Method and apparatus for providing authentication in a communication system

ES 2 360 943 T3

DESCRIPTION

Method and apparatus for providing authentication in a mobile communication system

Field of the invention

This invention relates to encrypted communications, including but not limited to air interface communications within secure communications systems.

Background of the Invention

Encrypted voice and data systems are well known. Many of these systems provide secure communications between two or more users by sharing an item of information between users, which allows only users who know it to properly decrypt the message. This piece of information is known as a variable encryption key, or key for short. Loading this key into the actual encryption device on the secure communications media unit is a basic requirement that enables secure communications to occur. To maintain security over a long period of time, the keys are changed periodically, typically weekly or monthly.

Encryption is known to be performed on an end-to-end basis within a communications system, for example, the encryption of a message at the source communications unit (also known as a mobile station), passing it transparently ( that is, without decrypting it) through any number of channels and / or infrastructure elements to the end-user communications unit, which decrypts the message.

The Trunk Terrestrial Radio (TETRA) communications regulations are currently used in Europe (hereinafter TETRA Regulations), with the potential for expansion to other locations. Calls in the TETRA Standard for the air interface are also known as encryption of air traffic or over the air. Air interface encryption protects information on the air interface between the infrastructure and the mobile subscriber. TETRA Regulations calls to an authentication center, also known as a key management service or key management center, are to generate, distribute, and authenticate encryption keys and users. However, the TETRA regulation does not specify how to implement an authentication center, nor how to generate, distribute and authenticate the key material for the system devices or mobile stations for the information that passes through the infrastructure or the SwMI (Switching Infrastructure and Management), as it is called in the TETRA Regulation.

The TETRA standard fails to provide the definition to minimize the load for call processing and bandwidth, to provide encryption and authentication in a fault-tolerant way for equipment, to support wide area communications, and to store data. keys to all communication units without the undue burden of storage at local sites.

GB2332 594 describes a method of processing a service request in a communication system in which at least part of the service request is encrypted. The method includes the steps of receiving a service request from a communications unit, attempting to authenticate the service request, determining, in response to a failure to authenticate the service request, the number of failures that have previously occurred for the service request. communication unit, and providing, in response to the number, the service of limited duration for the communication unit.

Accordingly, there is a need for a method and apparatus to provide a secure infrastructure for a communication system that uses encryption over the air interface and generates, distributes and authenticates encryption keys and users without causing undue burden on processing. of call, bandwidth, security and storage.

Summary of the Invention

According to one aspect of the invention there is provided a method comprising the steps of receiving, from a mobile station, a communication request in a communication system; determining if the request is encrypted; when the request is not encrypted, sending a request to authenticate the mobile station with a device of the system infrastructure in the communication system; when the request is encrypted, determining if the mobile station is powering up; when the mobile station is powering up and the request is encrypted, sending a request to authenticate the mobile station with the system infrastructure device in the communication system; when the mobile station is not powering up and the request is encrypted, determining if the request is encrypted using a valid key; when the mobile station is not powering up and the request is encrypted using a valid key, allowing the mobile station to access the system without request for authentication.

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Preferably, the method further comprises the steps of: storing authentication requests for a period of time when the system infrastructure device is not available; when the system infrastructure device becomes available, redirecting stored authentication requests to the system infrastructure device.

Preferably sending the authentication request of the mobile station to a device of the infrastructure of the system comprising sending the authentication request of the mobile station to a zone controller in the area in which the mobile station is located.

The method further comprising preferably receiving a confirmation that authentication has passed for the mobile station.

Preferably the authentication is performed by a first device of the system infrastructure using session authentication information that was received from a second device of the system infrastructure.

Preferably at least a segment of the received session authentication information is encrypted.

Preferably the, at least one segment of the received session authentication information is encrypted using an intrakey that is used only by the system infrastructure devices other than the mobile station within a zone to encrypt at least the information of the session. session authentication that is distributed within the zone.

Preferably, the first device of the system infrastructure is a visitor location register located in an area, and the second device of the system infrastructure is a local location register located in the same area.

Preferably, the, at least one segment of the received session authentication information is encrypted using an interkey that is shared by a plurality of zones and that is used by a system infrastructure device other than the mobile station in one zone in the plurality of zones to encrypt at least the session authentication information to convey to another device of the system infrastructure other than the mobile station in another zone in a plurality of zones.

Preferably, the first device of the system infrastructure is a visitor location record located in one area, and the second device of the system infrastructure is a local location record located in a different area.

Preferably the method is performed at any one of the base stations and base site

Brief Description of Drawings

FIG. 1 is a block diagram of a secure communication system according to the invention. FIG. 2 is a block diagram showing key distribution stacks in accordance with the invention. FIG. 3 and FIG. 4 are block diagrams showing key storage within a communication system according to the invention.

FIG. 5 is a diagram showing the storage of keys and the distribution of authentication information within a communication system according to the invention.

FIG. 6 is a diagram showing the storage of authentication information and the authentication decision that is made within a communication system according to the invention.

FIG. 7 is a diagram showing the authentication of a mobile station by an authentication center in accordance with the TETRA Standard.

FIG. 8 is a diagram showing the authentication of an authentication center by a mobile station in accordance with the TETRA Standard.

FIG. 9 is a diagram showing key storage and distribution of authentication information between a communication system and a mobile station in accordance with the invention.

FIG. 10 is a diagram showing a key extraction within a communication system according to the invention.

FIG. 11 is a diagram showing a key entry within a communication system according to the invention.

FIG 12 is a diagram showing the distribution of a static encryption key to a base station within a communication system according to the invention.

FIG. 13 is a diagram showing the distribution of a static encryption key to a mobile station within a communication system according to the invention.

FIG. 14 is a diagram showing the distribution of a common encryption key for a mobile station and a base station within a communication system according to the invention.

FIG. 15 is a diagram showing the distribution of a group encryption key to a base station

ES 2 360 943 T3 within a communication system according to the invention.

FIG. 16 is a diagram showing the distribution of a group encryption key to a mobile station within a communication system according to the invention.

FIG. 17 is a flow chart showing a method of persistence of keys at a site in a communication system according to the invention.

Description of a Preferred Embodiment

The following describes an apparatus and method for providing a secure infrastructure for a communication system that uses air interface encryption and generates, distributes, and authenticates encryption keys and users without causing undue burden on call processing. , bandwidth, security and storage. System devices are divided into groups or stacks, and encryption keys are defined to provide a secure transfer of key material between system devices.

In FIG. 1 shows a block diagram of a secure communication system that is comprised of a plurality of zones. The secure communications system is comprised of a plurality of system devices that comprise the infrastructure of the system. The Key Management Service (KMF) 101 transfers security data, such as session authentication information and encryption keys, to a User Configuration Server (UCS) 103, which redirects the information and data to the appropriate zone based on configuration data within UCS 103. Communications for a first zone are provided by a plurality of system devices including a Zone Manager (ZM) 105, a Zone Controller (ZC) 107 that includes the Local Location Register (HLR) 109 and a Location Register of Visited (also known as Visitor's or Visitor's) (VLR) 111, an air traffic routing device (ATR) 113, and a plurality of base stations (BS) 115 and 117 located at a plurality of communication sites within the first zone. Communications for the second zone are provided by a plurality of system devices including a ZM 119, a ZC 121 that includes a HlR 123 and a VLR 125, an ATR 127, and a plurality of BS 129 and 131 located in a plurality of communication sites within the second zone. BS 115, 117, 129, and 131 communicate with a plurality of mobile stations (see FIG. 4). The ZCs 107 and 121 communicate over a network 133, such as a local area network or a wide area network such as an IP (Internet Protocol) network. Only two zones and their associated system devices are shown for the sake of simplicity, although any number of zones can be successfully incorporated into the secure communication system.

For the sake of simplicity, not all system devices will be shown in each of the Figures, but rather a representative set of system devices will be provided illustrating a particular concept. Similarly, not all key material is shown stored on every device in the system for the sake of space. Each of the messages containing a key, key material, configuration, or other information is transferred with a related identity (ID) such as the ITSI or GTSI, although the ID is generally not shown in the drawings for space considerations. .

The KMF 101 is a secure entity that stores the authentication key (K) for each of the mobile stations (MS) or communications unit, such as a portable or mobile two-way radio, the access door of the Operation of the Direct Mode (DMO), receiver, scanner, or transmitter (eg, see devices 401, 403, and 405 in FIG. 4). The KMF 101 provides a random seed (RS) and associated session authentication keys (KS and KS ') for each of the mobile stations associated with the secure communication system. The KMF 101 also imports / generates various air interface keys, such as the Static Encryption Key (SCK), the Group Encryption Key (GCK), and the Common Encryption Key (CCK), for distribution on the web. system. The KMF 101 functions as the Authentication Center (AuC), as it is called in the TETRA communications standard, in the system. Typically, there is one KMF server per system, although there may be one or more KMF clients per system.

The UCS 103 is a single point of entry for configuration data in the system. In the preferred embodiment, UCS 103 stores and distributes session authentication information, such as RS, KS, and KS ', to the appropriate local area in the system. The UCS 103 functions as a non-real-time distribution point for session authentication information in the system.

