DE19511298A1 - Method of allotting and withdrawing reception authorisation for chargeable reception - Google Patents

Method of allotting and withdrawing reception authorisation for chargeable reception

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Publication number
DE19511298A1
DE19511298A1 DE1995111298 DE19511298A DE19511298A1 DE 19511298 A1 DE19511298 A1 DE 19511298A1 DE 1995111298 DE1995111298 DE 1995111298 DE 19511298 A DE19511298 A DE 19511298A DE 19511298 A1 DE19511298 A1 DE 19511298A1
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Prior art keywords
decoder
keys
key
nodes
node
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Granted
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DE1995111298
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German (de)
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DE19511298B4 (en
Inventor
Joerg Dr Rer Nat Schwenk
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Deutsche Telekom AG
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Deutsche Telekom AG
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Priority to DE1995111298 priority Critical patent/DE19511298B4/en
Publication of DE19511298A1 publication Critical patent/DE19511298A1/en
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Publication of DE19511298B4 publication Critical patent/DE19511298B4/en
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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H60/00—Arrangements for broadcast applications with a direct linking to broadcast information or broadcast space-time; Broadcast-related systems
    • H04H60/09—Arrangements for device control with a direct linkage to broadcast information or to broadcast space-time; Arrangements for control of broadcast-related services
    • H04H60/14—Arrangements for conditional access to broadcast information or to broadcast-related services
    • H04H60/23—Arrangements for conditional access to broadcast information or to broadcast-related services using cryptography, e.g. encryption, authentication, key distribution
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0819—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s)
    • H04L9/083—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s) involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP]
    • H04L9/0833—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s) involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP] involving conference or group key
    • H04L9/0836—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s) involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP] involving conference or group key using tree structure or hierarchical structure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/162—Authorising the user terminal, e.g. by paying; Registering the use of a subscription channel, e.g. billing
    • H04N7/163—Authorising the user terminal, e.g. by paying; Registering the use of a subscription channel, e.g. billing by receiver means only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
    • H04N7/1675—Providing digital key or authorisation information for generation or regeneration of the scrambling sequence
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H2201/00—Aspects of broadcast communication
    • H04H2201/70—Aspects of broadcast communication characterised in that receivers can be addressed

Abstract

The method could use a three-branch tree with two branching levels, such that the keys for the branches K (2,i) are stored in a decoder Di or a chip card, i having the values from 1 to 9. The root possesses the system key SK = K (O,1), while the keys for the other nodes are given. The keys stored in the decoder serve for decoding the received cryptograms or control words. Each cryptogram can allow a decoder to receive programmes, for example along the branch from K(2,1), through K(1,1) to SK = (0,1), when the decoder is D1 and the key is K(2,1).

Description

Die Erfindung betrifft ein Verfahren zur Erteilung und zum Entzug der Berechtigung zum Empfang von Rundfunksendungen, die durch Verschlüsselung geschützt sind, mit einem Decoder und einen zur Durchführung des Verfahrens geeigneten Decoder.The invention relates to a method for issuing and Revocation of the right to receive radio broadcasts, protected by encryption with a decoder and a suitable one for carrying out the method Decoder.

Gebührenpflichtige Rundfunksendungen, die auch unter den Stichworten Pay-TV, Pay-Radio, bekanntgeworden sind, werden mit einem Schlüssel CW verschlüsselt. Benutzer werden dadurch zum Empfang berechtigt, daß man ihnen den Schlüssel (Kontrollwort) CW vertraulich zukommenläßt. Dazu wird im allgemeinen dem Benutzer ein persönlicher Schlüssel PK zur Verfügung gestellt, der meist physikalisch gegen Vervielfältigung gesichert, beispielsweise auf einer Chip-Karte gespeichert ist.Chargeable radio broadcasts, which are also available under the Keywords Pay-TV, Pay-Radio, have become known encrypted with a key CW. Become a user authorized to receive them by giving them the key (Control word) CW sends confidentially. For this, in general a personal key PK for the user Provided that is usually physically against Duplication secured, for example on a Chip card is saved.

