KR100450763B1 - Communication system and key reusing method therefor - Google Patents

Abstract

A communication system and a key reuse method therefor are disclosed. In the method of reusing a key according to the present invention, determining whether to reuse a key through a security association setting between a first node and a second node performing authentication and authority verification through terminal-to-terminal security, and reusing the key. If the decision is made to include, the method includes reusing the key to encrypt and decrypt the first node in sending a message to the second node. By deciding whether to reuse the key in the security association setup step before sending the message, it is possible to reduce unnecessary data traffic and to know whether the key reuse technique between nodes in the system is reliable, thereby increasing the reliability and efficiency of the system.

Description

Communication system and key reusing method therefor}

The present invention relates to a communication system, and more particularly to a method for reusing a key in encryption and decryption.

In a communication system composed of nodes that perform authentication and authority verification through terminal-to-terminal security, such as a mobile Internet system, a message is encrypted and decrypted using a public key / private key pair.

In the Diameter protocol used to perform authentication, authorization, and accounting functions in a mobile IP system, a security association is established before transmission of a message. Based on this, the message is encrypted and decrypted. However, since the negotiation about the reuse of the key is not made when establishing the security association, the node receiving the message does not know whether the message transmitted from one node is encrypted by reusing the key. As a result, at least two message transmissions are additionally required in order to know whether a key is reused, which reduces the efficiency and reliability of the system.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a communication system having a high efficiency and reliability in message transmission and a key reuse method therefor, by determining whether to reuse a key prior to message transmission.

Another object of the present invention is to provide a computer readable recording medium having recorded thereon a program for executing the above key reuse method on a computer.

1 is a flowchart illustrating general information transmission of a Diameter CMS security application.

2 is a flowchart illustrating a case of reusing a key when transmitting a message in the system of FIG. 1.

3 is a flowchart illustrating a key reuse method according to the present invention.

4 is a configuration diagram of a header of Diameter AVP.

5 is a flowchart illustrating a case in which a requestor of a DSA supports a key reuse scheme and a receiver does not support the method of defining a new AVP.

According to an aspect of the present invention, there is provided a communication system including: a key reuse determiner configured to determine whether to reuse an encryption and decryption key through a security association with another node; A transmitter which reuses a key to encrypt a message and sends the message to the other node; And a receiving unit which receives a message from the other node and reuses a key to decrypt the message.

According to another aspect of the present invention, there is provided a method for reusing a key, including determining whether to reuse a key between a first node and a second node by establishing a security association; And in the case where it is determined to reuse the key, in the first node sending a message to the second node, encrypting and decrypting the key by reusing the key.

Hereinafter, a communication system and a key reuse method therefor according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart illustrating general information transmission of a Diameter CMS security application for providing a Cryptographic message syntax (CMS) security service in a mobile IP and AAA system.

The mobile IP system of the mobile Internet and mobile communication system (3rd generation IMT-2000 and later generation mobile communication system) is composed of a mobile terminal, a home agent, and a visiting agent. An AAA system (authentication, authorization, and accounting system) consists of a visited network AAA, a broker AAA, and a home network AAA. Each of these nodes is called a node, and these nodes use the Diameter protocol to perform authentication, authorization verification, and billing (AAA) functions for roaming subscribers, and end-to-end of the Diameter protocol. Diameter CMS Security Application, which is a security and public key infrastructure (PKI) technology, is applied.

The security association in the Diameter protocol is called DSA (Diameter Security Association). The DSA nodes 1 and 3 mean one of a visiting agent or home agent of a mobile IP system, a visiting network AAA, a broker AAA, or a home network AAA of an AAA system. A certification authority (CA) (2) is a system commonly applied by PKI and is used to issue certificates for DSA nodes. In the Diameter protocol, certificates are not used for individual subscribers, but are applied between PKI nodes to trust each other.

Initially, the DSA node A 1 generates its own public key / private key pair, registers its public key with the CA 2, and requests 111 to issue a certificate. If the CA determines that the node is legitimate, the CA issues a certificate of the DSA node A (112). The DSA node B 3, which is the other party to communicate with, generates its own public key / secret key pair in the same manner, registers its public key with the CA 2, and requests a certificate issuance (113). If the CA determines that the node is legitimate, it issues a certificate of the DSA node B (114).

After the authentication is completed, the DSA setup procedure starts between the Diameter node DSA node A and node B. The DSA node A 1 includes its certificate in a DSAR (Diameter Security Association Request) message, which is a DSA establishment request message, and transmits the certificate to the other party, ie, the DSA node B, which wishes to establish a DSA (115). Upon receiving this, Node B creates a DSAA (Diameter Security Association Answer) message, which is a DSA setup response message, and includes its certificate and forwards it to Node A (116). When the procedure is completed so far, the DSA is properly set up between Node A and Node B. Thereafter, node A and node B communicate on a secure secure association. The configured DSA must be reset before the expiration period (DSA Time-to-Live, DSA-TTL).

