Voucher Profile for Bootstrapping Protocols
draft-ietf-anima-voucher-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8366.
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|---|---|---|---|
| Authors | Kent Watsen , Michael Richardson , Max Pritikin , Toerless Eckert | ||
| Last updated | 2017-06-19 (Latest revision 2017-06-07) | ||
| Replaces | draft-kwatsen-anima-voucher | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | In WG Last Call | |
| Document shepherd | Sheng Jiang | ||
| IESG | IESG state | Became RFC 8366 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | "Sheng Jiang" <jiangsheng@huawei.com> |
draft-ietf-anima-voucher-03
#x27;s trust anchor certificate known to the pledges. The PKCS#7 structure MAY also contain revocation objects for any intermediate CAs between the voucher-issuer and the trust anchor known to the pledge. Watsen, et al. Expires December 9, 2017 [Page 6] Internet-Draft Voucher Profile June 2017 5.1. Tree Diagram The following tree diagram [I-D.bjorklund-netmod-yang-tree-diagrams] illustrates a high-level view of a voucher document. Each field in the voucher is fully described by the YANG module provided in Section 5.3. Please review this YANG module for a detailed description of the voucher format. module: ietf-voucher +--ro voucher +--ro created-on yang:date-and-time +--ro expires-on? yang:date-and-time +--ro assertion enumeration +--ro serial-number string +--ro idevid-issuer? binary +--ro pinned-domain-cert* binary +--ro domain-cert-revocation-checks? boolean +--ro nonce? binary +--ro last-renewal-date? yang:date-and-time 5.2. Examples This section provides a couple Voucher examples for illustration purposes. The following example illustrates an ephemeral voucher (uses a nonce) encoded in JSON. As is expected with a dynamically-generated voucher, only a single pledge (device-identifier) is specified. The MASA generated this voucher using the 'logged' assertion type, knowing that it would be suitable for the pledge making the request. { "ietf-voucher:voucher": { "created-on": "2016-10-07T19:31:42Z", "assertion": "logged", "serial-number": "JADA123456789", "serial-number-issuer": "some binary identifier", "domain-cert-trusted-ca": "base64-encoded X.509 DER", "domain-cert-identifier": { "subject": "base64-encoded Subject DER" }, "nonce": "base64-encoded octet string" } } The following illustrates a long-lived voucher (no nonce), encoded in XML. This particular voucher applies to more than one pledge Watsen, et al. Expires December 9, 2017 [Page 7] Internet-Draft Voucher Profile June 2017 (unique-id), which might relate to, for instance, they were all issued as part of the same purchase order. This voucher includes both a trust anchor certificate (trusted-ca-certificate) as well as some additional information (cn-id and dns-id) that can be used to identify a specific domain certificate issued, perhaps indirectly, by the trust anchor CA. { "ietf-voucher:voucher": { "created-on": "2016-10-07T19:31:42Z", "expires-on": "2016-10-21T19:31:42Z", "assertion": "verified", "serial-number": "JADA123456789", "serial-number-issuer": "some binary identifier", "domain-cert-trusted-ca": "base64-encoded X.509 DER", "domain-cert-identifier": { "subject": "base64-encoded Subject DER" }, "assert-revocations-on-PKIX-certs": "false", "last-renewal-date": "2017-10-07T19:31:42Z" } } 5.3. YANG Module <CODE BEGINS> file "ietf-voucher@2017-06-07.yang" module ietf-voucher { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-voucher"; prefix "vch"; import ietf-yang-types { prefix yang; reference "RFC 6991: Common YANG Data Types"; } import ietf-restconf { prefix rc; description "This import statement is only present to access the yang-data extension defined in RFC 8040."; reference "RFC 8040: RESTCONF Protocol"; } organization Watsen, et al. Expires December 9, 2017 [Page 8] Internet-Draft Voucher Profile June 2017 "IETF ANIMA Working Group"; contact "WG Web: <http://tools.ietf.org/wg/anima/> WG List: <mailto:anima@ietf.org> Author: Kent Watsen <mailto:kwatsen@juniper.net> Author: Max Pritikin <mailto:pritikin@cisco.com> Author: Michael Richardson <mailto:mcr+ietf@sandelman.ca>"; description "This module defines the format for a voucher, which is produced by a pledge's manufacturer or delegate (MASA) to securely assign one or more pledges to an 'owner', so that the pledges may establish a secure connection to the owner's network infrastructure. