KR20060063271A - The key distribution technique of link security on epon - Google Patents

Abstract

The key distribution technique devised in the present invention is part of the link security technique applied to the data link layer. In general, link security technology consists of an encryption module for encrypting a message and a key management module for providing a key required for the encryption module. The key management module is a function module for securely managing keys, and is responsible for periodic update and secure distribution of keys. The present invention is a method for secure key distribution in a key management module, and in particular, has devised a key distribution technology applicable to Ethernet PON (hereinafter referred to as EPON). EPON is a network of physically point-to-many tree structures. This structure of EPON makes the transmission form different from upstream and downstream data so that the upstream is unicast and the downstream is broadcast. In particular, since downlink data is also transmitted in a broadcast form, there is a vulnerability in that downlink data is transmitted to all ONUs. When security is applied to such an EPON link, a key management module for providing a key to the encryption module is required, and the key management module needs a secure and efficient key distribution technology. The key distribution technology devised in the present invention is designed using a slow protocol that can be created and destroyed at the data link layer to be applied to the EPON. We designed a key distribution scheme using a function. In addition, the protocol devised in the present invention is a technique that can efficiently use a channel because the number of messages used and the number of transmissions of the messages are small, and it is easy to control the messages.

Ethernet PON, EPON, Master Key, Session Key, Security, Encryption, PRF, Key Distribution Protocol, Hash Function

Description

The key distribution technique of link security on EPON in the EPO section

1 illustrates a MAC frame structure;

2 illustrates a key management protocol frame structure according to the present invention;

3 is a diagram illustrating an information frame structure of a key management protocol according to the present invention;

4 is a diagram illustrating a key update request frame structure of a key management protocol according to the present invention;

5 is a diagram illustrating a key update response frame structure of a key management protocol according to the present invention;

6 illustrates a key verification request frame structure of a key management protocol according to the present invention;

7 illustrates a key verification response frame structure of a key management protocol according to the present invention;

8 illustrates a key verification confirmation frame structure of a key management protocol according to the present invention;

9 is a diagram illustrating a key management procedure state transition diagram according to the present invention;

10 is a flowchart illustrating a key management procedure according to the present invention.

The present invention relates to a key distribution technique used in a key management module when using a symmetric key encryption technique for EPON.

When entity A attempts to deliver a message to B in a communication network, if the message is in danger of being stolen by any user during transmission, it must be encrypted before being sent to ensure the safety of the message. In general, the encryption techniques used for security are divided into symmetric key encryption and public key encryption. The two technologies differ greatly in encryption algorithms, and the key distribution method is also different.

First, symmetric key encryption is an encryption technique in which the key used for encryption and the key used for decryption are the same. For example, if entity A used K _C to encrypt a message, then entity B that received it should use K _C to decrypt the received encrypted message. Algorithms used for symmetric key encryption include DES (Data Encryption Standard) and AES (Advanced Encryption Standard), and key lengths of each algorithm are 56 bits and 128 bits. The longer the key, the more secure it is, but the longer it takes to process a message. At present, it is known that the key length in symmetric key encryption is more than 128 bits in the processor technology.

The symmetric key algorithm is used as a security algorithm in most encryption modules because the time to encrypt or decrypt a message is short. However, since symmetric key encryption must have the same key for each entity group to communicate with, N (N-1) / 2 keys are required if there are N entities in the communication network. In order to distribute such a key, there must be a key distribution center in the communication network, and each entity receives and uses a key of an entity to communicate with the key distribution center through a predetermined secure channel. In addition, since the keys must be replaced periodically, the cost of distributing the keys becomes large.

Public key encryption is an encryption technique in which a key used for encryption and a key used for decryption are different. For example, if entity A used K _p to encrypt the message, then entity B that received it should use K _{p '} to decrypt the message. If entity A creates K _p and K _{p '} in the network and then discloses K _p to other entities on the network, the other entity that wants to communicate with A encrypts K _p and sends a message to A. A receiving the message encrypted with the public key K _p decrypts the message with K _{p '} .

But where has the K _p and K _{p 'is} a key characteristic that exists only in pairs, K _p is released, even if it is computationally infeasible to find a K _p. This is due to the RSA algorithm used for public key encryption. Unlike symmetric key cryptography, public key cryptography requires two keys for each entity, and it is easier to distribute than symmetric key cryptography because there is no need to use a secure channel to distribute K _p used as a public key. The advantage is that fewer keys are distributed. However, in order for the message encrypted by the RSA algorithm to be secured, the key length must be 1024 bits or more. Therefore, the RSA algorithm has a long time to encrypt or decrypt a message, so it is rarely used as a message security algorithm in a communication network.