Das Kontrollwort CW wird verschlüsselt als Kryptogramm ECM (Entitlement Control Message) über einen Datenkanal des Rundfunksenders vom Empfänger bzw. Decoder empfangen. Durch Entschlüsselung dieses Kryptogramms mit Hilfe des persönlichen Schlüssels PK wird das Kontrollwort CW wiedergewonnen. Bei dem unter dem Namen EuroCrypt bekanntgewordenen System wird ein weiteres Kryptogramm EMM (Entitlement Management Message) eines Schlüssels SK gesendet. Dieses Kryptogramm kann mit Hilfe von PK entschlüsselt werden. Der so erhaltene Schlüssel SK dient zur Berechnung von CW aus dem Kryptogramm ECM. Dieses Zugangskontrollsystem ist in DIN EN 50094 beschrieben. Sicherheitshalber wird der Schlüssel CW häufig gewechselt.The control word CW is encrypted as a cryptogram ECM (Entitlement Control Message) via a data channel of the Broadcast transmitter received by the receiver or decoder. By  Decrypt this cryptogram using the personal key PK becomes the control word CW recovered. With the one under the name EuroCrypt known system is another cryptogram EMM (Entitlement Management Message) a key SK sent. This cryptogram can be created using PK be decrypted. The key SK thus obtained serves to calculate CW from the cryptogram ECM. This Access control system is described in DIN EN 50094. To be on the safe side, the CW key is changed frequently.

Eine wichtige Aufgabe des Zugangskontrollsystems besteht darin, Benutzern, die ihre Gebühren nicht bezahlt haben, die Berechtigung zum Empfang der Rundfunksendung zu entziehen. Dieses kann einerseits durch eine negative Adressierung geschehen, bei welchem an den Decoder eine Nachricht geschickt wird, in welcher dieser aufgefordert wird, seine Tätigkeit einzustellen. Diese Möglichkeit ist jedoch grundsätzlich unsicher, da derartige Nachrichten von einem betrügerischen Benutzer abgefangen werden können und damit unwirksam sind.An important task of the access control system is in giving users who haven't paid their fees the To withdraw authorization to receive the broadcast. This can be done on the one hand through negative addressing happen at which a message to the decoder is sent in which this is requested, his Cease activity. However, this possibility is generally insecure, since such messages from one fraudulent users can be intercepted and thus are ineffective.

Bei der positiven Adressierung wird eine Abschaltung des Decoders dadurch bewirkt, daß die in ihm enthaltene Information wertlos gemacht wird. Das geschieht dadurch, daß alle anderen Decoder neue Informationen erhalten, die zum Entschlüsseln zukünftiger Rundfunksendungen unbedingt gebraucht werden, nur der abzuschaltende Decoder nicht.With positive addressing, the Decoders thereby causes that contained in it Information is made worthless. This happens because all other decoders receive new information about the Decrypt future broadcasts unconditionally are needed, only the decoder to be switched off.

Das Verfahren der positiven Adressierung führt zwar mit Sicherheit zur Abschaltung des Decoders des jeweiligen Benutzers, es ist allerdings mit großem Aufwand verbunden, da zum Abschalten eines Decoders Nachrichten an alle anderen Decoder gesendet werden müssen.The procedure of positive addressing does lead Security for switching off the decoder of the respective User, but it takes a lot of effort, because to turn off one decoder messages to everyone else Decoder must be sent.

Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zur Erteilung und zum Entzug der Berechtigung zum Empfang von Rundfunksendungen vorzuschlagen, bei welchem die zur Entschlüsselung erforderlichen Informationen in einem bestimmten Decoder wertlos gemacht werden können, ohne daß alle anderen Decoder einzeln adressiert werden müssen.The invention has for its object a method for Granting and withdrawing authorization to receive To propose radio broadcasts, in which the to Decryption required information in one certain decoders can be made worthless without all other decoders must be addressed individually.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst,According to the invention, this object is achieved by

