DE102020003739A1 - Procedure for the distribution and negotiation of key material - Google Patents

Abstract

The invention relates to the distribution and negotiation of key material in a vehicle ecosystem. A central trust authority (TA) is set up as a trust anchor which, like the subscribers (TNi), has implemented at least one symmetrical authentication method (AUTH) and at least one symmetrical encryption method (ENCR). Each participant (TNi) is initially and securely equipped with an individual secret (SECTNiTA) shared exclusively with the central trust authority (TA) and stores it locally in a secure and protected manner. The same goes for the central trust authority (TA). When there is at least the first mutual need for secure communication between participants (TNi), key material is then negotiated, including: - Each participant (TNi) in the group sends an authenticated request, specifying the group, to the central trust authority (TA), which checks the request and generates a new secret (SECTNGNR) common to all participants (TNi) of the group that it transmits to the participants (TNi) in encrypted form. The respective participant (TNi) checks the answer, decrypts the new secret (SECTNGNR) and generates the at least one required group key (authKEYTNGNrencrKEYTNGNr) and saves it locally in a secure and protected manner. The participants (TNi) of the group can then communicate securely.

Description

The invention relates to a method for the distribution and negotiation of key material within a vehicle ecosystem according to the type defined in more detail in the preamble of claim 1.

Modern vehicles are characterized by increasing networking. The vehicles are not only connected to systems such as the WorldWideWeb but also to systems and servers operated by the vehicle manufacturer or OEM, for example manufacturer-specific applications and a manufacturer-specific server, which is often also referred to as the vehicle backend. These are developed, marketed and operated by the manufacturer exclusively for their own vehicle fleet. All of this together is also known as the vehicle ecosystem.

In practice, the diverse communication relationships between the individual system components within such a vehicle ecosystem result in a large number of new interfaces and applications, all of which have to be secured by suitable cryptographic methods such as mechanisms, protocols, etc. The protection serves on the one hand to preserve the privacy of the vehicle user and on the other hand not to allow any external intervention in the data traffic, which could be used by hackers, especially when transmitting data relating to the vehicle control, to attack the vehicles and to perform important functions manipulate.

Common practice is the use of asymmetric keys or methods based on asymmetric cryptography. These are typically used in the form of so-called TLS (Transport Layer Security), sometimes also IPSec (Internet Protocol Security), which in turn uses conventional asymmetrical procedures such as e.g. use RSA or ECC (Elliptic Curve Cryptography) based on prime number decomposition.

The patent DE 10 2009 037 193 B4 describes a system and a method for carrying out an exchange of such an asymmetric key between a vehicle and a server external to the vehicle in order to operate the data connection in a correspondingly cryptographically secured manner, that is to say with encryption and / or authentication.

The typically used asymmetric cryptographic methods such as ECC or RSA have the advantage that, according to the current state of the art, they offer relatively secure protection with minimal effort. However, all of these methods are based on cryptographic algorithms, the security of which is not considered to be robust against quantum computers. Quantum computers are able to crack asymmetrical cryptographic procedures and decrypt secured data within a very short time due to the way they calculate. The methods typically used today for communication between the vehicle and the backend for cryptographic protection, i.e. in particular for encryption and / or authentication, are then no longer secure. This so-called post-quantum threat has so far been a rather theoretical threat, since quantum computers were still considered pure research instruments and could only be implemented with great effort. In recent years, however, the development of quantum computers has accelerated significantly. A reliable prognosis that sufficiently powerful quantum computers will not be commercially available on the market in the next ten years can therefore no longer be guaranteed from today's perspective.

Vehicles that come onto the market today will generally be on the road for 10 to 15 years. This means that the post-quantum threat, i.e. the potential possibility of easily cracking the conventional asymmetrical cryptographic protection using quantum computers that are easily or especially commercially available at a later point in time, is already relevant for vehicles to be delivered today. The communication of a communication device of the vehicle with the external server, which today is mostly secured on RSA or ECC-based cryptographic protocols, would no longer be secure with the occurrence of this post-quantum threat, so that from today's point of view, secure communication would not take place across the board expected service life of the vehicles can be guaranteed. This threat is particularly serious for systems that cannot be updated or updated easily. For example for the electronic control units (ECU: Electronic Control Unit) installed in vehicles. This is easier with servers, smartphones or the like, which can usually be expanded much more quickly with regard to their hardware or have an assumed shorter service life than the vehicles.

In order to do justice to the post-quantum threat, research has been carried out for several years on asymmetrical algorithms that are resistant to the post-quantum threat. These are the approaches commonly known as post-quantum cryptography or PQC. However, these are not yet very mature, so that they are not yet suitable to replace the asymmetrical conventional methods. So can In other words, today's vehicles have not yet been designed with post-quantum-capable cryptographic security procedures, since such techniques are not yet mature enough to allow a final assessment of the security to be expected. In addition, there has been no standardization to date and the approaches require a lot of resources. A premature switch to such quantum computer-resistant cryptographic methods is neither sensible nor easy at this point in time. If there were already a standardized PQC method that is regarded as sufficiently secure, it would not make sense to implement it in today's communication devices of vehicles, since higher costs and high resource consumption are contrary to economic viability in the current vehicle ecosystem.

