Internet Engineering Task Force (IETF) M. Lepinski

Internet Engineering Task Force (IETF) M. Lepinski
Request for Comments: 6488 A. Chi
Category: Standards Track S. Kent
ISSN: 2070-1721 BBN
February 2012

Signed Object Template for
the Resource Public Key Infrastructure (RPKI)

Abstract

This document defines a generic profile for signed objects used in
the Resource Public Key Infrastructure (RPKI). These RPKI signed
objects make use of Cryptographic Message Syntax (CMS) as a standard
encapsulation format.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 5741.

Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6488.

Copyright Notice

Copyright (c) 2012 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
(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.

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RFC 6488 RPKI Signed Object Template February 2012

Table of Contents

1. Introduction ....................................................2
1.1. Terminology ................................................3
1.2. Note on Algorithms .........................................3
2. Signed Object Syntax ............................................3
2.1. Signed-Data Content Type ...................................4
2.1.1. version .............................................4
2.1.2. digestAlgorithms ....................................4
2.1.3. encapContentInfo ....................................4
2.1.3.1. eContentType ...............................5
2.1.3.2. eContent ...................................5
2.1.4. certificates ........................................5
2.1.5. crls ................................................5
2.1.6. signerInfos .........................................5
2.1.6.1. version ....................................6
2.1.6.2. sid ........................................6
2.1.6.3. digestAlgorithm ............................6
2.1.6.4. signedAttrs ................................6
2.1.6.4.1. Content-Type Attribute ..........7
2.1.6.4.2. Message-Digest Attribute ........7
2.1.6.4.3. Signing-Time Attribute ..........7
2.1.6.4.4. Binary-Signing-Time Attribute ...8
2.1.6.5. signatureAlgorithm .........................8
2.1.6.6. signatureValue .............................8
2.1.6.7. unsigneAttrs ...............................8
3. Signed Object Validation ........................................8
4. Definition of Specific Signed Objects ..........................10
5. Security Considerations ........................................10
6. IANA Considerations ............................................11
7. Acknowledgements ...............................................11
8. Normative References ...........................................11
9. Informative References .........................................12

1. Introduction

The purpose of the Resource Public Key Infrastructure (RPKI) is to
support assertions by current resource holders of IP (v4 and v6)
address space and AS numbers, based on the records of organizations
that act as Certification Authorities (CAs). IP address and AS
number resource information is carried in X.509 certificates via RFC
3779 extensions [RFC6487]. Other information assertions about
resources are expressed via digitally signed, non-X.509 data
structures that are referred to as "signed objects" in the RPKI
context [RFC6480]. This document standardizes a template for
specifying signed objects that can be validated using the RPKI.

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RFC 6488 RPKI Signed Object Template February 2012

RPKI signed objects make use of Cryptographic Message Syntax (CMS)
[RFC5652] as a standard encapsulation format. CMS was chosen to take
advantage of existing open source software available for processing
messages in this format. RPKI signed objects adhere to a profile
(specified in Section 2) of the CMS signed-data object.

The template defined in this document for RPKI signed objects is not
a complete specification for any particular type of signed object,
and instead includes only the items that are common to all RPKI
signed objects. That is, fully specifying a particular type of
signed object requires an additional document that specifies the
details specific to a particular type of signed object. Such details
include Abstract Syntax Notation One (ASN.1) [X.208-88] for the
object's payload and any additional steps required to validate the
particular type of signed object. Section 4 describes in more detail
the additional pieces that must be specified in order to define a new
type of RPKI signed object that uses this template. Additionally,
see [RFC6482] for an example of a document that uses this template to
specify a particular type of signed object, the Route Origination
Authorization (ROA).

1.1. Terminology

It is assumed that the reader is familiar with the terms and concepts
described in "Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile" [RFC5280], "X.509
Extensions for IP Addresses and AS Identifiers" [RFC3779], and
"Cryptographic Message Syntax (CMS)" [RFC5652].

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

1.2. Note on Algorithms

CMS is a general format capable of accommodating a wide variety of
signature and digest algorithms. The algorithms used in the RPKI
(and associated key sizes) are specified in [RFC6485].

2. Signed Object Syntax

The RPKI signed object is a profile of the CMS [RFC5652] signed-data
object, with the restriction that RPKI signed objects MUST be encoded
using the ASN.1 Distinguished Encoding Rules (DER) [X.509-88].

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The general format of a CMS object is:

ContentInfo ::= SEQUENCE {
contentType ContentType,
content [0] EXPLICIT ANY DEFINED BY contentType }

ContentType ::= OBJECT IDENTIFIER

The content-type is the signed-data type of id-data, namely the
id-signedData OID [RFC5652], 1.2.840.113549.1.7.2.

2.1. Signed-Data Content Type

According to the CMS standard, the signed-data content type is the
ASN.1 type SignedData:

SignedData ::= SEQUENCE {
version CMSVersion,
digestAlgorithms DigestAlgorithmIdentifiers,
encapContentInfo EncapsulatedContentInfo,
certificates [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT RevocationInfoChoices OPTIONAL,
signerInfos SignerInfos }

DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier

SignerInfos ::= SET OF SignerInfo

Additionally, the SignerInfos set MUST contain only a single
SignerInfo object.

2.1.1. version

The version is the syntax version number. It MUST be 3,
corresponding to the signerInfo structure having version number 3.

2.1.2. digestAlgorithms

The digestAlgorithms set contains the OIDs of the digest algorithm(s)
used in signing the encapsulated content. This set MUST contain
exactly one digest algorithm OID, and the OID MUST be selected from
those specified in [RFC6485].

