JP2001186119A - Key management method using tree structure and key management system, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a key management method and a key management system, that can continuously and efficiently add/delete subscribers. SOLUTION: Considering a dynamic tree structure B-tree with a root tree T, each subscriber ui corresponds to each leave 1i, a key KV is assigned to each vertex, v, each subscriber ui secretly has a set of keys corresponding to vertexes on a path from a corresponding leave 1i to a root R as the key of the subscriber ui, and since all the subscribers have a key KR corresponding to the root R in common, the key KR is used for a common key for contents distribution. In the case of adding/deleting a subscriber u, a leaf l corresponding to the subscriber u is added/deleted to/from a key management tree by the reconfiguration method of the B-tree to generate a new key management tree, keys corresponding to vertexes on a path from the added/deleted subscriber leaf 1 to the root R are newly generated, a message resulting from generated by encrypting the new key with a key corresponding to a slave of each apex on the path is broadcast to distribute the new key to subscribers belonging to partial trees of the slave of each vertex on the path.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an application technology of information security technology, and is applied to a broadcasting network such as a broadcasting network, a satellite broadcasting network, and the Internet.
The present invention relates to a key management method, a key management device, and a recording medium for managing a content encryption key for distributing useful electronic content (such as pay television broadcast) to a large number of subscribers among a large number of subscribers.

[0002]

2. Description of the Related Art As a typical example of the conventional method, the document CK
Wong, M. Gouda, SSLam [1], DMWallner, EJHarde
There is a key management method using a tree structure according to r, RCAgee [2] and literature [3]. [1] CKWong, M.Gouda, SSLam, Secure Group Communica
tion Using Key Graphs, SIGCOMM '98 (1998) [2] DMWallner, EJHarder, RCAgee, Key Management
for Multicast: Issues and Architectures, Internet Dr
aft draft-wallner-key-arch-01.txt (1998). [3] Japanese Patent Application Laid-Open No. 11-187003

[0003]

As described in the literatures [1], [2], and [3], a conventional method for sharing and managing keys using a key having a tree structure has been proposed. Has been studied. These use a tree-structured key to efficiently realize key updating accompanying addition / deletion of a subscriber. However, since the collapse of the balance of the tree structure due to the addition / deletion of the subscriber is not considered, there is a problem that the efficiency is deteriorated with the collapse of the balance of the tree structure. When key management is started, initial generation of a key management tree is required.

[0004]

SUMMARY OF THE INVENTION A key management method, a key management device, and a recording medium for managing a content encryption key between a large number of subscribers proposed in the present invention are provided in a static tree structure conventionally used. Instead of a dynamic tree structure
It is configured by using B-tree (see Ref. [4]) as a key management tree. The proposed key management method: ・ Even if the addition / deletion of subscribers is repeated, the balance of the key management tree is maintained, and the efficiency does not decrease. -It is not necessary to generate the key management tree initially, and the key management tree can be dynamically constructed according to the addition of the subscriber. It has the advantage that the conventional method does not have. As a result, a key management system that can add / delete subscribers more continuously and more efficiently than the conventional system is provided. [4] R. Bayer, E. McCreight, Organization and Maintenanc
e of Large Ordered indexes, Acta Infomatica 1 pp173
-189 (1972)

[0005]

[Embodiment CARRYING OUT THE INVENTION In the following examples, will be described an embodiment of the present invention. For example, when distributing useful electronic content (such as pay television broadcasting) to a large number of subscribers over a broadcast network such as a broadcasting network, satellite broadcasting network, or the Internet, the content can be viewed by anyone other than the subscriber. In order not to
It is necessary to broadcast the content after encrypting it using a common key cryptosystem. For that purpose, many subscribers need to share a content key for decryption. Also, when a subscriber subscribes / withdraws, the existing content key becomes unusable, so a new key must be redistributed to the subscriber. Therefore, a key management method for managing keys of a large number of subscribers is required.

