Internet DRAFT - draft-ietf-anima-voucher
draft-ietf-anima-voucher
ANIMA Working Group K. Watsen
Internet-Draft Juniper Networks
Intended status: Standards Track M. Richardson
Expires: July 28, 2018 Sandelman Software
M. Pritikin
Cisco Systems
T. Eckert
Huawei
January 24, 2018
Voucher Profile for Bootstrapping Protocols
draft-ietf-anima-voucher-07
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".
This document defines an artifact format as a YANG-defined JSON
document that has been signed using a CMS structure. Other YANG-
derived formats are possible. The voucher artifact is normally
generated by the pledge's manufacturer (i.e. the Manufacturer
Authorized Signing Authority).
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 https://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 July 28, 2018.
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Copyright Notice
Copyright (c) 2018 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
(https://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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
4. Survey of Voucher Types . . . . . . . . . . . . . . . . . . . 5
5. Voucher artifact . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 9
5.4. CMS format voucher artifact . . . . . . . . . . . . . . . 14
6. Design Considerations . . . . . . . . . . . . . . . . . . . . 15
6.1. Renewals instead of Revocations . . . . . . . . . . . . . 15
6.2. Voucher Per Pledge . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. Clock Sensitivity . . . . . . . . . . . . . . . . . . . . 16
7.2. Protect Voucher PKI in HSM . . . . . . . . . . . . . . . 17
7.3. Test Domain Certificate Validity when Signing . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. The IETF XML Registry . . . . . . . . . . . . . . . . . . 17
8.2. The YANG Module Names Registry . . . . . . . . . . . . . 18
8.3. The IETF MIME Registry . . . . . . . . . . . . . . . . . 18
8.4. The SMI Security for S/MIME CMS Content Type Registry . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Normative References . . . . . . . . . . . . . . . . . . 19
9.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
This document defines a strategy to securely assign a candidate
device (pledge) to an owner, using an artifact signed, directly or
indirectly, by the pledge's manufacturer, i.e. the Manufacturer
Authorized Signing Authority (MASA). This artifact is known as the
voucher.
The voucher artifact is a JSON [RFC7159] document, conforming to a
data model described by YANG [RFC7950], encoded using the rules
defined in [RFC7159], and signed using (by default) a CMS structure
[RFC5652].
A voucher's primary purpose is to securely convey to a pledge a
certificate, the "pinned-domain-cert", that the pledge can then use
to authenticate subsequent interactions. 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 is trying to take control of it.
The lifetimes of vouchers may vary. In some bootstrapping protocols
the vouchers may include a nonce restricting them to a single use,
whereas in others the vouchers may have an indicated lifetime. In
order to support long lifetimes this document recommends using short
lifetimes with programmatic renewal, see Section 6.1.
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
This document uses the following terms (sorted by name):
Artifact: The term "artifact" is used throughout to represent the
voucher as instantiated in the form of a signed structure.
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
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device that imprints on an attacker suffers a similar fate to a
duckling that imprints on a hungry wolf. Imprinting is a term
from psychology and ethnology, as describe in [imprinting]. The
analogy to Lorenz's work was first noted in
[Stajano99theresurrecting].
Domain: The set of entities or infrastructure under common
administrative control. The goal of the bootstrapping protocol is
to enable a Pledge to discover and join a domain.
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".
MASA: The Manufacturer Authorized Signing Authority (MASA) is the
entity that, for the purpose of this document, signs the vouchers
for a manufacturer's pledges. In some bootstrapping protocols,
the MASA may have Internet presence and be integral to the
bootstrapping process, whereas in other protocols the MASA may be
an offline service that has no active role in the bootstrapping
process.
Owner: The entity that controls the private key of the "pinned-
domain-cert" certificate conveyed by the voucher.
Pledge: The prospective device attempting to find and securely join
a domain. When shipped it only trusts authorized representatives
of the manufacturer.
Registrar See Join Registrar
TOFU: Trust on First Use. This is where a Pledge device makes no
security decisions but rather simply trusts the first domain
entity it is contacted by. Used similarly to [RFC7435]. This is
also known as the "resurrecting duckling" model.
Voucher: A signed statement from the MASA service that indicates to
a Pledge the cryptographic identity of the domain it should trust.
3. Requirements Language
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 BCP
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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
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 document defines a
mechanism to pin the domain certificate. Pinning a symmetric key,
a raw key, or [RFC6125] style "CN-ID" or "DNS-
ID" information is 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 (MiTM) Registrar gaining control over
the Pledge device. The following combinations are "types" of
vouchers:
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|Assertion |Registrar ID | Validity |
Voucher |Log-|Veri- |Trust |CN-ID or| RTC | Nonce |
Type | 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 directly prevent the MiTM but provides a response
mechanism that ensures the MiTM is unsuccessful. This advantage
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 Vouchers
for unauthorized Registrars. The Registrar uses audit techniques
to supplement the MASA. This provides a 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. The
MASA service mitigates a MiTM Registrar by identifying the
specific Registrar (via WebPKI) authorized to own the Pledge.
