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DOI: 10.32604/cmc.2023.035798

Article

Hidden Hierarchy Based on Cipher-Text Attribute Encryption for IoT Data Privacy in Cloud

Zaid Abdulsalam Ibrahim¹,* and Muhammad Ilyas²

1 Department of Electrical and Computer Engineering, Altinbas University, Istanbul, Turkey
2 Department of Computer Engineering, Altinbas University, Istanbul, Turkey
Corresponding Author: Zaid Abdulsalam Ibrahim. Email: Zaid.almatwari@ogr.altinbas.edu.tr
Received: 04 September 2022; Accepted: 17 April 2023; Published: 09 June 2023

Abstract: Most research works nowadays deal with real-time Internet of Things (IoT) data. However, with exponential data volume increases, organizations need help storing such humongous amounts of IoT data in cloud storage systems. Moreover, such systems create security issues while efficiently using IoT and Cloud Computing technologies. Ciphertext-Policy Attribute-Based Encryption (CP-ABE) has the potential to make IoT data more secure and reliable in various cloud storage services. Cloud-assisted IoTs suffer from two privacy issues: access policies (public) and super polynomial decryption times (attributed mainly to complex access structures). We have developed a CP-ABE scheme in alignment with a Hidden Hierarchy Ciphertext-Policy Attribute-Based Encryption (HH-CP-ABE) access structure embedded within two policies, i.e., public policy and sensitive policy. In this proposed scheme, information is only revealed when the user’s information is satisfactory to the public policy. Furthermore, the proposed scheme applies to resource-constrained devices already contracted tasks to trusted servers (especially encryption/decryption/searching). Implementing the method and keywords search resulted in higher access policy privacy and increased security. The new scheme introduces superior storage in comparison to existing systems (CP-ABE, H-CP-ABE), while also decreasing storage costs in HH-CP-ABE. Furthermore, a reduction in time for key generation can also be noted. Moreover, the scheme proved secure, even in handling IoT data threats in the Decisional Bilinear Diffie-Hellman (DBDH) case.

Keywords: Bilinear Diffie-Hellman (DBDH); Internet of Things (IoT); Ciphertext-Policy Attribute-Based Encryption (CP-ABE); Hidden Hierarchy CP-ABE (HH-CP-ABE)

1  Introduction

In recent times, modern technological tools have powerfully shaped people’s lifestyles. Not only do people use technology to meet their basic needs like transportation, education, health care, they now enjoy the great convenience that the internet of things (IoT) offers through innovative applications [1], such as intelligent homes and innovative education tools. However, resource-constrained devices cannot effectively handle large data sets for localized operations. Consequently, a server storing data on the cloud must be securely integrated into an IoT network, encouraging an IoT cloud to deliver valuable services such as storage, processing and computation. Individuals and organizations use cloud services to store and process massive data [2] efficiently. Such services help enterprises reduce the cost of equipment and IT management [3,4]. Generally, cloud providers host cloud services. However, on the cloud, the data and services are open to all, so there is a risk of data loss. Hence, the minimum mandatory requirement of an access-control policy ensures authorized users access data securely. In [5] the authors recommend that data transfer is handled through Attribute-based Encryption (ABE), which helps make access control scalable and fine-grained on the cipher text. Moreover, it reduces the risk of data leakage and protects data by encrypting the data hosted on the cloud. For example, in healthcare management, the cipher text is used to outsource patient data via cloud channels by the hospitals, while doctors decrypt the data when needed for patient treatment; such cases are handled by Key Policy Attribute-based Encryption (KP-ABE) and Ciphertext Policy Attribute-based Encryption (CP-ABE) [6,7]. The rest of the paper is organized as follows. Section 2 deals with the literature review, while Section 3 describes the main concepts, Section 4 provides a description of CP-ABE having a hierarchical hidden access structure. Section 5 illustrates the application process, and Section 6 applies to the medical environment. The results and discussion are presented in Section 7. Section 8 presented the complexity of the access policy. Finally, the concluding Section 9, sums up the work.

