ANIMA WG M. Pritikin Internet-Draft Cisco Intended status: Informational M. Richardson Expires: January 7, 2016 SSW M. Behringer S. Bjarnason Cisco July 6, 2015 Bootstrapping Key Infrastructures draft-pritikin-anima-bootstrapping-keyinfra-02 Abstract This document specifies automated bootstrapping of an key infrastructure using vendor installed IEEE 802.1AR manufacturing installed certificates, in combination with a vendor based service on the Internet. Before being authenticated, a new device has only link-local connectivity, and does not require a routable address. When a vendor provides an Internet based service, devices can be forced to join only specific domains but for constrained environments we describe a variety of options that allow bootstrapping to proceed. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 7, 2016. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents Pritikin, et al. Expires January 7, 2016 [Page 1]
Internet-Draft Bootstrapping Key Infrastructures July 2015 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Pritikin, et al. Expires January 7, 2016 [Page 2]
Internet-Draft Bootstrapping Key Infrastructures July 2015 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 2. Architectural Overview . . . . . . . . . . . . . . . . . . . . 5 3. Functional Overview . . . . . . . . . . . . . . . . . . . . . 7 3.1. Behavior of a new entity . . . . . . . . . . . . . . . . . 8 3.1.1. Discovery and Identity . . . . . . . . . . . . . . . . 10 3.1.2. Imprint . . . . . . . . . . . . . . . . . . . . . . . 11 3.1.3. Enrollment . . . . . . . . . . . . . . . . . . . . . . 12 3.1.4. Being Managed . . . . . . . . . . . . . . . . . . . . 12 3.2. Behavior of a proxy . . . . . . . . . . . . . . . . . . . 13 3.3. Behavior of the Registrar . . . . . . . . . . . . . . . . 13 3.3.1. Entity Authentication . . . . . . . . . . . . . . . . 14 3.3.2. Entity Authorization . . . . . . . . . . . . . . . . . 14 3.3.3. Claiming the New Entity . . . . . . . . . . . . . . . 15 3.3.4. Log Verification . . . . . . . . . . . . . . . . . . . 16 3.3.5. Forwarding Authorization Token plus Configuration . . 16 3.4. Behavior of the MASA Service . . . . . . . . . . . . . . . 16 3.4.1. Issue Authorization Token and Log the event . . . . . 17 3.4.2. Retrieve Audit Entries from Log . . . . . . . . . . . 17 3.5. Leveraging the new key infrastructure / next steps . . . . 17 3.5.1. Network boundaries . . . . . . . . . . . . . . . . . . 17 4. Domain Operator Activities . . . . . . . . . . . . . . . . . . 18 4.1. Instantiating the Domain Certification Authority . . . . . 18 4.2. Instantiating the Registrar . . . . . . . . . . . . . . . 18 4.3. Accepting New Entities . . . . . . . . . . . . . . . . . . 18 4.4. Automatic Enrolment of Devices . . . . . . . . . . . . . . 19 4.5. Secure Network Operations . . . . . . . . . . . . . . . . 19 5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 20 5.1. EAP-EST . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.2. Request bootstrap token . . . . . . . . . . . . . . . . . 21 5.3. Request MASA authorization token . . . . . . . . . . . . . 21 5.4. Basic Configuration Information Package . . . . . . . . . 22 5.5. Request MASA authorization log . . . . . . . . . . . . . . 23 6. Reduced security operational modes . . . . . . . . . . . . . . 23 6.1. New Entity security reductions . . . . . . . . . . . . . . 24 6.2. Registrar security reductions . . . . . . . . . . . . . . 24 6.3. MASA security reductions . . . . . . . . . . . . . . . . . 25 7. Security Considerations . . . . . . . . . . . . . . . . . . . 25 7.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 26 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 9.1. Normative References . . . . . . . . . . . . . . . . . . . 26 9.2. Informative References . . . . . . . . . . . . . . . . . . 27 Appendix A. Editor notes . . . . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 Pritikin, et al. Expires January 7, 2016 [Page 3]
Internet-Draft Bootstrapping Key Infrastructures July 2015 1. Introduction To literally "pull yourself up by the bootstraps" is an impossible action. Similarly the secure establishment of a key infrastructure without external help is also an impossibility. Today it is accepted that the initial connections between nodes are insecure, until key distribution is complete, or that domain-specific keying material is pre-provisioned on each new device in a costly and non-scalable manner. This document describes a zero-touch approach to bootstrapping an entity by securing the initial distribution of key material using third-party generic keying material, such as a manufacturer installed IEEE 802.1AR certificate [IDevID], and a corresponding third-party service on the Internet. The two sides of an association being bootstrapped authenticate each other and then determine appropriate authorization. This process is described as four distinct steps between the existing domain and the new entity being added: o New entity authentication: "Who is this? What is its identity?" o New entity authorization: "Is it mine? Do I want it? What are the chances it has been compromised?" o Domain authentication: "What is this domain's claimed identity?" o Domain authorization: "Should I join it?" A precise answer to these questions can not be obtained without leveraging an established key infrastructure(s). The domain's decisions are based on the new entity's authenticated identity, as established by verification of previously installed credentials such as a manufacturer installed IEEE 802.1AR certificate, and verified back-end information such as a configured list of purchased devices or communication with a trusted third-party. The new entity's decisions are made according to verified communication with a trusted third-party or in a strictly auditable fasion. Optimal security is achieved with IEEE 802.1AR certificates on each new entity, accompanied by a third-party Internet based service for verification. The concept also works with less requirements, but is then less secure. A domain can choose to accept lower levels of security when a trusted third-party is not available so that bootstrapping proceeds even at the risk of reduced security. Only the domain can make these decisions based on administrative input and known behavior of the new entity. The result of bootstrapping is that a domain specific key infrastructure is deployed. Since IEEE 802.1AR PKI certificates are used for identifying the new entity and the public key of the domain identity is leveraged during communiciations with an Internet based Pritikin, et al. Expires January 7, 2016 [Page 4]