The ZM 105 or 119 is a management database for a zone. In the preferred embodiment, the ZM 105 or 119 stores the session authentication information, such as the RS, KS, and KS ', for the zone managed by the particular ZM 105 or 119. The ZM functions as a non-storage service. in real time for authentication information in the zone.

The ZC 107 or 121 perform real-time authentication for mobile stations in your area. The ZC uses the session authentication information, such as RS, KS, and KS ', to perform real-time authentication. The HLR 109 or 123 stores the session authentication information for each of the MS that has the HLR 109 or 123 as its local HLR. The VLR 111 or 125 stores the session authentication information for each of the visiting MSs in the area of ​​the VLR 111 or 125. The ZC 107 or 121 perform the real-time distribution of your

ES 2 360 943 T3 session authentication information of the local mobile stations when the MS is roaming outside its home area. In the preferred embodiment, an HLR 109 or 123 and a VLR 111 or 125 are part of each of the zone controllers and operate on behalf of the same zone to which the zone controller is associated. The HLR 109 or 123 and the VLR 111 or 125 can be part of other devices in the system or they can be independent devices. The derived encryption key (DCK) is generated during authentication. The ZC 107 or 121 generate and distribute the DCK for MS to BS 115, 117, 129, and 131 that require the DCK for secure communications.

The ATR 113 or 127 is the conduit used by the KMF 101 to send the key re-provisioning or key update messages for an MS such as SCK and GCK. KMF 101 sends key updates for mobile stations to local area 113 or 127 ATR for dissemination. All key replenishment acknowledgments (ACKs), whether originating from infrastructure or MS, pass through ATR 113 or 127 to KMF 101.

Each of the BS 115, 117, 129 and 131 receives and transmits authentication messages over the air interface. Each of BS 115, 117, 129 and 131 acts as a transmitter for its associated ZC 107 or 121 and as a receiver for the MS in the system. BS 115, 117, 129 and 131 use the DCK for encryption of the air interface with the MS. BS 115, 117, 129 and 131 are responsible for sending key material to MS 401, 403, 405, and 407. The result of some of these operations (SCK, GCK) is sent back to KMF 101. Since each of the base sites is substantially comprised of one or more base stations, the terms base site (or site) and station base are used interchangeably in this document, both sharing the acronym BS. In the preferred embodiment, the TETRA site controller (TSC) connects all the base stations at one site, stores the key material, and distributes the key material to the base stations as needed, making the keys available, therefore , to all base stations at one site. Thus, when a key is said to be stored in a base station or base site, in the preferred embodiment, the TSC actually provides storage for the base station for the key material. Because key storage and distribution and other key-related functions can be performed by a base site, base station, or TSC, these terms are considered interchangeable for the purposes of this document.

The Mobile Station (MS) authenticates the system and / or is authenticated by the system using a challenge-response protocol. Each of the MS has its own key, K, for use during authentication. Each of the MS is assigned to an HLR, which typically remains the same. Each of the MS is also associated with only one VLR in the area in which the MS is currently located. An MS is not registered with a system until the MS is active and has passed authentication.

FIG. 2 is a block diagram showing key distribution stacks. Using a single key encryption key (KEK) to encrypt the keys for distribution throughout the system is a convenient choice, although a single KEK would result in degraded security due to the higher probability that the KEK can be compromised. and the resulting compromise would affect the entire system. Using a different KEK for each of the system devices would be more secure, but it would load the storage within the system devices and add unnecessary delays in call processing. FIG. 2 shows a system for using KEKs that is more secure than a single system-wide key, albeit without any burden, relative to a different KEK for each device in the system. Two types of KEKs are assigned to confidentially distribute key material (such as air interface keys, session authentication information, data used to generate encryption keys, and other key-related material) to devices. of the system of the infrastructure of a system: the intra-keys and the inter-keys. The KEKs are 80 bits in the preferred embodiment.

The first type of KEK is an intra-key, also referred to as an intra-stack key or an intra-zone key, KEKz. The devices in the system are divided into stacks or groups 201, 203, 205, and 207. Each of the stacks is assigned its own unique intrakey, KEKz. In the preferred embodiment, each of the device stacks corresponds to a zone in the communication system, and each of the stacks has a mutually exclusive collection of system devices, that is, each of the system devices only belongs to to a pile. The first stack 201 uses a KEKz1 to encrypt key material, such as encryption keys and / or session authentication information, to transfer within the first stack (or zone in the preferred embodiment) and comprises the first data controller. zone ZC1 107 and its associated BS 115, 117 and 211. The second stack 203 uses KEKz2 to encrypt the key material for transfers within the second stack (or zone in the preferred embodiment) and comprises the second zone controller zC2 121 and its associated BSs 129, 131 and 213. The third stack 205 uses KEKz3 to encrypt key material for transfers within the third stack (or zone in the preferred embodiment) and comprises the third zone controller ZC3 223 and its associated BSs 225, 227, and 229. The fourth stack 207 uses KEKz4 to encrypt the key material for transfers within the fourth stack (or zone in the preferred embodiment) and comprises the fourth zone controller ZC4 215 and its associated BSs 217, 219, and 221. In the embodiment Preferably, the intra-key is used by a zone controller to distribute the key material to base sites / base stations within its zone. KEKz is also used by the KMF 101 to distribute the SCK.

The second type of KEK is an inter-key, KEKm, also referred to as an inter-stack key or an inter-zone key. The interkey is used to encrypt key material sent between stacks or zones in the preferred embodiment, or within

ES 2 360 943 T3 of a certain group 209 of system devices, particularly from the KMF 101. In the preferred embodiment, the inter-key is used by the kMf 101 to distribute the GCK and individual authentication information to the infrastructure. In the preferred embodiment the interkey is stored in a system device in each of the zones, in each of the zone controllers 107 and 121, and is also stored in the KMF101. The connections shown between the KMF 101 and the zone controllers 107, 121, 215, and 223 are virtual connections in the preferred embodiment, where other devices, such as the UCS 103 and the ZMs 105 and 119 are physically located between the KMF. 101 and zone controllers 107, 121, 215, and 223. The UCS and ZM 105 and 119 pass the encrypted key information transparently between the KMF 101 and the zone controllers 107, 121, 215, and 223, that is, the UCS 103 and ZM 105 and 119 do not decrypt or They encrypt the information, thus no KEK storage is required in UCS 103 and ZM 105 and 119, although key material can be stored in encrypted form in UCS 103 and ZM 105 and 119.

Preferably, a message is encrypted by one of the intrakey and one interkey, typically using TA31 (decrypted using TA32), based on a device in the system to which the message is redirected. For example, when the message is intended for a system device in an area other than the area containing the transmitting device, the interkey is used. When the message is intended for a system device in the same zone as the zone containing the transmitting device, the intrakey is used. In the preferred embodiment, when the KMF 101 encrypts the key material, such as the SCK, CCK, SAI, and GCK, with either the interkey or the intrakey, the KMF 101 uses TA31.

For example, from time to time, key material is distributed from the HLR to a VLR and then to base sites within the VLR area. In this case, the key material is encrypted by KEKM and passed transparently from the HLR to the VLR. The target VLR decrypts the key material using its KEKm and re-encrypts it with the zone's KEKZ for distribution to sites within the zone.

Each of the system devices that an infrastructure KEK contains has its own unique infrastructure or protection key, KI, in the preferred embodiment. The protection key is only used to decrypt / encrypt the KEKs sent by the KMF 101 to the devices in the system infrastructure. Preferably, the KI can only be loaded by a variable key loader and cannot be updated with an OTAR (key over-the-air) operation. In addition to distribution by the KMF 101, the KEKs can also be provided manually with a Variable Key Loader. KI is 128 bits long in the preferred embodiment.

As shown at the bottom of Table 1, KEKm is only stored by zone controllers 107 and 121 and KMF 101. The KEKZ intrakey is maintained only by KMF 101, sites / base stations, and zone controllers 107 and 121 within each of the zones. Each of the zones has a unique KEKZ. Each of the system devices has its own KI.

Table 1

<td colspan="3">Key Encryption Key Types Distribution</td>

<td>Infrastructure Element</td><td>Zone 1</td><td>Zone 2</td>

<td>Zone Controller (HLR, VLR)</td><td>KI1, KEKm, KEKz1</td><td>KI2, KEKm, KEKz2</td>

<td>Base Sites</td><td>KI3, KEKz1</td><td>KI4, KEKz2</td>

The use of intra-keys and inter-keys undermines the unique compromise between the security and complexity of key management as well as the speed of call processing. The KMF 101 only needs to maintain one interkey plus one intrakey for each of the stacks or zones in the system. If a KEZz is compromised, the condition and response are localized to that zone, rather than the entire system, and KI remains intact to redistribute a new KEKz to that zone. The KEKm is stored only in the KMF 101 and the HlR 109 and 123 and the VLR 111 and 125 in each of the zones, these devices are typically more physically protected from attack. If KEKm is compromised, KMF 101 changes KEKm at ZC 107 and 121, leaving the sites unaffected.