Furthermore, symmetric methods such as AES (Advanced Encryption Standard) or hash methods such as SHA-512 (Secure Hash Algorithm) or symmetric authentication methods such as HMAC (Hashed Message Authentication Code) according to the current state of knowledge of the postal service Quantum threats are not fundamentally affected. According to current knowledge, the security of these procedures would be halved by the occurrence of the post-quantum threat, so that a 128-bit key still provides 64-bit security if quantum computers are available. However, such a weakening can be compensated relatively easily by increasing the key length.

Compared with asymmetric methods, it is the case that such symmetric methods have the major problem that, with symmetric cryptographic methods, the distribution and negotiation of keys and their potentially very large number is difficult. This applies in particular to equipping the components involved with initial symmetrical keys, known as provisioning. It also concerns the, in particular demand-driven, negotiation of, in particular common, symmetrical keys or session keys between two or more communication partners who are not in possession of a common symmetrical key, ie who do not or do not yet “know” each other. Furthermore, for each component with which a communication relationship already existed and a common symmetric key has already been agreed, this must be held accordingly. Because of the very large number of communication relationships that typically arise, managing the symmetrical keys in a component is extremely complex

For this reason, it is common for TLS to negotiate symmetric keys between the communication partners, for example, for asymmetric cryptographic methods based on certificates to be used. If the symmetric keys are negotiated using such procedures, then only symmetric authentication and encryption are carried out with TLS. As explained above, negotiating via asymmetric cryptographic methods is not post-quantum-resistant.

• - Es basiert auf wenigen abgestimmten und vorgegebenen Schnittstellen bzw. Protokollen, die alle Teilnehmer implementieren müssen. Dies kann beispielsweise TCP/IP, gegebenenfalls TLS usw. sein. Alles weitere bleibt dabei in der Hoheit der verschiedenen Hersteller der Komponenten, welche später miteinander kommunizieren.
• - Das ganze System ist dabei offen, das heißt, die obigen Schnittstellen und Protokolle sind offengelegt und alle Systeme von allen (verschiedenen) Herstellern können teilnehmen, solange sie diese Schnittstellen und Protokolle implementieren.
• - Das ganze Internet ist dabei global, was bedeutet, dass sich nicht weiter kennende Teilnehmer aus der ganzen Welt teilnehmen und miteinander kommunizieren können. Dies bedingt insbesondere, dass die Teilnehmer einander nicht vertrauen oder nicht vertrauen können.
• - Dabei ist das Internet dezentral, sodass beispielsweise zwei beliebige Teilnehmer jederzeit eine Kommunikationsbeziehung zueinander aufbauen können, ohne dass dafür eine weitere Instanz, wie beispielsweise eine Zentrale, einbezogen werden muss.
• - Das Internet unterstützt dabei die sichere Kommunikation, sodass zwei miteinander kommunizierende Teilnehmer ihre Kommunikation bei Bedarf absichern können, indem sie bilateral, also ohne Einbeziehung einer Zentrale oder dergleichen, Schutzmechanismen auswählen und sich auf diese einigen.
• - Dabei werden oft einseitige Kommunikationsbeziehungen verwendet, bei denen nur der Client die Identität des Servers sicher kennt. Der Client selbst bleibt für den Server anonym. Es handelt sich dabei um eine sogenannte reine Serverauthentifizierung, welche den Aufwand der Absicherung der Kommunikationsbeziehung erheblich vereinfacht.
• - Im Idealfall kann das Internet zustandslos betrieben werden. Das heißt, die Teilnehmer müssen sich die Kommunikation betreffend keine Vergangenheit merken. Insbesondere kann jede Kommunikationsbeziehung immer auf die gleiche Art und Weise aufgebaut werden, unabhängig davon, ob es die erste Kommunikation zwischen diesen Teilnehmern ist, oder ob diese sich bereits „kennen“.

The conventional Internet is characterized by the following essential features:

• - It is based on a few coordinated and specified interfaces or protocols that all participants have to implement. This can be, for example, TCP / IP, possibly TLS, etc. Everything else remains in the sovereignty of the various manufacturers of the components, which later communicate with each other.
• - The whole system is open, that is, the above interfaces and protocols are open and all systems from all (different) manufacturers can participate as long as they implement these interfaces and protocols.
• - The whole Internet is global, which means that participants from all over the world who don't know each other can take part and communicate with each other. In particular, this means that the participants do not or cannot trust each other.
• The Internet is decentralized, so that, for example, any two subscribers can establish a communication relationship with one another at any time without having to involve another entity, such as a control center.
• - The Internet supports secure communication so that two participants communicating with one another can secure their communication if necessary by bilaterally selecting protective mechanisms and agreeing on these without involving a control center or the like.
• - One-way communication relationships are often used in which only the client reliably knows the identity of the server. The client itself remains anonymous to the server. This is what is known as pure server authentication, which considerably simplifies the work involved in securing the communication relationship.
• - Ideally, the Internet can be operated statelessly. This means that the participants do not have to remember a past regarding the communication. In particular, each communication relationship can always be established in the same way, regardless of whether it is the first communication between these participants or whether they already “know” each other.