Internet-Draft Bootstrapping Key Infrastructures July 2015 service, which is itself authenticated using HTTPS, bootstrapping of a domain specific Public Key Infrastructure (PKI) is fully described. Sufficient agility to support bootstrapping alternative key infrastructures (such as symmetric key solutions) is considered although no such key infrastructure is described. 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. The following terms are defined for clarity: Domain Identity: The domain identity is the 160-bit SHA-1 hash of the BIT STRING of the subjectPublicKey of the domain trust anchor that is stored by the Domain CA. This is consistent with the RFC5280 Certification Authority subject key identifier of the Domain CA's self signed root certificate. (A string value bound to the Domain CA's self signed root certificate subject and issuer fields is often colloquially used as a humanized identity value but during protocol discussions the more exact term as defined here is used). drop ship The physical distribution of equipment containing the "factory default" configuration to a final destination. In zero- touch scenarios there is no staging or pre-configuration during drop-ship. imprint the process where a device that wishes to join a network acquires it's domain specific identity. This term is taken from Konrad Lorenz's work in biology with new ducklings: during a critical period, the duckling would assume that anything that looks like a mother duck is in fact their mother. [imprinting] pledge the prospective device, which has the identity provided to at the factory. Neither the device nor the network knows if the device yet knows if this device belongs with this network. This is definition 6, according to [pledge] 2. Architectural Overview The logical elements of the bootstrapping framework are described in this section. Figure 1 provides a simplified overview of the components. Each component is logical and may be combined with other components as necessary. Pritikin, et al. Expires January 7, 2016 [Page 5]
Internet-Draft Bootstrapping Key Infrastructures July 2015 Vendor components . .+---------------+ +--------------Drop Ship------------------------.| Manufacturer | | .+---------------+ | .| M anufacturer | | .| A uthorized | | .| S igning | | .| A uthority | | .+---------------+ V ...... ^ +-------+ | | New | +------------+ +-----------+ | | Entity|<--L2-->| Proxy |<----->| | | | | +------------+ | | | | | | Registrar | | | | | | | | |<-----L3---------------------( may proxy )---------+ | | +-----------+ | | | | | +----------------------------+ | |<-----Enroll---->| Domain Certification | ^ | |<-----Config---->| Authority | . +-------+ . | Management and etc | . . +----------------------------+ . . . ......................................... "domain" components Figure 1 Domain: The set of entities that trust a common key infrastructure trust anchor. Domain CA: The domain Certification Authority (CA) provides certification functionalities to the domain. At a minimum it provides certification functionalities to the Registrar and stores the trust anchor that defines the domain. Optionally, it certifies all elements. Registrar: A representative of the domain that is configured, perhaps autonomically, to decide whether a new device is allowed to join the domain. The administrator of the domain interfaces with a Registrar to control this process. Typically a Registrar is "inside" its domain. Pritikin, et al. Expires January 7, 2016 [Page 6]
Internet-Draft Bootstrapping Key Infrastructures July 2015 New Entity: A new device or virtual machine or software component that is not yet part of the domain. Proxy: A domain entity that helps the New Entity join the domain. A Proxy facilitates communication for devices that find themselves in an environment where they are not provided L3 connectivity until after they are validated as members of the domain. MASA Service: A Manufacturer Authorized Signing Authority (MASA) service on the global Internet. At a minimum the MASA provides a trusted repository for audit information concerning privacy protected bootstrapping events. The MASA is recommended to provide ownership validation services which allows for fully secure zero-touch bootstrap of domain certificates with mutual authentication. We assume a multi-vendor network. In such an environment, there could a MASA for each vendor that supports devices following this document's specification, or an integrator could provide a MASA service for all devices. This document describes a secure zero-touch approach to bootstrapping a key infrastructure; if certain devices in a network do not support this approach, they can still be bootstrapped manually. Although manual deployment is not scalable and is not a focus of this document the necessary mechanisms are called out in this document to ensure all such edge conditions are covered by the architectural and protocol models. 3. Functional Overview Entities behave in an autonomic fashion. They discover each other and autonomically bootstrap into a key infrastructure deliminating the autonomic domain. See [I-D.irtf-nmrg-autonomic-network-definitions] for more information. This section details the state machine and operational flow for each of the main three entities. The New Entity, the Domain (primarily the Registrar) and the MASA service. The overall flow is shown in Figure 2: Pritikin, et al. Expires January 7, 2016 [Page 7]
Internet-Draft Bootstrapping Key Infrastructures July 2015 +---------+ +----------+ +-----------+ | New | | | | MASA | | Entity | | Domain | | Service | | | | | | (Internet)| +---------+ +----------+ +-----------+ | | | |<-------discovery--------->| | |---802.1AR credential----->| | | | | | [ accept device? ] | | | | | |---802.1AR identity-------->| | |---Domain ID--------------->| | | | | | [device belongs] | | [to domain? ] | | | | | [update audit log] | | | | |<---device history log------| | |<-- authorization token-----| | | | | [ still accept device?] | | | | |<----authorization token---| | |<----config information----| | | | | [authorization token valid?] | | [apply config information] | | | | | |----domain enrolment------>| | |<----domain certificate----| | | | | Figure 2 3.1. Behavior of a new entity A New Entity that has not yet been bootstrapped attempts to find a local domain and join it. States of a New Entity are as follows: Pritikin, et al. Expires January 7, 2016 [Page 8]