Five basic types of air interface keys are used to encrypt air interface traffic in the secure communications system: a Static Encryption Key (SCK), a Common Encryption Key (CCK), a Group Encryption Key ( GCK), a Derived Encryption Key (DCK), and a Modified Group Encryption Key (MGCK). Three basic types of keys are used between system devices: an infrastructure key (KI) also known as a protection key, an inter-zone or inter-stack key encryption key (KEKm) also known as an inter-stack key. key and an intra-zone or intra-stack key encryption key also known as an intra-key (KEKZ).

The Static Encryption Key (SCK) is the most basic of the air interface keys and is used to encrypt the incoming (from the MS to the infrastructure) and outgoing (from the infrastructure to the MS) information when authenticating and / or the dynamic encryption of the air interface is not available. Thus, the generation and distribution of this key has nothing to do with authentication.

The Derived Encryption Key (DCK) is a session key derived within the authentication procedure. The

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DCK changes every time an authentication is performed with the MS and the infrastructure, also called SwMI in the TETRA Standard. The DCK is also used for encryption of incoming traffic. The DCK is also used for outgoing traffic directed individually to the MS. The DCK is used when using a dynamic encryption of the air interface that operates in security class 3 of the TETRA Standard. This Common Encryption Key (CCK) is a group key in the sense that multiple MSs have the same CCK. Unlike the GCK, however, the CGK has no relation to a particular talk group (TG). The CCK is geographically specific, that is, the CCK serves all units within a given location area. The location area as defined in the TETRA standard can be as small as a site or as large as an entire system. Each of the units within a location area use the same CCK. Group communications in the outbound direction use the CCK when there is no GCK / MGCK available for that group call. The CCK is used for encryption of outgoing group traffic and identities only. Incoming identities are encrypted with CCK when DCK is in use.

Indirectly, the Group Encryption Key (CCK) is used to encrypt outgoing talk group calls. In the preferred embodiment, a GCK is defined for each of the talkgroups in the system. Actually, the GCK is only used indirectly for the encryption of traffic information; The Modified Group Encryption Key (MGCK), which is derived from the GCK, is used directly for encryption of traffic. The GCK is never used for actual encryption of traffic as it is considered a long-term key.

The Modified Group Encryption Key (MGCK) is used to encrypt outgoing talk group call traffic. MGCK is formed by the combination of GCK and CCK. Each of the GCKs has a corresponding MGCK defined within a location area.

Each of the infrastructure elements has an infrastructure or protection key, KI, which is used as the encryption key for any infrastructure key encryption key updates. KI is similar in operation to the authentication key, K, in a mobile station. In the preferred embodiment, KI is updated only by a provisioning device such as a variable key loader. In the preferred embodiment, updates to the infrastructure key encryption key (KEK) cannot be performed without this key.

Each of the zone controllers has a KEKm interkey, also referred to as an inter-zone or inter-stack key, which is used to encrypt all key traffic that passes between the KMF and each of the zones. The KEKm is also used by the zone controller to pass GCK, CCK, and DCK, as well as session authentication information, between zones. In the preferred embodiment, a KEKm is present in the KMF and each of the zone controllers in each of the systems.

Each of the zones has its own intra-key, KEKz, also referred to as an intra-zone or intra-stack key. The intrakey is used to encrypt all key traffic within the zone, between the zone controller and each of the sites within the zones. Each of the base sites and the zone controller have the same KEKZ in a zone. The KMF stores the KEKZ for each of the zones in the system.

A method of the present invention establishes an expected lifetime, or key re-provisioning interval for an encryption key. Table 2 below shows an example of key update intervals for each of the keys stored in the secure communications system. When the expected lifetime for an encryption key expires, that is, when the key update interval occurs, the encryption key is replaced.

The number of storage locations is determined for each of the types of system devices within a communication system. For example, one KMF 101, one UCS 103, one ZM 105 or 109 per zone, one zone controller per zone 107 or 121, one hLr 109 or 123 per zone, one VLR 111 or 125 per zone, and the number of sites and the corresponding base stations per site that depend on the coverage requirements for each of the zones. Based on the expected lifetime for each of the encryption keys and the number of storage locations for each of the system devices, a system device type is assigned to store each of the encryption keys, and the encryption keys are stored on the system device of the assigned type. For example, derived encryption keys are stored in base stations and in the HLR / VLR, common encryption keys are stored in base stations, modified group encryption keys are stored in base stations, and keys Group ciphers are stored in HLRs and VLRs.

Table 2 shows the target (user) of each of the keys and the key update interval, ie the time between changes or updates of the specific key in a preferred embodiment. For example, the MGCK, which is a combination of the CCK and the GCK, is updated each time the CCK is changed and each time the GCK is changed. Table 2 can be changed by the KMF operator.

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Table 2

<td></td><td>key target</td><td>KEY UPDATE INTERVAL</td>

<td>SCK</td><td>All MS and BS</td><td>1 year / or if compromised</td>

<td>DCK</td><td>MS, BS, HLR, VLR</td><td>&lt;24 hours, each time the unit authenticates</td>

<td>CCK</td><td>Group (TG HLR), all MS, all BS</td><td>24 hours</td>

<td>GCK</td><td>Group (TG HLR)</td><td>6 months</td>

<td>MGCK</td><td>Group (bS, MS)</td><td>24 hours - Low of CCK, GCK interval</td>

<td>KI</td><td>All devices using KEKz or KEKm (BS, ZC)</td><td>Never change</td>

<td>KEKz</td><td>Zone</td><td>6 months / or if compromised</td>

<td>KEKm</td><td>System</td><td>6 months / or if compromised</td>

There are software programs based on PC (personal computer) that provision both the mobile stations and the devices of the system infrastructure with the keys. A more secure method uses the capabilities of the Variable Key Loader (KVL), or the key loader for short, to load the keys into infrastructure devices as well as MSs. The key loader has a hardware-based encryption device for the security of the keys stored within the device. The KVL can obtain keys directly from the KMF by acting as a storage and redirection agent to disseminate the key encryption keys to the various devices.

Although a KVL is a very secure way to provide keys, it is a time-consuming process to use one or more KVLs to provide keys to each of the system devices and mobile stations. A key management method is required to store and distribute KEKs and other key material to system devices such as zone controllers and base sites.

The KMF 101 is responsible for the generation, key distribution, and tracking of most of the air interface keys (not DCK or MGCK) in the system. The base sites 115 and 117 and each of the zone controllers 107 serve as a proxy to the KMF 101 for key distribution. The KMF 101 distributes the key material to the zones through the UCS 103, the ZM 105 and 119, and / or the ATR 113 and 127 depending on the key to distribute. KMF 101 processes confirmation information from ATR 113 and 127 to keep system devices and MS 401, 403, 405, and 407 updated. FIG. 3 and FIG. 4 show the storage of key material within the communication system.

As shown in FIG. 3, the KMF 101 stores a protection key and associated KEKs for each of the devices in the system. The KMF 101 stores a protection (infrastructure) key, an interkey, and an intrakey for each of the zone controllers. For example, the first zone controller 107 is associated with keys KIzci, KEKm, and KEKz1. The KMF 101 stores these keys encrypted by a hardware key and the first zone controller 107 stores KIzci and the encrypted KEKm and KEKzi. The KMF101 stores a protection key and an intrakey, both protected by a hardware key, for each of the BSs. For example, the KMF 101 and the first BS 115 both store the protection key KIbsi and the intra-key KEKzi. In the preferred embodiment, the KMF 101 stores keys encrypted / protected by a hardware key.

Prior to the distribution of a KEK in a predetermined embodiment, the KMF 101 encrypts the KEKs with the protection key KI, and using the encryption algorithms TA41 and TA51, similar to what is shown in FIG. 10 entitled Distribution of SCK for an individual by an authentication center and its associated text on the Terrestrial Trunk Radio (TETRA); Voice plus Data (V + D), Part 7: Security, EN 300 392.7 v2.1.1, 2000-12 (referred to in this document as the TETRA Standard), which is incorporated in its entirety in this document by reference. The KMF 101 stores an encryption process 301 that combines RSO and the appropriate key KEK, KeKn, and KEK-VN using the encryption algorithms TA41 303 and tA51 obtaining SKEK, which is a sealed version of the KEK. RSO, SKEK, KEKN, and KEK-VN are redirected to the target system device. Braces {} followed by a key name indicate that the material within the braces was created using TA41 and T151 and the key name after the parentheses.

For example, it is intended to transfer KEKzi to the first zone controller 107 and to the BS1 115. RSO, KEKzi, KEKzi-VN, and KeKzi-N and KIzci are combined using the TA41 and TA51 encryption algorithms, obtaining SKEKzi, RSO, SKEKzi, KEKzi-VN and KEKziN ​​key material are transparently redirected through the ZM1 105 to the first zone controller 107, which combines this key material with KIzci using TA41 and TA52 (as described in the TETRA Standard), obtaining KEKzi, which is stored in ZC1 107. RSO, KEKzi, KEKzi-Vn, and KEKziN ​​and KIbsi are combined using the TA41 and TA51 encryption algorithms, obtaining SKEKzi. RSO, SKEKzi, KEKzi-VN and KEKziN ​​key material are transparently redirected through ZM1 105 to BS1 115, which combines this key material with KIbsi using TA41 and TA52, obtaining KEKzi, which is stored in BS1 115. In the referred embodiment, an unencrypted confirmation of a successful receipt of each of the keys is returned to the KMF 101 via the ATR 113.