2  Related Work

Along with generating the private key and access policy, the CP-ABE is a powerful mechanism to protect user information. This scheme only allows for decryption when the user attributes satisfy the access structure [2–8]. The privacy issues in policy get exposed in a basic CP-ABE scheme [9,10]. However, CP-ABE can have applications in the education, health care, and industrial fields. Using data encryption access policies in medical applications can disclose personal information. In [11], authors developed the initial CP-ABE system as a standard model, utilizing the AND gate. In [12] they proposed a non-pairing CP-ABE technique to enable access to AND gates. According to [13], CP-ABE is a hidden policy with entirely hidden attributes in access policies while creating a hidden access policy using Linear Secret Sharing Schemes (LSSS). Katz et al. [14] have developed a hidden policy approach with an access policy concealed as ciphertext. This approach employs the LSSS access structure and the hidden vector encryption method to check the attribute locations in an access policy. Though these approaches restrict access to the attribute in its entirety in the access policy, they have drawbacks such as increased computational complexity and false positive [15], & [8–15]. As presented in [16–19], some researchers developed partially hidden policies in CP-ABE. There are two phases to specify the attribute in the proposed schemes: the attribute name, and attribute values, with a hidden attribute value. Although this solution preserves the policy’s privacy to a certain level, it does not resolve privacy concerns [20,21]. However, only the restricted access structures, described as AND gates on multi-valued characteristics with wildcards, are supported by these schemes [22], suggesting a completely secure CP-ABE method with partial-concealed access structures stated in Linear Secret Sharing Scheme as LSSS, exhibiting greater flexibility and expression over earlier works [19–26]. Anyone accessing the ciphertext can get the following information about the access policy only if the data owner employs a CP-ABE scheme to encrypt his medical record under this updated paradigm:

SID#:∗ OR (Institute :∗ AND Department :∗)(1)

More significantly, sensitive attribute values, such as “234-379,” “AU,” and “SE,” do not appear in public. Fig. 1 shows a specimen with a partially hidden access structure.

Figure 1: Example of a student record with an access structure and sensitive access structure

Recent studies in [26] suggested a completely secure (as opposed to selectively safe) CP-ABE system using partially disguised access mechanisms. It should be noted, however, that their method enables only limited access structures, like [26–29]. The suggested technique is secure (CPA Attack), handling all access structures represented as Linear Secret Sharing Scheme (LSSS), with ciphertext sizes scaling in linear terms having access structure complications. Fig. 1 compares our CP-ABE system with previous CP-ABE methods based on disguised access structures. Another issue with previous CP-ABE systems [30–34] relates to the proportionate correlation between pairing frequency and exponentiation operations for ciphertext decryption and access policy complications, implying high user cost calculations [35]. This trait is appropriate for people who do not use smart mobile devices and decreases end-user computational overhead by performing cryptographic procedures when third-party service providers handle a significant computing burden [36].

3  Methods and Materials

This section describes the critical methods and concepts that support the Security mechanism, including Access Structure, Access Tree, and Bilinear Assumptions.

3.1 Access Structure

The set of entities to be denoted as P={p1,p2,...,pn}. The specific set A⊆2P to be treated as monotone that satisfies the condition:

f∀B∈A and B⊆C then C∈A(2)

A, the access structure (a monotone set), including non-empty subsets of P, gets denoted as AP⊆2P{ϕ}. Further, there is a classification of authorized sets and unauthorized sets depending on the existence of A. The approved groups consist of A and others not.

3.1.1 Access Tree

The access structure represents the tree as T. From T, every non-leaf node of the tree characterizes as an individual threshold gate. The corresponding children of the non-leaf node are also specified as threshold values and represented by kx. Let nx be the number of children at node x while the time threshold value falls within 0<kx<nx.