Internet-Draft Bootstrapping Key Infrastructures July 2015 +--------------+ | Start | | | +------+-------+ | +------v-------+ | Discover | +------------> | | +------+-------+ | | | +------v-------+ | | Identity | ^------------+ | | rejected +------+-------+ | | | +------v-------+ | | Imprint | Optional ^------------+ <--+Manual input | Bad MASA +------+-------+ | response | | +------v-------+ | | Enroll | ^------------+ | | Enroll +------+-------+ | Failure | | +------v-------+ | | Being | ^------------+ Managed | Factory +--------------+ reset Figure 3 State descriptions are as follows: 1. Discover a communication channel to the "closest" Registrar by trying the following steps in this order: A. Search for a Proxy on the local link using a link local discovery protocol (no routable addresses are required for this approach). If multiple local proxies are discovered attempt communications with each before widening the search to other options. The proxy relays information to the registrar. If this fails: B. Obtain an IP address using existing methods, such as SLAAC or DHCPv6, and search for a local registrar using DNS service discovery. If this fails: Pritikin, et al. Expires January 7, 2016 [Page 9]
Internet-Draft Bootstrapping Key Infrastructures July 2015 C. Obtain an IP address (as above), and search for the domain registrar using a pre-defined Factory provided Internet based re-direct service. Various methods could be used, such as DNS or RESTful APIs. 2. Identify itself. This is done by presenting an IEEE 802.1AR credentials to the discovered Registrar (via a Proxy if necessary). Included is a generated nonce that is specific to this attempt. 3. Imprint on the Registrar. This requires verification of the MASA service generated authorization token as provided by the contacted Registrar. The authorization token contains the valid domain(s) for this device and is signed by the MASA service. The device uses a pre-installed certificate of the MASA service to validate the signature of the MASA. The nonce information previously provided is also checked, if it was not removed by the Registrar. 4. Enroll by accepting the domain specific information from the registrar, and by enrolling a domain certificate from the registrar using a standard enrollment protocol, e.g. Enrolment over Secure Transport (EST) [RFC7030]. 5. The New Entity is now a member of and Being Managed by the domain and will only repeat the discovery aspects of bootstrapping if it is returned to factory default settings. The following sections describe each of these steps in more detail. 3.1.1. Discovery and Identity Existing architectures provide the functionality for discovery of the Domain Registrar. Use of an existing architecture is preferred over development of a new architecture. Discovering of a Domain Proxy that facilitates communication through to the Domain Registrar is simplified as "discovery of the domain". A proxy is included in Figure 1 although the simplified flow in Figure 2 does not include a proxy - under the assuption that the proxy forwarding is mostly transparent to the New Entity. Existing architectures for investigation include: IEEE 802.1X Where the New Entity can be cast as the "supplicant" and the Proxy is the "authenticator". The bootstrapping protocol messages are encapsulated as EAP methods. The "authenticator" reencapsulates the EAPOL frames and forwards them to the "Authentication Server", which provides Registrar functionalities. PANA [RFC5191] [[EDNOTE: TBD]] ND [RFC2461] / [RFC4861] [[EDNOTE: TBD]] NOTE: Neighbor Discovery protocols do not describe a mechanism for forwarding messages. Each provides a method for the New Entity to discover and initiate communication with a local neighbor which is assumed to be a member of the domain infrastructure. In each protocol methods are available Pritikin, et al. Expires January 7, 2016 [Page 10]
Internet-Draft Bootstrapping Key Infrastructures July 2015 to support encapsulation of the bootstrapping protocol messages described elsewhere in this document. Other protocols for transporting bootstrapping messages can be added in future references. All security assocaitions established are between the new device and the Registrar regardless of proxy operations. [[EDNOTE: this is the simplest and most direct threat model but should be evaluated against the anima use cases. It may be preferable to engage in secure communications with the proxy itself?]] The New Entity is expected to identify itself during one of the communication protocol exchanges. For example using EAP-TLS. If the client identity is rejected the New Entity repeats the Discovery process using the next proxy or discovery method available. If multiple proxies are available the New Entity tries each until a successful bootstrapping occurs. The New Entity may prioritize proxies selection order as appropriate for the anticipated environment. If Proxy discovery fails the New Entity moves on to discovering a Registrar directly using an appropriate L3 protocol mechanisms. [[EDNOTE: it is unclear yet if discovery happens on a per interface basis or once per device. What is the requirement around joining multiple domains; is this a bootstrapping requirement or is this a broader autonomic requirement]] 3.1.2. Imprint The domain trust anchor is received by the New Entity during the boostrapping protocol methods in the form of a MASA authorization token containing the domainID. The goal of the imprint state is to securely obtain a copy of this trust anchor without involving human interaction. An enrollment protocol such as EST [RFC7030] details a set of non- autonomic bootstrapping methods such as: o using the Implicit Trust Anchor database (not an autonomic solution because the URL must be securely distributed), o engaging a human user to authorize the CA certificate using out- of-band data (not an autonomic solution because the human user is involved), o using a configured Explicit TA database (not an autonomic solution because the distribution of an explicit TA database is not autonomic), Pritikin, et al. Expires January 7, 2016 [Page 11]