[0006] Suppose simply that a new content key is distributed to each subscriber by encrypting it using the public key of the individual.
When the number of subscribers is n, O (n) broadcast transmission is required, which is not practical. Therefore, a key management method using the following tree structure is used. This is O (log (n))
This is a very efficient key management method in which the content key can be redistributed by broadcast transmission. FIG. 1 is a diagram showing an outline of the system of the present invention. Subscriber _{u 1, u 2, ···,} u n 100 is coupled through a broadcast channel 300 (network) and key manager C200.

A key management method using a tree structure according to [1], [2] and [3] and a B-tree according to [4] will be described below.
A proposed key management method and apparatus using -tree will be described. (Key Management Method Using Tree Structure) The key management method using the tree structure is as follows. Each leaf considering rooted tree T
Make each subscriber u _i correspond to l _i . For each vertex v, the key K _v
Assign. Each subscriber u _i has a key set corresponding to a vertex on the path from the corresponding leaf l _i to the root R.

[0008]

(Equation 4) Is secretly held as the key of the subscriber u _i . (However, P (v) represents the parent vertex of the vertex v.) All subscribers, because they share a key K _R corresponding to the root R, the key K _R and the common key for content distribution .

When the subscriber u _i is deleted, a key corresponding to the vertex on the path from the parent P (l _i ) of the leaf l _i to the root R of the deleted subscriber u _i is newly generated. I do. Then, a new key corresponding to the vertex on the path from the vertex v to the root R is added to the subtree under each vertex v on the path.

[0010]

(Equation 5) Is the child c _j (j = 1,2,) of the vertex v (other than the ancestor P ^a (l _i ) of the leaf l _i )
..., m)

[0011]

(Equation 6) By broadcasting this, it is distributed to subscribers belonging to the subtree rooted at their children. Similarly, in the case of performing the addition of new subscribers u _i, leaf l _i of the added subscriber u _i
A key corresponding to a vertex on the path from to the root R is newly generated, and the new key is encrypted and distributed to the subscribers belonging to the subtree below each vertex on the path using the root key of the subtree. .

Since the height of the rooted tree T is O (log (n)) with respect to the number n of subscribers, the content key can be redistributed by O (log (n)) broadcast transmission. FIG. 2 shows an example of a key management method using a tree structure. The key for subscriber u ₆ is

[0013]

(Equation 7) It is. If subscriber u ₆ is deleted, a new encrypted key

[0014]

(Equation 8) To all subscribers. (B-tree) Below, B-tree [4], one of the dynamic tree structures
Will be described. [B-tree] A B-tree of degree d means that every vertex other than the leaf and the root R has d + 1 ≦ m ≦ 2d + 1 children, and the root is 2 ≦ m ≦
A rooted tree T that has 2d + 1 children and all paths from leaves to roots are the same length. Let n be the number of leaves and h be the height of the tree. [Add leaf] Add a leaf to B-tree T and add a new B-tree
T 'can be made with O (log (n)).

A vertex v is added next to a leaf l having a B-tree T as follows. When the vertex v is added next to a certain vertex c, there are the following three cases. (The parent P (c) of the vertex c is written as f.) CaseA-0 When the vertex c is the root R of the B-tree T, a new root R ′ is created, and the vertices v and c are defined as children of the new root R ′. I do. CaseA-1 As shown in Fig.4. At this time, the vertices f is m <2d + 1 single child c _1, c _2, ···, because it has a c _m, vertex the vertex v f
And the child of CaseA-2 As shown in Fig.5. At this time, the vertex f is 2d + 1 children
c ₁ , c ₂ ,..., c _{2d + 1} , a new vertex f ′
And make the d children cd _{+ 2} , cd _{+ 3} , _{c2d + 1} of vertex f and vertex v the children of vertex f ', and add vertex f' recursively next to vertex f. [Delete leaf] Delete one leaf from B-tree T and create a new B-tree
T 'can be made with O (log (n)).