ES 2 360 943 T3

A block diagram showing key storage within a communication system is shown in FIG 4. In particular, the storage of the session authentication information through the communication system is shown. In the preferred embodiment, the session authentication information includes a random seed, RS, and two session keys, KS, for authentication of an MS and KS 'for authentication of the infrastructure, for each of the mobile stations 401 , 403, and 405 (only three are shown due to space restrictions, although numerous MS are part of the system). Session Authentication Information (SAI) is used to generate a Derived Encryption Key (DCK) for each of the MS 401s.

For each of the MS 401, 403, and 405, the KMF 101 stores an individual TETRA Subscriber Identity (ITSI), the TETRA Equipment Identity (TEI), and an MS authentication key (MS key) which is unique to each of MS 401, 403, and 405 and is stored within each. In the preferred embodiment, the air interface keys and the MS keys are stored in a hardware encrypted form using a hardware key Kh within the KMF 101. The DVI-XL algorithm, available from Motorota, Inc., is used to encrypt the keys for storage in the KMF 101 in the preferred embodiment. Straight parentheses [] followed by a key name indicate that the material within the straight parentheses is encrypted by that key.

The KMF 101 generates session authentication information for each of the MS 401, 403, and 405, whose UPS is at least partially encrypted and is redirected non-real-time to UCS 103 for storage. For each of the MS 401,403, and 405, the UcS 103 stores the ITSI, TEI and ID of the HLR associated with each of the MS, as well as the SAI. In the preferred embodiment, KS and KS 'are stored encrypted by the inter-key (as received from KMF 101) in UCS 103 for quick and easy transport, and RS is stored unencrypted UCS 103 is a device transparent in the preferred embodiment, so that it does not perform any encryption or decryption functions. To eliminate the potential for double entry of information, the KMF 101 receives configuration information from the UCS 103. Examples of configuration information are: TETRA Individual Subscriber Identity (ITSI), TETRA Subscriber Group Identity (GTSI), local zone, and zone managers. The KMF uses a lookup table, such as a DNS (Domain Name Server) lookup table, to obtain the addresses of ATR 113 and 127. The distribution of each of the different types of keys has different configuration requirements. , as described in this document.

The UCS 103 redirects the appropriate UPS to each of the ZM 105 not in real time, based on the ID of the HLR associated with each of the MS 401. The ZM 105, like the UCS 103, is a transparent device and does not performs no encryption or decryption function. The ZM 105 stores, for each of the MS that has the HLR 109 as its local location, an ITSI, TEI and SAI. In the preferred embodiment, KS and KS 'are stored encrypted by the interkey (as received from UCS 103) in ZM 105 or 119 for quick and easy transport, and RS is stored unencrypted.

The ZM 1.05 redirects the UPS to the HLR 109 not in real time. The HLR 109 stores an ITSI and the SAI for each of the MS 401, 403, and 405. In the preferred embodiment, KS and KS 'are stored encrypted by the inter-key (as received from ZM 103) in the HLR 109, and RS is stored unencrypted. In the referred embodiment, RS, KS, and KS 'are stored unencrypted in the VLR 111 for faster authentication. In an alternative embodiment, KS and KS 'can be stored unencrypted in the HLR 109 for faster authentication.

When an MS 401 is authenticated in the zone, a new DCK is generated for the MS 401 by the VLR 111 in the zone controller 107 from the real-time UPS, after any encrypted UPS is decrypted due to handover from the SAI from HLR 109. (The old ITSI, SAI, and DCK associated with that MS 401 are redirected to VLR 111 in real time before the new DCK is created). The ITSI, SAI and the new DCK are redirected to the HLR 109 in real time for storage. In the preferred embodiment the ITSi, SAI and DCK come from the HLR for the MS 401, thus this information may come from a different area if the MS 401 does not use the HLR 109 for its local area. When the SAI / DCK comes from a different zone, that zone encrypts / decrypts the information if necessary, with the interkey for transport to the appropriate zone, which also provides the appropriate encryption / decryption within the zone. The DCK is stored encrypted by the intra-key KEKZ for the area in which it is stored, for easy and fast transport to local BS 115 or 117. In the example shown in FIG. 4, each of the DCKs is stored encrypted by the KEKZ1. In the preferred embodiment, KS and KS 'are always encrypted with the KEKM interkey, for easy and fast transport during the authentication process, even when the transfer is within the same zone.

During the authentication process, the BS 115 that communicates with the MS 401 receives, from the ZC1 107 in real time, the DCK of the MS 401, encrypted by the intra-key KEKZ1. The BS 115 stores the decrypted ITSI and DCK for immediate use while the MS 401 is in the BS 115 coverage area. See FIG. 17 and its associated text for information regarding the persistence of keys in each of the sites.

Each of the MS 401, 403, and 405 store their own ITSI, TEI, and DCK in decrypted form, and K is stored in scrambled or encrypted form. Each of the MS 401, 403, and 405 also stores the relevant CCK, GCK, MGCK, and SCK as received in decrypted form. These keys can be stored encrypted in the infrastructure in an alternative embodiment.

ES 2 360 943 T3

Zone controller 107 is responsible for real-time key distribution and key mobility management. It holds keys that may be needed for real-time mode distribution needed when roaming, for example. The group encryption key is an item in each of the talk group records and is maintained in the talk group HLR. The common encryption key is a zone or site-specific key and is also maintained at the zone controller. The ZC is responsible for the creation of the MGCK (based on the GCK and the CCK) and its distribution to the sites.

Since the keys reside in the talk group and individual HLR 109, the zone controller 107 is not transparent regarding the encryption of the key material. The ZC 107 maintains a protection key KI, and two encryption keys of the infrastructure keys, the inter-key KEKm and the intra-key KEKz, for the distribution of the key material. KI is used to seal (encrypt) KEKM and KEKZ when sent to KMF 101. Most of the key information is encrypted by the KMF 101 with the interkey, KEKM. The zone controller 107 decrypts the key material using KEKm and re-encrypts the same information using KEKz when the information is sent to a site within the zone. Thus, the zone controller, 107 has the TETRA algorithms used for encryption / decryption of infrastructure keys (such as TA41 and TA52 and TA31 and TA32), as described in this document.

The zone controller sends ACK acknowledgments of the infrastructure key replenishment operations to the KMF 101 via the ATR 113. When a ZC 107 or HLR 109 receives a key update, the device first decrypts the key update and it checks the absence of corruption by verifying the integrity of the data and sends the result of this operation to the KMF 101 through the ATR 113 in the form of an ACK confirmation.

The site is an endpoint for air interface encryption. Audio over the air interface between BS 115 and MS 401 is encrypted. Audio within the infrastructure is not encrypted. Outgoing traffic is encrypted with algorithms that use MGCK, CCK, and SCK, or DCK for individual calls. All incoming traffic is encrypted with algorithms that use DCK or SCK. The sites maintain the traffic algorithms and key storage for SCK, CCK, and MGCK, as well as DCK. Since the base site has a traffic key store, the base site is not transparent regarding the encryption of the key material. All key material distributed to base sites is encrypted by the intrakey, KEKz. In this way, the base site maintains a protection key, KI, and an inter-key KEKz. Thus, the base sites have the TETRA algorithms used for encryption / decryption of infrastructure keys (such as TA41 and TA52 and TA31 and TA32), as described in this document.

The MS is another endpoint for air interface encryption. Outgoing traffic is encrypted with algorithms that use MGCK, CCK, and SCK, or the DCK if they are addressed individually. All incoming traffic is encrypted with algorithms that use DCK or SCK, and identities can be encrypted with SCK or CCK. The MS maintains the traffic algorithms and key storage for SCK, CCK, GCK, and MGCK as well as DCK.

The following figures provide examples of the role of the zone controller 107 or 121 in some of its key generation, key distribution and authentication functions, as well as the operations of the base station / base site and MS in the processes of key generation, key distribution and authentication.

A diagram showing an example of key storage and distribution of authentication information within a communication system is shown in FIG. 5. The session authentication information (RS, KS and KS ') is necessary to facilitate the real-time authentication of the MS 401 by the ZC 107 and the real-time authentication of the system by the MS, as well as mutual authentication. . The activations for the UPS transfer can be a manual initiation by the KMF operator, an automatic fraud trigger from the system, or a periodic change of the UPS by the KMF 101.

