ANIMA Working Group K. Watsen
Internet-Draft Juniper Networks
Intended status: Standards Track M. Richardson
Expires: September 14, 2017 Sandelman Software
M. Pritikin
Cisco Systems
T. Eckert
March 13, 2017
Voucher Profile for Bootstrapping Protocols
draft-ietf-anima-voucher-01
Abstract
This document defines a strategy to securely assign a pledge to an
owner, using an artifact signed, directly or indirectly, by the
pledge's manufacturer. This artifact is known as a "voucher".
The voucher artifact is a YANG-defined JSON document that has been
signed using a PKCS#7 structure. The voucher artifact is generated
by the pledge's manufacture or delegate (i.e. the MASA).
This document only defines the voucher artifact, leaving it to other
documents to describe specialized protocols for accessing it.
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 September 14, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
Watsen, et al. Expires September 14, 2017 [Page 1]
Internet-Draft Voucher Profile March 2017
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
4. Survey of Voucher Types . . . . . . . . . . . . . . . . . . . 4
5. Voucher . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 8
6. Design Considerations . . . . . . . . . . . . . . . . . . . . 14
6.1. Renewals instead of Revocations . . . . . . . . . . . . . 14
6.2. Voucher Per Pledge . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. Clock Sensitivity . . . . . . . . . . . . . . . . . . . . 16
7.2. Protect Voucher PKI in HSM . . . . . . . . . . . . . . . 16
7.3. Test Domain Certificate Validity when Signing . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. The IETF XML Registry . . . . . . . . . . . . . . . . . . 17
8.2. The YANG Module Names Registry . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
This document defines a strategy to securely assign a pledge to an
owner, using an artifact signed, directly or indirectly, by the
pledge's manufacturer or delegate (i.e. the MASA). This artifact is
known as the voucher.
The voucher artifact is a JSON document, conforming to a data model
described by YANG [RFC7950], that has been signed using a PKCS#7
structure.
Watsen, et al. Expires September 14, 2017 [Page 2]
Internet-Draft Voucher Profile March 2017
A voucher may be useful in several contexts, but the driving
motivation herein is to support secure bootstrapping mechanisms.
Assigning ownership is important to bootstrapping mechanisms so that
the pledge can authenticate the network that's trying to take control
of it.
The lifetimes of vouchers may vary. In some bootstrapping protocols
the vouchers may be ephemeral, whereas in others the vouchers may be
potentially long-lived. In order to support the second category of
vouchers, this document recommends using short-life vouchers with
programatic renewal, enabling the MASA to communicate the ongoing
validity of vouchers.
This document only defines the voucher artifact, leaving it to other
documents to describe specialized protocols for accessing it. Some
bootstrapping protocols using the voucher artifact defined in this
draft include: [I-D.ietf-netconf-zerotouch],
[I-D.ietf-6tisch-dtsecurity-secure-join], and
[I-D.ietf-anima-bootstrapping-keyinfra]).
2. Terminology
The following terms are defined for clarity:
Imprint: The process where a device obtains the cryptographic key
material to identify and trust future interactions with a network.
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. An equivalent for a device is to obtain the fingerprint
of the network's root certification authority certificate. A
device that imprints on an attacker suffers a similar fate to a
duckling that imprints on a hungry wolf. Securely imprinting is a
primary focus of this document.[imprinting]. The analogy to
Lorenz's work was first noted in [Stajano99theresurrecting].
Pledge: The prospective device attempting to find and join a secure
remote key infrastructure. When shipped it only trusts authorized
representatives of the manufacturer.
Voucher: A signed statement from the MASA service that indicates to
a Pledge the cryptographic identity of the Registrar it should
trust. There are different types of vouchers depending on how
that trust asserted. This document describes vouchers in detail.
Domain: The set of entities that trust a common key infrastructure
trust anchor. This includes the Proxy, Registrar, Domain
Watsen, et al. Expires September 14, 2017 [Page 3]
Internet-Draft Voucher Profile March 2017
Certificate Authority, Management components and any existing
entity that is already a member of the domain.
Domain CA: The domain Certification Authority (CA) provides
certification functionalities to the domain. At a minimum it
provides certification functionalities to a Registrar and stores
the trust anchor that defines the domain. Optionally, it
certifies all elements.