Without the mechanism of a so-called PKI (Public Key Infrastructure), i.e. without certificates and thus without asymmetric cryptography, this conventional global Internet in its current form with the properties described above could not be operated at all. Only the PKI based on asymmetric cryptography makes it possible to establish a kind of “offline trust authority” so that participants who do not know each other and who do not trust each other can communicate securely without involving a control center. An efficient and at the same time secure operation of the Internet with the properties described above is not possible in practice on the basis of symmetrical cryptography alone, due to the effort involved. Such a system is therefore very susceptible to the post-quantum threat.

For the further state of the art can also refer to WO 98/37661 A1 be pointed out. This describes a device and a method for authentication and encryption of a remote terminal via a wireless connection. In essence, a separate encryption is established between the remote terminal and the respective participant, which is comparable to the scenario described above, correspondingly complex. When used in a larger network, this is only possible with the inclusion of asymmetric cryptography, which is currently not, however, post-quantum-secure.

The object of the present invention now consists in specifying an improved method for distributing and negotiating key material within a vehicle ecosystem which is post-quantum-resistant.

According to the invention, this object is achieved by the method having the features in claim 1. Further advantageous refinements and developments of this method are specified in the dependent claims.

The inventors have recognized that the situation in a vehicle ecosystem is significantly different than in the previously known Internet. It is true that the same communication and security technologies are used today within such vehicle ecosystems as with the conventional Internet. In the opinion of the inventors, however, this happens more out of “habit” and “convenience” than out of an absolute necessity resulting from the given framework. The particular differences between a vehicle ecosystem and the conventional Internet lie in the fact that the vehicle manufacturer or OEM (Original Equipment Manufacturer) has control over virtually all participants in the vehicle ecosystem during their entire life cycle. This applies in particular from manufacture to scrapping, for example, of the electronic control units installed in the vehicle, the vehicle backend and third-party devices manufactured by or on behalf of him, for example OBD dongles for on-board diagnostic systems and those installed on third-party smartphones, for example Apps that are generated by or on behalf of the OEM.

The OEM has the option of introducing individual secrets into the participating components and systems of the vehicle ecosystem during production; depending on the component or system, this secret can be made more or less secure. The vehicle ecosystem is organized centrally, that is, there is a central vehicle-external server with the vehicle backend that is always accessible and is known directly or indirectly to all participants in the vehicle ecosystem. It is permanently connected directly or indirectly to almost all participants and can exchange messages with them bidirectionally. The entire vehicle ecosystem is almost closed, since most participants, apart from the vehicle backend, only communicate with a few other participants, all of whom are typically also participants in the same vehicle ecosystem. For most of the vehicle's electronic control units, the vehicle backend is the only server with which they communicate. Similarly, a vehicle usually only communicates with a few app instances or smartphones of its users. In the same way, these apps usually only communicate with a few vehicles, for example the vehicles of a family or a company network, whereby the number of vehicles is still within a manageable range, especially since not all employees typically have equal access to all vehicles.

Another advantageous aspect of such a vehicle ecosystem is that the participants in such a system trust each other in principle. Before they can confidently communicate with one another, they only have to ensure the identity of their counterpart and thus their affiliation to the vehicle ecosystem. The one-sided authentication known from the general Internet, i.e. the pure server Authentication is hardly used within such a vehicle ecosystem, because due to the high security requirements for the operation and communication of vehicles and their drive systems in a vehicle ecosystem, both participants in the communication must always know with whom they are communicating.

In summary, it can be said that the vehicle ecosystem is much more centralized than the conventional Internet in almost every respect. In particular, the participants trust each other. In addition, the vehicle ecosystem has a central instance, in particular the OEM. It is a closed system for which the OEM is responsible, developed and operated, which has only a few interfaces to the “outside world”.

The method according to the invention therefore does not require any certificates or asymmetric cryptography to operate a vehicle ecosystem, but can centrally coordinate and generate the initial symmetric crypto material required for secure communication and incorporate it into the participating components or systems during production. Accordingly, at least one symmetrical authentication method and at least one symmetrical encryption method, which according to a very advantageous development of the idea can, however, be combined into one method, are implemented for all participants. These must be the same at least in pairs so that the two or more participants can communicate with each other, whereby a participant can also implement more than one authentication method and more than one encryption method in order to communicate with different partners. At least one common symmetric authentication method and at least one common symmetric encryption method are simple and efficient, so that all participants can communicate with one another using the same common symmetric authentication method and the same common symmetric encryption method. Due to the exclusively symmetrical cryptographic procedures, post-quantum resistance is already given today.

According to the invention, it is now the case that a central trust authority, which in particular can be a particularly secure part of the vehicle backend, is set up. This includes at least one symmetrical authentication method and at least one symmetrical encryption method. This must again match in pairs to the subscriber with whom communication is to take place, as a result of which the central trust instance or the vehicle backend can also implement more than one authentication method and more than one encryption method. Here, too, one can benefit from a common symmetric authentication method and a common symmetric encryption method so that each participant does not need a separate authentication method and encryption method. Intermediate stages are conceivable, so that e.g. the participants are combined into clusters, with each of the clusters (e.g. a certain vehicle series) having its own common symmetric authentication method and its own common symmetric encryption method. This reduces the effort compared to paired individual authentication methods and encryption methods, albeit not as much as an authentication method and a common encryption method in the vehicle ecosystem. Nevertheless, this allows greater independence from the processes used than with the one common approach. Furthermore, the authentication method and the encryption method in all of the variants described can also be used in combination.