FIG. 5 shows SAI handover for two mobile stations, ITSI1 401 and ITSI2 403 (neither shown). The KMF 101 encrypts at least part of the UPS (for example, KS and KS ') with the interkey KEKm for the system, and redirects ITSI1, ITSI2, RS, and KS and KS' encrypted by the KEKm to UCS 103. The UCS 103 stores a copy and redirects it to its local ZM 105 or 119 for each of the ITSIs. Dashed lines within a system device indicate the transparent passage of information through the system device. The ZM 105 or 109 also stores a copy and directs it to its ZC 107 or 121, in particular the HLR 107 or 123. The ZC 107 or 121 stores encrypted KS and KS 'together with RS in the HLR 107 or 123. Once the HLR 109 or 123 receives the UPS, an acknowledgment whether to encrypt (ACK) is sent, when decryption using KEKm fails, back to the KMF 101 via ATR 113 or 127 from the area in which the HLR resides 109 or 123. If there is a VLR 111 for the MS 403, such as the ITSI2, the ZC 121 sends KS and KS 'encrypted with the interkey KEKM to the VLR 111. The coordination between a previous authentication session information and the Information from a new authentication session is not required. The HLR 109 or 123 only need one copy of the registered ITSI UPS. The UCS 103 and ZM 105 or 119 store copies of the authentication session information to provide recovery from system failures or maintenance.

Providing storage and redirecting session authentication information and keys not in time

ES 2 360 943 T3 real time (that is, if time constraint) between the first level system devices and in real time (that is, on demand) between the second level system devices as described above, the system Authentication provides a fault-tolerant system that also enables rapid recovery from faults. If the KMF 101, UCS 103, and / or ZM 105 and 119 fail or are separated from the rest of the system, full authentication can still be performed without interruption on a real-time basis with the session authentication information, for example for the MS2 403, stored in the HLR 123 and the VLR 111. A failure in any of these devices 101, 103, 105 and 119 is not catastrophic, since the stored data can be downloaded from any of the other devices that store the information. If a zone controller 107, HLR 109, and / or VLR 119 experiences a fault or failure, the UPS can immediately unload from the zM 105 in the zone. By eliminating the need for the KMF 101 to participate in real time in the authentication process, there is less load on the KMF 101 and less overall traffic on the communication links between the devices in the system infrastructure.

In FIG. 6 shows a diagram showing the storage of authentication information and making the authentication decision within a communication system. Four mobile stations are shown within a system where three mobile stations 401, 403, and 405 use the HLR1 109 of the first zone controller 107, one mobile station 407 uses the HLR2 123 of the second zone controller 121, the two mobile stations 401 and 403 use the VLR1 111, and the two mobile stations 405 and 407 use the VLR2 125. UPS storage across the system devices is shown. The base station's decisions as to whether or not to authenticate a mobile on a particular trigger are also shown. For example, power-on messages, both encrypted and unencrypted, require authentication. Any message sent in the clear (that is, unencrypted) requires authentication. Encrypted roaming messages can be implicitly authenticated, that is, the challenge and response mechanism can be avoided if the encrypted roaming message is successfully decrypted by BS 131. Power-on messages, roaming messages, location updates and others types of messages are considered requests to communicate within the communication system. When authentication is required the BS 115, 117, 129, or 131 sends an authentication request from the MS with the infrastructure (with a zone controller in the preferred embodiment). In the event that the infrastructure device to which the authentication requests are sent becomes unavailable, for example when the device fails, is out of service for maintenance, or the communication link with the device is not operational, the BS stores authentication requests during the period of time when the infrastructure device is not available. When the infrastructure device becomes available, for example if the device returns to service after a failure or maintenance or when the communication link is restored, the BS redirects the stored authentication requests to the infrastructure device.

In a situation shown in FIG. 6, a first MS 401 sends a clear (unencrypted) power-on message to the first BS 115. In the preferred embodiment, authentication of the MS 401 is required in this situation. Since MS 401 uses HLR 109 in the zone where BS 115 is located, session authentication information SAI1 for MS 401 is redirected from HLR 109 to VLR 111 in the authentication process termination zone.

The second MS 403 is roaming from BS1 115 to BS2 117 and sends a clear (unencrypted) roaming message to the second BS 117. In the preferred embodiment, authentication of MS 403 is required in this situation. Since MS 403 uses HLR 109 in the area where BS 115 is located, and since MS 403 transited from a site served by the same VLR as the new site, the SAI2 session authentication information for MS 403 is now located in the VLR 111 in the zone for the completion of the authentication process.

The third MS 405 sends an encrypted power-on message to the third BS 129. In the preferred embodiment, authentication of the MS 405 is required in this situation. Since the MS 405 uses the HLR 123 in the zone where the BS 129 is located, the session authentication information SAI3 for the MS 405 is redirected from the HLR 123 to the VLR 125 in the zone for completion of the authentication process.

The fourth MS 407 is roaming from BS2 117 to BS4 131 and sends an encrypted roaming message to the fourth BS 131. In the preferred embodiment, the (full) authentication of the MS 403 is not required in this situation. Instead, the MS is implicitly authenticated, that is, the challenge and response mechanism is bypassed if the encrypted roaming message is successfully decrypted by BS 131, as MS 407 uses HLR 109 in a zone other than the zone where BS 131 is located, the encryption key (and if necessary, session authentication information SAI4) for the MS 407 must be redirected from the HLR 109 to the VLR 125 where the MS 407 has transited for the completion of the authentication process.Typically, at least a part of the SAI is encrypted by the inter- key before transferring it to another area. If Digest authentication fails, then full MS 407 authentication is performed.

In FIG. 7 shows a diagram showing the challenge and response process to authenticate a mobile station by an authentication center in accordance with the TETRA Standard. When authentication of an MS 707 occurs, an authentication center 701, such as a KMF 101, combines the mobile authentication key, K, with RS using the encryption algorithm TA11, as defined in the TETRA Standard. The process output of TA11 703 is KS, which is input with RAND1 (a random number) to the TA12 encryption algorithm, as defined in

ES 2 360 943 T3

TETRA regulations. The TA12 process 705 outputs XRES1, an expected response, and DCK1, a derived encryption key for the mobile. RAND1 and RS are provided to MS 707. MS 707 goes through a similar process combining its mobile authentication key, K, with RS received from AuC 701 using process TA11 703. Process TA11 703 outputs KS, which is introduced with RAND1 to the TA12 705 process. The TA12 705 process in the MS 707 outputs RES1, a challenge response, and DCK1, the derived encryption key for the mobile. The MS 707 redirects RES1 to the AuC 701. If XRES1 and RES1 match, the AuC 701 sends an authentication pass message to the MS 707, and communication over the air interface with the newly created DCK1 can begin. If XRES and RES do not match, the AuC 701 sends an authentication failure message, to the MS 707, and communication over the air interface with the newly created DCK1 is prohibited, although the old DCK1 can be used once it has failed. authentication.

In FIG. 8 shows a diagram showing the challenge and response process to authenticate an authentication center by a mobile station in accordance with the TETRA Standard. When authenticating an AuC 701, such as the KMF 101, an MS 707 combines the mobile authentication key, K, with RS using the TA21 encryption algorithm, as defined in the TETRA Standard. The process TA21 801 of the AuC 701 outputs KS ', which is input with RAND2 (a random number) to the encryption algorithm TA22, as defined in the TETRA standard. Process TA22 803 outputs XRES2, an expected response, and DCK2, a derived encryption key for mobile 707. RAND2 is provided to AuC 701. AuC 701 goes through a similar process combining the mobile authentication key, K, for MS 707 with RS using process TA21 801. Process TA21 801 from AuC 701 outputs KS ', which is entered with RAND2 to process TA22 803. The output of process TA22 803 on AuC 701 is RES2, an answer to the challenge, and DCK1, the derived encryption key for the mobile . The AuC 701 redirects RES and RS to the MS 707. If XRES and RES match, the MS 707 sends an authentication pass message to the AuC 701, and communication over the air interface with the newly created DCK1 can begin. If XRES and RES do not match, the MS 707 sends an authentication failure message to AuC 701, and communication over the air interface with the newly created DCK1 does not take place.

In FIG. 9 shows a diagram showing UPS distribution and authentication process between a communication system and a real-time mobile station according to the invention. FIG. 9 shows an implementation of the authentication process of the TETRA Standard including how the various devices of the system within the infrastructure act within the authentication process. FIG 9 shows how the ZC 107, including the HLR 109 and the VLR 111, and the BS 115 act as Proxy, or authentication agents, for the KMF 101 in the authentication process. In non-real time, KS and KS 'encrypted by the interkey, and RS are passed through the KMF 101 to the UCS 103, the first ZM 105, and the HLR 109 of the first zone controller 107.

