base measurement, Alice uses it to be non-orthogonal. The other set of bases performs quantum measurements and she will get an unpredictable random result. For example, Alice uses a base $B_Z$ for photon A in the entangled state to make a quantum measurement along the +z direction (which can be done in practice with 50% probability). Then, after photon A is measured, it will be collapsed to the state $|0_A〉$ , as shown in equation (8). The quantum coherence of the entangled state shows that photon B must collapse to the state $|0_B〉$ . If Bob also uses the base $B_Z$ to measure photon B, the measurement result must be $|0_B〉$ ; conversely, if Bob uses another set of measurement base $B_X$ different from Alice’s measurement base $B_Z$ to measure photon B, it can be known from equation (2) that he will have 50% probability to measure $|+\mathrm{〉}$ , 50% probability to measure $|-\mathrm{〉}$ , and the measurement result is random.

Scheme description

Scenario setting. Assume that the important sensitive message M for transmission between the wearable device user Alice and the base station (BS) is $M=\{m(i)\}$ . The scenario model is shown in Figure 1. M is a sensitive message involving important privacy or security of the user. The leakage thereof may have serious consequences, such as jeopardizing the life safety of the patient. Therefore, the transmission of information between the user and the base station needs to ensure unconditional security. We use quantum secure communication to ensure its unconditional security.

Figure 1.

The quantum security communication model of wearable device and base station.

The idea behind the solution is as follows: sensitive information is loaded on the quantum state, the coherence of the entangled quantum state is used, and sensitive information is obtained using the correct non-orthogonal measurement basis for quantum measurement. The selection of the correct measurement base is determined by the value of the shared key K_AB distributed by the mature QKD so as to guarantee the unconditional security of the system.

System initialization

• Step 1: quantum channel preparation and security detection. The base station BS prepares group $N\prime$ of EPR quantum entangled photons as shown in equation (8). The base station leaves the particles B and sends the particles A to the user Alice. You can select $(N\prime -N)$ groups entangled photon pairs to confirm the security of the quantum channel, by contrasting their entanglement coherence if it satisfies equation (8), and finally the remaining N sets of entangled photon pairs were used as quantum channels. ⁸ In this way, a secure quantum channel is established between the user Alice and the base station BS.

• Step 2: quantum key distribution. The base station BS can establish a shared key K_AB (N-bit) with the user Alice through the well-known BB84, BBM92, or other mature QKD protocol.^9–13 Let $K_{\mathrm{AB}}=\{k(i);i=1,2,\dots ,N\}$ .

Sensitive message transmission

For simplicity, let us assume that the wearable device user Alice has a sensitive message $M=\{m(i);i=1,2,\dots ,N\}$ to be transmitted to the base station BS. Alice sends sensitive messages through the following quantum measurements:

• Step 1: select the correct measurement base. Alice uses the following formula to determine the measurement base to be used based on the value of her shared key $K_{A\mathrm{B}}=\{k(i)\}$ and the base station BS

$$\{\begin{array}{cc}k(i)=0\hfill & \to B_Z\hfill \\ \multicolumn{1}{c}{k(i)=1}& \to B_X\hfill \end{array}$$

(9)

• Step 2: use correct quantum state to express sensitive messages. After the measurement base is selected by K_AB, Alice can use a certain measurement result to express the sensitive message $M=\{m(i)\}$ . Specifically, if $m(i)=0$ , Alice measures the photon A sequence in her hand according to equation (9), causing photon A to collapse into the state $|0〉$ (or $|+\mathrm{〉}$ ) with 50% probability and $|1〉$ (or $|-\mathrm{〉}$ ) with 50% probability; then, Alice abandons the states which collapse into $|1〉$ (or $|-\mathrm{〉}$ ) and saves the states which collapse into $|0〉$ (or $|+\mathrm{〉}$ ) to express message $m(i)=0$ , which can be expressed as

$$\{\begin{array}{cc}m(i)=0\hfill & \begin{array}{cc}\leftrightarrow \hfill & |0〉\mathrm{or}|+〉\hfill \end{array}\hfill \\ \multicolumn{1}{c}{m(i)=1}& \begin{array}{cc}\leftrightarrow \hfill & |1〉\mathrm{or}|-〉\hfill \end{array}\hfill \end{array}$$

(10)

Every time Alice abandons or saves a measuring result, she tells BS through public channels.

Sensitive message reception

• Step 1. The base station BS performs quantum measurement on the photon B sequence in its own hand using the correct measurement base $B_X$ or base $B_Z$ according to equation (9) based on the key $K_{\mathrm{AB}}=\{k(i)\}$ shared with Alice.

• Step 2. The base station BS converts the quantum measurement result of photon B with the number i into the classical information m(i) according to equation (10), thereby obtaining the sensitive message $M=\{m(i)\}$ which Alice wants to transmit.

Since the base station BS and Alice share the same key $K_{\mathrm{AB}}=\{k(i)\}$ , they must use the same measurement basis according to equation (9). Therefore, according to the entanglement coherence of photons A and B shown in equation (3), the quantum measurement result of the BS and the user Alice must be the same, so that the base station BS can obtain the sensitive message to be delivered according to equation (10) from the measurement result.