Join Registrar (and Coordinator): 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 Join Registrar (and Coordinator) to
control this process. Typically a Join Registrar is "inside" its
domain. For simplicity this document often refers to this as just
"Registrar". The term JRC is used in common with other bootstrap
mechanisms.
MASA Service: A third-party Manufacturer Authorized Signing
Authority (MASA) service on the global Internet. The MASA signs
vouchers. It also provides a repository for audit log information
of privacy protected bootstrapping events. It does not track
ownership. It is trusted by the Pledge.
TOFU: Trust on First Use. Used similarly to [RFC7435]. This is
where a Pledge device makes no security decisions but rather
simply trusts the first Registrar it is contacted by. This is
also known as the "resurrecting duckling" model.
3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the
sections below are to be interpreted as described in RFC 2119
[RFC2119].
4. Survey of Voucher Types
A voucher is a cryptographically protected statement to the Pledge
device authorizing a zero-touch "imprint" on the Join Registrar of
the domain. The specific information a voucher provides is
influenced by the bootstrapping use case.
The voucher can impart the following information to the Join
Registrar and Pledge:
Assertion Basis: Indicates the method that protects the imprint
(this is distinct from the voucher signature that protects the
Watsen, et al. Expires September 14, 2017 [Page 4]
Internet-Draft Voucher Profile March 2017
voucher itself). This might include manufacturer asserted
ownership verification, assured logging operations or reliance on
Pledge endpoint behavior such as secure root of trust of
measurement. The Join Registrar might use this information. Only
some methods are normatively defined in this document. Other
methods are left for future work.
Authentication of Join Registrar: Indicates how the Pledge can
authenticate the Join Registrar. This might include an indication
of the private PKIX trust anchor used by the Registrar, or an
indication of a public PKIX trust anchor and additional CN-ID or
DNS-ID information to complete authentication. Symmetric key or
other methods are left for future work.
Anti-Replay Protections: Time or nonce based information to
constrain the voucher to time periods or bootstrap attempts.
A number of bootstrapping scenarios can be met using differing
combinations of this information. All scenarios address the primary
threat of a Man-in-The-Middle Registrar gaining control over the
Pledge device. The following combinations are "types" of vouchers:
|Assertion |Registrar ID | Validity |
Voucher |Log-|Veri- |Trust |CN-ID or| RTC | Nonce |
Name | ged| fied |Anchor |DNS-ID | | |
---------------------------------------------------------|
Audit | X | | X | | | X |
-------------|----|-------|-------|--------|-----|-------|
Nonceless | X | | X | | X | |
Audit | | | | | | |
-------------|----|-------|-------|--------|-----|-------|
Owner Audit | X | X | X | | X | X |
-------------|----|-------|-------|--------|-----|-------|
Owner ID | | X | X | X | X | |
-------------|----|-------|----------------|-----|-------|
Bearer | X | | wildcard | optional |
out-of-scope | | | | |
-------------|----|-------|----------------|-------------|
NOTE: All voucher types include a 'Pledge ID serial number'
(Not shown for space reasons)
Audit Voucher: An Audit Voucher is named after the logging assertion
mechanisms that the Registrar then "audits" to enforce local
policy. The Registrar mitigates a MiTM Registrar by auditing that
an unknown MiTM registrar does not appear in the log entries.
This does not direct prevent the MiTM but provides a response
mechanism that ensures the MiTM is unsuccessful. This advantage
Watsen, et al. Expires September 14, 2017 [Page 5]
Internet-Draft Voucher Profile March 2017
is that actual ownership knowledge is not required on the MASA
service.
Nonceless Audit Voucher: An Audit Voucher without a validity period
statement. Fundamentally the same as an Audit Voucher except that
it can be issued in advance to support network partitions or to
provide a permanent voucher for remote deployments.
Ownership Audit Voucher: An Audit Voucher where the MASA service has
verified the Registrar as the authorized owner. The MASA service
mitigates a MiTM Registrar by refusing to generate Audit Voucher's
for unauthorized Registrars. The Registrar uses audit techniques
to supplement the MASA. This provides an ideal sharing of policy
decisions and enforcement between the vendor and the owner.