The threshold gate becomes the OR gate during kx=1, whereas the AND gate designates as kx=nx. Every leaf node of x in the tree is specified by an attribute attx and a threshold value kx=1. The corresponding index associated with node x represents ind(x). The set of functions used to return the parent and index ix of node x is denoted as par(x) & ind(x). For example, in the student information, the data owner uses a hidden access policy to encrypt their record, as follows:

SID#:∗ OR (Institute :∗ AND Department :∗)(3)

The attribute values, such as “234-379,” “AU,” and “SE,” are hidden and not exposed to anyone. A representation of the partially hidden policy is presented in Fig. 2.

Figure 2: (a) Access tree (b) access tree with hidden attribute

3.1.2 Access an Access Tree of HA (Hidden Attributes) T~

The given T~ is like T. However, it hides the transaction among leaf nodes and their specific attributes, denoted as ax. Verifying whether the leaf node satisfies the access structure is simple. The complete information about node attributes is all hidden, leading to difficulty finding them in the structure.

3.2 Bilinear Map and Decisional Bilinear Diffie-Hellman (DBDH) Assumption

3.2.1 Bilinear Map

Consider a set of multiplicative cyclic groups (GO,GT) of prime order P from this theory. Next, g will be considered a bilinear group GO. Moreover, the bilinear map e concerning the bilinear group represented as:GO×GO→GT. The properties to be held by bilinear map e include Bilinearity:

∀[(u,v)∈GO&&(a,b)∈Zp],e(ua,vb)=e(u,v)ab[10](4)

Non−degeneracy e(g,g)≠1.(5)

3.2.2 Decisional Bilinear Diffie-Hellman (DBDH) Assumption

The number of operations in both GO and e is known to be computationally efficient. In addition, it observes that the bilinear map e satisfies the property of being symmetric, and which is denoted as follows:

e(ga,gb)=e(g,g)ab=e(gb,ga)(6)

Corresponding bilinear parameters (GO,GT,p,e,g) are the random elements (x,y,z)∈zp3. It is known that Probabilistic Polynomial Time (PPT) does not exist, and adversary B can have the differentiation between the two tuples G1 and G2, which are specified as G1=(g,gx,gy,gz,e(g,g)xyz) and G2=(g,gx,gy,gz,v) respectively. The above discussion proves that the DBDH assumption holds, and v selects from GT. The DBDH problem is specified as follows:

gset={gx,gy,gz}|Pr[A(g,gset,e(g,g)xyz=1)]−Pr[A(g,gset,v)=1]|(7)

4  Proposed Methods Hidden Hierarchy Access Structure (HH-CP-ABE)

The proposed scheme contains system architecture, formal methods, and security models. The constructed model describes as follows:

4.1 System Architecture

Fig. 3 illustrates the framework of the proposed system. The number of components in the structure includes (1) Key Authority Center (KAC), (2) Data Owner (DO), (3) Cloud Server (CS), (4) End User (EU), and (5) Proxy Node (PN).

Figure 3: Proposed system framework

•   Trusted Key Authority Center (TKAC): The trusted authority generates public key besides the secret key.

•   Data Owner (DO): An authorized owner who wishes to design the concerned access structure based on user attributes. Later, this is used to encrypt the desired ciphertext CT using proxy nodes.

•   Cloud Server (CS): This campaign has a high capacity for computation and storage for extensive data processing. In addition, it allows the data owner and the end user to access such a massive capacity at the time of decryption.

•   End User (EU): The trusted user initiates requests by submitting the trapdoor to the CS for ciphertext decryption.

•   Proxy Node (PN): In this study, the computational overhead of encryption is outsourced from the DO to proxy nodes.

4.2 Formal Model

The proposed scheme uses four algorithms, as described below:

•   Setup (1λ,U)→(PK,MSK): Out of two input values, one is the security parameter λ, while the other is the universe attribute U. These two values are considered by the Trusted Key Authority Center (TKAC) and produce two output values, i.e., the Public Key (PK) and the Master Secret Key (MSK).

