Information Technology Reference
In-Depth Information
3.
After receiving Π(
r
), the TPA runs Algorithm 2 to verify the skip
list stored on the cloud server and retrieves
f
(
S
), where
f
(
S
) is the
label of the start node.
4.
Now, the TPA determines a suitable
c
(the number of blocks to be
verified) according to the desired probability of error detection
and ω.
5.
The TPA generates a challenge Ψ, picks a random
c
-element sub-
set
I
= {
s
1
,
s
2
, … ,
s
c
} of set [1,
n
], where we assume
s
1
≤ … ≤
s
c
. Then,
a random element ν
i
⊆
p
. The challenge Ψ specifies the positions
of the blocks to be checked. The TPA sends Ψ=
(
{
}
≤≤
)
i
, ν
to
i
sis
c
1
the prover (server).
6. After this, the server generates the proof
P
for each of the chal-
lenges sent by the TPA. On receiving a challenge Ψ=
(
{
}
≤≤
)
i
, ν
,
i
sis
c
1
s
s
c
c
∑
i
∏
i
is
σ
ν
the server computes
=
ν
m
∈
and σ
=
∈
G
, where
i
i
q
is
=
=
1
1
both the data blocks and the corresponding signature blocks are
aggregated into a single block, respectively. The server also sends
the signatures of the requested blocks as the set
{}
≤≤
1
. The
i
sis
c
{
}
=
{}
server then sends the proof
P
,,
to the TPA.
i
sis
c
≤≤
1
7.
After receiving the proof
P
to the corresponding challenge Ψ, the
TPA verifies the integrity by checking
s
c
?
∏
1
(
)
=
()
⋅
ν
e
σ
,
ge
Hmuv
i
i
,
is
=
If this equation holds, then TPA returns
TRUE
,
FA LSE
, otherwise.
A similar technique is used during an update.
Zhu et al. [43] (MULTI-PDP or multiple PDP) addressed the construction of
an efficient PDP scheme for distributed cloud storage to support the dynamic
scalability of service and data migration. For this, they consider the coexis-
tence of multiple CSPs to cooperatively store and maintain the client's data.
This scheme is based on a homomorphic verifiable response and hash index
hierarchy. Security for this scheme is based on a multiprover zero-knowledge
proof system, which can satisfy knowledge soundness, zero-knowledge, and
completeness properties.
3.4.7 Proof-of-Retrievability Schemes
The idea of PoR schemes is to verify a small number of blocks, chosen at
random, instead of the whole file. If there are errors, then the file can be
retrieved using error-correcting codes.
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