  • - daß die Schlüssel aller betroffenen Decoder eine Baumstruktur bilden, deren Wurzel ein Systemschlüssel zugeordnet ist, der zur Entschlüsselung eines mit der jeweiligen Rundfunksendung empfangenen Kontrollwortes dient,- That the keys of all affected decoders one Form tree structure, the root of which is a system key assigned to decrypt one with the respective radio broadcast received control word serves
  • - daß den der Wurzel und den einzelnen Knoten nachfolgenden Knoten Schlüssel zugeordnet sind,- That following the root and the individual nodes Nodes are assigned to keys
  • - daß den Blättern dieses Baumes feste Schlüssel zugeordnet sind, die eindeutig einem Decoder oder einem Teil eines Decoders (z. B. einer Chipkarte) zugeordnet sind,- That the leaves of this tree assigned fixed keys that are clearly a decoder or part of a Decoders (e.g. a chip card) are assigned,
  • - daß die Schlüssel, die jeweils einen Ast der Baumstruktur bilden, in jeweils einem Decoder gespeichert werden und- that the keys, each a branch of the tree structure form, are stored in a decoder and
  • - daß die in jeweils einem Decoder gespeicherten Schlüssel zur Entschlüsselung von empfangenen Kryptogrammen dienen, welche Änderungen der gespeicherten Schlüssel und des gespeicherten Systemsschlüssels bewirken,- That the keys stored in one decoder serve to decrypt received cryptograms, what changes to the saved keys and stored system key,
  • - daß diejenigen Schlüssel, die solchen Knoten zugeordnet sind, welche einem bestimmten Knoten unmittelbar nachfolgen, dazu dienen, Kryptogramme zu entschlüsseln, die einen Schlüssel enthalten, der dem bestimmten Knoten neu zugeordnet werden soll.- That those keys assigned to such nodes are what a particular node immediately follow, serve to decrypt cryptograms, which contain a key assigned to the particular node reallocated.

Bei 1.000.000 Decodern müßten bei dem bekannten Verfahren 999.999 Nachrichten übertragen werden, um einen der Decoder zu deaktivieren. Bei dem erfindungsgemäßen Verfahren mit beispielsweise einem 2-ären Baum der Tiefe 20 sind etwa nur 40 Nachrichten notwendig. With 1,000,000 decoders, the known method would have to transmit 999,999 messages in order to deactivate one of the decoders. In the method according to the invention, for example with a 2-ary tree of depth 20 , only about 40 messages are necessary.

Zur Verschlüsselung der Daten können bei dem erfindungsgemäßen Verfahren sowohl symmetrische als auch asymmetrische Verfahren angewendet werden.To encrypt the data, the inventive method both symmetrical as well asymmetrical methods can be applied.

Eine vorteilhafte Ausführungsform des erfindungsgemäßen Verfahrens besteht darin, daß die Baumstruktur m-regulär ist, wobei mtn gilt mit m = Zahl der einem Knoten oder der Wurzel nachfolgenden Knoten, t = Zahl der von Knoten gebildeten Ebenen und n = Zahl der Decoder. Dadurch ist eine einfache Zuordnung der Kryptogramme, welche Änderungen der gespeicherten Schlüssel bewirken, möglich.An advantageous embodiment of the method according to the invention is that the tree structure is m-regular, where m t n applies with m = number of nodes following a node or the root, t = number of levels formed by nodes and n = number of decoders. This makes it easy to assign the cryptograms that change the stored keys.

Zum Entzug der Berechtigung eines bestimmten Decoders kann bei dem erfindungsgemäßen Verfahren vorgesehen sein, daßYou can withdraw the authorization of a specific decoder be provided in the inventive method that

  • - für jeden Decoder außer dem bestimmten Decoder, der zusammen mit dem bestimmten Decoder demselben Knoten nachfolgt, ein Kryptogramm gesendet wird das den mit dem festen Schlüssel des Decoders verschlüsselten Schlüssel enthält, der dem gemeinsamen Knoten neu zugeordnet wird,- for each decoder except the particular decoder that together with the particular decoder the same node follows, a cryptogram is sent to the one with the fixed key of the decoder encrypted key contains that is reassigned to the common node,
  • - beginnend mit dem Knoten, der dem gemeinsamen Knoten vorausgeht, bis zur Wurzel für jeweils alle nachfolgenden Knoten aller dem bestimmten Decoder mittelbar vorausgehenden Knoten jeweils ein Kryptogramm gesendet wird, das den mit dem Schlüssel des jeweils nachfolgenden Knotens verschlüsselten Schlüssel enthält, der dem dem bestimmten Decoder mittelbar vorausgehenden Knoten neu zugeordnet wird.- starting with the node that is the common node precedes to the root for all subsequent ones Nodes all indirectly to the particular decoder previous nodes each sent a cryptogram the one with the key of the following one Node's encrypted key, which contains the certain decoders indirectly preceding nodes is assigned.