•   Key Gen(PK,MSK,S)→SKS: Here, we have taken three input values viz., (1) the PK, (2) the Master Secret Key (MSK) and (3) a set of attributes S. Later, these input values are submitted to the Trusted Key Authority Center (TKAC) to generate the final output value, i.e., the Secret Key (SKS) for the end user (DU).

•   Encrypt(PK,AT1,AT2,M)→C: These takes four input parameters (1) input the PK, (2) a message M and (3) public access structure 1 AT1 (3) Hidden access structure2 AT2. The DO generates the output, i.e., the ciphertext CT.

•   Trap SK→Td: In this algorithm, DUuses his own SKS and generates the trapdoor Td, which is submitted to the CS.

•   Tran(C,Td)→CT∞or ψ

•   Step1: The CS approaches trapdoor Td and then checks whether DU has the authority to decrypt CT or not. Then, it checks the condition {(S≠AT1)∨(S≠AT2)} to produce the result ψ.

•   Step2: The condition {(S=AT1)∧(S=AT2)} is checked. If found OK, then CS can attempt partial decryption of CT and send the computed ciphertext CT∞ to DU.

Decrypt(CT∞,SKS)→M: Here, two input values i.e., CT∞ and the secret key SKS are taken by the DU for decrypting CT∞ and generating message M

4.3 Security Model

The suggested approach uses the security game between a Probabilistic Polynomial-Time (PPT) attacker and a challenger to achieve the desired plaintext security.

Adversary(A) Challenger(C)

Initialization−{–––––––––→Challenge:Submit access structures :AT1∗&AT2∗Setup−{←–––––––––––retuns the Public KeyPKSetup(1λ,U)

 PhaseI−{ −−−−−−−−−−−−−−−−−−−−−→Submit attributes etS, Condition = { (S ≠ AT1*)∨(S ≠ AT2*) }←−−−−−−−−−−−−−−−−−−−retuns the SecretKey PKKeyGen(PK,MSK,S)

Challenge−{ −−−−−−−→chooses2 equal length challenge messages (m0,m1)←−−−−−−−−−−−−−−−−−−−−retuns the computed Ciphertext CT* picksbitϑ={ 0,1 } Encrypt(PK,AT1*,AT2*,Mϑ)

PhaseII−same as PhaseI

Gusess−{ guessϑ′ofϑ,Awinsifϑ′=ϑadvantageoftheAwinis:Adv(A)=| Pr[ϑ′=ϑ]−12 |

The proposed scheme accesses the Chosen Sensitive Policy Attack (CSPA) under the DBDH assumption by conducting a game (i.e., aPPT) between the adversary and the challenger.

Adversary(A) Challenger(C)

Initialization−{ −−−−−−−−−−−−−−−−−−−−−−−→Challenge:Submit acess structures:AT1*Setup−{ ←−−−−−−−−−−−−−−−−−−−−−−−−−retuns the Public Key PKSetup(1λ,U)PhaseI−{ −−−−−−−−−−−−−−−−−−−−−−−−−→Submit attributes etS, Condition : (S ≠ AT1*)←−−−−−−−−−−−−−−−−−−−−−−−−retuns a Trap door TdTrapSK()

Challenge−{ −−−−−−−−−−−−−−−−−−−−−−−−−→submits message m*and two hidden policies ATh0*, ATh1*←−−−−−−−−−−−−−−−−−−−−−−−−−retuns the challenge Ciphertext CT* picksbitϑ={ 0,1 }Encrypt(PK,ATh0*,ATh1*,Mϑ)

 PhaseII−{same as PhaseI

Gusess−{ guessϑ′ofϑ,Awinsifϑ′=ϑadvantageoftheAwinis:Adv(A)=| Pr[ϑ′=ϑ]−12 |

5  Construction of Proposed Method: HH-CP-ABE

Let ℒ={a1,a2,…,ak} be the k possible attributes with GO&GT multiplicative cyclic groups. However, these groups GO&GT work with the two elements; one is the prime order of P, and the second one is ω and results in the GO. Next, take the bilinear map e which is represented as e:GO×GO→GT. The hash function is H:{0,1}∗→Zk, and mapping to the desired element of Zk.