The participants in the vehicle ecosystem then have a communication unit and / or interface in order to communicate directly or indirectly bidirectionally with this central trust authority, the so-called Trust Authority (TA). To this end, each participant initially receives at least one individual secret that is secured and shared exclusively with the central trust authority. Each participant stores their individual secret locally, safely and securely. The central trust authority also stores the individual secret for each participant securely and protected in a crypto material database of the central trust authority.

According to a very advantageous alternative to this, it can also be provided that the individual secrets for each participant are not stored in the central trust authority, but that the latter has a specially secured master key. An individual secret can be generated from this master key together with, for example, the identity of the respective participant and, if necessary, further data, which can be generated again if necessary, so that storage of the individual secrets is unnecessary when using such a master key.

• - Jeder Teilnehmer der Gruppe schickt eine authentifizierte Anfrage mit Angabe der Gruppe an die zentrale Vertrauensinstanz. Zur Authentifizierung nutzt jeder Teilnehmer sein eigenes individuelles Geheimnis beziehungsweise das darauf aufgebaute symmetrische Authentifizierungsverfahren, welches als gemeinsames und sicheres Authentifizierungsverfahren zwischen dem jeweiligen Teilnehmer und der zentralen Vertrauensinstanz implementiert ist, und welches als symmetrisches Authentifizierungsverfahren insbesondere post-quanten-resistent ist. Bei dem Verfahren kann es sich beispielsweise um HMAC handeln. Gemäß einer sehr vorteilhaften Weiterbildung dieser Idee kann dabei die Anfrage auch zusätzlich verschlüsselt sein, wobei wiederum ein auf dem individuellen Geheimnis basierendes gemeinsames sicheres symmetrisches Verschlüsselungsverfahren, beispielsweise AES-256, verwendet werden kann, welches ebenfalls als post-quanten-resistent anzusehen ist.
• - Die zentrale Vertrauensinstanz prüft nun die Authentifizierung und entschlüsselt gegebenenfalls die Anfrage der jeweiligen Teilnehmer und erzeugt ein neues für alle Teilnehmer der Gruppe gemeinsames Geheimnis. Im Anschluss verschlüsselt die zentrale Vertrauensinstanz diese neuen Geheimnisse jeweils basierend auf dem individuellen Geheimnis und verschickt das neue Geheimnis jeweils authentifiziert an die jeweiligen Teilnehmer als Absender der Anfrage. Die jeweiligen Teilnehmer können dann die Authentifizierung, welche wiederum auf ihrem mit der zentralen Vertrauensinstanz geteilten individuellen Geheimnis basiert, entsprechend prüfen und entschlüsseln nun das neue Geheimnis. Sie speichern dieses sicher und geschützt lokal ab. Jeder einzelne Teilnehmer generiert nun aus diesem neuen gemeinsamen Geheimnis der Gruppe den wenigstens einen benötigten Gruppenschlüssel und speichert diesen geschützt lokal ab. Dabei sind selbstverständlich auch mehrere Gruppenschlüssel denkbar, insbesondere zwei, um einerseits einen Schlüssel für die Authentifizierung und andererseits für die Verschlüsselung zu haben, wobei auch hier diese beiden Maßnahmen wieder zu einer zusammengefasst werden könnten, sodass ein gemeinsamer Schlüssel für die symmetrische Authentifizierung und die symmetrische Verschlüsselung ausreicht, wie es beispielsweise die Authenticated Encryption-Betriebsmodi erlauben.

At least when there is an initial mutual need for secure communication between participants in the vehicle ecosystem who have not yet communicated with each other or who want to renew their key material, a few steps are now carried out to negotiate and distribute secrets or key material. The at least two participants form a group with regard to the planned communication. The steps include the following:

• - Each participant in the group sends an authenticated request specifying the group to the central trust authority. For authentication, each participant uses his own individual secret or the symmetrical authentication method based on it, which is implemented as a common and secure authentication method between the respective participant and the central trust authority and which, as a symmetrical authentication method, is particularly post-quantum-resistant. The method can be, for example, HMAC. According to a very advantageous development of this idea, the request can also be encrypted, in which case a common, secure symmetrical encryption method based on the individual secret, for example AES-256, can be used, which is also to be regarded as post-quantum-resistant.
• The central trust authority now checks the authentication and, if necessary, decrypts the request of the respective participant and generates a new secret common to all participants in the group. The central trust authority then encrypts these new secrets based on the individual secret and sends the new secret authenticated to the respective participant as the sender of the request. The respective participants can then check the authentication, which in turn is based on their individual secret shared with the central trust authority, and then decrypt the new secret. You save this safely and securely locally. Each individual participant now generates the at least one required group key from this new shared secret of the group and saves it locally in a protected manner. Of course, several group keys are also conceivable, in particular two, in order to have one key for authentication on the one hand and one key for encryption on the other, whereby these two measures could again be combined into one, so that a common key for symmetric authentication and symmetric Encryption is sufficient, as for example the Authenticated Encryption operating modes allow.