Ein vorteilhafter Decoder zur Durchführung des Verfahrens nach einem der vorhergehenden Ansprüche ist dadurch gekennzeichnet, daß mehrere Schlüssel speicherbar sind, wobei mindestens ein Teil der Schlüssel durch mit den Rundfunksendungen empfangene Kryptogramme, die mit Hilfe eines der gespeicherten Schlüssel entschlüsselbar sind, veränderbar sind.An advantageous decoder for performing the method according to one of the preceding claims characterized in that several keys can be stored, whereby at least part of the key is passed through with the Broadcasts received cryptograms using one of the stored keys can be decrypted, are changeable.

Ein Ausführungsbeispiel der Erfindung ist in der Zeichnung anhand mehrerer Figuren dargestellt und in der nachfolgenden Beschreibung näher erläutert. Es zeigt:An embodiment of the invention is in the drawing represented with several figures and in the following Description explained in more detail. It shows:

Fig. 1 eine schematische Darstellung der eine Baumstruktur bildenden Knoten, denen jeweils ein Schlüssel zugeordnet ist, wobei die Zahl der Decoder gegenüber der Wirklichkeit stark verringert ist, und Fig. 1 is a schematic representation of the nodes forming a tree structure, each of which is assigned a key, the number of decoders being greatly reduced compared to reality, and

Fig. 2 eine Abfolge von auszusendenden Nachrichten zum Entzug der Berechtigung eines bestimmten Decoders. Fig. 2 shows a sequence of messages to be sent to withdraw the authorization of a particular decoder.

Fig. 1 zeigt als Beispiel einen 3-ären Baum der Tiefe 2 mit Schlüsseln, welche den Knoten des Baums zugeordnet sind. Die Schlüssel K(2,i) sind fest jeweils einem Decoder Di bzw. einer Chipkarte zugeordnet. In dem dargestellten Beispiel gilt i=1, . . . , 9. Der Wurzel des Baums ist der Systemschlüssel SK=K(0,1) zugeordnet, während den m Nachfolgeknoten desjenigen Knoten, dem der Schlüssel K(r,s) zugeordnet ist, die Schlüssel K(r+1, ms-1+1), . . . K(r+1, ms-1+m) zugeordnet sind. Fig. 1 shows an example of a 3-ary tree of depth 2 with keys, which are assigned to the nodes of the tree. The keys K (2, i) are permanently assigned to a decoder Di or a chip card. In the example shown, i = 1,. . . , 9. The root of the tree is assigned the system key SK = K (0,1), while the m successor nodes of the node to which the key K (r, s) is assigned the keys K (r + 1, m s- 1 +1),. . . K (r + 1, m s-1 + m) are assigned.

Einem Decoder mit dem Schlüssel K(m, x) - beim in Fig. 1 dargestellten Beispiel K(2,i) - kann die Berechtigung, ein gebührenpflichtiges Rundfunkprogramm zu empfangen, dadurch erteilt werden, daß ihm gültige Schlüssel auf dem Weg innerhalb des Baums von K(m,x) nach K(0,1) mitgeteilt werden. Dazu sind maximal t-1 Nachrichten mit den Kryptogrammen der jeweils nächst höheren Schlüssel notwendig. Einem Decoder mit dem Schlüssel K(m,x) kann die Berechtigung, ein gebührenpflichtiges Rundfunkprogramm zu empfangen, dadurch entzogen werden, daß man alle Schlüssel auf dem Weg von K(m,x) nach K(0,1) ersetzt. Dazu sind maximal t·m Nachrichten mit den Kryptogrammen der neuen Schlüssel erforderlich. Die Schlüssel, die zur Erteilung oder zum Entzug der Berechtigung ausgetauscht werden müssen, können bei Verwendung einer regulären Baumstruktur leicht berechnet werden.A decoder with the key K (m, x) - in the example K (2, i) shown in FIG. 1 - can be granted the authorization to receive a radio program that is subject to a fee by having valid keys on its way within the tree from K (m, x) to K (0.1). This requires a maximum of t-1 messages with the cryptograms of the next higher key. A decoder with the key K (m, x) can be withdrawn from the authorization to receive a broadcast program subject to a fee by replacing all keys on the way from K (m, x) to K (0,1). This requires a maximum of t · m messages with the cryptograms of the new keys. The keys that need to be exchanged to grant or withdraw authorization can easily be calculated using a regular tree structure.