After the security association is established, the CMS security service, which is a process of exchanging Diameter messages between nodes, is performed. To transmit a Diameter message to Node B, Node A encrypts and digitally signs the Diameter message using B's public key in Node B's certificate included in the DSAA message (117). The result of encryption and digital signature is put in the Result Code Attribute Value Pair (AVP) and added to the message, and the message is transmitted to the DSA node B (118). AVP is a unit that composes Diameter protocol messages. Node B checks whether the result of the Result Code AVP of the received Diameter message is successful, and if successful, decrypts it with its private key, extracts the original text, and verifies that the sender is node A through signature verification (119). If this procedure completes normally, the Diameter text sent by DSA node A can be obtained. The translated text is used in other applications (120). However, if the result of the Result Code AVP contains a failure, it is notified to other applications.

To transmit a Diameter message to Node A, Node B encrypts and digitally signs the Diameter message with A's public key in Node A's certificate previously included in the DSAR message (121). The result of encryption and digital signature is put in the Result Code AVP and added to the message, and the message is transmitted to the DSA node A (122). Node A checks whether the result of the Result Code AVP of the received Diameter message is successful, and if successful, decrypts it with its private key, extracts the original text, and verifies that the sender is Node B through signature verification (123). If this procedure completes normally, you can obtain the Diameter text from DSA Node B. The translated text is used in other applications (124). However, if the result of the Result Code AVP contains a failure, it is notified to other applications. This communication applies to all subsequent Diameter messages.

2 is a flowchart illustrating a case of reusing a key when transmitting a message in the system of FIG. 1. As the security association is not negotiated for reuse of keys, problems that occur when communicating messages using CMS applications can be examined.

First, the authentication processes 211 to 214 and the security association setting processes 215 and 216 described with reference to FIG. 1 are performed.

According to the Diameter standard proposed by the Internet Engineering Task Force (IETF), when establishing a security association through DSAR and DSAA messages, related matters for future message communication are discussed. It ensures that the validity of security associations (DSA-TTL), certificates, various parameters required for certificate validation, and many other options are included in DSAR and DSAA messages. However, it does not contain a discussion of the key reuse mechanism. Diameter CMS security applications use RSA (Rivest, Shamir, and Adelman), a public key cryptosystem, in AAA systems, which leads to a decrease in the efficiency of AAA systems. Key reuse techniques are required to reduce the load on using these RSA cryptography. Therefore, in the initial message transmission, Node A does not know if Node B uses the key reuse scheme.

If Node A supports a key reuse scheme, Node A reuses the key to encrypt and digitally sign the Diameter message (217) and sends this Diameter message to Node B (218). If the node B receives the key reuse scheme, the node B can decrypt it, verify the signature, and send it to another application without any problem. However, if this technique is not supported, the Diameter specification states that it will be treated as a cryptographic error (219). Therefore, in response to this message, Node B contains the content indicating the cryptographic error in Result Code AVP (220) and sends it to Node A (221). In this case, Node A does not know whether Node B uses a key reuse scheme even after checking the Result Code AVP of the received message. This is because it is not possible to determine whether a cryptographic error actually occurred or whether it is an error on a key reuse technique. Therefore, this communication may occur again later, and to verify this, the Diameter message is encrypted and digitally signed (223) and sent to Node B (224) without the use of a key reuse technique (224), and the next message sent from Node B that confirmed it again. After receiving (228) and decrypting and signing verification (229) without using a key reuse technique, it may be determined whether to reuse the key for message transmission with the Node B. That is, at least two failure messages occur.

3 is a flowchart illustrating a key reuse method according to the present invention.

The number and order of messages shown in FIG. 3 are the same as those of FIG. 1. However, as will be described below, the key reuse method according to the present invention is characterized in that a content for key reuse is added in a transmission / reception step of a security association setup message.

First, the authentication process is performed as shown in FIG. 1 (311 to 314).

Node A then generates 315 a DSA setup request message that includes information indicating whether the key can be reused and sends it to Node B (316).

Node B knows from the DSA setup request message whether Node A can reuse the key, and based on this information and whether Node B itself can reuse the key, it sends the key when it sends a message to the subsequent CMS security services. You decide whether to reuse and encrypt and decrypt.