After BS 115 sends an authentication request from MS 401 to ZC 107, VLR 111 generates PAND1 and uses KS and PAND1 with process TA12 to generate XRES1 and DCK1, according to FIG. 7, in this document, and redirects RAND1 and RS to BS 115, which redirects RAND1 and RS over the air to MS 401. MS 401 combines its own K and RS with the TA11 process to generate KS, then combines RAND1 and KS according to FIG. 7 in this document, getting rES1 and DCK1, and redirecting RES1 to BS 115, which redirects RES1 to VLR 111 in ZC 107. VLR 111 compares RES1 and XRES1, and the result is R1. When RES1 and XRES1 match, DCK1 and SAI for MS 401 are stored in VLR 111 and HLR 109 and DCK1 (encrypted by interkey). In the preferred embodiment, DCK1 is encrypted with the intrakey for the first zone before it is sent to the BS 115. R1 redirects to BS 115 in recognition that it passed authentication, and BS 115 stores DCK1 and sends R1 to MS 401 indicating that it passed authentication, When RES1 and XRES1 do not match, VLR 111 rejects the newly created DCK1 without storing or redirecting it to BS 115 and redirects R1, a negative confirmation of the authentication process, to BS 115, and BS 115 sends R1 to MS 401 indicating that authentication has failed.

To request infrastructure authentication, MS 403 sends RAND2 to BS 129, which redirects RAND2 to VLR 125 in ZC 121. VLR 125 looks up RS and KS 'and generates RES2 and DCK2 using process TA22 according to FIG. 8 in this document, and redirects RES2 and RS to BS 129, which redirects RES2 and RS over the air to MS 403. MS 403 combines RS and its own K with the TA21 process, obtaining KS ', which is it is then combined with RAND2 in process TA22 according to FIG. 8 in this document, getting XRES2 and DCK2. The MS 403 compares RES2 and XRES2. When RES2 and XRES2 match, MS 403 sends message R2 to BS 129 confirming that authentication passed, BS 129 sends R2 to ZC 121, and VLR 125 causes DCK2 and UPS for mobile 403 to be stored in VLR 125 and HLR 123 for MS 403 and redirects DCK2 to BS 129, which stores DCK2. In the preferred embodiment, DCK2 is encrypted with the intrakey for the second zone before being sent to BS 129. When RES2 and XRES1 do not match, MS 403 sends message R2 to BS 129 indicating authentication failed, BS 129 sends R2 to ZC 121, and VLR 125 rejects the newly created DCK2 without sending it to BS 129.

In any authentication process, if the VLR 111 in the zone where MS 401 or 403 is currently located does not have the UPS stored for the MS 401 or 403, the VLR 111 obtains the UPS from the HLR for the MS 401 or 403 When the HLR 109 for the MS 401 or 403 is in the same zone, the UPS simply passes inside the ZC 107 to the VLR 111. When the HLR 109 for the MS 401 or 403 is in a different zone, the zone for the local HLR is determined from a local zone mapping table that maps the ITSI to its Local Zone, and the UPS is

ES 2 360 943 T3 redirects to ZC 107 for VLR 111. In the preferred embodiment, when key material is redirected from HLR for MS 401 or 403 to VLR 111, at least part of the UPS, in particular KS and KS ', are encrypted with the interkey. When the DCK is transferred within a zone, the DCK is encrypted with KEKZ. Similarly, if the zone where the authentication takes place is not the local zone for the MS 401 or 403, the updated information from SAI and DCK will be encrypted with the interkey, at least in part, and redirected to the appropriate VLR. . As the keys are passed between devices that require a different encryption key, a device receives a message, decrypts it with one key, and re-encrypts the result with another key for the next device.

Mutual authentication, when the MS and the infrastructure mutually authenticate each other, is described with respect to FIG. 3 entitled Mutual Authentication Initiated by SwMI and FIG. 4 entitled Mutual authentication initiated by the MS and its associated texts of the TETRA Regulation. The resulting DCKs (DCK1 and DCK2) from each of the processes are combined using the TB4 encryption algorithm, and the resulting DCK is used for communication. The MS 403 has sent an encrypted message, eg, a location update message encrypted by the DCK. The BS 115 can optionally redirect an acknowledgment of receipt of the encrypted message to the mobile station MS 403. The identity, ITSI2, of the MS 403 is encrypted with the CCK, so that the BS 115 is able to determine which MS has sent the message, even if it does not have the DCK2 for the MS 403. The BS 115 requests the DCK2 from the ZC 107. ZC 107 determines if it needs to request DCK2 from a different zone, which is required in this case, because MS2 403 is roaming from a different zone, zone 2, and HLR 123 for MS 403 is in zone 2 The ZC 107 determines which zone has the necessary key material and sends a request to the target zone for the key material. In the example, DCK2 is in HLR 123 for zone 2, which is the target zone, and DCK2 is sent to ZC 107 from the HLR of that zone 123 after being encrypted with the inter-key, KEKM. The ZC 107 sends DCK2 to the BS 115 encrypted with the intrakey KEKZ1. BS 115 uses DCK2 to decrypt the location update message for MS 403; and any subsequent messages from MS 403, and redirects the location update to ZC 107. RS, KS, KS 'are requested at a later time from HLR 123 so that full authentication can be performed if necessary. In the preferred embodiment, the VLR 111 for the MS 403 is not updated with the location of the MS until the MS either implicitly authenticates or performs a full authentication. Receipt of the properly decrypted location update message is considered to be implicit authentication, at which time the VLR 111 would be updated.

In the situation where it may be desired to introduce a GCK / MGCK, the process is the same as described above with respect to DCK, except that the VLR 111 obtains the GCK, combines it with the CCK, as described later in the section. FIG. 15 and its associated text, and redirects the resulting MGCK, encrypted with the intrakey KEKz1, to BS 115 or 117.

In FIG. 11 shows a diagram illustrating a key entry within a communication system. The key entry procedure is used to redirect a key, such as the DCK or GCK / MGCK, to a redirect site when an MS switches between sites from its current site to the redirect site. This process thus provides a mechanism to redirect a key to a site prior to the arrival of the MS 401 or 403, so that encrypted handovers and roaming can occur without disruption. FIG. 11 shows an example of a DCK2 handover between zones and a DCK1 handover within a zone. The MS initiates the procedure. Although the KS, KS ', and DCK are stored encrypted in the HLR, and the DCK is stored encrypted in the HLR and VLR in the preferred embodiment, they are shown unencrypted in FIG. 11 for the sake of simplicity.

MS1 401 begins the roaming process from BS1 115, which has Location Area Identification 1 (LAID1), at site 1 to BS2 117, which has Location Area Identification 2 (LAID2) at site 2 in zone 1. MS 401 sends BS1 115 a message indicating that MS1 will transit to site 2. In the preferred embodiment, this message is an OTAR Readiness message. BS 115 relays this message to ZC 107. The ZC 107 determines whether or not the DCK needs to be transferred to another area by determining whether the site to which the MS 401 is roaming is in its area or not. In this example, site 2 is also served by ZC 107, so there is no need to transfer the DCK to another area. As the DCK is transferred within the zone, the ZC 107 responds to the BS 115 with the use of a short delay message. In this case, BS 115 rejects the MS 401's handover to site 2 by a delay equivalent to the short delay, which delays approximately the time it will take to redirect the DCK to the next site from VLR 111 in the same area. In the preferred embodiment, the short delay is less than 50 ms. The MS 401 waits for an OK from the BS 115 before operating at the new site, eg, roaming, switching sites, or communicating, and the BS 115 sends the OK after the short delay period expires. During the delay period, VLR 111 at ZC1 107 encrypts DCK1 with the intrakey and redirects it to BS2 117 at site 2, where MS 401 and BS2 117 will be able to exchange encrypted messages using DCK1. In the preferred embodiment, the VLR 111 for the MS 401 is not updated with the location of the MS until the MS 401 either implicitly authenticates or performs a full authentication.

MS2 403 begins the roaming process from BS3 129, which has Location Area Identification 3 (LAID3) at site 3 in zone 2 for BS1 115, which has Location Area Identification 1 (LAID1) at site 1 in zone 1. MS 403 sends BS3 129 a message indicating that MS2 will transit to site 1. In the preferred embodiment, this message is a Prepare OTAR message. BS 129 relays this message to ZC 121. The ZC 121 determines whether or not the DCK needs to be transferred to another zone by determining if the site to

ES 2 360 943 T3 which is transiting the MS 401 is in your area or not. In this example, site 1 is not served by ZC 121, thus it is necessary to transfer the DCK to another area. As the DCK is transferred to another zone, the ZC 121 responds to the BS 129 with the use of a long delay message. In this case the BS 129 rejects the handover of the MS 403 to site 1 by a delay equivalent to the long delay, which delay approximates the time it will take to redirect DCK from VLR 111 to the site in the next zone. In the preferred embodiment, the long delay is greater than or equal to 50 ms. MS 403 waits for an OK from BS 129 before switching between sites, and BS 129 sends the OK after the long delay period expires. During the delay period, the VLR 125 in ZC1 121 encrypts DCK2 with the interkey and redirects it to ZC1 107, which decrypts it with the interkey, encrypts it with the intrakey KEKz1, and redirects the result to the BS1 115 at site 1, where MS 403 and BS2 115 will be able to exchange encrypted messages using DCK2. In the preferred embodiment, the VLR 111 for the MS 403 is not updated with the location of the MS until the MS 403 either implicitly authenticates or performs a full authentication, at which time the VLR 125 for the MS2 in ZC2 121 is cleared. RS, KS, KS 'are requested a time later from the HLR in ZC3 223 (the local area HLR for MS 403) so that full authentication can be performed if necessary.