Fig. 2 zeigt eine Folge von Nachrichten, um den Decoder D9 mit Hilfe der in Fig. 1 beschriebenen Baumstruktur der Schlüssel zu deaktivieren. Jede Nachricht kann über einen Rundfunkkanal ausgestrahlt werden. Sie besitzt eine Adresse und eine Nutzlast, die in Fig. 2 durch einen senkrechten Strich getrennt sind. Mit Hilfe der Adresse erkennt jeder Decoder, ob eine bestimmte empfangene Nachricht von ihm verarbeitet werden muß. Die Nutzlast enthält ein Kryptogramm, das nur von den adressierten Decodern ausgewertet werden kann. Dabei bedeutet die Notation A<B<, daß die Information B mit dem Schlüssel A verschlüsselt wurde. Der Algorithmus zur Entschlüsselung ist im Decoder bekannt. FIG. 2 shows a sequence of messages in order to deactivate the decoder D9 using the tree structure of the keys described in FIG. 1. Each message can be broadcast on a broadcast channel. It has an address and a payload, which are separated by a vertical line in FIG. 2. With the help of the address, each decoder recognizes whether it needs to process a specific received message. The payload contains a cryptogram that can only be evaluated by the addressed decoders. The notation A <B <means that the information B has been encrypted with the key A. The decoding algorithm is known in the decoder.

Zeile a der Fig. 2 zeigt eine Nachricht an den Decoder D7, mit welchem dieser einen neuen Schlüssel K(1,3) neu erhält. Der Decoder D8 erhält ebenfalls den gleichen neuen Schlüssel, der jedoch in diesem Fall über den Schlüssel K(2,8) entschlüsselt wird (Zeile b). In der Nachricht gemäß Zeile c wird eine Adresse angegeben, die den Decodern D1 bis D3 gemeinsam ist und in Fig. 2 mit Gruppe 1 bezeichnet ist. Diese haben gemeinsam den Schlüssel K(1,1), der zur Entschlüsselung des neuen Systemschlüssels SKneu dient. In gleicher Weise wird dann für die Gruppe 2 (Decoder D4 bis D6) und für die Gruppe 3 (Decoder D7 bis D9) der neue Systemschlüssel SKneu übertragen (Zeilen d und e). Dabei ist allerdings der Decoder D9 nicht in der Lage, das Kryptogramm K(1,3) neu <SKneu< zu entschlüsseln. Der Decoder D9 erhält somit keine neuen Systemschlüssel SKneu und kann die darauf folgend übertragenen Nutzsignale nicht mehr decodieren.Line a of Fig. 2 shows a message to the decoder D7, with which it receives a new key K (1,3) new. The decoder D8 also receives the same new key, but in this case it is decrypted using the key K (2.8) (line b). In the message according to line c an address is given which is common to the decoders D1 to D3 and which is designated with group 1 in FIG. 2. These have in common the key K (1,1), which is used to decrypt the new system key SKneu. The new system key SKneu is then transmitted in the same way for group 2 (decoders D4 to D6) and for group 3 (decoders D7 to D9) (lines d and e). However, the decoder D9 is not able to decrypt the cryptogram K (1,3) new <SKnew <. The decoder D9 thus does not receive any new SKneu system keys and can no longer decode the useful signals transmitted subsequently.

Claims (4)