In the following manner, the leaf v can be deleted from below a certain vertex f of the B-tree T. When the vertex v is deleted from below a certain vertex f, there are the following four cases. CaseD-0 When the vertex f is the root R of B-treeT. If the root R = f has two children c ₁ , v, the vertex R = f, v is deleted and the vertex c _{1 is set} to a new root R ′ = c ₁ . Root R = f is m + 1> 2 children
If c ₁ , c ₂ ,..., _cm , v are present, the vertex v is deleted. CaseD-1 As shown in Fig.6. At this time, the vertices f is m + 1> d + 1 pieces of child _{c 1, c 2, ··· c} m, since it has the v, to delete the vertex v. CaseD-2 As shown in Fig.7. At this time, the vertex f has d + 1 children c ₁ , c
₂ , ... c _d , v and m> d + 1
Number of child _{c 1 ', c 2',} ···, there are vertices f'with c _m '. The vertex v is deleted, and the child _cm 'of the vertex f' is set as the child of the vertex f. CaseD-3 As shown in Fig.8. At this time, the vertex f has d + 1 children c ₁ , c
₂ , ..., c _d , v and all siblings of vertex f are d + 1
Has children. One of the siblings of vertex f is defined as vertex f ', and its children are defined as c ₁ ', c ₂ ', ..., cd _{+ 1} '. Remove the vertex v, the rest of the d number of child c ₁ of the vertex f, c _2, ···, vertices c _d f
, And recursively delete the vertex f ′ from below the vertex P (f).

FIG. 3 shows examples T _{1 and} T ₂ of a B-tree of degree 1.
Add a vertex v next to leaf 4 of T ₁ The T _2. T ₂
The T ₁ If you delete a vertex v from. (Proposed key management method using B-tree) First subscriber
make leaves l ₁ consisting only of _{B-tree T 0 = {l} 1 = R} for u _1, the key K _l1 with the private communication channel (e.g., encrypted with the public key of the subscriber u ₁₎ It is transmitted to the subscriber u _1. Thereafter, a subscriber is added / deleted by the following procedure [addition of subscriber] / [deletion of subscriber], and key management is performed dynamically and continuously. [Key Update] A key corresponding to a vertex on the path from the vertex w to the root R is newly generated. A new key corresponding to the vertex on the path from the vertex v to the root R is added to the subtree under each vertex v on the path.

[0018]

(Equation 9) To the child c _j (j = (other than the ancestor P ^a (w) of the vertex w) of the vertex v
1,2, ..., m)

[0019]

[Equation 10] Broadcast. This distributes the new key to the subscribers belonging to the subtree below the vertex v. Create a vertex v and the key K _v for the Add subscriber] new subscribers u, the key K _v using a secret communication channel (for example, encrypted with the public key of the subscriber u) transmitted to the subscriber u I do.

Next, the vertex v is added to the B-tree T
Add to When performing the [Add leaf] procedure, the key is updated as follows. CaseA-0 In case A-0, a new key K _{R '} ^new for a new root _R'
And broadcast the following:

[0021]

[Equation 11] CaseA-1 Case A-1 is as shown in FIG. Choose a new key K _f ^new for vertex f and broadcast the following:

[0022]

(Equation 12) Then, the key of the vertex on the path from the vertex P (f) to the root R is updated by [key update]. CaseA-2 Case A-2 is as shown in FIG. Choose a new key K _f ^new for vertex f and broadcast the following:

[0023]

(Equation 13) A new key K _{f ′} ^new is selected for vertex f _′ and the following is broadcast.

[0024]

[Equation 14] [Delete Subscriber] The vertex v corresponding to the subscriber u is deleted from the B-tree T by [Delete Leaf]. When performing the [delete leaf] procedure, the key is updated as follows. CaseD-0 Case D-0. If the root R = f has two children c ₁ , v, then
No key updates are required. Root R = f is m + 1> 2 children c ₁ , c
_2, if you have a ··· c _m, v, a new key to the root _R K R
Select ^new and broadcast the following.

[0025]

(Equation 15) CaseD-1 CaseD-1 is as shown in FIG. A new key K _f ^new is selected for vertex f and the following is broadcast.

[0026]

(Equation 16) Then, the key of the vertex on the path from the vertex P (f) to the root R is updated by [key update]. CaseD-2 Case D-2 is as shown in FIG. Choose a new key K _f ^new for vertex f and broadcast the following:

[0027]

[Equation 17] A new key K _{f ′} ^new is selected for vertex f _′ and the following is broadcast.