In order to apply such security technology to the network layer, an encryption module and a key management module are required. The encryption module is a module that encrypts a message using an encryption algorithm and uses the symmetric key encryption or public key encryption technology described above. Each technology implements encryption using the keys provided by the key management module. The key management module manages keys to be provided to the encryption module. Key management includes key generation, storage, distribution, update, and revocation. In the case of using the symmetric key encryption technology, the key distribution is performed at the key distribution center through a secure channel. In the case of using the public key encryption technology, the key distribution is performed through the public channel.

EPON is a network of physically point-to-many tree structures. Applying symmetric key cryptography security technology to these EPONs, the encryption module will not be able to avoid the complexity of key distribution even with fast execution times. However, as described above, EPON is not a network structure, and logically has a point-to-point structure even though it has a physical point-to-many structure. That is, all ONUs are connected to one OLT. Thus, no effort is needed to distribute multiple keys to an entity, which is a disadvantage of symmetric key encryption.

For example, one ONU needs only one key to communicate with the OLT, and the ONU uses the same key when the destination transmits different data because it must pass the OLT to communicate with the other ONU. This is because the security of EPON is limited to security for a single link since its scope of application is the data link layer. Therefore, even if the symmetric key encryption technique is used in EPON, the number of keys required for encryption becomes the number of channels established by each ONU with the OLT, and is similar to the number of keys distributed when the public key encryption technique is used. In addition, the structural feature of the EPON is a key distribution in the form of one OLT to control a number of ONU.

EPON is a network of physically point-to-many tree structures. When transmitting data in EPON, downlink data from OLT to ONU is broadcast, and uplink data from ONU to OLT is unicast. In particular, although uplink data is transmitted with a single destination, downlink data cannot be physically prevented even if it has a single destination. Thus, a situation occurs in which an unintended ONU is sent. In such cases, security is needed to protect the message or to prevent misuse of the data in the EPON by any user.

In order to apply security technology to EPON, an encryption module for encrypting a message and a key management module for providing a key to the encryption module are required. The key distribution technique devised in the present invention is a link security technique applied to the data link layer and is a key distribution technique used by the key management module. Thus, this technique can be used in key management modules when link security is implemented in EPON. The key provided by the key management module to the encryption module must be generated in the OLT or ONU and distributed to the OLT or ONU.

It must be replaced periodically for security. What is needed is key distribution technology, and key distribution should be done using the most secure key distribution technology. Key distribution may be performed using a secure channel provided by the encryption module or by separately configuring a secure channel in the key management module. However, if the encryption module operates only in one direction when using the secure channel provided by the encryption module, that is, only the data from the OLT to the ONU is encrypted and the data from the ONU to the OLT is not encrypted, the key management module may be used. It is unavoidable to establish a secure channel in.

However, if a separate secure channel is configured in the key management module, the key management complexity is that the key management module has to separate modules that use encryption algorithms, such as encryption modules, and manage necessary keys separately from providing the encryption module. Significantly increased. Therefore, the best way is not to use a secure channel for key distribution in the key management module, but it is inevitable to use a secure channel when transferring keys through the channel. In view of such a situation, the present invention devised a technique for safely distributing a key to an EPON without transmitting a key through a channel.

In EPON, OLT and ONU have one master key (MK) with the same key, which is pre-distributed before encryption. The present invention is a technique for generating and distributing a session key, which is a key used for encryption, from a master key, and is not a technique for distributing a master key. The present invention has a hierarchical structure on the key to generate the key. Accordingly, the master key generates a pairwise master key (PMK), and the PMK generates a session key. At this time, the use of the PMK without directly generating the session key from the master key is to increase the security of the key by periodically replacing the PMK generating the session key.

The algorithm for generating keys uses the well-known pseudo random function (PRF). PRF is a hash function and has two characteristics and three characteristics.

Hash Function Properties

1. Convert any finite length input bit string x to a fixed length output bit string H (x).

2. For a given H and x, it is easy to calculate H (x).

Characteristics of Hash Functions

1. It is impossible to calculate the input value for a given output.

2. It is computationally impossible to find another input that produces the same output for a given input.

3. It is computationally impossible to find any two different input messages that produce the same output.

If you use more than 160bit output value for the unidirectionality and collision avoidance of PRF, it is difficult to find the key through the whole attack, so it has strong security. A total attack is an attack method that calculates by substituting all the numbers to find the key value. Therefore, an average of 2 ⁸⁰ or more attempts are required for an attacker to find a key.

The formula for generating a key using the PRF is as follows.