FIG. 12 is a diagram showing the distribution of a static encryption key for a BS within a communication system. SCK is a system-level voice traffic key that is used to encrypt voice or data, ESI (Encrypted Short Identity), and signaling traffic when authentication is not available. The SCKs are identified by SCKN and SCK-VN and are stored in the KMF 101 encrypted by a hardware key and in the ZM 105 and 119 encrypted with TA31. In the preferred embodiment, there can be up to 32 different SCKs throughout the system. Each of the BS stores one SCK, identified by a SCK number (SCKN), each of which has a SCK version number (SCK-VN), although the SCK can have multiple versions that are used or were used. in the system. Each of the SCKNs has a version number SCK-VN, and in the preferred embodiment, two version numbers, ie, two keys, are stored for each of the SCKNs. The MS must be able to store 32 SCKs for one SCK-VN, in addition to 32 SCKs for another SCK-VN. The additional 31 SCKs in the MS are defined for direct operation between mobile stations. A new SCK replaces the older SCK-VN. The SCK can be provided to BSs and mobile stations in a number of ways, including through a Variable Key Loader (KVK), through computer software such as RSS Software available from Motorola, Inc., and through OTAR (Over-the-Air Key Replenishment) through the ATR of the local area of ​​the MS. Although not shown in the drawing due to space restrictions, SCKN and SCK-VN are shipped together with SCK for identification purposes.

A process for transferring an SCK to each of the BSs in the system is shown in FIG. 12. When the KMF 101 determines that the SCK should be updated, the KMF 101 generates a new SCK. To determine the local zone of a BS, in the preferred embodiment, the KMF 101 uses a BS map for the local ZC from the UCS 103 and the zone-based lookup table to obtain the address for the ATR in the zone. The KMF 101 encrypts the SCK with the intrakey, KEKz, for the zone in which the BS is located, and sends the encrypted key to the ZM for that BS. The ZM stores a copy and redirects it to the intended BS. An unencrypted ACK acknowledgment is sent from the BS to the ZC and KMF 101 via the ATR in the area where the BS resides. The ACK confirmation represents that the SCK was successfully received by the BS.

A specific example of a transfer from SCK to BS1 115 includes a transfer of site information, including a BS map for the local zone controller, from UCS 103 to KMF 101. KMF 101 uses the map to determine what BS1 115 is located in zone 1. KMF 101 generates the SCK and the encryption with the intrakey KEKz1, for zone 1 where BS1 is located. KMF 101 redirects the encrypted SCK to ZM 105 for zone 1. The ZM1 105 stores a copy of the encrypted SCK and redirects it to the BS1 115 over a wired link. The BS1 115 decrypts the encrypted SCK using KEKZ1 and stores the decrypted SCK. When the SCK is correctly received by BS1, BS1 115 sends an unencrypted ACK confirmation to KMF 101 via ZC1 107 and ATR 13 in zone 1. SCK transfers for BS3 and BS4 are performed similarly.

In FIG. 13 shows a diagram showing the distribution of a static encryption key for a mobile station within a communication system. When the KMF 101 determines that the SCK for an MS 401 should be updated, the KMF 101 generates a new SCK key material for the MS 401 in accordance with FIG 10 titled Distribution of SCK to an individual by an authentication center and its associated text in the TETRA Regulations. The SCK generation process obtains the key material SSCK (a sealed SCK), SCKN (the SCK number), SCK-VN (the version number of SCK), and RSO (the random seed used in the process) . To determine the ATR for the local area of ​​the MS 401, in the preferred embodiment, the KMF 101 uses the ITSI for its local ZC map from the UCS 103 and the area-based lookup table to obtain the address of the ATR for the local area. In the example of FIG. 13, the local zone for MS1 401 is zone 2. KMF 101 redirects SSCK, SCKN, SCK-VN, and RSO to local zone ATR 127 (2) for MS 401. If MS 401 is not over the system, the ATR 127 sends a negative NACK acknowledgment back to the KMF 101. If the MS 401 is on the system, the SCK is supplied to the MS 401 through the area in which the MS 401 is currently located. In the preferred embodiment the SCK key material (eg, SSCK, SCKN, SCK-VN, and RSO) are not encrypted for transfer between system devices. The SCK key material can optionally be encrypted for transfer between system devices.

When the MS 401 is not located in its home zone, the local zone controller 121 of zone 2 determines in

ES 2 360 943 T3 which zone the MS 401 (zone 1 in FIG. 12) is currently located by looking for it in the HLR 123 of zone 2. The ZC2 121 redirects SSCK, SCKN, SCK-VN and RSO to the zone controller 107 of the area where MS 401 is currently located. ZC1 107 redirects SSCK, SCKN, SCK-VN, and RSO to BS 115 where MS 401 is located. BS 115 decrypts SSCK, SCK-VN, and RSO with the intrakey KEKZ1, and redirects the result to MS 401. An unencrypted ACK acknowledgment is sent from MS 401 to BS 115 to ZC 107 and KMF 101 via ATR 113 in the area where BS 115 resides. The ACK acknowledgment represents that the SCK was received and successfully unsealed in the MS (the unsealing process is described in the TETRA Regulation).

When the MS 401 is located in its local zone (not shown, but it is assumed to be BS3 129 for the benefit of this example), the VLR of the local zone controller 121 redirects SSCK, SCKN, SCK-VN and RSO to the BS 129 where the MS 401 is located (not shown but assumed for this example). BS 129 redirects SSCK, SCKN, SCKVN and RSO to MS 401. An unencrypted ACK is sent from MS 401 to BS 129 to ZC 121 and KMF 101 via ATR 127 in the area where BS 115 resides . The ACK confirmation represents that the SCK was received and successfully deselled in the MS (the de-sealing process is described in the TETRA Standard).

FIG. 14 is a diagram showing the distribution of a common encryption key for a mobile station and a BS within a communication system. The CCK is a location area based traffic key that is used to encrypt voice, data and signaling within the location area (LA) and is used only for outbound communications. The CCK is intended for use with encryption of group call traffic in the TETRA Standard. The CCK is also used to encrypt the subscriber's identity by creating the Encrypted Short Identity (ESI). Group call traffic within LA uses the CCK when no GCK is available or is inhibited. There is one CCK per location area. A locate area can be as small as a site, so there could be as many CCKs as there are sites in the system. It is possible for more than one location area to have the same CCK. The CCK is identified by the CCK-ID (eg, CCK1, CCK2, and so on) and the LAID (location area identification). Two copies of each of the CCKs (the last two CCK-IDs) are in the ZC and the BS to allow a gradual key update of the MS in the system. While one CCK is in use, the next one is distributed to the MS. In the preferred embodiment, each of the sites maintains a CCK for each site adjacent to the site, for seamless transfers between sites and to facilitate consistent mobility management. When a CCK occurs adjacent to an Ms, the last two CCKs are transferred to the MS. A new CCK replaces the last CCK-ID. Long-term storage of CCKs occurs in ZM 105 and 119. The TETRA Standard supports several methods for the provision of CCK over the air, and the same request / provision methodology used for each of the keys of the air interface, and also allows the request of keys under registration and cell change by the mobile station.

The CCK procedure for BS illustrated in FIG. 14 is used to transfer a CCK from KMF 101 to BS (site) 115. KMF 101 determines that it is time to update the CCK of a BS 115 and generates the appropriate CCK. In the preferred embodiment, each of the BSs is a Location Area (LA) and has its own Location Area Identification (LAID). FIG. 14 shows CCK1 and CCK2 pass-through for zone 1 and CCK3 pass-through for zone 2. CCKs are encrypted with the intrakey, KEKz, for the zone where LA is located. The UCS 103 provides a site-to-zone map and a ZM-to-zone map for the KMF 101. The KMF 101 uses these maps to send the keys directly to the appropriate ZM 105 or 119, which stores the CCK and redirects the CCK to the zone controller 107 or 121. UCS 103 obtains site parameters from ZM 105 and 119 to create the adjacent site list which is sent to KMF 101 and redirected to ZM 105 and 119 to redirect to zone controllers 107 and 121 for their use. If an adjacent site is in a different zone, the key is transferred between the ZCs involved. The ZC encrypts the CCK with the interkey, KEKM, for transfer between zone controllers. Using the adjacent site list, zone controllers 107 and 121 send CCKs from adjacent sites to the appropriate sites. Thus, each of the sites on the list of adjacent sites will have the CCKs for the sites adjacent to that site. The adjacent CCKs are used so that the MS can request the CCK for the adjacent site before the MS switches between sites. BS 115 can also redirect CCKs to MS as new CCKs are received in BS 115. The CCKs are encrypted with the DCK for the particular MS 401 before transmitting the encrypted CCK to the MS 401. ACK acknowledgments are sent by the BS to the ZC and returned to the KMF 101 via the ATR (where the BS resides). Since KMF 101 has no adjacency, it does not need ACK acknowledgments of adjacent CCK distributions. As the KMF 101 tracks which BS is given a CCK, the BS tracks the circulation of the CCKs, that is, which MS have a CCK for a predetermined Location Area, and redirects the ACKs once the CCK is current.

