PrivBCS: a privacy-preserving and efficient crowdsourcing system with fine-grained worker selection based on blockchain

Figures & data

Figure 1. A typical block structure.

Figure 2. System architecture of PrivBCS.

Figure 3. The structure of PrivBCS.

Table 1. Symbols used in our scheme.

Notation	Description
R	Requesters of crowdsourcing task
$W=\{W_1,\dots ,W_n\}$	Workers performing crowdsourcing tasks, where $W=\{W_i,i=1,2,\dots ,n\}$
KMC	Key Generation Center and Computing Center
$P_s=(x_s,y_s)$	Position of entities in BCS
MK	System master key generated by KMC
PK	System public key generated by KMC
Γ	Access control structure of data
$(P\mathrm{\_}pk,P\mathrm{\_}sk)$	Key pairs based on Paillier cryptosystem
$(EG\mathrm{\_}pk,EG\mathrm{\_}sk)$	Key pairs based on El-Gamal cryptosystem

Figure 4. The data flow of PrivBCS.

Table 2. Comparison of existing crowdsourcing systems.

	Decentralisation	Task assignment	Privacy protection	Access control	Collaborative storage
BFC	✓	✗	✓	✗	✗
zkCrowd	✓	✗	✓	✓	✗
MCS-Chain	✓	✗	✗	✗	✗
CrowdBC	✓	✗	✓	✗	✓
SecBCS	✓	✗	✓	✗	✗
Zebralancer	✓	✗	✓	✗	✗
SenseChain	✓	✓	✓	✗	✗
TSWCrowd	✓	✓	✗	✗	✗
Our Scheme	✓	✓	✓	✓	✓

Figure 5. Time overhead for encryption and decryption.

Figure 6. Computational time cost of encrypted data.

Figure 7. Time cost of file upload.