PMK = PRF (Anonce || Bnonce || MK) TK = PRF (Anonce || Bnonce || Aaddr || Baddr || PMK)                                              Pairwise Master Key (PMK): 16 bytes Anonce: Random random value generated by A, 16 bytes Bnonce: Random random value generated by B, 16 bytes Temporal Key (TK): 64 bytes Aaddr: MAC address of A, 6 bytes Baddr: MAC address of B, 6 bytes

When OLT creates Anonce and passes it to ONU, ONU creates Bnonce and passes it to OLT. OLT and ONU, which have received Anonce and Bnonce, generate PMK through PRF, and both have the same key value according to the hash function characteristic 2. In the same way that PMK is created, Anonce and Bnonce are regenerated and passed between OLT and ONU, and then each other's MAC address is added to the input value to create a TK. TK also has the same key value depending on the hash function characteristic 2. TK is divided into AK, BK, SAK and ICV, of which SAK is used for security for unicast communication between OLT and ONU. The function of each key is as follows.

AK (Authentication Key): Used to authenticate OLT and ONU. BK (Broadcast Key): Encrypts broadcast data in OLT and decrypts it in ONU. SAK (Secure Association Key): Used to encrypt and decrypt unicast data between OLT and ONU. ICV (Integrity Check Value): Used to check data integrity between OLT and ONU.

Such a key distribution method can avoid direct key delivery through the channel, thus eliminating the need to separately configure a secure channel for key delivery. If the key is delivered through the secure channel without using this method, the risk of double exposure is always present because the secure channel key is exposed to the attacker, and the data encryption key is also exposed to the attacker. The present invention avoids this risk. If the TK is exposed to the attacker, the PMK that created the TK is not exposed, so the updated TK can be used safely. In addition, the PMK, which is difficult to expose, is periodically replaced, so it has stronger security, and MK, which is the basis of key generation, has the strongest security since it has never been disclosed to the channel.

The present invention devised a technique for transmitting information necessary for key generation to an OLT and an ONU by using a key management protocol in a key distribution scheme that distributes a TK between an OLT and an ONU. Since the protocol devised in the present invention is a technology used in the data link layer, a frame generated and destroyed between the OLT and the ONU is used. That is, the key management protocol uses MAC frames that are generated and destroyed in the EPON interval to transfer necessary information between the OLT and the ONU. An OAM frame exists as a MAC frame that is generated and destroyed in the EPON section. The key management protocol uses a slow protocol as in the OAM protocol.

The MAC frame used in the data link layer has a frame structure as shown in FIG. 1, and when configured as a frame suitable for a key management protocol, it has a frame structure as shown in FIG. The frame used for the key management protocol is called a key management frame. Each field of the key management frame has the following meaning.

DA (Destination Address): 6 bytes. MAC address of the destination. Source Address (SA): 6 bytes. Sender's MAC address. Length / Type: 2 bytes. Length and Type Information Subtype: 1 byte. Subtype Information Flag: 1 byte. Defines the contents to be checked each time a key management frame is transmitted. Code: 1 byte. Identifies the type of key management frame. Data / Pad: Up to 107 bytes. Variable length. Defines the content of the message sent in the key management frame. FCS: 4 bytes. Defines the value to check for errors in the key management frame.

By applying the rules of Slow Protocol, DA should have a value of "1-80-c2-00-00-02", Length / Type should have a value of "88-09", and Subtype is 1 Use "4" in 4-10 except the value of -3. Since the minimum length of the MAC frame is 64 bytes, Data / Pad must have a value of at least 43 bytes, and the maximum length is 107 bytes. Here, even if the maximum length of the MAC frame is 1522 bytes, the maximum length of the frame used for the slow protocol is limited to 128 bytes, so the key management frame can extend information to only 107 bytes.

The Flag field consists of 1 byte and the function of each bit is as follows.

beat name Explanation 0 Local set done 0 = Local device does not have an encryption module or is not set 1 = Local device has an encryption module and is set One Remote set done 0 = Remote module does not have encryption module or is not set 1 = Remote device has encryption module and is set 2-7 reserved

The Set Done bit is divided into Local and Remote. When the OLT transmits a key management frame to the ONU, the Local Set done indicates the encryption module information of the OLT, and the Remote Set done indicates the encryption module information of the ONU. If the bit value is 0, it means that the encryption operation is not performed because there is no encryption module or the setting between each other is not correct. If there is no encryption module, there may or may not be a key management module.