Internet-Draft Bootstrapping Key Infrastructures July 2015 o and using a Certificate-Less TLS mutual authentication method (not an autonomic solution because the distribution of symmetric key material is not autonomic). This document describes an additional autonomic method: MASA authorization token Authorization tokens are obtained by the Registrar from the MASA service and presented to the New Entity for validation. An arbitrary basic configuration information package that is signed by the domain can be delivered alongside the authorization token. This information is signed by the domain private keys and is a one time delivery containing information such as which enrollment server to communicate with and which management system to communicate with. It is intended as a limited basic configuration for these purposes and is not intended to deliver entire final configuration to the device. If the autonomic methods fails the New Entity returns to discovery state and attempts bootstrapping with the next available discovered Registrar. 3.1.3. Enrollment As the final step of bootstrapping a Registrar helps to issue a domain specific credential to the New Entity. For simplicity in this document, a Registrar primarily facilitates issuing a credential by acting as an RFC5280 Registration Authority for the Domain Certification Authority. Enrollment proceeds as described in Enrollment over Secure Transport (EST) [RFC7030]. The New Entity contacts the Registrar using EST as indicated: o The New Entity is authenticated using the IEEE 802.1AR credentials. o The EST section 4.1.3 CA Certificates Response is verified using the MASA authorization token provided domain identity. 3.1.4. Being Managed Functionality to provide generic "configuration" information is supported. The parsing of this data and any subsequent use of the data, for example communications with a Network Management System is out of scope but is expected to occur after bootstrapping enrollment is complete. This ensures that all communications with management systems which can divulge local security information (e.g. network topology or raw key material) is secured using the local credentials Pritikin, et al. Expires January 7, 2016 [Page 12]
Internet-Draft Bootstrapping Key Infrastructures July 2015 issued during enrollment. See Section 3.5. 3.2. Behavior of a proxy The role of the Proxy is to facilitate communications. The Proxy forwards messages between the New Entity and a Registrar. Where existing protocols, as detailed in Section 3.1.1, already provide this functionality nothing additional is defined. 3.3. Behavior of the Registrar Once a registrar is established it listens for new entities and determines if they can join the domain. The registrar delivers any necessary authorization information to the new device and facilitates enrollment with the domain PKI. Registrar behavior is as follows: Pritikin, et al. Expires January 7, 2016 [Page 13]
Internet-Draft Bootstrapping Key Infrastructures July 2015 Contacted by New Entity + | +-------v----------+ | Entity | fail? | Authentication +---------+ +-------+----------+ | | | +-------v----------+ | | Entity | fail? | | Authorization +---------> +-------+----------+ | | | +-------v----------+ | | Claiming the | fail? | | Entity +---------> +-------+----------+ | | | +-------v----------+ | | Log Verification | fail? | | +---------> +-------+----------+ | | | +-------v----------+ +----v-------+ | Forward | | | | Authorization | | Reject | | token + config | | Device | | to the Entity | | | +------------------+ +------------+ Figure 4 3.3.1. Entity Authentication The applicable authentication methods detailed in EST [RFC7030] are: o the use of an IEEE 802.1AR IDevID credential, o or the use of a secret that is transmitted out of band between the New Entity and the Registrar (this use case is not autonomic). 3.3.2. Entity Authorization In a fully automated network all devices must be securely identified. A Registrar accepts or declines a request to join the domain, based on the authenticated identity presented and other policy defined criteria such as Proxy identity. Automated acceptance criteria include: Pritikin, et al. Expires January 7, 2016 [Page 14]
Internet-Draft Bootstrapping Key Infrastructures July 2015 o allow any device of a specific type (as determined by the IEEE 802.1AR device identity), o allow any device from a specific Factory (as determined by the IEEE 802.1AR identity), o allow a specific device from a Factory (as determined by the IEEE 802.1AR identity) In all cases a Registrar must use the globally available MASA service to verify that the device's history log does not include unexpected Registrars. Because if a device had previously registered with another domain, the registrar of that domain would show in the log. If a device is accepted into the domain, it is then invited to request a domain certificate through a certificate enrolment process. The result is a common trust anchor and device certificates for all autonomic devices in a domain. These certificates can subsequently be used to determine the boundaries of the homenet, to authenticate other domain nodes, and to autonomically enable services on the homenet. For each entity that will be accepted a Registrar maintains the Factory CA identity and the entity's unique identifier. The Factory CA identity could be implemented as the Factory CA root certificate keyIdentifier (the 160-bit SHA-1 hash of the value of the BIT STRING subjectPublicKey). For user interface purposes the keyIdentifier information can be mapped to a colloquial Factory name (Registrars can be shipped with the keyIdentifier of a significant number of third-party manufacturers). 3.3.3. Claiming the New Entity During initial bootstrapping the New Entity provides a nonce specific to the particular bootstrapping attempt. The registrar should include this nonce when claiming the New Entity from the Internet based MASA service. If a nonce is provided by the Registrar, then claims from an unauthenticated Registrar are serviced by the MASA resource. The Registrar can claim a New Entity that is not online by forming the request using the entities unique identifier but not including a nonce in the claim request. MASA authorization tokens obtained in this way do not have a lifetime and they provide a permanent method for the domain to claim the device. Evidence of such a claim is provided in the audit log entries available to any future Registrar. Such claims reduce the ability for future domains to secure bootstrapping and therefore the Registrar MUST be authenticated by the MASA service. Claiming an entity establishes an audit log at the MASA server and Pritikin, et al. Expires January 7, 2016 [Page 15]