Bearer Voucher: A Bearer Voucher is named after the inclusion of a
Registrar ID wildcard. Because the Registrar identity is not
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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 artifact
The voucher's primary purpose is to securely assign a pledge to an
owner. The voucher informs the pledge which entity it should
consider to be its owner.
This document defines a voucher that is a JSON encoded instance of
the YANG module defined in Section 5.3 that has been, by default,
CMS-signed.
This format is described here as a practical basis for some uses
(such as in NETCONF), but more to make it clear what vouchers look
like in practice. This description also serves to validate the YANG
model.
Future work is expected to define new mappings of the voucher to CBOR
(from JSON), and to change the signature container from CMS to JOSE
or COSE. XML or ASN.1 formats are also conceivable.
This document defines a MIME type and a filename extension for the
CMS encoded JSON type. Future documents on additional formats would
define additional MIME types. Signaling is in the form of a MIME
Content-Type, an HTTP Accept: header, or more mundane methods like
use of a filename extension when a voucher is transfered on a USB
key.
5.1. Tree Diagram
The following tree diagram illustrates a high-level view of a voucher
document. The notation used in this diagram is described in
[I-D.ietf-netmod-yang-tree-diagrams]). Each node in the diagram is
fully described by the YANG module in Section 5.3. Please review the
YANG module for a detailed description of the voucher format.
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module: ietf-voucher
yang-data voucher-artifact:
+---- voucher
+---- created-on yang:date-and-time
+---- expires-on? yang:date-and-time
+---- assertion enumeration
+---- serial-number string
+---- idevid-issuer? binary
+---- pinned-domain-cert binary
+---- domain-cert-revocation-checks? boolean
+---- nonce? binary
+---- last-renewal-date? yang:date-and-time
5.2. Examples
This section provides voucher examples for illustration purposes.
That these examples conform to the encoding rules defined in
[RFC7159].
The following example illustrates an ephemeral voucher (uses a
nonce). 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",
"idevid-issuer": "base64encodedvalue==",
"pinned-domain-cert": "base64encodedvalue==",
"nonce": "base64encodedvalue=="
}
}
The following example illustrates a non-ephemeral voucher (no nonce).
While the voucher itself expires after two weeks, it presumably can
be renewed for up to a year later. The MASA generated this voucher
using the 'verified' assertion type, which should satisfy all
pledges.
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{
"ietf-voucher:voucher": {
"created-on": "2016-10-07T19:31:42Z",
"expires-on": "2016-10-21T19:31:42Z",
"assertion": "verified",
"serial-number": "JADA123456789",
"idevid-issuer": "base64encodedvalue==",
"pinned-domain-cert": "base64encodedvalue==",
"domain-cert-revocation-checks": "true",
"last-renewal-date": "2017-10-07T19:31:42Z"
}
}
5.3. YANG Module
Following is a YANG [RFC7950] module formally describing the
voucher's JSON document structure.
<CODE BEGINS> file "ietf-voucher@2018-01-24.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
"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
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<mailto:pritikin@cisco.com>
Author: Michael Richardson
<mailto:mcr+ietf@sandelman.ca>
Author: Toerless Eckert
<mailto:tte+ietf@cs.fau.de>";
description
"This module defines the format for a voucher, which is produced by
a pledge's manufacturer or delegate (MASA) to securely assign a
pledge to an 'owner', so that the pledge 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.
Copyright (c) 2017 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, is permitted pursuant to, and subject to the license
terms contained in, the Simplified BSD License set forth in Section
4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see the RFC
itself for full legal notices.";
revision "2018-01-24" {
description
"Initial version";
reference
"RFC XXXX: Voucher Profile for Bootstrapping Protocols";
}
// Top-level statement
rc:yang-data voucher-artifact {
uses voucher-artifact-grouping;
}
// Grouping defined for future augmentations
grouping voucher-artifact-grouping {
description
"Grouping to allow reuse/extensions in future work.";
container voucher {
description
"A voucher assigns a pledge to an owner (pinned-domain-cert).";
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leaf created-on {
type yang:date-and-time;
mandatory true;
description
"A value indicating the date this voucher was created. This
node is primarily for human consumption and auditing. Future
work MAY create verification requirements based on this
node.";
}
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 the voucher has been issued after
minimal verification of ownership or control. The
issuance has been logged for detection of
potential security issues (e.g. recipients of
vouchers might verify for themselves that unexpected
vouchers are not in the log). This is similar to unsecured
trust-on-first-use principles but with the logging
providing a basis for detecting unexpected events.";
}
enum proximity {
description
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"Indicates that the voucher has been issued after
the MASA verified a proximity proof provided by the
device and target domain. The issuance has been logged
for detection of potential security issues. This is
stronger than just logging, because it requires some
verification that the pledge and owner are
in communication, but is still dependent on analysis of
the logs to detect unexpected events.";
}
}
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, per
local policy, before processing the voucher.";
}
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 pinned-domain-cert {
type binary;
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mandatory true;
description
"An X.509 v3 certificate structure, as specified by RFC 5280,
using distinguished encoding rules (DER) encoding, as defined
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:
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
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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.";
}
} // end voucher
} // end voucher-grouping
}
<CODE ENDS>
5.4. CMS format voucher artifact
The IETF evolution of PKCS#7 is CMS [RFC5652]. A CMS signed voucher,
the default type, contains a ContentInfo structure with the voucher
content. An eContentType of TBD1 indicates the content is a JSON-
encoded voucher.