[0028]

(Equation 18) Then, the key of the vertex on the path from the vertex P (f) to the root R is updated by [key update]. CaseD-3 CaseD-3 is as shown in FIG. A new key K _{f ′} ^new is selected for vertex f _′ and the following is broadcast.

[0029]

(Equation 19) (Proposed Key Management Device Using B-tree) FIG. 9 is a block diagram of a key management device of the present invention. The administrator's key management device includes a command unit 1, a key management tree reconstructing unit 2, a key management tree storage unit 3, an encrypted message generation unit 4, and a broadcast transmission unit 5. The key management tree storage means 3 considers a dynamic tree structure B-tree as the rooted tree T, associates each leaf l _i with each subscriber u _i , and assigns a key K _v to each vertex v. The management tree is stored and stored. The command means 1 instructs the key management tree reconstructing means 2 to add / delete the subscriber u according to a command from the key manager 200. The key management tree reconstructing means 2 stores the key management tree held by the key management tree storage means 3 in the leaf l corresponding to the subscriber u.
Is added / deleted to create a new key management tree, and a key corresponding to the vertex on the path from the leaf l to the root R of the added / deleted subscriber is newly generated and stored in the key management tree storage means 3. . The encrypted message generating means 4 generates a new key corresponding to a vertex on the path from the leaf 1 to the root R of the added / deleted subscriber using a key corresponding to a vertex of a child of each vertex on the path. Generate an encrypted message. The broadcast transmitting means 5 broadcasts the encrypted message and distributes the new key to the subscribers belonging to the subtree below the child of each vertex on the path.

Each subscriber 100 receives the encrypted message broadcasted via the broadcast channel 300 by the receiving means 6 and obtains a new key by the subscriber key reconstructing means 7.
It is stored in the subscriber key storage means 8. Each subscriber 100 transmits the encrypted electronic content to the content decrypting means 9.
Decrypts using the key stored in the subscriber key storage means 8 to obtain electronic contents. The present invention is applied to an information system including a computer having a CPU, a memory, and the like, a user terminal used by a subscriber serving as an access main body, and a recording medium, and mechanically reads a CD-ROM, a magnetic disk device, a semiconductor memory, and the like. A program recorded using a possible recording medium is read into a computer to realize each component in the above-described embodiment.

[0031]

The key management method and the key management apparatus proposed by the present invention in which B-tree [4] is applied to the key management tree are as follows: The balance of the key management tree is maintained even if the addition / deletion of subscribers is repeated. It is kept and efficiency does not decrease. -It is not necessary to generate the key management tree initially, and the key management tree can be dynamically constructed according to the addition of the subscriber. It has the advantage that the conventional method does not have. As a result, a key management system that can add / delete subscribers more continuously and more efficiently than the conventional system is provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a system of the present invention.

FIG. 2 is a diagram showing an example of a key management method using a tree structure.

FIG. 3 is a diagram showing an example of a B-tree of degree 1.

FIG. 4 is a view for explaining B-tree leaf addition CaseA-1.

FIG. 5 is a view for explaining B-tree leaf addition CaseA-2.

FIG. 6 is a diagram for explaining Case D-1 of deleting a leaf of a B-tree.

FIG. 7 is a diagram illustrating Case D-2 in which a leaf of a B-tree is deleted.

FIG. 8 is a view for explaining a case D-3 in which a leaf of a B-tree is deleted.

FIG. 9 is a block diagram showing a key management device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Command means 2 Key management tree reconstruction means 3 Key management tree storage means 4 Encrypted message generation means 5 Broadcast transmission means 6 Receiving means 7 Subscriber key reconstruction means 8 Subscriber key storage means 9 Content decryption means 100 Subscription User u _i 200 key manager C 300 broadcast channel

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J104 AA01 AA16 EA04 EA17 NA02 PA05 PA07 5K030 GA15 HB18 HB21 HC01 JL02 JT10 KA05 KA06 LA07 LA19 LD07 LD19 MD04 5K033 AA08 BA13 BA15 CB01 CB13 CC04 DA01 DA18 DB10 EC02 9 BB03 BB04 CC02 DD09 EE03 FF03 JJ13 JJ18 JJ25 JJ67 KK43 KK57 LL03

Claims (5)

