Information Technology Reference
In-Depth Information
checking that
H
2
,
0
computed from the
P
ath
c
1
matches
H
2
,
0
included in the
D
igest,
H
root
=
H
2
,
0
=
h
(
h
(
h
(
c
1
)
|
H
0
,
0
)
|
H
1
,
1
)
.
(4)
Remark 2.
Notice that the MHT can be built by a TTP and distributed to a
repository because a leaf cannot be added or deleted to
Φ
without modifying
H
root
2
which is included in the
D
igest and as the
D
igest is signed, it cannot be
forged by a non-TTP.
The 2-3 Tree.
In the AD, a 2-3 tree is chosen to build the MHT. In a 2-3 tree, each internal node
has two or three children (
t
). The main advantage of this type of tree
is that performing management tasks such as searching, adding and removing
a leaf can be performed in
o
(
log
(
n
)) [1] where
n
is the number of leaves. Each
leaf within the tree represents a certificate; certificates are distinguished by their
serial number and leaves are ordered by serial number. The leaves' order is
essential to prove that a certain certificate, identified by serial number
c
target
,
is not revoked (
c
target
∈{
2
,
3
}
Φ
). To do so, it is enough to demonstrate the existence
of two
adjacent leaves
: a minor adjacent leaf and a major adjacent leaf which
fulfill that
c
minor
∈ Φ
,
c
major
∈ Φ
and
c
minor
<c
target
<c
major
.
∈
/
5 Status Checking Protocol
We have developed a JAVA implementation of the AD called AD-MHT
3
. Next,
we briefly describe the fields that contain the two main JAVA classes of our
implementation:
-
The
TwoThreeTree
class contains the following fields: the number of levels,
the
RDI
ID
, a reference to the private key used to sign the
igest, the validity
period for the current
H
root
and a reference to the root node.
-
The
Node
class contains the following fields: a reference to the left child,
a reference to the middle child, a reference to the right child (this child
only exists if the node has 3 children), the biggest element of the subtree
that descends from this node denoted by
max
, the smallest element of the
subtree that descends from this node denoted by
min
and the cryptographic
value of this node (
H
i,j
).
D
Fig. 3 shows a sample 2-3 that represents a set of revoked certificates
Φ
=
{
. Notice that leaves on the left represent smaller serial num-
bers than leaves on the right.
2
To do such a thing, an attacker needs to find a pre-image of a OWHF which is
computationally infeasible by definition.
3
The software for the AD-MHT client and the AD-MHT server can be downloaded
from
http://isg.upc.es/cervantes
2
,
5
,
7
,
8
,
12
,
16
,
19
}