The participants in the group can now communicate securely with one another using the at least one derived group key.

The individual or new secrets can be generated randomly and independently of one another by a secure random number generator implemented in the generating system or can be derived from a central master key of sufficient length from the identification of the respective participants or the respective participants in the group. This is done with the help of post-quantum-resistant processes such as a so-called KDF (Key Derivation Function).

According to an extremely favorable development of the method according to the invention, the new secrets can be deleted again by the central trust authority immediately after they have been sent, so that they do not cause any secure storage requirements in the area of the central trust authority.

As an alternative to this, it would also be conceivable here, comparable to the individual secrets, to generate these new secrets accordingly via a stored master key by using the identification of the respective participants in the group accordingly. As with the individual secrets, this can be done via the central master key, for example by the central trust authority or a dedicated crypto material server, as provided in accordance with an advantageous development.

A very advantageous development of the method according to the invention also provides that each secret used, be it for use as an individual or new secret, has sufficient entropy to generate at least one secure key for authentication and at least one secure key for the To derive encryption.

The individual keys, which are based on the individual and / or new secret and can be used, for example, for authentication and / or encryption, can each have different lengths according to a further, very advantageous embodiment of the method according to the invention.

The method according to the invention in any of its configurations described above or also in a combination of several of the configurations described thus uses the central trust authority which is permanently available online in a vehicle ecosystem and which can in particular be formed by part of the vehicle backend. Since this trustworthy entity is always present, it can be used, if necessary, for the secure agreement and distribution of a symmetrical key between the not yet “knowing” communication participants. Since this center is per se trustworthy as a central trust authority, it is also justifiable in terms of security that it also knows the key assigned to the participants in the communication. In particular, it can delete this after sending it, as explained above, but of course still knows it in principle. The participants in the vehicle ecosystem usually only communicate with a few other participants. As a rule, you only have to manage a few symmetrical keys, which is easy to solve with a reasonable amount of effort. Using the method according to the invention, a vehicle ecosystem can thus be operated very well with exclusively symmetrical cryptography, securely, post-quantum-resistant and nevertheless efficiently.

The invention therefore uses a cryptosystem based exclusively on symmetric cryptography to secure the communication between the participants in a vehicle ecosystem against the post-quantum threat. This virtually creates a new type of Shared Key Infrastructure (SKI), in contrast to the PKI that is common in the conventional Internet.

Further very advantageous configurations of the method according to the invention for distributing and negotiating key material within a vehicle ecosystem also result from the exemplary embodiments which are described in more detail below with reference to the figures.

• 1 zwei Möglichkeiten der initialen Verteilung und -verwaltung von Schlüsselmaterial bzw. Geheimnissen bei dem erfindungsgemäßen Verfahren; und
• 2 eine Möglichkeit der Schlüsselaushandlung und Verteilung von Schlüsselmaterial bzw. Geheimnissen bei der beispielhaften Gruppe mit drei Teilnehmern.

Show:

• 1 two options for the initial distribution and management of key material or secrets in the method according to the invention; and
• 2 a possibility of key negotiation and distribution of key material or secrets in the exemplary group with three participants.

• - Das Einrichten einer zentralen Vertrauensinstanz, einer sogenannten Trust Authority (TA). Die zentrale Vertrauensinstanz TA bildet ein vertrauenswürdiges, zentrales, durchgehend verfügbares mit allen Teilnehmern (direkt oder indirekt) verbundenes System. Diese zentrale Vertrauensinstanz TA ist für das Verfahren elementar. Sie kann beispielsweise in einem besonders gesicherten Teil eines Vehicle Backends eingerichtet werden.
• - Das Ausstatten aller Teilnehmer TN_i, wobei i für einen die Teilnehmer TN nummerierenden Index steht, mit mindestens einem gemeinsamen sicheren symmetrischen Authentifizierungsverfahren AUTH und einem gemeinsamen sicheren symmetrischen Verschlüsselungsverfahren ENCR. Alternativ dazu können die symmetrische Authentifizierung und die symmetrische Verschlüsselung zusammen durch ein gemeinsames Verfahren unter Nutzung eines gemeinsamen Schlüssels realisiert werden, wie es beispielsweise die Authenticated-Encryption-Betriebsmodi AuthEncr erlauben. Beispielsweise kann die Ausstattung eines jeden Teilnehmers TN_i mit HMAC auf Basis SHA-512 als Authentifizierungsverfahren AUTH und mit AES-256 als Verschlüsselungsverfahren ENCR erfolgen.

The proposed procedure consists of the following individual steps, which must first be carried out once and generally for each vehicle ecosystem:

• - The establishment of a central trust authority, a so-called Trust Authority (TA). The central trust authority TA forms a trustworthy, central, continuously available system that is (directly or indirectly) connected to all participants. This central trust authority TA is elementary for the procedure. It can be set up, for example, in a specially secured part of a vehicle backend.
• Equipping all subscribers TN _i , where i stands for an index numbering the subscribers TN, with at least one common secure symmetric authentication method AUTH and a common secure symmetric encryption method ENCR. Alternatively, the symmetrical authentication and the symmetrical encryption can be implemented together by a common method using a common key, as allowed, for example, by the authenticated encryption operating modes AuthEncr. For example, each subscriber TN _{i can be} equipped with HMAC based on SHA-512 as the authentication method AUTH and with AES-256 as the encryption method ENCR.