Internet-Draft Bootstrapping Key Infrastructures July 2015 provides the Registrar with proof, in the form of a MASA authorization token, that the log entry has been inserted. As indicated in Section 3.1.2 a New Entity will only proceed with bootstrapping if a validated MASA authorization token has been recieved. The New Entity therefore enforces that bootstrapping only occurs if the claim has been logged. 3.3.4. Log Verification The Registrar requests the log information for the new entity from the MASA service. The log is verified to confirm that the following is true to the satisfaction of the registrar's configured parameters: o Any nonceless entries in the log are associated with domainIDs recognized by the registrar. The registar MAY be configured to ignore the history of the device but it is RECOMMENDED that this only be configured if the MASA server is known to perform ownership validation or if Trusted Computing Group secure boot and remote attestation is available. o Any nonce'd entries are older than when the domain is known to have physical possession of the new entity or that the domainIDs are recognized by the registrar. If any of these criteria are unacceptable to the registrar the entity is rejected. 3.3.5. Forwarding Authorization Token plus Configuration The Registrar forwards the received authorization token to the new entity. To simplify the message flows an initial configuration package can be delivered at this time which is signed by a representative of the domain. [[EDNOTE: format TBD. The configuration package signature data must contain the full certificate path sufficient for the new entity to use the domainID information (as a trust anchor) to accept and validate the configuration)]] 3.4. Behavior of the MASA Service The MASA service is provided by the Factory provider on the global Internet. The URI of this service is well known. The URI should be provided as an IEEE 802.1AR IDevID X.509 extension (a "MASA authorization token Distribution Point" extension). The MASA service provides the following functionalities to Registrars: Pritikin, et al. Expires January 7, 2016 [Page 16]
Internet-Draft Bootstrapping Key Infrastructures July 2015 3.4.1. Issue Authorization Token and Log the event A Registrar POSTs a claim message optionally containing the bootstrap nonce to the MASA server. If a nonce is provided the MASA service responds to all requests. The MASA service verifies the Registrar is representative of the domain and generates a privacy protected log entry before responding with the authorization token. If a nonce is not provided then the MASA service MUST authenticate the Registrar as a valid customer. This prevents denial of service attacks. The specific level of authentication provided by the customer is not defined here. An MASA Practice Statement (MPS) similar to the Certification Authority CPS, as defined in RFC5280, is provided by the Factory such that Registrar's can determine the level of trust they have in the Factory. 3.4.2. Retrieve Audit Entries from Log When determining if a New Entity should be accepted into a domain the Registrar retrieves a copy of the audit log from the MASA service. This contains a list of privacy protected domain identities that have previously claimed the device. Included in the list is an indication of the time the entry was made and if the nonce was included. 3.5. Leveraging the new key infrastructure / next steps As the devices have a common trust anchor, device identity can be securely established, making it possible to automatically deploy services across the domain in a secure manner. Examples of services: o Device management. o Routing authentication. o Service discovery. 3.5.1. Network boundaries When a device has joined the domain, it can validate the domain membership of other devices. This makes it possible to create trust boundaries where domain members have higher level of trusted than external devices. Using the autonomic User Interface, specific devices can be grouped into to sub domains and specific trust levels can be implemented between those. Pritikin, et al. Expires January 7, 2016 [Page 17]
Internet-Draft Bootstrapping Key Infrastructures July 2015 4. Domain Operator Activities This section describes how an operator interacts with a domain that supports the bootstrapping as described in this document. 4.1. Instantiating the Domain Certification Authority This is a one time step by the domain administrator. This is an "off the shelf" CA with the exception that it is designed to work as an integrated part of the security solution. This precludes the use of 3rd party certification authority services that do not provide support for delegation of certificate issuance decisions to a domain managed Registration Authority. 4.2. Instantiating the Registrar This is a one time step by the domain administrator. One or more devices in the domain are configured take on a Registrar function. A device can be configured to act as a Registrar or a device can auto-select itself to take on this function, using a detection mechanism to resolve potential conflicts and setup communication with the Domain Certification Authority. Automated Registrar selection is outside scope for this document. 4.3. Accepting New Entities For each New Entity the Registrar is informed of the unique identifier (e.g. serial number) along with the manufacturer's identifying information (e.g. manufacturer root certificate). This can happen in different ways: 1. Default acceptance: In the simplest case, the new device asserts its unique identity to the registrar. The registrar accepts all devices without authorization checks. This mode does not provide security against intruders and is not recommended. 2. Per device acceptance: The new device asserts its unique identity to the registrar. A non-technical human validates the identity, for example by comparing the identity displayed by the registrar (for example using a smartphone app) with the identity shown on the packaging of the device. Acceptance may be triggered by a click on a smartphone app "accept this device", or by other forms of pairing. See also [I-D.behringer-homenet-trust-bootstrap] for how the approach could work in a homenet. 3. Whitelist acceptance: In larger networks, neither of the previous approaches is acceptable. Default acceptance is not secure, and a manual per device methods do not scale. Here, the registrar is provided a priori with a list of identifiers of devices that Pritikin, et al. Expires January 7, 2016 [Page 18]