[Claims] 1. Consider a dynamic tree structure B-tree as a rooted tree T, associate each subscriber u _i with each leaf l _i , assign a key K _v to each vertex v, and assign each subscriber u _i is a key set corresponding to a vertex on the path from the corresponding leaf l _i to the root R Is kept secret as the key of its subscriber u _i ,
P (v) represents the parent vertex of vertex v. ) All subscribers, because they share a key K _R corresponding to the root R, the key K _R and the common key for content distribution, if you make the add / remove subscribers u, a B-tree Add leaf l corresponding to subscriber u to key management tree by reconfiguration method /
A new key management tree is created by deleting the key, a key corresponding to a vertex on the path from the leaf 1 to the root R of the added / deleted subscriber is newly generated, and the new key is created by a child of each vertex on the path. Generating an encrypted message using the key corresponding to the vertex, broadcasting the encrypted message, and distributing the new key to the subscribers belonging to the subtree under the child of each vertex on the path. A key management method using a characteristic tree structure. 2. An administrator's key management device includes command means, key management tree storage means, key management tree reconstructing means, encrypted message generation means, and broadcast transmission means. The key management tree reconstructing means instructs the key management tree reconstructing means to add / delete the subscriber u according to the command of the user.
The idea, in correspondence to each subscriber u _i in each leaf l _i, the key management tree assigned the key K _v stored and held for each vertex v, the key management tree reconstructing unit, the key management tree storage means Subscriber u in the key management tree held by
Is added / deleted to create a new key management tree, and a key corresponding to the vertex on the route from the leaf l to the root R of the added / deleted subscriber is newly generated and stored in the key management tree. The encrypted message generating means stores a new key corresponding to a vertex on the path from the leaf l to the root R of the added / deleted subscriber to a child vertex of each vertex on the path. A message encrypted using the key is generated, and the broadcast transmitting unit broadcasts the encrypted message,
A key management device for an administrator, which distributes a new key to subscribers belonging to a subtree below a child of each vertex on a route. 3. A subscriber key management apparatus includes a receiving unit, subscriber key storage unit, subscriber key reconstruction means is constituted by a content decryption unit, subscriber key storage means of each subscriber u _i is A set of keys corresponding to vertices on the path from the corresponding leaf l _i to the root R Is kept secret as the key of its subscriber u _i ,
P (v) represents the parent vertex of vertex v. The receiving means receives the encrypted new key broadcasted by the manager key management device, and the subscriber key reconstructing means encrypts the key using the key held in the subscriber key storage means. Decrypts the new key, updates the subscriber key held in the subscriber key storage means with the new key, and decrypts the key K _R corresponding to the root R shared by all subscribers with the content. Used as a common key for distribution, the key
Subscriber key management apparatus characterized by decoding the content to be distributed is encrypted with K _R. 4. A key management device using a tree structure is composed of an administrator key management device according to claim 2 and a subscriber key management device according to claim 3, which are connected via a network. The key corresponding to the root R shared by all the subscribers is used as a common key for content distribution, and when a subscriber u is added / deleted, the key management device for the administrator updates the key management tree. , Broadcast the updated key,
The subscriber key management device receives a new key and updates its own subscriber key. 5. Consider a dynamic tree structure B-tree as a rooted tree T, associate each subscriber u _i with each leaf l _i , assign a key K _v to each vertex v, and assign each subscriber u _i is a key set corresponding to a vertex on the path from the corresponding leaf l _i to the root R Is kept secret as the key of its subscriber u _i ,
P (v) represents the parent vertex of vertex v. ) All subscribers, because they share a key K _R corresponding to the root R, the key K _R and the common key for content distribution, if you make the add / remove subscribers u, a B-tree Add leaf l corresponding to subscriber u to key management tree by reconfiguration method /
A new key management tree is created by deleting the key, a key corresponding to a vertex on the path from the leaf 1 to the root R of the added / deleted subscriber is newly generated, and the new key is created by a child of each vertex on the path. A procedure for generating an encrypted message using a key corresponding to a vertex, broadcasting the encrypted message, and distributing a new key to subscribers belonging to a subtree below a child of each vertex on a path. A computer-readable recording medium that records a program to be executed by a computer.