Ldasip: A Lightweight Dynamic Audit Approach for Sensitive Information Protection in Cloud Storage

Table 1

Symbol description table.

Symbol	Meaning
λ	A security parameter as input
G	Additive cyclic group whose two orders are big prime numbers q > 2^k
GT	Multiplicative cyclic group whose two orders are big prime numbers q > 2^k
e:G×G⟶GT	Bilinear mapping
H1/H2/H3	Hash functions:
	H1:{0,1}⟶G, H2:{0,1}⟶,
	H3 : G⟶
g,u	Generators of group G
ppub (mpk)	PKG randomly selects x0∈ and calculates Ppub = g^x0
Msk	s selected randomly by PKG
skID	The corresponding private key to ID, skID = b + x0H2(ID,B)modq, where b ∈ , B = g^b
Pk	Public key:pk = B·Ppub^H2(ID,B)modq
PP	Public parameter
	PP = {G, GT, e, q, , u, H1, H2, H3, ppub (mpk)}
formula (1)	= B·Ppub^H2(ID,B)modq
Entrust	Entrust = (H1(ID,IDTPA))^x. x ∈  as the secret key to generate authorization, and calculate V =  as the legal authority verification value.
mi	Data block of the file
C	The improved multibranch tree authentication structure
I	The index of the data block mi
Name	The file identifier
Vn	The current version number
ti	The timestamp
σi	File authentication tagσi=(H1(name||Vn||ti)·u^H3(mi))^skID
Φ	The ordered set of σi
Γ	Deputy root nodes signed by skID, Γ=(H1(R)) ^skID
γ	Root node signed by skID, γ=(H1(R)) ^skID
Chal	Challenge chal = {1, } i ∈ I, where  ∈  randomly generated by TPA
formula (2)	e (Entrust, g) = e(H1(ID,IDTPA),V)
formula (3)	e (γ,g) = e(H1(R),pk)
formula (4)	e (Γ,g) = e(H1(R),pk)
formula (5)