Ownership ID Voucher: An Ownership ID Voucher is named after
inclusion of the Pledge's CN-ID or DNS-ID within the voucher. An
example Ownership Voucher is defined in
[I-D.ietf-netconf-zerotouch]. The MASA service mitigates a MiTM
Registrar by identifying the specific Registrar authorized to own
the Pledge. [DISCUSS: still needed?]
Bearer Voucher: A Bearer Voucher is named after the inclusion of a
Registrar ID wildcard. Because the Registrar identity is not
indicated this voucher type must be treated as a secret and
protected from exposure as any 'bearer' of the voucher can claim
the Pledge device. Publishing a nonceless bearer voucher
effectively turns the specified Pledge into a "TOFU" device with
minimal mitigation against MiTM Registrars. Bearer vouchers are
out-of-scope.
5. Voucher
The voucher's purpose is to securely assign a pledge to an owner.
The voucher informs the pledge which entity it should consider to be
its owner.
The voucher is signed a PKCS#7 SignedData structure, as specified by
Section 9.1 of [RFC2315], encoded using ASN.1 distinguished encoding
rules (DER), as specified in ITU-T X.690.
The PKCS#7 structure MUST contain JSON-encoded content conforming to
the YANG module specified in Section 5.3.
The PKCS#7 structure MUST also contain a 'signerInfo' structure, as
described in Section 9.1 of [RFC2315], containing the signature
generated over the content using the MASA's private key.
Watsen, et al. Expires September 14, 2017 [Page 6]
Internet-Draft Voucher Profile March 2017
The PKCS#7 structure SHOULD also contain all of the certificates
leading up to and including the MASA's trust anchor certificate known
to the pledges.
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 authority-key-identifier? binary
+--ro created-on yang:date-and-time
+--ro expires-on? yang:date-and-time
+--ro assertion enumeration
+--ro device-identifier string
+--ro trusted-ca-certificate binary
+--ro domain-certificate-identifier
| +--ro subject? binary
| +--ro cn-id? string
| +--ro dns-id? string
+--ro assert-certificate-revocations? 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.
Watsen, et al. Expires September 14, 2017 [Page 7]
Internet-Draft Voucher Profile March 2017
{
"ietf-voucher:voucher": {
"assertion": "logged",
"trusted-ca-certificate": "base64-encoded X.509 DER",
"device-identifier": "JADA123456789",
"created-on": "2016-10-07T19:31:42Z",
"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
(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": {
"assertion": "verified",
"trusted-ca-certificate": "base64-encoded X.509 DER",
"domain-certificate-identifier": {
"subject": "base64-encoded Subject DER"
},
"device-identifier": "JADA123456789",
"created-on": "2016-10-07T19:31:42Z"
}
}
5.3. YANG Module
<CODE BEGINS> file "ietf-voucher@2017-03-13.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 {
Watsen, et al. Expires September 14, 2017 [Page 8]
Internet-Draft Voucher Profile March 2017
prefix rc;
description
"This import statement is only present to access the yang-data
extension defined in RFC 8040. The yang-data extension doesn't
itself have anything to do with RESTCONF, but was placed in the
that RFC for convenience. This extension is being tracked to
be moved to the next version of the YANG modeling language.
Regardless where or how this extension statement is defined,
there should not be any impact to a voucher's encoding.";
reference "RFC 8040: RESTCONF Protocol";
}
organization
"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.";
revision "2017-03-13" {
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;
Watsen, et al. Expires September 14, 2017 [Page 9]
Internet-Draft Voucher Profile March 2017
description
"A voucher that can be used to assign one or more
pledges to an owner.";
leaf authority-key-identifier {
type binary;
description
"The Subject Key Identifier of the MASA's leaf certificate.
Enables the pledge a definitively identify the voucher's
issuer's certificate. This field is optional as not all
vouchers will be signed by a private key associated with
an X.509 certificate.";
}
leaf created-on {
type yang:date-and-time;
mandatory true;
description
"A value indicating the date this voucher was created. This
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 the pledge supports expirations and the expires-on value
is less then the current time, then the pledge MUST not
process this voucher.";
}
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
Watsen, et al. Expires September 14, 2017 [Page 10]
Internet-Draft Voucher Profile March 2017
"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.";
}
leaf device-identifier {
type string;
mandatory true;
description
"A unique identifier (e.g., serial number) within the scope
of the MASA.