• - Das sogenannte Provisioning ist ein einmaliges initiales und sicheres Ausstatten jedes Teilnehmers TN_i mit einem mit der zentralen Vertrauensinstanz TA geteilten Geheimnis SEC_TNi ^TA, das über ausreichend Entropie verfügt, um daraus mindestens einen sicheren Schlüssel für das symmetrischen Authentifizierungsverfahren AUTH (authKEY_TNi ^TA) und einen sicheren Schlüssel für das symmetrische Verschlüsselungsverfahren ENCR (encrKEY_TNi ^TA) erzeugen bzw. extrahieren bzw. ableiten zu können. Mit diesen Schlüsseln authKEY_TNi ^TA und encrKEY_TNi ^TA kann der Teilnehmer TN_i anschließend bei Bedarf sicher mit der zentralen Vertrauensinstanz TA unter Nutzung von AUTH und ENCR kommunizieren.
• - Die sichere lokale Ablage des Schlüsselmaterials authKEY_TNi ^TA, encrKEYT_Ni ^TA und/oder des diesem zugrundeliegenden Geheimnisses SEC_TNi ^TA sowohl in einem sichereren lokalen Speicherort beim Teilnehmer TN_i als auch bei der zentralen Vertrauensinstanz. Dies ist in 1a) so dargestellt. Die Speicherung kann beispielsweise in einem HSM erfolgen.

As mentioned above, it would also be sufficient if the authentication method AUTH and encryption method ENCR used are not common for all subscribers TN _i and the central trust authority TA in the vehicle ecosystem, but only “in pairs”. In this case, the central trust authority TA and / or one or the other of the participants TN _{i would have to} implement several methods, depending on the partners, but this would not be problematic because of the limited number. This enables greater independence from the processes used. However, the exemplary embodiment concentrates on the variant of the common authentication method AUTH and encryption method ENCR.

• - So-called provisioning is a one-time initial and secure provision of each participant TN _i with a secret SEC _TNi TA shared with the central trust _authority ^TA , which has sufficient entropy to generate at least one secure key for the symmetrical authentication method AUTH (authKEY _TNi ^TA ) and to be able to generate or extract or derive a secure key for the symmetric encryption method ENCR (encrKEY _TNi ^TA ). With these keys authKEY _TNi ^TA and encrKEY _TNi ^TA , the subscriber TN _{i can} then, if necessary, communicate securely with the central trust authority TA using AUTH and ENCR.
• The secure local storage of the key material authKEY _TNi ^TA , encrKEYT _Ni ^TA and / or the secret SEC _TNi ^TA on which it is based, both in a secure local storage location at the subscriber TN _i and at the central trust authority. This is in 1a) so represented. The storage can for example take place in an HSM.

The initial secure secrets SEC _TNi ^TA can be generated and distributed both by the central trust authority TA itself and by a dedicated crypto material server KMS. The generation and distribution of the secrets SEC _TNi ^TA by the central trust authority TA has the advantage that none of the secrets SEC _TNi ^{TA are known to} any authority other than the subscriber TN _i itself and the central trust authority TA. The disadvantage is that the actual role of the central trust authority TA is to ensure the safe operation of the vehicle ecosystem. Provisioning does not necessarily take place, however, but usually before operation during the production of the respective subscriber TN _i (for example an ECU). However, the crypto material server KMS is much more suitable than the central trust authority TA for transmitting the secret SEC _TNi ^TA to be introduced to the supplier producing the ECU. In the 1a) and 1b) an example is therefore shown in each case using the crypto material server KMS.

An alternative to storing the individual secrets SEC _TNI ^TA for each of the participants TN _i in a secure crypto-material database, as in 1a) shows the use of a master key or Master Key MK. This is in 1b) shown without the analogous to 1a) parts shown are explained again in detail.

Provisioning takes place once per master key MK. For this purpose, a random 1024-bit master key MK is generated in the crypto material server KMS. This master key MK is then transmitted from the crypto material server KMS to the central trust authority TA via a secure connection. In addition, the crypto material server KMS derives an individual secret SEC _TNI ^TA 512 + 256 = 768 bits long for each participant TN _i with the unique identity TN _i ID from the master key MK with the help of a secure key derivation function (KDF): $${\text{SEC}}_{\text{TNI}}{}^{\text{TA}}:=\text{KDF}\left(\text{MK},{\text{TN}}_{\text{i}}-\text{ID},...\right)$$

As a simple example, a first number of bits of the individual secret SEC _TNi ^{TA can be used} for the common symmetric authentication AUTH as the key authKEY _TNi ^TA and the remaining bits of the SEC _TNi ^{TA can be used} as the key encrKEYT _Ni ^TA for the common symmetric encryption ENCR.

For each participant TN _i , the secret SEC _TNi ^TA is now _securely introduced, for example during its production. Because all the individual secrets SEC _TNi ^TA can be derived from the master key MK and the central trust authority TA knows this master key MK, if it knows the identity ID of the subscriber TN _{i, it can} also derive his key if necessary and thus communicate with him securely. A storage / management of the secrets SEC _TNi ^{TA of} all subscribers TN _i or their keys based on them in the central trust authority TA is therefore unnecessary.