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in the module text are to be interpreted as described in RFC 2119."; revision "2017-06-07" { description "Initial version"; reference "RFC XXXX: Voucher Profile for Bootstrapping Protocols"; } rc:yang-data voucher-artifact { uses voucher-grouping; } grouping voucher-grouping { description "Grouping only exists for pyang tree output..."; container voucher { config false; description "A voucher that can be used to assign one or more pledges to an owner."; leaf created-on { type yang:date-and-time; mandatory true; description "A value indicating the date this voucher was created. This Watsen, et al. Expires December 9, 2017 [Page 9] Internet-Draft Voucher Profile June 2017 node is optional because its primary purpose is for human consumption. However, when present, pledges that have reliable clocks SHOULD ensure that this created-on value is not greater than the current time."; } leaf expires-on { type yang:date-and-time; must "not(../nonce)"; description "A value indicating when this voucher expires. The node is optional as not all pledges support expirations, such as pledges lacking a reliable clock. If this field exists, then the the pledges MUST ensure that the expires-on time has not yet passed. A pledge without an accurate clock cannot meet this requirement. The expires-on value MUST NOT exceed the expiration date of any of the listed 'pinned-domain-cert' certificates."; } leaf assertion { type enumeration { enum verified { description "Indicates that the ownership has been positively verified by the MASA (e.g., through sales channel integration)."; } enum logged { description "Indicates that this ownership assignment has been logged into a database maintained by the MASA, after first verifying that there has not been a previous claim in the database for the same pledge (voucher transparency)."; } } mandatory true; description "The assertion is a statement from the MASA regarding how the owner was verified. This statement enables pledges to support more detailed policy checks. Pledges MUST ensure that the assertion provided is acceptable before processing the voucher."; } Watsen, et al. Expires December 9, 2017 [Page 10] Internet-Draft Voucher Profile June 2017 leaf serial-number { type string; mandatory true; description "The serial number of the hardware. When processing a voucher, a pledge MUST ensure that its serial number matches this value. If no match occurs, then the pledge MUST NOT process this voucher."; } leaf idevid-issuer { type binary; description "The RFC5280 4.2.1.1 Authority Key Identifier OCTET STRING from the pledge's IDevID certificate. Optional since some serial-numbers are already unique within the scope of a MASA. Inclusion of the statistically unique key identifier ensures statistically unique identification of the hardware. When processing a voucher, a pledge MUST ensure that its IDevID Authority Key Identifier matches this value. If no match occurs, then the pledge MUST NOT process this voucher. When issuing a voucher, the MASA MUST ensure that this field is populated for serial numbers that are not otherwise unique within the scope of the MASA."; } leaf-list pinned-domain-cert { type binary; min-elements 1; description "An X.509 v3 certificate structure as specified by RFC 5280, Section 4 encoded using the ASN.1 distinguished encoding rules (DER), as specified in ITU-T X.690. This certificate is used by a pledge to trust a public key infrastructure, in order to verify a domain certificate supplied to the pledge separately by the bootstrapping protocol. The domain certificate MUST have this certificate somewhere in its chain of certificates. This certificate MAY be an end-entity certificate, including a self-signed entity."; reference "RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile. ITU-T X.690: Information technology - ASN.1 encoding rules: Watsen, et al. Expires December 9, 2017 [Page 11] Internet-Draft Voucher Profile June 2017 Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)."; } leaf domain-cert-revocation-checks { type boolean; must "../expires-on"; description "A processing instruction to the pledge that it MUST verify the revocation status for the domain certificate. This instruction is only available for vouchers that expire. If this field is not set, then normal PKIX behaviour applies to validation of the domain certificate."; } leaf nonce { type binary { length "8..32"; } must "not(../expires-on)"; description "A value that can be used by a pledge in some bootstrapping protocols to enable anti-replay protection. This node is optional because it is not used by all bootstrapping protocols. When present, the pledge MUST compare the provided nonce value with another value that the pledge randomly generated