If there is no key management module, there is no response to the request. If there is a key management module, the bit value will be filled with "0" and the rest with "Null". In both cases, since the encryption module cannot operate normally, it is treated as "0" which is the same state. If the bit value is " 1 ", it indicates a state in which the encryption modules exist and the encryption modules can operate because the settings are correct. Therefore, when the Local Set done and the Remote Set done are "1" at the same time, the encryption module can be actually operated. The Flag field is included in every key management frame and is configured to be processed as the first information about the frame. This allows the key management module to respond quickly to changes in the encryption module that occur during normal operation with the flag's two bit values set to "1". That is, when Local Set done or Remote Set done is changed to "0", the encryption module should be stopped. In addition, since the status information of the encryption module on the receiving side is transmitted to the Remote Set done each time the frame is transmitted, it is also possible to confirm whether the transmitting side manages the status information on the receiving side correctly in the received frame.

The Code field serves to distinguish the types of key management frames by one byte. The types of key management frames defined in the present invention are as follows.

Code value name Explanation One Information key management frame Configuration Information for Cryptographic Modules and Key Management Modules 2 Key update request key management frame Request a key update 3 Key update response key management frame Response to key renewal request 4 Key Validation Request Key Management Frame Key validation requirements 5 Key Validation Response Key Management Frame Response to key verification request 6 Key Validation Verification Key Management Frame Notice the success of key validation

Information key management frame

The structure of the information key management frame is shown in FIG. This frame is used when the key management module delivers its key management module configuration information and configuration information of the encryption module to the counterpart key management module. Bit information of the configuration information is as follows. The configuration information is information transmitted only when there is an encryption module. If there is no encryption module, if the Set done bit of the flag indicates "0", then all the configuration information will be filled with "Null". However, when the encryption module is present and does not operate, even if the set done bit of the flag indicates "0", if the operation status bit of the configuration information is "on", all configuration information should be filled.

beat name Explanation 0 Operating status 0 = encryption module off 1 = encryption module on 1-2 Encryption mode 0 = provide encryption only 1 = provide decryption only 2 = provide all 3-6 Encryption algorithm 0 = GCM-AES-128 1 = CCM-AES-128 2 = OCB-AES-128 3 = RSA 7-10 Key distribution algorithm 0 = no-Diffie-Hellman 1 = Diffie-Hellman 11-15 Reserved

The operating state is a bit that checks if the current encryption module is actually in operation in the system. That is, the bit information of the flag may be set when the operation state is “on” and the remaining information of the configuration information is synchronized with each other. However, if the encryption module does not operate and the operation state information indicates "0", all remaining bits of the configuration information are filled with "Null".

The encryption mode is a bit for a function provided by the encryption module. In the EPON, since the downlink is broadcast data and the uplink is unicast data, the encryption operation may not be performed on the uplink data in some cases. Or vice versa if necessary. If the security modules cannot synchronize with each other by processing the encryption mode information, the Flag bit should be filled with "0".

The encryption algorithm is an algorithm used when encrypting and decrypting data in the encryption module. All of the above algorithms are symmetric key algorithms except RSA. In some cases, the encryption module may have an independent module for operating a plurality of encryption algorithms. If the security module cannot be synchronized with each other by processing the encryption algorithm information, the Flag bit should be filled with "0".

The key distribution algorithm is a bit that conveys the method used by the key management module for distributing keys. The two algorithms are described as examples, but this part is used in the key distribution encryption module when a separate encryption channel is configured for key distribution. Pointer to the algorithm information. When a separate encryption channel is configured for key distribution, the data / pad field of the key management frame may be changed or a new key management frame may be defined and used. The key distribution algorithm devised in the present invention is a variation of the Diffie-Hellman method and does not separately constitute an encryption channel. If the security module cannot synchronize with each other by processing key distribution algorithm information, the Flag bit should be filled with "0".

Key update request key management frame

Encrypted messages can always be stolen by attackers, and message theft is the possibility that the key used for encryption can be exposed. Therefore, for security purposes, the key used for encryption should be replaced periodically. The structure of the key update request key management frame is shown in FIG. This frame is used to update the TK and PMK, which must be updated periodically. Since the PMK is not used for data encryption, the update cycle is relatively long. However, since the TK is used for data encryption and continuously exposed to the channel, the update cycle is short. Here, the reason for periodically replacing the PMK that is not used for data encryption is that PMK is used to replace the TK, and the factor for generating the TK is exposed on the channel and should be replaced periodically for strong security.                     

In the frame, the key index field identifies the type of key to be updated, and the Anonce field carries a random value necessary to generate the key. The key index of PMK is "0", and the key index of TK is "1". When the key update request key management frame is transmitted, the key cannot be generated until the key update response key management frame arrives. Key Update Response When the key management frame arrives, the key management module generates the requested key using its Anonce value and the sender's Bnonce value.