The signing structure is a CMS SignedData structure, as specified by
Section 5.1 of [RFC5652], encoded using ASN.1 distinguished encoding
rules (DER), as specified in ITU-T X.690 [ITU.X690.1994].
To facilitate interoperability, Section 8.3 in this document
registers the MIME type "application/voucher-cms+json" and the
filename extension ".vcj".
The CMS structure MUST contain a 'signerInfo' structure, as described
in Section 5.1 of [RFC5652], containing the signature generated over
the content using a private key trusted by the recipient. Normally
the recipient is the pledge and the signer is the MASA. A possible
other use could be as a "signed voucher request" format originating
from pledge or registrar toward the MASA. Within this document the
signer is assumed to be the MASA.
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Note that Section 5.1 of [RFC5652] includes a discussion about how to
validate a CMS object which is really a PKCS7 object (cmsVersion=1).
Intermediate systems (such the BRSKI Registrar) which might need to
evaluate the voucher in flight MUST be prepared for such an older
format. No signaling is necessary, as the Manufacturer knows the
capabilities of the pledge, and will use an appropriate format
voucher for each pledge.
The CMS structure SHOULD also contain all the certificates leading up
to and including the signer's trust anchor certificate known to the
recipient. The inclusion of the trust anchor is unusual in many
applications, but without it third parties can not accurately audit
the transaction.
The CMS structure MAY also contain revocation objects for any
intermediate certificate authorities (CAs) between the voucher-issuer
and the trust anchor known to the recipient. However, the use of
CRLs and other validity mechanisms is discouraged, as the pledge is
unlikely to be able to perform online checks, and is unlikely to have
a trusted clock source. As described below, the use of short-lived
vouchers and/or pledge provided nonce provides a freshness guarantee.
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 time delay
between when a voucher is created and when it is consumed. In cases
when there is a time delay, there is a need for the pledge to ensure
that the assertions made when the voucher was created are still
valid.
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, where the
'expires-on' leaf is set to some distant date, the expectation is for
the MASA to instead issue a short-lived voucher, where the 'expires-
on' leaf is set to a relatively near date, along with a promise
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(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 validity 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
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 understanding of time. The device can not trust
NTP as a time reference, as an attacker could control the NTP stream.
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 ephemeral vouchers.
Thirdly, vouchers without expiration times may be used, which will
appear in the audit log, informing the security decision.
This document defines a voucher format that contains time values for
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
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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 compromised 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
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.
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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
8.3. The IETF MIME Registry
This document registers a URIs in the IETF XML registry [RFC3688].
Following the format in [RFC3688], the following registration is
requested:
Type name: application
Subtype name: voucher-cms+json
Required parameters: none
Optional parameters: none
Encoding considerations: CMS-signed JSON vouchers are ASN.1/DER
encoded.
Security considerations: See Security Considerations, Section 7
Interoperability considerations: The format is designed to be
broadly interoperable.
Published specification: THIS RFC.
Applications that use this media type: ANIMA, 6tisch and NETCONF
zero-touch imprinting systems
Additional information:
Magic number(s): None
File extension(s): .vcj
Macintosh file type code(s): none
Person & email address to contact for further information: IETF
ANIMA WG
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Intended usage: LIMITED
Restrictions on usage: NONE
Author: ANIMA WG
Change controller: IETF
Provisional registration? (standards tree only): NO
8.4. The SMI Security for S/MIME CMS Content Type Registry
This document registers an OID in the "SMI Security for S/MIME CMS
Content Type" registry (1.2.840.113549.1.9.16.1), with the value:
Decimal Description References
------- -------------------------------------- ----------
TBD1 id-ct-animaJSONVoucher [ThisRFC]
9. References
9.1. Normative References
[ITU.X690.1994]
International Telecommunications Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>.
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[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References
[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-09 (work in progress), October 2017.
[I-D.ietf-netconf-zerotouch]
Watsen, K., Abrahamsson, M., and I. Farrer, "Zero Touch
Provisioning for NETCONF or RESTCONF based Management",
draft-ietf-netconf-zerotouch-19 (work in progress),
October 2017.
[I-D.ietf-netmod-yang-tree-diagrams]
Bjorklund, M. and L. Berger, "YANG Tree Diagrams", draft-
ietf-netmod-yang-tree-diagrams-04 (work in progress),
December 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,
<https://www.rfc-editor.org/info/rfc3688>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
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[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://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>.
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Appendix A. Acknowledgements
The authors would like to thank for following for lively discussions
on list and in the halls (ordered by last name): William Atwood,
Toerless Eckert, Sheng Jiang.
Russ Housley provided the upgrade from PKCS7 to CMS(RFC5652), along
with the detailed CMS structure diagram.
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
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