and sent to a bootstrap server in an earlier bootstrapping message. If the values do not match, then the pledge MUST NOT process this voucher."; } leaf last-renewal-date { type yang:date-and-time; must "../expires-on"; description "The date that the MASA projects to be the last date it will renew a voucher on. This field is merely informative, it is not processed by pledges. Circumstances may occur after a voucher is generated that may alter a voucher's validity period. For instance, a vendor may associate validity periods with support contracts, which may be terminated or extended over time."; } Watsen, et al. Expires December 9, 2017 [Page 12] Internet-Draft Voucher Profile June 2017 } // end voucher } // end voucher-grouping } <CODE ENDS> 6. Design Considerations 6.1. Renewals instead of Revocations The lifetimes of vouchers may vary. In some bootstrapping protocols, the vouchers may be created and consumed immediately whereas, in other bootstrapping solutions, there may be a significant delay between when a voucher is created and when it is consumed. In cases when there is a delay, there is a need for the pledge to ensure that the assertions made when the voucher was created are still valid when it is consumed. A revocation artifact is generally used to verify the continued validity of an assertion such as a PKIX certificate, web token, or a "voucher". With this approach, a potentially long-lived assertion is paired with a reasonably fresh revocation status check to ensure that the assertion is still valid. However, this approach increases solution complexity, as it introduces the need for additional protocols and code paths to distribute and process the revocations. Addressing the short-comings of revocations, this document recommends instead the use of lightweight renewals of short-lived non-revocable vouchers. That is, rather than issue a long-lived voucher, the expectation is for the MASA to instead issue a short-lived voucher along with a promise (reflected in the 'last-renewal-date' field) to re-issue the voucher again when needed. Importantly, while issuing the initial voucher may incur heavyweight verification checks (are you who you say you are? does the pledge actually belong to you?), re-issuing the voucher should be a lightweight process, as it ostensibly only updates the voucher's validatity period. With this approach, there is only the one artifact, and only one code path is needed to process it, without any possibility for a pledge to choose to skip the revocation status check because, for instance, the OCSP Responder is not reachable. While this document recommends issuing short-lived vouchers, the voucher artifact does not restrict the ability to create a long-lived vouchers, if required, however no revocation method is described. Note that a voucher may be signed by a chain of intermediate CAs leading up to the trust anchor certificate known by the pledge. Even Watsen, et al. Expires December 9, 2017 [Page 13] Internet-Draft Voucher Profile June 2017 though the voucher itself is not revocable, it may still be revoked, per se, if one of the intermediate CA certificates is revoked. 6.2. Voucher Per Pledge The solution described herein originally enabled a single voucher to apply to many pledges, using lists of regular expressions to represent ranges of serial numbers. However, it was determined that blocking the renewal of a voucher that applied to many devices would be excessive when only the ownership for a single pledge needed to be blocked. Thus, the voucher format now only supports a single serial- number to be listed. 7. Security Considerations 7.1. Clock Sensitivity An attacker could use an expired voucher to gain control over a device that has no understand of time. To defend against this there are three things: devices are required to verify that the expires-on field has not yet passed. Devices without access to time can use nonces to get ephermal vouchers. Thirdly, vouchers without expiration times may be used, which will appear in the audit log, informing the security decision. This document defines artifacts containing time values for voucher expirations, which require an accurate clock in order to be processed correctly. Vendors planning on issuing vouchers with expiration values must ensure devices have an accurate clock when shipped from manufacturing facilities, and take steps to prevent clock tampering. If it is not possible to ensure clock accuracy then vouchers with expirations should not be issued. 