Analysis of scheme characteristics

Correctness and unconditional security of the scheme

Correctness. If the user Alice and the base station BS comply with the protocol and follow the steps specified by the protocol, they will be able to successfully deliver the sensitive message $M=\{m(i)\}$ . For example, Alice has bit of a sensitive message $m(i)=0$ to be delivered on the hand, because she and the base station BS have shared the key $K_{\mathrm{AB}}=\{k(i)\}$ . They need to select the measurement base according to the value $k(i)$ and inevitably use the same measurement base. Suppose $k(i)=1$ , from formula (9) they use the same measurement base $B_X$ . So Alice measures photon A in the entangled photon pair shown in equations (3) and (10) in the +x direction. After measurement, the state of photon A collapses into $|{+}_A〉$ . Due to the quantum coherence of the entangled state, the state of photon B at the base station BS is inevitably collapsed into $|{+}_B〉$ . The base station BS measures photon B with a measurement base $B_X$ . Since the state $|{+}_B〉$ is the eigenstate of the base $B_X$ , the measurement result of the BS must be $|{+}_B〉$ , so that the BS infers from equation (10) that the bit sensitive message that Alice wants to transmit is $m(i)=0$ .

Unconditional security. In this scheme, it is the shared key K_AB that determines the measurement base of both parties of the communication, and K_AB is distributed through the QKD protocol that has been proved to have unconditional security. Therefore, the security of the measurement base used by both parties of the communication has unconditional security. Assume that the photon sequence of one of the communication parties is intercepted by the attacker Eve. Since Eve does not know which measurement base should be used, her measurement is random and it is not possible to obtain any relevant information of sensitive information from the intercepted photon sequence. Therefore, our scheme has unconditional security.

Comparison between this scheme and the work by Wen et al.

The design idea of Wen et al. ⁷ is to load sensitive information on the quantum state, transmit the quantum state in a teleportation state, and then obtain sensitive information using the quantum measurement of the correct basis. Some quantum principles and features, such as the quantum state unclonable theorem and the stochastic collapse feature of quantum measurement, are used to protect the security of sensitive information. Teleportation requires the transmission of classical information, which can instruct the recipient to perform appropriate corrective transformations to restore the waited quantum state. The classical information has nothing to do with sensitive information, and it is not afraid of eavesdropping and disclosure.

The biggest difference between this scheme and that of Wen et al. ⁷ is that the quantum information is directly transmitted through the quantum channel shown in equation (3), and quantum teleportation is not adopted. It thereby eliminates the need for the classical channel and the receiver’s quantum unitary transformation operation in the scheme described by Wen et al. ⁷ The sender expresses the sensitive message by making a proper measurement base of the photon in his own hand in equation (3). It uses the coherence of the entangled quantum state, and the receiver performs quantum measurement using the correct non-orthogonal measurement basis. The sensitive message is obtained. The selection of the correct measurement base is determined by the value of the shared key K_AB which is distributed by the mature and unconditional security quantum key QKD.

Resistance attack performance of the scheme

Quantum channel security. The security detection of quantum channels performed in step 1 of section “System initialization” can effectively prevent attack methods such as man-in-the-middle attacks, interception/retransmission, or entanglement/measurement attacks.

Anti-eavesdropping. Due to the use of quantum state entanglement coherence to achieve information transmission, any eavesdropping behavior will be disturbed by the entanglement coherence of the quantum state and be found, so the program is anti-eavesdropping.

Anti-spoofing. Assume that the wearable device user Alice is impersonated by the attacker Eve. Due to the unconditional security of QKD, Eve cannot obtain the shared key K_AB. In the section “System initialization,” the correct measurement base cannot be used according to equation (9). If the base $B_X$ and the base $B_Z$ were alternately randomized by guessing alone, her measurement results were random because the quantum state in her hand could not completely complete the eigenstate of the measurement base she used. In this case, the measurement bases used by both parties are inconsistent, so the measurement results are different. In the section “System initialization,” it will be found that Alice has been impersonated by the attacker Eve. Similarly, assuming that the base station BS has been hijacked by the attacker Eve and is impersonated by Eve, similar analysis as above shows that the impersonation behavior of Eve will also be found in step 1 of section “System initialization.”

Conclusion

Wearable devices have become an inseparable part of our everyday life. They are used to transmit an ever-increasing amount of sensitive health, financial, and personal information. This exposes us to the growing scale and sophistication of cyber-attacks. QKD can provide unconditional and future-proof data security but implementing it for handheld mobile devices comes with specific challenges. To establish security, secret keys of sufficient length need to be transmitted during the time of a handheld transaction (~1 s) despite device misalignment, ambient light, and user’s inevitable hand movements. Transmitters and receivers should ideally be compact and of low cost, while avoiding security loopholes.

The good news is that recently Chun et al. ¹⁴ demonstrated the first QKD transmission from a handheld transmitter with a key rate large enough to overcome finite key effects. Using dynamic beam steering, reference-frame-independent encoding, and fast indistinguishable pulse generation, they obtained a secret key rate above 30 kb/s over a distance of 0.5 m. Therefore, using their handheld QKD technology, combined with our quantum information coding and transmission scheme, it will not be long before we achieve the high-security transmission of sensitive information on wearable devices.