Key update response key management frame

The structure of the key update request key management frame is shown in FIG. The key update response key management frame is transmitted when a key update request key management frame is received. The key index field identifies the type of key to be updated, and the Bnonce field carries the value required to generate the key. The key index of PMK is "0", and the key index of TK is "1". After transmitting the key update response key management frame, the receiving key management module generates the requested key using the Anonce value and its own Bnonce value of the key update request key management frame.

Key Validation Request Key Management Frame

Even if a key is updated using a key update request and response key management frame, it is not 100% certain that the key is correctly delivered in the present invention which does not directly deliver the key. Therefore, verification of the updated key is required, and the message requesting this is the key verification request key management frame. The structure of the key verification request key management frame is shown in FIG. Key Validation Key management frame transmits index and key of Anonce and Bnonce to verify key to verify key. This value derives the value VK (Verification Key) for key verification by the following equation.

VK = PRF (Anonce || Bnocne || K _i ) K _i : Type of key to verify (i: (0) AK, (1) BK, (2) SAK)

The key management module on the transmitting side must generate a VK after transmitting the key verification request key management frame and wait for the reception of the key verification response key management frame.

Key Validation Response Key Management Frame

Key Verification Request The key management frame is sent with all the factors that can create a VK. The received key management module generates a key verification response key management frame, and the structure thereof is shown in FIG. The key verification response key management frame transmits the index of the verification target key and the verification value VK. The VK is generated in the same manner as described above.

Key Validation Verification Key Management Frame

In order to verify and generate a key, the key verification request / response key management frame shall transmit and receive the key verification request to the receiving party. If the key is verified after the key is updated, the key can be updated only after verifying the verification result. However, it is not necessary to pass this frame unless key validation is required due to key updates. The key verification confirmation key management frame is transmitted after receiving the key verification response key management frame from the transmitting side of the key verification request key management frame. The structure thereof is shown in FIG. Key Validation Verification If a key management frame is received and the result is not successful, the key MUST NOT be updated.

All the key management frames described so far are transmitted in the EPON section without being encrypted. As described above, the security characteristic of PRF is that even if the information to be delivered in the key management frame is leaked by the attacker, the key cannot be found within the valid time.

The state transition diagram of each procedure for the key distribution technique devised in the present invention is shown in FIG. The procedure for key distribution consists of three steps: key generation, key distribution, and key verification. The key update procedure executes a key distribution procedure to generate a key and distribute the generated key at a key update cycle. The key distribution procedure distributes the keys and, when the key distribution is complete, executes the key verification procedure. The key verification processor executes the key generation procedure after the key verification is completed. The key update procedure will wait for the next distribution cycle after updating the validated key. A state transition process of such a procedure will be described with reference to FIG. 10.

The invention can also be embodied as computer readable code on 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 media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, which are also implemented in the form of a carrier wave (for example, transmission over the Internet). It also includes. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

The key distribution technology described in the present invention is designed for application and use in EPON as part of network security technology. According to the present invention, the key management module in the OLT and ONU of EPON can distribute the key used in the encryption module safely and efficiently, and its features are as follows.

First, there is no need to separately configure a secure channel for key distribution by using PRF. PRF is a well-known hash function that has unidirectionality and collision avoidance. It is cryptographically secure when the output value is set to 160 bits or more. The present invention avoids direct key delivery in the channel by using a key distribution method using PRF. Therefore, it does not require a secure channel for a separate key distribution can reduce the complexity of the key management module.

Second, it uses a slow protocol. Slow protocol is a protocol using MAC frames in the data link layer. In the present invention, the key management frame is not leaked out of the EPON section by using the slow protocol. Therefore, the key management frame cannot be obtained outside of EPON, so it is safe within EPON. In addition, the slow protocol limits the number of frames that can be transmitted in one second and the maximum frame length to 128 bytes, which does not affect the amount of traffic in the EPON.

Third, key distribution can be accomplished with a relatively simple protocol. The present invention performs five steps of key update request / response, key verification request / response, and key verification verification while performing key distribution using a key management protocol. At this time, since the information transmitted in the frame is composed of a simple algorithm having only a simple input value and an output value, the complexity of the protocol can be reduced.

In addition, when the security technology is applied to the data link layer in a general network, the present invention has the scalability to be used in the key management module independently of the algorithm of the encryption module. If you install a device on the network and only set the master key between the devices, the key distribution will be done automatically according to the key distribution procedure. In addition, in the case of a shared LAN having a network structure, in order to use the present invention, a central control device such as an OLT that functions as a key distribution center is required.

Claims (1)

Key distribution scheme among link security technologies applicable to the data link layer in EPON.

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