2 then illustrates the negotiation of keys, the so-called key agreement, which must take place during operation at least when there is an initial mutual need for secure communication between participants TN _i who have not yet known each other. Once keys have been negotiated, they can also be used when communicating again. Alternatively, however, it is always possible to repeat the key agreement if necessary and thus renew the key material or the secret on which it is based. The participants TN _i entering into communication form a group or participant group. A group typically has two participants TN _i , but there can also be more participants TN _i .

The example of 2 shows the key agreement for a group consisting of three participants TN, here participants TN _a , TN _b and TN _c .

• - Art der Anforderung („Schlüsselanforderung“): requestNewSecret
• - Die Identität ID des anfordernden Teilnehmers TN_i: TN_i-ID
• - Die Identität ID der zentralen Vertrauensinstanz TA: TA-ID
• - Liste der Teilnehmer TN_i der Gruppe, innerhalb derer das Geheimnis genutzt werden soll: TNG
• - Ausgehandelte Nummer der Anforderung: Nr

Each of the participants TN _i who would like to be part of the group first takes part in the negotiation of a common unique number No. for the request with the other participants TN _i from the group. Each participant TN _{i then} generates a request to the central trust authority TA from the following data:

• - Type of request ("key request"): requestNewSecret
• The identity ID of the requesting participant TN _i : TN _i -ID
• - The identity ID of the central trust authority TA: TA-ID
• - List of participants TN _{i of} the group within which the secret is to be used: TNG
• - Negotiated number of the requirement: No.

A Message Authentication Code (MAC) is then created with the help of the HMAC method via the request (requestNewSecret, TN _i -ID, TA-ID, TNG, Nr) with the help of the authentication key authKEY _TNi ^TA for each of the participants TN _i . The message can optionally be encrypted with encrKEY _TNi ^TA before the MAC _i is formed. Each of the participants TN _i , in the example of 2 So the participants TN _a , TN _b and TN _c , then send the request together with the generated MAC _i , for example: ((requestNewSecret, TNi-ID, TA-ID, TNG, No), MAC _i ) to the central trust authority TA.

When the respective request ((requestNewSecret, TNi-ID, TA-ID, TNG, Nr), MAC _i ) is received by the central trust authority TA, it extracts the authentication key authKEY _TNi belonging to the respective subscriber TN _i recognizable by his identity TN _{i ID} ^TA from the secret SEC _TNI ^TA in the crypto material database or derives this from the master key MK. The central trust authority TA then _uses the extracted authentication key authKEY _TNi ^{TA to} _check the correctness of the received MAC _i . If this is incorrect, the request is rejected. However, if the received MAC _i is correct and the received request is the first from the group defined via the subscriber list TNG and the request number Nr, the central trust authority TA derives a new secret SEC _TNG 512 + 256 = 768 bits long from the master key MK ^NR for the group by means of a secure key derivation function (KDF) from: SEC _TNG ^NR: = KDF (MK, TNG, Nr, ...) If the received request with a correct MAC, however, not the first _i from the group (TNG , No), it checks the central confidence instance TA based on the identity TN _i -ID of the subscriber TN _i whether the subscriber TN _i in TNG is included and whether the request matches the date of the one or more other subscribers TN _i from TNG been sent requirements . If this is the case, the central trust authority TA uses the new secret SEC _TNG ^{Nr of} the group that has already been created.

The shared new secret SEC _TNG ^{Nr of} the group is then encrypted in both cases by means of AES-256 with the help of encrKEYT _Ni ^{TA in} order to obtain the group secret encrSEC _TNG ^NI _i individually encrypted for the respective participant TN _i . The central trust authority TA then generates a response with the data (responseNewSecret, TA-ID, TN _i -ID, TNG, Nr, encrSEC _TNG ^Nr _i ) for each of the participants TN _{i in} response to their request. It forms the MAC _i over the Response (responseNewSecret, TA-ID, TN _i -ID, TNG, Nr, encrSEC _TNG ^Nr _i ) using the HMAC procedure and the authentication key authKEY _TNi ^TA , which applies between you and the respective participant TN _i . Then the central trust authority TA sends the response together with the generated MAC _i , for example: ((responseNewSecret, TA-ID, TN _i -ID, TNG, Nr, encrSEC _TNG ^Nr _i ), MAC _i ) to the respective participant TN _i .

Upon receipt of the response: ((responseNewSecret, TA-ID, TN _i -ID, TNG, Nr, encrSEC _TNG ^Nr _i ). MAC _i ) from the central trust authority TA the respective participant TN _i with the identity TN _i -ID also checks Using the authentication key authKEY _TNi ^TA the correctness of the received MAC _i . If the MAC _i wrong, the response is rejected, the MAC _i is correct, it can be decrypted. For this purpose, the respective subscriber TN _i uses his encryption key encrKEY _TNi ^TA in order to decrypt the common group _secret SEC _TNG ^Nr from the group secret enerSEC _TNG ^NR _i which is individually encrypted for him. Each of the participants TN _i then uses, for example, the first 512 bits of the group secret SEC _TNG ^Nr as the authentication key authKEY _TNG ^Nr for the group and the remaining 256 bits of SEC _TNG ^Nr as the encryption key encrKEY _TNG ^Nr for the group. It saves the two keys authKEY _TNG ^Nr and encrKEY _TNG ^Nr persistently and securely locally and uses them to secure future communication with participants TN _i from the participant group.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102009037193 B4 [0005]
• WO 9837661 A1 [0014]