7.2. Protect Voucher PKI in HSM A voucher is signed by a CA, that may itself be signed by a chain of CAs leading to a trust anchor known to a pledge. Revocation checking of the intermediate certificates may be difficult in some scenarios. The voucher format supports the existing PKIX revocation information distribution within the limits of the current PKI technology (a PKCS7 structure can contain revocation objects as well), but pledges MAY accept vouchers without checking X.509 certificate revocation (when 'domain-cert-revocation-checks' is false). Without revocation checking, a compromized MASA keychain could be used to issue vouchers ad infinitum without recourse. For this reason, MASA implementations wanting to support such deployments SHOULD ensure that all the CA Watsen, et al. Expires December 9, 2017 [Page 14] Internet-Draft Voucher Profile June 2017 private keys used for signing the vouchers are protected by hardware security modules (HSMs). 7.3. Test Domain Certificate Validity when Signing If a domain certificate is compromised, then any outstanding vouchers for that domain could be used by the attacker. The domain administrator is clearly expected to initiate revocation of any domain identity certificates (as is normal in PKI solutions). Similarly they are expected to contact the MASA to indicate that an outstanding (presumably short lifetime) voucher should be blocked from automated renewal. Protocols for voucher distribution are RECOMMENDED to check for revocation of any domain identity certificates before automated renewal of vouchers. 8. IANA Considerations 8.1. The IETF XML Registry This document registers a URIs in the IETF XML registry [RFC3688]. Following the format in [RFC3688], the following registration is requested: URI: urn:ietf:params:xml:ns:yang:ietf-voucher Registrant Contact: The ANIMA WG of the IETF. XML: N/A, the requested URI is an XML namespace. 8.2. The YANG Module Names Registry This document registers a YANG module in the YANG Module Names registry [RFC6020]. Following the format defined in [RFC6020], the the following registration is requested: name: ietf-voucher namespace: urn:ietf:params:xml:ns:yang:ietf-voucher prefix: vch reference: RFC XXXX 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. Watsen, et al. Expires December 9, 2017 [Page 15] Internet-Draft Voucher Profile June 2017 [RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax Version 1.5", RFC 2315, DOI 10.17487/RFC2315, March 1998, <http://www.rfc-editor.org/info/rfc2315>. [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, <http://www.rfc-editor.org/info/rfc6020>. [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, <http://www.rfc-editor.org/info/rfc7950>. 9.2. Informative References [I-D.bjorklund-netmod-yang-tree-diagrams] Bjorklund, M. and L. Berger, "YANG Tree Diagrams", 2017. [I-D.ietf-6tisch-dtsecurity-secure-join] Richardson, M., "6tisch Secure Join protocol", draft-ietf- 6tisch-dtsecurity-secure-join-01 (work in progress), February 2017. [I-D.ietf-anima-bootstrapping-keyinfra] Pritikin, M., Richardson, M., Behringer, M., Bjarnason, S., and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- keyinfra-06 (work in progress), May 2017. [I-D.ietf-netconf-zerotouch] Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning for NETCONF or RESTCONF based Management", draft-ietf- netconf-zerotouch-13 (work in progress), March 2017. [imprinting] Wikipedia, "Wikipedia article: Imprinting", July 2015, <https://en.wikipedia.org/wiki/Imprinting_(psychology)>. [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, <http://www.rfc-editor.org/info/rfc3688>. [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection Most of the Time", RFC 7435, DOI 10.17487/RFC7435, December 2014, <http://www.rfc-editor.org/info/rfc7435>. Watsen, et al. Expires December 9, 2017 [Page 16] Internet-Draft Voucher Profile June 2017 [Stajano99theresurrecting] Stajano, F. and R. Anderson, "The resurrecting duckling: security issues for ad-hoc wireless networks", 1999, <https://www.cl.cam.ac.uk/~fms27/papers/1999-StajanoAnd- duckling.pdf>. Watsen, et al. Expires December 9, 2017 [Page 17] Internet-Draft Voucher Profile June 2017 Appendix A. Acknowledgements The authors would like to thank for following for lively discussions on list and in the halls (ordered by last name): Authors' Addresses Kent Watsen Juniper Networks EMail: kwatsen@juniper.net Michael C. Richardson Sandelman Software EMail: mcr+ietf@sandelman.ca URI: http://www.sandelman.ca/ Max Pritikin Cisco Systems EMail: pritikin@cisco.com Toerless Eckert Futurewei Technologies Inc. 2330 Central Expy Santa Clara 95050 USA EMail: tte+ietf@cs.fau.de Watsen, et al. Expires December 9, 2017 [Page 18]