•   Setup(1λ,ℒ)→(PK,MSK) Took two inputs: a security parameter λ, and the attribute ℒ. Later, these inputs submit to the Trusted Key Authority Center (TKAC), resulting in two output values, the PK and the MSK.

PK=[ GO,ω,h,ωα,e(ω,ω)β,e(ω,h)β[ ωui,hui,ωui′,hui,ai|∀ai∈ℒ ] ](8)

MSK=[ α,β,[ ui,ui′,ai|∀ai∈ℒ ] ](9)

The algorithm selects α,β,∈RZk∗ and h∈RGO. Every attribute ai∈ℒ, and chooses ui,ui′∈RZk*.

•   Key Gen(PK,MSK,S)→SKS The algorithm considers three input parameters: PK, MSK, S, and attribute set. Here, DU receives after that TKAC picks γ,γ′∈RZk* with the output of a private key SKS for the Data User (DU).

SKS=[ ωβ+αγ,hβ+αγ,ωαγhγ′,hαγ+γ′,ωγ′,[ ωαγui,hαγui,ωαγui′,hαγui′,ai|∀ai∈S ] ](10)

•   Encrypt (PK,AT1,AT2,M)→C Took, the set of input parameters includes (1) PK, (2) M, (3) AT1 public access structure, and (4) hidden access structure AT2. DO outputs cipher text CT. However, DO considers the encryption key as Ckey∈RZk∗ and Message (M) and performs EnCkey(M) with symmetric encryption Advanced Encryption Standard (AES) using Proxy Node (PN). The procedure follows a tree-based access structure.

•   First, PN receives AT1 from DO and then randomly selects QX of AT1 in each node of x from the root node R1, PN picks QR1(0)=S1:(i.e.,S1∈RZk∗), and for the remaining nodes, it considers as QX(0)=Qparent(X)(index(X)). Now computed CT1′

CT1′=[ AT1,ωS1,hS1,[C1X=ωuiQX(0)],C2X=huiQX(0),x|∀x∈X1] ](11)

From the above, C is a set of attributes of all leaf nodes AT1. The privacy of AT1 is public because it describes in CT1'.

•   Next, PN generates CT1′ by collecting ωS2,hS2,e(ω,h)βS2 and S2∈RZk∗ from the DO.

CT1′=(ωS2,hS2,e(ω,h)βS2,CT1′)(12)

•   Next, PN generates CT^2 by collecting ωS3,hS4,e(ω,h)βS3,e(ω,h)βS4 and S3,S4∈RZk∗ from

The DO corresponding to AT2 from the root node R2, like to CT1′. Here, QR2(0)=S3;(i.e.,S3∈RZk∗).

CT2=(ωS4,hS4,CT2′)(13)

At final, DO  generates C=(AT1,AT2,EnCkey(M),CT1,CT2) and sends to PN and the uploaded C to the CS.

•   Trap SK→Td: DU first generates an index of attribute Hi for each ai∈S, and trapdoor Td is sent to CS through DU.

Td=[ T0=x′+y′,T1=hα(x′+y′),T2=ωα(x′+y′),T3=ω(β+αγ)x′,T4=h(β+αγ)y′,T5=ωαγx′hαγy′,T6=ωαγx′,[ T10i=ωαγui,T11i=hαγui,ai|∀ai∈S ][ T12Hi=ωαγui,T13Hi=hαγui,Hi|∀ai∈S ], ](14)

•   Tran (C,Td)→CT∞orψ: This algorithm mainly focuses on the first verification of access structure and estimation of cipher text.

•   Verification: The CS approach to trapdoor Td and then check that DU has the authority to decrypt CT checks the condition {(S≠AT1)∨(S≠AT1)}, and results in ψ.