Similarly, Node B also generates (317) a security association setup response message that includes information indicating whether it can reuse the key and sends it to Node A (318). Node A can know from the DSA setup response message whether Node B can reuse the key and, depending on this information and whether Node A itself can reuse the key, it will reuse the key in future messages sent by the CMS security service. To determine whether to encrypt and decrypt.

Subsequently, when sending a message from Node A to Node B (320) and when sending a message from Node B to Node A (324), as determined, respectively, the encryption and digital signature of the message with or without key reuse The message is then sent. In this case, unlike the case of FIG. 2, since failure messages for determining whether a key is reused do not occur, reliability and efficiency of the AAA system itself can be increased.

There are two ways to add a negotiation for key reuse to security association setup messages (DSAR, DSAA). The first is to use header reservation bit of CMS related AVP among security association setup message, and the second is to define and use key reuse AVP for each operator by Diameter. The following two methods will be described in turn.

The first method is to use the reserved bit in the header of the CMS related AVP. To this end, look at Diameter AVP.

4 is a configuration diagram of a header of Diameter AVP.

The 8 bits after the AVP-Length field 401 (402 to 405) represent AVP Flags and indicate the characteristics of the corresponding AVP. The 'V' bit 402 is a Vendor-Specific bit indicating whether an optional field Vendor-ID appears in the AVP header. The 'M' bit 403 is a Mandatory bit and if this bit is set the AVP must be interpretable at the Diameter node that received the message. If this bit is set and the message is uninterpretable, the message is rejected at the node. 'P' bit 404 indicates whether a CMS security application has been applied. Finally, the 'r' bit 405 is a reserved bit and is not used previously and is set to zero. This bit can be defined and used in various Diameter applications, and the key reuse method according to the present invention uses this 'r' bit to negotiate key reuse at both nodes.

In order to negotiate key reuse through the method according to the present invention, there should be an AVP that appears in common in both the security association setup message DSAR and the DSAA message, and must be included and does not affect other applications. In addition, AVP, which contains other agreements for using CMS security applications, is most desirable. Therefore, in the key reuse method according to the present invention, it is preferable to use the 'r' bit of the DSA-TTL AVP header that can satisfy all these conditions for negotiation of key reuse.

Depending on whether or not the key reuse scheme is supported, the following four cases occur: If the two nodes that want to establish a security association do not support the key reuse scheme, then the node sending the request message to establish the security association must use the key reuse. If the node that supports the mechanism and receives the request message does not support this technique, the node that sends the request message to establish a security association does not support the key reuse scheme and the node that receives the request message supports this technique. In this case, both nodes wishing to establish a security association support both key reuse techniques.

The first case is the case of sending and receiving without setting the last bit of DSA-TTL AVP 'r' Flag of DSAR, DSAA. In the second case, the node sending the DSAR sets the last bit of the DSA-TTL AVP 'r' Flag, but the node sending the DSAA sets the last bit of the DSA-TTL AVP 'r' Flag of the DSAA message since the node sending the DSAA does not support key reuse. If you do not send. Therefore, the key reuse scheme is not used for communication between two nodes.

In the third case, the node sending the DSAR does not support key reuse, so the last bit of the DSA-TTL AVP 'r' Flag is not sent. The node receiving this message supports key reuse but sends the DSA-TTL AVP 'r' Flag last bit of the DSAA message without setting the last bit because the DSA-TTL AVP 'r' Flag last bit of the request message is not set. Therefore, the key reuse scheme is not used for communication between two nodes.

In the last case, the sending node of the DSAR sets the last bit of the DSA-TTL AVP 'r' Flag, and the node receiving this message supports the key reuse scheme, so the last bit of the DSA-TTL AVP 'r' Flag is set in the DSAA message. Send it. Therefore, in this case, the two nodes will use the key reuse technique to perform subsequent communication.

The second method to negotiate the key reuse technique is to define and use the key reuse AVP for each provider by the operators using Diameter. The following AVPs can be defined. This definition follows the AVP definition of the Diameter protocol.

First, the KeyReuse-Request-Flags AVP is an AVP included in a DSAR message and indicates whether to use a key reuse. The content of this AVP is of type Enumerated and is defined to have the following values:

NO_KeyReuse_RESPONSE is 0. If this value is present, the sender of the message does not use the key reuse scheme. Therefore, it should not include the key reuse response AVP in the response message.

KeyReuse_RESPONSE indicates 1. If this value is present, the sender of the message can support the key reuse scheme, and therefore requires that the key reuse response AVP be included in the response message.

The following KeyReuse-Responses AVP is an AVP included in the DSAA message and represents a response to the key reuse request. KeyReuse-Request-Flags If AVP contains KeyReuse_RESPONSE, it shall be included in the DSAA message. The content of this AVP is of type Enumerated and is defined to have the following values:

KeyReuse_Support represents 0. If this value is present, the sender of the message uses the key reuse scheme.