Claims (10)

Method for distributing and negotiating key material within a vehicle ecosystem, in which participants (TN _i ) of the vehicle ecosystem each have a unique identity (TN _i ID) and via a communication unit and / or interface with at least one other participant (TN _i ) communicate, with at least one symmetric authentication method (AUTH) and at least one symmetric encryption method (ENCR) being implemented for all participants (TN _i ), characterized in that a central trust authority (TA) is set up as a trust anchor, which at least one has implemented symmetrical authentication method (AUTH) and at least one symmetrical encryption method (ENCR), whereby the participants (TN _i ) communicate directly or indirectly bidirectionally with the central trust authority (TA) via the communication unit and / or interface, for which each participant (TN _i ) initially safe mi t least one individual divided exclusively with the central trust authority (TA) individual secret (SEC _TNi ^TA), is provided, each subscriber (TN _i) safe and protected locally stores its individual secret (SEC _TNi ^TA) and for each subscriber (TN _i ) the individual secret (SEC _TNi ^TA ) is _stored securely and protected in the central trust authority (TA) or can be generated at any time from a master key (MK) stored securely and protected in the central trust authority (TA), according to which at least the first time mutual need for secure communication between participants (TN _i ) who have not yet communicated with each other and now form a group of at least two participants (TN _i ) with regard to communication, the following steps are carried out by them: - each participant (TN _i ) the group sends an authenticated request specifying the group to the central Ve trust authority (TA); - the central trust authority (TA) checks the authenticity of the respective inquiries and generates a new secret (SEC _TNG ^NR ) common to all participants (TN _i ) in the group, - the central trust authority (TA) encrypts the new secret (SEC _TNG ^NR ), each based on the individual secret (SEC _TNi ^TA ) and sends it authenticated to the respective participant (TN _i ) as the sender of the request, - the respective participant checks the authenticity of the received response, decrypts the new secret (SEC _TNG ^NR ) and saves it locally in a secure and protected manner, - the respective participant (TN _i ) generates the at least one required group key (authKEY _TNG ^Nr , encrKEY _TNG ^Nr ) from the new secret (SEC _TNG ^NR ) and saves it locally in a secure and protected manner , according to which the participants (TN _i ) of the group securely communicate with one another with the help of the at least one derived group key (authKEY _TNG ^NR encrKEY _TNG ^Nr ) can nect. Procedure according to Claim 1 , characterized in that the symmetrical authentication (AUTH) and the symmetrical encryption (ENCR) are implemented together by a common method (AuthEncr) using a common key. Procedure according to Claim 1 or 2 , Characterized in that in the case of derivation of the respective individual secrets (SEC _TNi ^TA) from a protected stored master key (MK), these individual secrets (SEC _TNi ^TA) from the central trust authority (TA) are not stored. Procedure according to Claim 1 , 2 or 3 , characterized in that the new secrets (SEC _TNG ^NR ) are deleted in the central trust authority (TA) after they have been sent. Method according to one of the Claims 1 to 4th , characterized in that the authenticated request to the central trust authority (TA) is additionally encrypted. Method according to one of the Claims 1 to 5 , characterized in that the subscribers (TNi) belonging to a group can renew the at least one group key (authKEY _TNG ^Nr , encrKEY _TNG ^Nr ) as often as they want via requests to the central trust authority (TA). Method according to one of the Claims 1 to 6th , characterized in that the secrets (SEC _TNi ^TA , SEC _TNG ^NR ) have sufficient entropy to generate at least one secure key (authKEY _TNi ^TA , authKEY _TNG ^Nr ) for authentication (AUTH) and at least one secure key (encrKE _YTNi ^TA , encrKEY _TNG ^Nr ) for the encryption (ENCR). Method according to one of the Claims 1 to 7th , characterized in that the central trust authority (TA) is implemented as a specially secured part of a vehicle backend. Method according to one of the Claims 1 to 8th , characterized in that the individual and new secrets (SEC _TNi ^TA , SEC _TNG ^NR ) are _generated by a dedicated crypto material server (KMS) and / or by the central trust authority (TA) itself, the secrets (SEC _TNi ^TA , SEC _TNG ^NR ) randomly and independently of one another by one in the generating system implemented secure random number generator or generated from a secure central symmetrical master key (MK) of sufficient length from the identification (TN _i ID) of the respective participant (TN _i ) or the respective participant (TN _i ) of the group with the help of post-quantum more resistant methods can be derived. Method according to one of the Claims 1 to 9 , characterized in that at least some of the keys (authKEY _TNi ^TA ) derived from the individual secret (SEC _TNi ^TA ) and / or the new secret (SEC _TNG ^NR ) for the respective authentication (AUTH) and / or the respective encryption (ENCR) , encrKEY _TNi ^TA ) and / or group keys (authKEY _TNG ^Nr , encrKEY _TNG ^Nr ) have different lengths.

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