•   Case 1: From AT1, if x is a leaf node and its attributes are a1, run the Fx algorithm recursively by CS.

Fx={ ωuiQX(0),huiQX(0),T10i,T11i,X }={ e(ω,h)αβQX(0)(x′+y′)ai∈SNullai∉S(15)

•   Case 2: The case in which x is considered a non-leaf node and XC is represented as its children. The attributes of a child node and its attributes sx are ai, and run the FXC algorithm recursively by CS.

FXC={ωuiQparent(XC)(index(XC)),huiQparent(XC)(index(XC)),T10i,T11i,XC}(16)

={ e(ω,h)αβQparent(XC)(index(XC))(x′+y′)ai∈SNullai∉S(17)

•   Case 3: R1 root of AT1, then runs the FR1 algorithm recursively by CS and computes D.

FR1=e(ω,h)αβS1(x′+y′)(18)

D=e(ω,h)αβS2(x′+y′)(19)

Similarly, from AT1, if y is a leaf node and its attributes are ai, runs the Fx algorithm recursively CS

FYHi={ωuiQY(0),huiQY(0),T11Hi,T12Hi,Y}(20)

Therefore, by observing the results of the mentioned functions, CS checks whether the concerned DU has the authority to access C at leaf node AT2. Once the results are confirmed, the DU can access true C with a hash value of yt=Ht∈. The failure case outputs will be ψ.

•   Ciphertext Computation CT∞: Checks the condition ((S=AT1)∧(S=AT2)); if it is OK, then CS attempts decryption with partial decryption of CT and returns CT∞ to the DU.

CT∞=(EnCkey(M),A,B,C)(21)

A=e(ω,h)βS2(x′)(i.e.,x=non leaf node)(22)

B=e(ω,h)βS4(x′)(23)

C=Ckge(ω,ω)β(S2+S4)(24)

•   Dec(CT∞,x′)→M: The algorithm runs End User (EU) and produces the symmetric secret key ck by performing decryption over Eck(M) using the decryption algorithm.

ck=C(AB)1x′=ck×e(ω,h)β(S2+S4)e(ω,h)β(S2+S4)x′x′(25)

6  The IoT Embedded Medical Environment

The proposed system applies to the medical industry. The system is illustrated in Fig. 4, and the complete details are as follows:

Figure 4: Application in IoT embedded medical environment

The Trusted Key Authority Center (TKAC), the government, generates the public parameter Pk. The hospital is the data owner and maintains the patients’ records as PRec from IoT devices such as B-scan ultrasound machines, Polymerase Chain Reaction (PCR) machines, and other instruments. Next, encryption is performed with the AS hidden access structure with the help of a trusted third party (a software company). Subsequently, the generated ciphertext CT is stored in the cloud server. Components that retain the access structure can prepare to access the data stored in the cloud.

Hospital–––→Enc(PRec,AS)Cloud(26)

A data user (clinician) accesses patient records from the cloud server by generating Td by running the Trap SK→Td.

The cloud server confirms the generated Td and verifies the access structure of the data user. If it is satisfied, the precomputed ciphertext CT∞ sent by the cloud server to the data user.

CS–––→Tran(C,Td)→CT∞orψDU(27)

Finally, the clinician performs decryption and receives the patient’s records.

Dec(CT∞)→PRec(28)

ck=C(AB)1x′=ck×e(ω,h)β(S2+S4)e(ω,h)β(S2+S4)x′x′(29)

7  Results and Discussion

7.1 IoT Infrastructure Setup

The wrist of the dominant arm, the chest, and the ankle on the dominant side were covered by three wireless Colibri Inertial Measurement Units (IMU). Using the In.dat file format, the raw data could be accessed from sensors. Not a Number (NaN) was used to indicate missing values that resulted from issues with the hardware configurations (such as a loss of sensor connectivity). Each record in all subject data files includes the fields given below:

•   Timestamp

•   Activity ID

•   Heart rate (bpm)

•   IMU hand temperature (c)