Internet-Draft Bootstrapping Key Infrastructures July 2015 belong to the network. This list can be extracted from an inventory database, or sales records. If a device is detected that is not on the list of known devices, it can still be manually accepted using the per device acceptance methods. 4. Automated Whitelist: an automated process that builds the necessary whitelists and inserts them into the larger network domain infrastructure is plausible. Once set up, no human intervention is required in this process. Defining the exact mechanisms for this is out of scope although the registrar authorization checks is identified as the logical integration point of any future work in this area. None of these approaches require the network to have permanent Internet connectivity. Even when the Internet based MASA service is used, it is possible to pre-fetch the required information from the MASA a priori, for example at time of purchase such that devices can enrol later. This supports use cases where the domain network may be entirely isolated during device deployment. Additional policy can be stored for future authorization decisions. For example an expected deployment time window or that a certain Proxy must be used. 4.4. Automatic Enrolment of Devices The approach outlined in this document provides a secure zero-touch method to enrol new devices without any pre-staged configuration. New devices communicate with already enrolled devices of the domain, which proxy between the new device and a Registrar. As a result of this completely automatic operation, all devices obtain a domain based certificate. 4.5. Secure Network Operations The certificate installed in the previous step can be used for all subsequent operations. For example, to determine the boundaries of the domain: If a neighbor has a certificate from the same trust anchor it can be assumed "inside" the same organization; if not, as outside. See also Section 3.5.1. The certificate can also be used to securely establish a connection between devices and central control functions. Also autonomic transactions can use the domain certificates to authenticate and/or encrypt direct interactions between devices. The usage of the domain certificates is outside scope for this document. Pritikin, et al. Expires January 7, 2016 [Page 19]
Internet-Draft Bootstrapping Key Infrastructures July 2015 5. Protocol Details For simplicity the bootstrapping protocol is described as extensions to EST [RFC7030]. EST provides a bootstrapping mechanism for new entities that are configured with the URI of the EST server such that the Implicit TA database can be used to authenticate the EST server. Alternatively EST clients can "engage a human user to authorize the CA certificate using out-of-band data such as a CA certificate". EST does not provide a completely automated method of bootstrapping the PKI as both of these methods require some user input (either of the URI or authorizing the CA certificate). This section details additional EST functionality that support automated bootstrapping of the public key infrastructure. These additions provide for fully automated bootstrapping. These additions are to be optionally supported by the EST server within the same .well-known URI tree as the existing EST URIs. The "New Entity" is the EST client and the "Registrar" is the EST server. The extensions for the client are as follows: o The New Entity provisionally accept the EST server certificate during the TLS handshake as detailed in EST section 4.1.1 ("Bootstrap Distribution of CA Certificates"). o The New Entity request and validates a "bootstrap token" as described below. At this point the New Entity has sufficient information to validate domain credentials. o The New Entity calls the EST defined /cacerts method to obtain the current CA certificate. These are validated using the "bootstrap token". o The New Entity completes bootstrapping as detailed in EST section 4.1.1. These extensions could be implemented as an independent protocol from EST but since the overlap with basic enrollment is extensive, particularly with respect to client authorization, they are presented here as additions to EST. In order to obtain a validated bootstrap token and history logs the Registrar contacts the MASA service Service using REST calls. Pritikin, et al. Expires January 7, 2016 [Page 20]
Internet-Draft Bootstrapping Key Infrastructures July 2015 5.1. EAP-EST In order to support Proxy environments EAP-EST is defined. [[EDNOTE: TBD. EST is TLS with some data. EAP-TLS and other similar protocols provide an example framework for filling out this section]] 5.2. Request bootstrap token When the New Entity reaches the EST section 4.1.1 "Bootstrap Distribution of CA Certificates" [[EDNOTE: out of date xref]] state but wishes to proceed in a fully automated fashion it makes a request for a MASA authorization token from the Registrar. This is done with an HTTPS POST using the operation path value of "/requestbootstraptoken". The request format is JSON object containing a nonce. Request media type: application/masanonce Request format: a json file with the following: {"nonce":"<64bit nonce value>"} [[EDNOTE: exact format TBD. There is an advantage to having the client sign the nonce (similar to a PKI Certification Signing Request) since this allows the MASA service to confirm the actual device identity. It is not clear that there is a security benefit from this.]] The Registrar validates the client identity as described in EST [RFC7030] section 3.3.2. The registrar performs authorization as detailed in Section 3.3.2. If authorization is successful the Registrar obtains a MASA authorization token from the MASA service (see Section 5.3). The recieved MASA authorization token is returned to the New Entity. 5.3. Request MASA authorization token A registrar requests the MASA authorization token from the MASA service using a REST interface. This is done with an HTTP POST using the operation path value of "/requestMASAauthorization". The request format is a JSON object optionally containing the nonce Pritikin, et al. Expires January 7, 2016 [Page 21]