1. Verfahren zur Erteilung und zum Entzug der Berechtigung zum Empfang von Rundfunksendungen, die durch Verschlüsselung geschützt sind, mit einem Decoder, dadurch gekennzeichnet,
  • - daß die Schlüssel aller betroffenen Decoder eine Baumstruktur bilden, deren Wurzel ein Systemschlüssel zugeordnet ist, der zur Entschlüsselung eines mit der jeweiligen Rundfunksendung empfangenen Kontrollwortes dient,
  • - daß den der Wurzel und den einzelnen Knoten nachfolgenden Knoten Schlüssel zugeordnet sind,
  • - daß den Blättern dieses Baumes feste Schlüssel zugeordnet sind, die eindeutig einem Decoder oder einem Teil eines Decoders (z. B. einer Chipkarte) zugeordnet sind,
  • - daß die Schlüssel, die jeweils einen Ast der Baumstruktur bilden, in jeweils einem Decoder gespeichert werden und
  • - daß die in jeweils einem Decoder gespeicherten Schlüssel zur Entschlüsselung von empfangenen Kryptogrammen dienen, welche Änderungen der gespeicherten Schlüssel und des gespeicherten Systemschlüssels bewirken,
  • - daß diejenigen Schlüssel, die solchen Knoten zugeordnet sind, welche einem bestimmten Knoten unmittelbar nachfolgen, dazu dienen, Kryptogramme zu entschlüsseln, die einen Schlüssel enthalten, der dem bestimmten Knoten neu zugeordnet werden soll.
1. A method for granting and withdrawing authorization to receive radio broadcasts which are protected by encryption using a decoder, characterized in that
  • that the keys of all affected decoders form a tree structure, the root of which is assigned a system key which is used to decrypt a control word received with the respective broadcast,
  • that keys are assigned to the nodes following the root and the individual nodes,
  • that the leaves of this tree are assigned fixed keys which are clearly assigned to a decoder or part of a decoder (e.g. a chip card),
  • - That the keys, which each form a branch of the tree structure, are stored in a decoder and
  • that the keys stored in each decoder are used to decrypt received cryptograms, which change the stored keys and the stored system key,
  • - That those keys that are assigned to nodes that immediately follow a particular node are used to decrypt cryptograms that contain a key that is to be reassigned to the particular node.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Baumstruktur m-regulär ist, wobei in mtn gilt mit m = Zahl der einem Knoten oder der Wurzel nachfolgenden Knoten, t = Zahl der von Knoten gebildeten Ebenen und n = Zahl der Decoder.2. The method according to claim 1, characterized in that the tree structure is m-regular, where in m t n with m = number of nodes following a node or the root, t = number of levels formed by nodes and n = number of Decoder. 3. Verfahren nach einem der Ansprüche 1 oder 2, dadurch gekennzeichnet, daß zum Entzug der Berechtigung eines bestimmten Decoders
  • - für jeden Decoder außer dem bestimmten Decoder, der zusammen mit dem bestimmten Decoder demselben Knoten nachfolgt, ein Kryptogramm gesendet wird, das den mit dem festen Schlüssel des Decoders verschlüsselten Schlüssel enthält, der dem gemeinsamen Knoten neu zugeordnet wird,
  • - beginnend mit dem Knoten, der dem gemeinsamen Knoten vorausgeht, bis zur Wurzel für jeweils alle nachfolgenden Knoten aller dem bestimmten Decoder mittelbar vorausgehenden Knoten jeweils ein Kryptogramm gesendet wird, das den mit dem Schlüssel des jeweils nachfolgenden Knotens verschlüsselten Schlüssel enthält, der dem dem bestimmten Decoder mittelbar vorausgehenden Knoten neu zugeordnet wird.
3. The method according to any one of claims 1 or 2, characterized in that to withdraw the authorization of a particular decoder
  • a cryptogram is sent for each decoder apart from the particular decoder which follows the same node together with the particular decoder, which contains the key encrypted with the fixed key of the decoder which is reassigned to the common node,
  • - Starting with the node that precedes the common node, a cryptogram is sent to the root for all subsequent nodes of all nodes indirectly preceding the particular decoder, which contains the key encrypted with the key of the subsequent node that corresponds to the particular one Decoder is indirectly reassigned to previous nodes.
4. Decoder zur Durchführung des Verfahrens nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß mehrere Schlüssel speicherbar sind, wobei mindestens ein Teil der Schlüssel durch mit den Rundfunksendungen empfangene Kryptogramme, die mit Hilfe eines der gespeicherten Schlüssel entschlüsselbar sind, veränderbar sind.4. Decoder for performing the method according to one of the preceding claims, characterized in that several keys can be stored, at least one Part of the keys through with the broadcasts received cryptograms, which are created using one of the stored keys are decryptable, changeable are.
DE1995111298 1995-03-28 1995-03-28 Procedure for issuing and revoking the authorization to receive broadcasts and decoders Expired - Lifetime DE19511298B4 (en)

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DE19511298B4 DE19511298B4 (en) 2005-08-18

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