When processing a vouchers, pledges MUST ensure that their
unique identifier matches at least one regular expression in
the list. If no matching regular expression is found, the
pledge MUST NOT process this voucher.";
}
leaf trusted-ca-certificate {
type binary;
mandatory true;
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 field is optional because it may not be needed by all
bootstrapping protocols.
Note: the expiration date of this certificate effectively
imposes an upper limit on the voucher's expiration.";
Watsen, et al. Expires September 14, 2017 [Page 11]
Internet-Draft Voucher Profile March 2017
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:
Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER).";
}
// DISCUSS: do we need this anymore, if short-lived vouchers
// are expected, shouldn't the leaf certificate be pinned, or
// perhaps just the immediate issuer CA?
container domain-certificate-identifier {
must "../trusted-ca-certificate" {
description
"A trusted-ca-certificate must be present whenever
this node is present";
}
description
"This container identifies specific values that a domain
certificate, provided to the pledge separately by the
bootstrapping protocol, MUST contain. This is useful
when, for instance, the trust anchor is a long-lived
public CA certificate, while the domain certificate is
reissued periodically.
When provided, the pledge MUST perform RFC 6125 style
validation of the domain certificate against all of
the provided values.
This container is optional because it is unneeded when,
for instance, the trusted CA certificate is owned by the
domain (i.e. a private PKI), and hence the trust model
can be more relaxed.";
leaf subject {
type binary;
description
"The certificate's entire subject field MUST match
this value. This value is the Subject structure, as
specified by RFC ???? Section ???, encoded using the
ASN.1 distinguished encoding rules (DER), as specified
in ITU-T X.690.";
}
leaf cn-id {
type string;
Watsen, et al. Expires September 14, 2017 [Page 12]
Internet-Draft Voucher Profile March 2017
description
"The certificate's subject field's 'common name' value
MUST match this value.";
}
leaf dns-id {
type string;
description
"A subjectAltName entry of type dNSName in the
certificate MUST match this value.";
}
}
// DISCUSS: does the transition to 'pinning' model mean we can
// drop this leaf for now? future proofing allows it to be added
// if needed but its a edge condition?
//
// DISCUSS: there must be such future proofing. not clear where
// to add it in the voucher document. This is probably the most
// important point of these discusses
leaf assert-certificate-revocations {
type boolean;
must "../expires-on";
default true;
description
"A processing instruction to the device that it should
verify revocation information for the PKIX certificates
involved in bootstrapping. This is available only if
the pledge has a real-time-clock. This is in addition
to any revocation checks performed by the MASA.";
// DISCUSS: should this be a boolean or an enum indicating
// "fail open" vs "fail closed" to make the meaning clearer.
}
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
Watsen, et al. Expires September 14, 2017 [Page 13]
Internet-Draft Voucher Profile March 2017
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 last date that the MASA projects to be the last date it
will renew a voucher on (assuming the same validity duration
used in this voucher. This field is merely infomrative, it
is not processed by pledges.
Circustances may occur after when a voucher was generated
that can 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.";
}
} // end voucher
} // end voucher-grouping
}
<CODE ENDS>
6. Design Considerations
6.1. Renewals instead of Revocations
A revocation artifact is generally used to verify the continued
validity of an assertion such as a PKIX certificate, web token, or a
"voucher". Conceptually revocation allows for issuance of assertions
using long lifetimes and thereby avoiding ongoing protocol operations
to renew the assertion. In practice the use of revocation artifacts
increases the solution complexity. Rather than a single protocol, or
operation, to obtain or renew the assertion the resulting solution
instead has two or more protocols: one for assertion maintanence and
the other(s) for revocation verification.
The PKIX use of CRLs and OCSP responses provides an illustrative
example. Relying parties that verify revocation information must
obtain and parse the CRL or OCSP information. Each revocation method
has its own validity period that effectively shortens the certificate
validity period (since without valid revocation checks the
certificate would be rejected). In addition to having multiple
revocation protocol options the resulting space is further
Watsen, et al. Expires September 14, 2017 [Page 14]
Internet-Draft Voucher Profile March 2017
complicated by inline distribution of the revocation information.