KeyReuse_Not_Support represents 1, and if this value is present, the sender of the message does not support the key reuse scheme.

As in the case of using the first method, the DSA-TTL AVP 'r' Flag, four cases may occur depending on whether each node supports key reuse. If the sender of the DSAR uses the key reuse scheme, the content of the KeyReuse-Request-Flags AVP is set to KeyReuse_RESPONSE, and if it is not supported, it is sent with NO_ KeyReuse_RESPONSE. The receiver of the DSAR is the key reuse scheme if the KeyReuse-Request-Flags AVP is NO_KeyReuse_RESPONSE. Since this is not used, it is not necessary to include the KeyReuse-Responses AVP in the DSAA message. If KeyReuse_RESPONSE, the KeyReuse-Responses AVP set to KeyReuse_Support or KeyReuse_Not_Support is included in the DSAA message according to whether or not the key is supported.

5 is a flowchart illustrating a case in which a requestor of a DSA supports a key reuse scheme and a receiver does not support the method of defining a new AVP.

Since Node A supports the key reuse scheme, the DSA setup request is generated by setting the content of the KeyReuse-Request-Flags AVP to KeyReuse_RESPONSE (501), and transmitted to Node B (502). Node B receives the DSAR and includes the KeyReuse-Responses AVP in the DSAA message because the KeyReuse-Request-Flags AVP is KeyReuse_RESPONSE and generates a DSAA message with the KeyReuse-Responses AVP set to KeyReuse_Not_Support because it does not support key reuse. 503, and transmits to Node B (504).

As described above, the key reuse method according to the present invention can minimize the occurrence of error messages that may occur when transmitting and receiving messages of the AAA protocol applied to the mobile Internet and mobile communication. By further improving the usage of the key reuse scheme, it is possible to reduce unnecessary data traffic and to know whether the key reuse scheme of the counterpart node that was unknown is clear, thus making a more reliable and efficient AAA system.

The present invention can be embodied as code that can be read by a computer (including all devices having an information processing function) in a computer-readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording devices include ROM, RAM, CD-ROM, magnetic tape, floppy disks, optical data storage devices, and the like.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

According to the communication system and the key reuse method according to the present invention, by determining whether or not to reuse the key in the security association setting step before the transmission of the message, unnecessary data traffic can be reduced and the key reuse technique can be clearly known between nodes in the system. It can increase the reliability and efficiency of the system.

Claims (9)

A communication system including a plurality of nodes performing authentication and authority verification through terminal-to-device security, (a) determining whether to reuse a key between the first node and the second node in the process of establishing a security association before sending the message; And (b) if the key is to be reused in step (a), encrypting and decrypting the key by reusing the key in the transmission of the message between the first node and the second node. A key reuse method, characterized by reusing encryption and decryption keys. The method of claim 1, wherein step (a) comprises: (a1) sending a security association establishment request from the first node to the second node, the information including information indicating whether the key can be reused at the first node; (a2) at the second node, determining whether to reuse the key according to whether the key is reusable at the first node and whether the key is reusable at the second node; (a3) sending, from the second node to the first node, a security association establishment response that includes information indicating whether the key can be reused at the second node; And (a4) determining whether to reuse the key according to whether the key is reusable at the second node and whether the key is reusable at the first node. 3. The method of claim 2, wherein said communication system is based on a Diameter protocol. 4. The method of claim 3, wherein the information indicating whether or not the key is reusable is indicated by setting a reservation bit included in a header of Diameter AVP to 0 or 1. 5. The method of claim 4, wherein the Diameter AVP is a DSA-TTL AVP. 4. The method of claim 3, wherein the information indicating whether the key can be reused is represented by using a new AVP defined according to the AVP definition method of the Diameter protocol. A communication system including a plurality of nodes performing authentication and authority verification through terminal-to-device security, A key reuse determiner configured to determine whether to reuse an encryption and decryption key by establishing a security association with another node before transmitting a message; A transmitter which reuses a key to encrypt a message and sends the message to the other node; And And a node including a receiver which receives a message from the other node and reuses a key to decrypt the message. 8. A communication system as claimed in claim 7, wherein said communication system is based on Diameter protocol. (a) determining whether to reuse a key through a process of establishing a security association before message transmission between a first node and a second node performing authentication and authority verification through terminal-to-terminal security; And (b) in the case of determining to reuse the key in step (a), recording a program for causing the computer to execute the step of reusing, encrypting and decrypting the key in transmitting the message to the first node and the second node. Computer-readable recording media.