Since the MGCK is a combination of the CCK and the GCK, the zone controller will create four MGCKs using the last two CCK-IDs and the last two GCK-VNs and distribute them accordingly (see FIG. 15 and FIG. 16) .

The CCK is a zone specific parameter so there is no need to go through the UCS 103. Thus, the KMF 101 sends the CCK information directly to the appropriate zone manager 105 or 119, which is different. than the methodology of replenishment of the other keys of the air interface. The UCS 103 obtains the site information from the zone managers 105 or 119 to create the list of adjacent sites. By placing CCKs in adjacent sites, real-time CCK processing is reduced, i.e. the BS does not need to request the CCK for an adjacent BS from the zone controller when an MS requests a CCK for a neighboring site, thus the MS does not need to process a CCK when the MS switches between sites.

ES 2 360 943 T3

FIG. 15 is a diagram showing the distribution of a group encryption key for a BS within a communication system. The GCK is identified by GTSI (TETRA Group Subscriber ID as it is called in the TETRA regulations) and the GCK-VN. In the preferred embodiment, GCKN is logically equivalent to GTSI from a key management perspective. Long-term storage of GCK occurs in the UCS and ZM. MgCK, which is a combination of GCK and CCK, is identified by GTSI (or GCKN), CCK-ID (with LAID), and GCK-VN. Four MGCKs per talk group (GTSI) are identified by the last two CCK-IDs and the last two GCK-VNs. MGCKs are not stored in a ZC 107 or 121, but are created by a ZC 107 or 121 and sent to BS 115 assuming that an MS affiliated with that GTSI is on the BS 115 site, which does not receive the GCK because it is a long-term key. Although not shown in the drawing due to space restrictions, the GCK-VN is shipped with the GCK and MGCK for identification purposes.

The procedure for updating a GCK for a Talkgroup record has two parts. The first part includes updating the actual GCK for the talkgroup, the second part includes generating the resulting MGCK as a result of updating and distributing the MGCK to the sites.

The procedure of FIG. 15 transfers a GCK from the KMF 101 to the talkgroup HLR at the zone controller in the local zone for the talkgroup. When the KMF 101 determines that it is time for the GCK update, the KMF 101 generates a GCK for each of the talkgroups and maintains a GTSI-GCK table. GCKs are stored in hardware encryption on the KMF 101. The KMF 101 does not know which ZC has the HLR for the GTSI, so the KMF 101 sends the encrypted GCK with the interkey, KEKm, to the UCS 103. The UCS 103 stores the key material and redirects it to its local ZM 105 or 110 for the talk group (GTSI) associated with the GCK. The ZM 105 or 119 redirects the key material to its ZC 107 or 121, which stores the key material in the group HLR for the GTSI encrypted by the KEKm. The ZC 107 verifies that the key material can be decrypted correctly and sends an ACK confirmation back to the KMF 101 via the ATR 113, where the group HLR 109 for the GTSI resides. The ACK confirmation reflects that the HLR 109 contains a correct encrypted copy of the GCK. The ZC 107 decrypts the key material with KEKm and re-encrypts it with the intrakey KEKz, for storage in the VLR 111. Any other VLRs, such as VLR2 125, outside the local area associated with the GTSI will have the KEKm-encrypted GCK redirected to them. FIG. 15 shows both cases of the inter-zone and the intra-zone.

Since the MGCK is a combination of the GCK and CCK generated by a ZC using the TA71 1501, 1503, or 1505 algorithm, when the GCK changes or the CCK changes, the MGCK must also change accordingly. The four MGCKs are sent to all sites that have a conversation group membership that matches the GTSI for the GCK. Since the last two CCK-IDs and the last two GCK-VNs are stored, four versions of MGCK need to be sent to the BS.

As in other cases, when the MGCK is sent to a site, it needs to be encrypted using the KEKZ intrakey. The GCK is obtained from the VLR talkgroup record and decrypted with the intrakey KEKZ, and combined with CCK to create the MGCK. The resulting MGCK is encrypted using the intrakey KEKZ, and sent to the appropriate sites.

The transfer from an MGCK to a BS can be triggered by various events. Examples of triggers include a mobile station associated with the GCK for the MGCK residing in the BS when either the GCK or the CCK is generated; a mobile station arriving at the BS when no previous talkgroup affiliation has occurred at the BS; and a mobile station that changes the talkgroup membership, while residing in the BS, for a talkgroup not previously associated with the BS.

In FIG. 16 shows a diagram showing a distribution of a group encryption key for a mobile station within a communication system. When the KMF 101 determines that the GCK for an MS 401 should be updated, the KMF 101 generates a new GCK key material for the MS 401 in accordance with FIG. 8 entitled Distribution of a group encryption key to an individual and its associated text in the TETRA Regulations. The GCK generation process obtains the material from the SGCK key (a sealed GCK), the GCKN (the GCK Number), the GCK-VN (GCK Version Number), and RSO (the random seed used in the process). To determine the ATR for the local area of ​​the MS 401, in the preferred embodiment, the KMF 101 uses the ITSI for the local ZC map from the UCS 103 and an area-based lookup table to obtain the address of the ATR for the local area. In the example of FIG. 16, the local zone for MS1 401 is zone 2. KMF 101 redirects SGCK, GCKN, GCK-VN, and RSO to local zone ATR 127 (2) for MS 401. If MS 401 is not in the system, the ATR 127 sends a negative NACK confirmation back to the KMF 101. If the MS 401 is in the system, the GCK is supplied to the MS 401 through the area in which the MS 401 is currently located. In the preferred embodiment, the GCK key material (eg, SGCK, GCKN, GCK-VN, and RSO) are not encrypted for transfer between system devices. The GCK key material can optionally be encrypted for transfer between devices in the system.

When the MS 401 is not located in its home zone, the local zone controller 121 of zone 2 determines in which zone the MS 401 is currently located (zone 1 in FIG. 16) by looking for it in the HLR 123 of zone 2 . The

ES 2 360 943 T3

ZC2 121 redirects SGCK, GCKN, GCK-VN, and RSO to zone controller 107 of the zone where MS 401 is currently located. ZC1 107 redirects SGCK, GCKN, GCK-VN, and RSO to BS 115 where it is located MS 401. BS 115 redirects SGCK, GCKN, GCK-VN, and RSO to MS 401. An unencrypted ACK acknowledgment is sent from MS 401 to BS 115, ZC 107 and KMF 101 via ATR 113 in the area where BS 115 resides. The ACK confirmation represents that the GCK was received and successfully deselled at the MS (the de-sealing process is described in the TETRA Standard).

When MS 401 is located in its local zone (not shown, but assuming it is BS3 129 for the benefit of this example), local zone 121 controller redirects SgCk, GCKN, GCK-Vn, and RSO to BS 129 where the MS 401 is located (not shown but assumed for this example). BS 129 redirects SGCK, GCKN, GCKVN, and RSO to MS 401. An unencrypted aCk acknowledgment is sent from MS 401 to BS 120, ZC 121, and KMF 101 via ATR 127 in the area where resides BS 115. The ACK confirmation represents that the GCK was received and successfully deselled at the MS (the de-sealing process is described in the TETRA Standard).

FIG. 17 is a flow chart showing a method of persistence of keys at a site in a communication system according to the invention. Key persistence refers to the length of time that a key is stored in a key on any system device or MS. If an air interface traffic key is cleared from a site when the MS leaves the site, and the key is removed too quickly, the MS may return to the site requiring the key to be set again. If the MS is traveling between zone boundaries or site boundaries for a period of time, the key material for the MS may need to be constantly established if the key material is cleared from a site too quickly after the MS leave the site. If key material is left in one place for too long, duplicate keys can be established, creating ambiguity and the likelihood of authentication failures, particularly for Digest authentication. Thus, the persistence of the key needs to be properly set for each of the keys to prevent such problems. In the preferred embodiment, the persistence time is based on the expected average authentication rate in the communication system and preferably the persistence time is less than the expected average authentication rate in the communication system. The expected average authentication rate is based on the average number of times a mobile station authenticates in a period of time.

At step 1701, when an MS arrives at a site, the key and / or key material associated with the MS 401 is stored at the site. If it is determined at step 1703 that the mobile has left the site, the persistence timer is set at step 1705, unless it has already been set or initialized, in which case the process simply continues at step 1709. When the timer expires at step 1707, the process continues to step 1709 where the key and / or key material associated with mobile 401 is deleted from the site, and the process ends. If the mobile 401 has not left the site in step 1703, and it is time to replace the mobile key or key material in step 1711, the keys or key material are replaced in step 1713 and the process continues. with step 1703. Step 1709 can also be reached if a system device, such as a zone controller, goes to the site to delete certain keys and / or key material for some reason. The zone controller typically determines when the mobile leaves a site based on the HLR and VLR updates.

The present invention can be carried out in other specific ways without departing from its essential characteristics. The described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the invention is therefore indicated by the appended claims rather than by the foregoing description. All changes that fall within the meaning and range of equivalence of the claims are encompassed within their scope.