Internet-Draft Bootstrapping Key Infrastructures July 2015 value (as obtained from the bootstrap request) and the IEEE 802.1AR identity of the device as a serial number (the full certificate is not needed and no proof-of-possession information for the device identity is included). The New Entity's serial number is extracted from the subject name : {"nonce":"<64bit nonce value>", "serialnumber", "<subjectname/ subjectaltname serial number>"} Inclusion of the nonce is optional because the Registar might request an authorization token when the New Entity is not online, or when the target bootstrapping environment is not on the same network as the MASA server. This information is encapsulated in a PKCS7 signed data structure that is signed by the Registrar. The entire certificate chain, up to and including the Domain CA, is included in the PKCS7. The MASA service checks the internal consistency of the PKCS7 but is unable to actually authenticate the domain identity information. The domain is not know to the MASA server in advance and a shared trust anchor is not implied. The MASA server verifies that the PKCS7 is signed by a Registrar (by checking for the cmc-idRA field in the Registrar certificate) certificate that was issued by the root certificate included in the PKCS7. The domain ID is extracted from the root certificate and is used to generate the MASA authorization token and to update the audit log. [[EDNOTE: The authorization token response format needs to be defined here. It consists of the nonce, if supplied, the serialnumber and the trust anchor of the domain. For example: {"nonce":"<64bit nonce value>", "serialnumber", "<subjectname/ subjectaltname serial number>","domainID":} ]] [[EDNOTE: This assumes the Registrar can extract the serial number successfullly from the cilent certificate. The RFC4108 hardwareModuleName is likely the best known location.]] 5.4. Basic Configuration Information Package When the MASA authorization token is returned to the New Entity an arbitrary information package can be signed and delivered along side it. This is signed by the Domain Registar. The New Entity first verifies the MASA authorization token and, if it is valid, then uses Pritikin, et al. Expires January 7, 2016 [Page 22]
Internet-Draft Bootstrapping Key Infrastructures July 2015 the domain's TA to validate the Information Package. [[EDNOTE: The package format to be specified here. Any signed format is viable and ideally one can simply be specified from netconf. The Registar knows the New Entity device type from the 802.1AR credential and so is able to determine the proper format for the configuration]] 5.5. Request MASA authorization log A registrar requests the MASA authorization log from the MASA service using this EST extension. This is done with an HTTP GET using the operation path value of "/requestMASAlog". The log data returned is a file consisting of all previous log entries. For example: "log":[ {"date":"<date/time of the entry>"}, "domainID":"<domainID as extracted from the root certificate within the PKCS7 of the authorization token request>", "nonce":"<any nonce if supplied (or NULL)>"}, {"date":"<date/time of the entry>"}, "domainID":"<domainID as extracted from the root certificate within the PKCS7 of the authorization token request>", "nonce":"<any nonce if supplied (or NULL)>"}, ] Distribution of a large log is less than ideal. This structure can be optimized as follows: only the most recent nonce'd log entry is required in the response. All nonce-less entries for the same domainID can be condensed into the single most recent nonceless entry. The Registrar uses this log information to make an informed decision regarding the continued bootstrapping of the New Entity. [[EDNOTE: certificate transparency might offer an alternative log entry method]] 6. Reduced security operational modes A common requirement of bootstrapping is to support less secure Pritikin, et al. Expires January 7, 2016 [Page 23]
Internet-Draft Bootstrapping Key Infrastructures July 2015 operational modes for support specific use cases. The following sections detail specific ways that the New Entity, Registrar and MASA can be configured to run in a less secure mode for the indicated reasons. 6.1. New Entity security reductions Although New Entity can choose to run in less secure modes this is MUST NOT be the default state because it permanently degrades the security for all other uses cases. When configured into lower security modes by a trusted administrator: 1. The device may have an operational mode where it skips authorization token validation. For example if a physical button is depressed during the bootstrapping operation. This may occur when: A device Factory goes out of business or otherwise fails to provide a reliable MASA service or when local staging has pre- configured the New Entity with a known good Trust Anchor. 2. The device may be configured during staging or requested from the factory to not require the MASA service authorization token. An entity that does not validate the domain identity is inherently dangerous as it may have had malware installed on it by a man-in- the-middle. This risk should be mitigated using attestation and measurement technologies. In order to support an unsecured imprint the New Entity MUST support remote attestation technologies such as is defined by the Trusted Computing Group. [[EDNOTE: How to include remote attestation into the boostrapping protocol exchange is TBD]]. This may occur when: The device Factory does not provide a MASA service. 6.2. Registrar security reductions The Registrar can choose to accept devices using less secure methods. These methods are RECOMMENDED when low security models are needed as the security decisions are being made by the local administrator: 1. The registrar may choose to accept all devices, or all devices of a particular type, at the administrator's discretion. This may occur when: Informing the Registrar of unique identifiers of new entities might be operationally difficult. 2. The registrar may choose to accept devices that claim a unique identity without the benefit of authenticating that claimed identity. This may occur when: The New Entity does not include an IEEE 802.1AR factory installed credential. 3. The registrar may request nonce-less authorization tokens from the MASA service. These tokens can then be transmitted to the Registrar and stored until they are needed during bootstrapping operations. This is for use cases where target network is protected by an air gap and therefore can not contact the MASA Pritikin, et al. Expires January 7, 2016 [Page 24]