•   IMU hand 3D-acceleration (unit: ms−2, 13-bit resolution, 16 g scale)

•   IMU hand 3D-acceleration (unit: ms−2, 6 g scale, 13-bit resolution)

•   IMU hand 3D-gyroscope (unit: rad/s)

•   IMU hand 3D-magnetometer (unit: T)

•   IMU hand orientation

•   IMU chest temperature (c)

•   IMU chest 3D-acceleration (unit: ms−2, 13-bit resolution, 16 g scale)

•   IMU chest 3D-acceleration (unit: ms−2, 6 g scale, 13-bit resolution)

•   IMU chest 3D-gyroscope (unit: rad/s)

•   IMU chest 3D-magnetometer (unit: T)

•   IMU chest orientation

•   IMU ankle temperature (c)

•   IMU ankle 3D-acceleration (unit: ms−2, 13-bit resolution, 16 g scale)

•   IMU ankle 3D-acceleration (unit: ms−2, 6 g scale, 13-bit resolution)

•   IMU ankle 3D-gyroscope (unit: rad/s)

•   IMU ankle 3D-magnetometer (unit: T)

•   IMU ankle orientation

7.2 Data Set/Medical Record

We have presented a framework for intelligent healthcare delivery that can be utilized to detect chronic diseases through remote monitoring, including cardiovascular disease, Tele-mammography, Teleophthalmology, asthma, diabetes, Alzheimer’s, dementia, blood pressure, and cognitive impairments.

In this work, features that may be used to measure an athlete’s activity status using IoT-based infrastructure that leverages linked sensors were partially extracted from the Physical Activity Monitoring Dataset (PAMAP2). The selected datasets have 3850505 entries in their vast repository [37] that reflect a total of 18 primary diverse physical activities.

Such planned activities include:

1.    Lying down during idle time

2.    Slouching on the sofa in comfort

3.    Speaking in standing position

4.    Pressing a few T-shirts

5.    Vacuum Cleaning office spaces and shifting wares

6.    Climbing five-storied buildings

7.    Coming down five floors

8.    Walking at a decent pace (4–6 km/h)

9.    Nordic walking

10.   Cycling on a real bike at a steady speed

11.   Fast-paced Running

12.   Basic Rope Jumping or alternate foot jump

13.   Watching TV at home

14.   Working on a computer in the office

15.   Driving car crisscrossing office and home

16.   Shelving Laundry

17.   House Cleaning and dusting shelves

18.   Kicking a soccer ball

Nine subjects—one female and eight males —with an average age of 27.22 years and a range of 3.31 years—performed the primary 18 tasks while wearing three sensors and a heart-rate monitor.

7.3 System Configuration

The proposed scheme implements the specifications: (1) A personal computer with a 3.4 GHz processor, (2) 8 GB RAM, and Ubuntu 16.04.

7.4 Results

The complete results of the proposed system are clarified in Fig. 5 and Table 1. The total time required to complete encryption and decryption is shown in Fig. 5a. The storage costs related to the ciphertext for various attributes having Hidden Hierarchy (HH) data are shows in Fig. 5c. Moreover, the time and storage costs for different access structures with characteristics N = 30 are in Figs. 5b and 5d shown respectively.

Figure 5: Results analysis for CP-ABE schemes: (a) encryption time analysis of access structures (b) decryption time analysis of access structures (c) storage cost analysis of access structures (d) key generation time analysis of CP-ABE algorithms

Compared to other standard methods, the proposed scheme significantly improves the efficiency of encryption and decryption algorithms by reducing time. Moreover, it can be observed that the results show a significant linear relationship among the access structure attributes, as shown in Fig. 5a. The work in this scheme extends to several access structures, while the cost of encryption and decryption is low in HH-CP-ABE compared to the standard methods.