The TLS extension "Certificate Status Request" [RFC6066] for when
"constrained clients may wish to use a certificate-status protocol"
is an example of this. Including revocation information into
Cryptographic Message Syntax [RFC5652] is another example.
If vouchers included revocation similar complexities would propagate
to all related voucher distribution and assertion protocols. Instead
vouchers do not support revocation. Instead of the asserting party,
or relying party, obtaining and distributing revocation information
the asserting party MUST obtain an up-to-date valid voucher. The
protocol and operations infrastructures for this are expected to be
the same as the initial methods used to obtain a voucher in the first
place, with one important clarification: the MASA services MUST issue
updated validity period vouchers to the same Registrar ID with
minimal friction. This is similar to how an OCSP revocation system
is always willing to confirm that a certificate is not revoked.
There is no requirement implied that vouchers be contiguously
renewed. For example if a two-week lifetime voucher is not used
before it expires there is no requirement that it be still valid when
renewed. The domain MAY renew an expired voucher at any time. The
MASA always has authoritative control and MAY reject such renewals
(such as when requested by domain owner's to "block" renewals or if
the device has been successfully claimed by an alternate domain).
Allowing non-contiguous lifetimes significantly reduces the
operational load on the domain as it is not required to maintain
valid vouchers; only to ensure a valid voucher is available during
the time window in which it needs to be used.
[[EDNOTE: It might be worth including an indication of maximum
lifetime for which such automated renewal is available. If so the
language we'd use would be similar to the RFC5280 statement that
certificate validity period is "the time interval during which the CA
warrants that it will maintain information about the status of the
certificate" only here used to inform the Registrar of "the time
interval during which the MASA warrants that it will maintain
information about the status of the ownership claim". Such a field
would be independent of the actual validity period of the voucher and
is not intended for consumption by the Pledge. A suggested name for
this field would be "last-renewal-date".]]
The communications to the MASA service regarding claiming and
blocking of devices is out of scope of this specification. Similarly
if revocation methods had been described, the method of reporting a
revocation would have been out-of-scope.
The lifetimes of vouchers may vary. In some bootstrapping protocols
the vouchers may be ephemeral, whereas in others the vouchers may be
Watsen, et al. Expires September 14, 2017 [Page 15]
Internet-Draft Voucher Profile March 2017
potentially long-lived. For bootstrapping protocols that support
ephemeral vouchers, there is no need to support renewal. For
bootstrapping protocols that support long-lived vouchers, final
protocol complexity is reduced when short lifetime vouchers are
easily renewed rather than layering on additional revocation methods.
Manufacturers MAY issue long-lived vouchers to customers if required
but no revocation method is described.
6.2. Voucher Per Pledge
The solution 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.
7. Security Considerations
7.1. Clock Sensitivity
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
This document favors using voucher-renewals over needing to support
voucher-revocations (Section 6.1). However, a voucher may be signed
by a chain of intermediate CAs leading to the trust anchor known to a
pledge. Revocation checking of these certificates is similarly
difficult. The current voucher format supports the existing PKIX
revocation information distribution within the limits of the current
PKI technology; but pledges MAY accept vouchers without checking
X.509 certificate revocation. Without revocation checking, a
compromized MASA keychain could be used to issue vouchers ad
infinitum without recourse. For this reason, MASA implementations
SHOULD ensure that all the CA private keys 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
Watsen, et al. Expires September 14, 2017 [Page 16]
Internet-Draft Voucher Profile March 2017
domain identity certificates (as in normal in PKI solutions).
Similarly they are expected to contact the MASA to indicate that an
outstanding (presumably short lifetime) voucher 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>.
[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>.
Watsen, et al. Expires September 14, 2017 [Page 17]
Internet-Draft Voucher Profile March 2017
[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-04 (work in progress), October 2016.
[I-D.ietf-netconf-zerotouch]
Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning
for NETCONF or RESTCONF based Management", draft-ietf-
netconf-zerotouch-12 (work in progress), January 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>.
[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 September 14, 2017 [Page 18]
Internet-Draft Voucher Profile March 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
EMail: tte+anima@cs.fau.de
Watsen, et al. Expires September 14, 2017 [Page 19]