Internet-Draft Bootstrapping Key Infrastructures July 2015 service during New Entity deployment. 6.3. MASA security reductions Lower security modes chosen by the MASA service effect all device deployments unless paired with strict device ownership validation, in which case these modes can be provided as additional features for specific customers. The MASA service can choose to run in less secure modes by: 1. Not enforcing that a Nonce is in the authorization token. This results in distribution of authorization tokens that never expire and effectly makes the Domain an always trusted entity to the New Entity during any subsequent bootstrapping attempts. That this occured is captured in the log information so that the Domain registrar can make appropriate security decisions when a new device joins the domain. This is useful to support use cases where Registrars might not be online during actual device deployment. 2. Not verifying ownership before responding with an authorization token. Doing so relieves the vendor providing MASA services from having to tracking ownership during shipping and supply chain. The registrar uses the log information as a defense in depth strategy to ensure that this does not occur unexpectedly. For example when purchasing used equipment a MASA response is necessary for autonomic provisioning but the greatest level of security is achieved when the MASA server is also performing ownership validation. 7. Security Considerations In order to support a wide variety of use cases, devices can be claimed by a registrar without proving possession of the device in question. This would result in a nonceless, and thus always valid, claim. Or would result in an invalid nonce being associated with a claim. The MASA service is required to authenticate such Registrars but no programmatic method is provided to ensure good behavior by the MASA service. Nonceless entries into the audit log therefore permanently reduce the value of a device because future Registrars, during future bootstrap attempts, would now have to be configured with policy to ignore previously (and potentially unknown) domains. Future registrars are recommended to take the audit history of a device into account when deciding to join such devices into their network. If the MASA server were to have allowed a significantly large number of claims this might become onerous to the MASA server which must maintain all the extra log entries. Ensuring the registar Pritikin, et al. Expires January 7, 2016 [Page 25]
Internet-Draft Bootstrapping Key Infrastructures July 2015 is representative of a valid customer domain even without validating ownership helps to mitigate this. It is possible for an attacker to send an authorization request to the MASA service directly after the real Registrar obtains an authorization log. If the attacker could also force the bootstrapping protocol to reset there is a theoretical opportunity for the attacker to use the authorization token to take control of the New Entity but then proceed to enrol with the target domain. To prevent this the MASA service is rate limited to only generate authorization tokens at a rate of 1 per minute. The Registrar therefore has at least 1 minute to get the response back to the New Entity. [[EDNOTE: a better solution can likely be found. This text captures the issue for now. Binding the logs via a ]] Also the Registrar can double check the log information after enrolling the New Entity. The MASA service could lock a claim and refuse to issue a new token. Or the MASA service could go offline (for example if a vendor went out of business). This functionality provides benefits such as theft resistance, but it also implies an operational risk. This can be mitigated by Registrars that request nonce-less authorization tokens. 7.1. Trust Model [[EDNOTE: (need to describe that we need to trust the device h/w. To be completed.)]] 8. Acknowledgements We would like to thank the various reviewers for their input, in particular Markus Stenberg, Brian Carpenter, Fuyu Eleven. 9. References 9.1. Normative References [IDevID] IEEE Standard, "IEEE 802.1AR Secure Device Identifier", December 2009, <http://standards.ieee.org/findstds/ standard/802.1AR-2009.html>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC7030] Pritikin, M., Yee, P., and D. Harkins, "Enrollment over Secure Transport", RFC 7030, October 2013. Pritikin, et al. Expires January 7, 2016 [Page 26]
Internet-Draft Bootstrapping Key Infrastructures July 2015 9.2. Informative References [I-D.behringer-homenet-trust-bootstrap] Behringer, M., Pritikin, M., and S. Bjarnason, "Bootstrapping Trust on a Homenet", draft-behringer-homenet-trust-bootstrap-02 (work in progress), February 2014. [I-D.irtf-nmrg-autonomic-network-definitions] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A., Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic Networking - Definitions and Design Goals", draft-irtf-nmrg-autonomic-network-definitions-07 (work in progress), March 2015. [imprinting] Wikipedia, "Wikipedia article: Imprinting", July 2015, <https://en.wikipedia.org/wiki/Imprinting_(psychology)>. [pledge] Dictionary.com, "Dictionary.com Unabridged", July 2015, <http://dictionary.reference.com/browse/pledge>. Appendix A. Editor notes [[EDNOTE: This section is to capturing rough notes between editors and Anima Bootstrapping design team members. This entire section to be removed en masse before finalization]] Change Discussion: 02 Moved sections for readability, Updated introduction, simplified functional overview to avoid distractions from optional elements, addressed updated security considerations, fleshed out state machines. The following is a non-prioritized list of work items currently identified: o Continue to address gaps/opportunities highlighted by community work on bootstrappping. Refs: IETF92 "Survey of Security Bootstrapping", Aana Danping He, behcet Sarikaya. "NETCONF Zero Touch Update for ANIMA" https://www.ietf.org/proceedings/92/anima.html and "Bootstrapping Key Infrastructures", Pritikin, Behringer, Bjarnason o Intergrate "Ownership Voucher" as a valid optional format for the MASA response. So long as the issuance of this is logged and captured in the log response then the basic flow and threat model is substantially the same. Pritikin, et al. Expires January 7, 2016 [Page 27]
Internet-Draft Bootstrapping Key Infrastructures July 2015 o Attempt to re-use existing work as per the charter: Toerless notes: a) are existing [eap] options? or too complex? or doens't work? b) our own method (e.g. EAP-ANIMA c) if b then investigate using signaling protocol). o Authors' Addresses Max Pritikin Cisco Email: pritikin@cisco.com Michael C. Richardson Sandelman Software Works 470 Dawson Avenue Ottawa, ON K1Z 5V7 CA Email: mcr+ietf@sandelman.ca URI: http://www.sandelman.ca/ Michael H. Behringer Cisco Email: mbehring@cisco.com Steinthor Bjarnason Cisco Email: sbjarnas@cisco.com Pritikin, et al. Expires January 7, 2016 [Page 28]