For example, in Fig. 5a, the cost of the encryption in HH-CP-ABE is 12 s compared to the previous systems (i.e., 8 and 3.5 s at N = 30). Similarly, at N = 50, the values are 13.7, 10, and 4.2 s. The increase in possible attributes in the respective access structures requires more time to perform the encryption times. Similarly, the decryption time reduction can be noticed in HH-CP-ABE compared to the existing systems; for example, in Fig. 5b the cost of decryption time in HH-CP-ABE is 3.1 s as contrasted to the current systems (2.3 and 2.1 s at N = 30). Also, at N = 50, the values are 3.8, 2.6, and 2.4 s.

Table 2 and Fig. 5c, show the proposed scheme has improved the storage cost efficiencies that decrease with two access structures, i.e., public and hidden. When this scheme is extended to several access structures, even adding more attributes, the storage capacity was significantly reduced by the HH-CP-ABE compared to the existing schemes. For example, in Fig. 5c, the storage cost in HH-CP-ABE is 17 KB compared to the existing systems (i.e., 21 and 32 KB at N = 30). Similarly, at N = 50, the values are 25, 36, and 48 KB. The increase in possible attributes in the respective access structures leads to better storage in the proposed scheme compared to the existing systems. Similarly, storage cost reduction can be noted in HH-CP-ABE as compared to the existing systems.

The study also focused on modifying an essential key generation time by different CP-ABE algorithms. From Table 3 and Fig. 5d the proposed HH-CP-ABE took less time to generate cipher text than all other standard techniques in all possible attributes.

The study also focused on modifying an essential key generation time by different CP-ABE algorithms. From Table 3 and Fig. 5d the proposed HH-CP-ABE took less time to generate cipher text than all other standard techniques in all possible attributes.

For example, in the case of the number of attributes at 30, the proposed method took only 3.5 s to generate the key. In contrast, the other two techniques run the same algorithm in 12 and 8 s. Similarly, when the number of attributes is 40, the proposed method took only 4.2 s to complete the key generation. In contrast, the existing methods ran 13 and 10 attributes, respectively, for key generation at the same time.

8  Complexity of Access Policy

A comparative analysis of the computational tasks related to access policies between the suggested method and other standard methods is done in this section. Most existing schemes, however, are non-tree-based, such as AND-gate, OR-gate, and LSSS matrix access policies [38–43].

The proposed scheme depends on a tree-based access policy combining conjunctive and disjunctive typical forms. In other words, it refers to a tree in which every attribute holds two types of values, one public and another hidden. The corresponding access policy is defined as follows:

AccessPolicy(A)=(Att1,1∨Att1,2)∧(Att2,1∨Att2,2)∧⋅⋅⋅(Attn,1∨Attn,2)(30)

Further, all the non-tree-based schemes are seen producing Linear and Polynomial Cipher texts. It is also observed that these methods failed to perform decryption operations at outsourcing, thereby leading to higher computation. Also, it is observed that the proposed process takes a minimum amount of constant decryption time over the known schemes. Hence, our suggested approach best fits such resource-constrained devices, as shown in Table 4. Resource-constrained devices can completely outsource decryption tasks by adopting the proposed concept.

9  Conclusions

This work proposes a Hierarchy Hidden Policy Ciphertext-policy Attribute-Based Encryption (HH-CP-ABE) scheme having an essential key search function. It can handle access structures in a hierarchical or graded manner. The non-hierarchical structures are compatible with existing CP-ABE methods with partially hidden access structures. In addition, the proposed system is particularly suitable for resource-constrained devices, where some tasks (especially encryption/decryption/searching) typically outsource. The implementation of the work in this paper proves that it is possible to maintain the privacy of the access policy with a simple function like a keyword search. Moreover, the scheme also proves to be secure in handling IoT data threats in the presence of a Decisional Bilinear Diffie-Hellman (DBDH).

Acknowledgement: We are grateful to all those with whom we have enjoyed working on this and other related papers.

Funding Statement: The authors received no specific funding for this study.

Conflicts of Interest: The authors declare they have no conflicts of interest to report regarding the present study.

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