2.1.3. encapContentInfo

encapContentInfo is the signed content, consisting of a content type
identifier and the content itself. The encapContentInfo represents
the payload of the RPKI signed object.

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RFC 6488 RPKI Signed Object Template February 2012

EncapsulatedContentInfo ::= SEQUENCE {
eContentType ContentType,
eContent [0] EXPLICIT OCTET STRING OPTIONAL }

ContentType ::= OBJECT IDENTIFIER

2.1.3.1. eContentType

This field is left undefined by this profile. The eContentType is an
OID specifying the type of payload in this signed object and MUST be
specified by the Internet Standards Track document that defines the
object.

2.1.3.2. eContent

This field is left undefined by this profile. The eContent is the
payload of the signed object and MUST be specified by the Internet
Standards Track document that defines the RPKI object.

Note that the signed object profile does not provide version numbers
for signed objects. Therefore, in order to facilitate transition to
new versions of the signed objects over time, it is RECOMMENDED that
each type of signed object defined using this profile include a
version number within its eContent.

2.1.4. certificates

The certificates field MUST be included, and MUST contain exactly one
certificate, the RPKI end-entity (EE) certificate needed to validate
this signed object.

2.1.5. crls

The crls field MUST be omitted.

2.1.6. signerInfos

SignerInfo is defined in CMS as:

SignerInfo ::= SEQUENCE {
version CMSVersion,
sid SignerIdentifier,
digestAlgorithm DigestAlgorithmIdentifier,
signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unsignedAttrs [1] IMPLICIT UnsignedAttributes OPTIONAL }

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RFC 6488 RPKI Signed Object Template February 2012

2.1.6.1. version

The version number MUST be 3, corresponding with the choice of
SubjectKeyIdentifier for the sid.

2.1.6.2. sid

The sid is defined as:

SignerIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
subjectKeyIdentifier [0] SubjectKeyIdentifier }

For RPKI signed objects, the sid MUST be the SubjectKeyIdentifier
that appears in the EE certificate carried in the CMS certificates
field.

2.1.6.3. digestAlgorithm

The digestAlgorithm MUST consist of the OID of a digest algorithm
that conforms to the RPKI Algorithms and Key Size Profile
specification [RFC6485].

2.1.6.4. signedAttrs

The signedAttrs is defined as:

SignedAttributes ::= SET SIZE (1..MAX) OF Attribute

Attribute ::= SEQUENCE {
attrType OBJECT IDENTIFIER,
attrValues SET OF AttributeValue }

AttributeValue ::= ANY

The signedAttrs element MUST be present and MUST include the content-
type and message-digest attributes [RFC5652]. The signer MAY also
include the signing-time attribute [RFC5652], the binary-signing-time
attribute [RFC6019], or both attributes. Other signed attributes
MUST NOT be included.

The signedAttrs element MUST include only a single instance of any
particular attribute. Additionally, even though the syntax allows
for a SET OF AttributeValue, in an RPKI signed object, the attrValues
MUST consist of only a single AttributeValue.

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2.1.6.4.1. Content-Type Attribute

The content-type attribute MUST be present. The attrType OID for the
content-type attribute is 1.2.840.113549.1.9.3.

The attrValues for the content-type attribute MUST match the
eContentType in the EncapsulatedContentInfo. Thus, attrValues MUST
contain the OID that specifies the payload type of the specific RPKI
signed object carried in the CMS signed data structure.

2.1.6.4.2. Message-Digest Attribute

The message-digest attribute MUST be present. The attrType OID for
the message-digest attribute is 1.2.840.113549.1.9.4.

The attrValues for the message-digest attribute contains the output
of the digest algorithm applied to the content being signed, as
specified in Section 5.4 of [RFC5652].

2.1.6.4.3. Signing-Time Attribute

The signing-time attribute MAY be present. Note that the presence or
absence of the signing-time attribute MUST NOT affect the validity of
the signed object (as specified in Section 3). The attrType OID for
the signing-time attribute is 1.2.840.113549.1.9.5.

id-signingTime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) 5 }

The attrValues for the signing-time attribute is defined as:

SigningTime ::= Time

Time ::= CHOICE {
utcTime UTCTime,
generalizedTime GeneralizedTime }

The Time element specifies the time, based on the local system clock,
at which the digital signature was applied to the content.

The definition of Time matches the one specified in the 1997 version
of X.509. Additional information regarding the use of UTCTime and
GeneralizedTime can be found in [RFC5652].

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2.1.6.4.4. Binary-Signing-Time Attribute

The binary-signing-time attribute MAY be present. Note that the
presence or absence of the binary-signing-time attribute MUST NOT
affect the validity of the signed object (as specified in Section 3).
The attrType OID for the binary-signing-time attribute is
1.2.840.113549.1.9.16.2.46.

id-aa-binarySigningTime OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) aa(2) 46 }
The attrValues for the signing-time attribute is defined as:

BinarySigningTime ::= BinaryTime

BinaryTime ::= INTEGER (0..MAX)

The BinaryTime element specifies the time, based on the local system
clock, at which the digital signature was applied to the content.
The precise definition of the BinaryTime element can be found in
[RFC6019].

2.1.6.5. signatureAlgorithm

The signatureAlgorithm MUST conform to the RPKI Algorithms and Key
Size Profile specification [RFC6485].

2.1.6.6. signature

The signature value is defined as:

SignatureValue ::= OCTET STRING

The signature characteristics are defined by the digest and signature
algorithms.

2.1.6.7. unsignedAttrs

unsignedAttrs MUST be omitted.

3. Signed Object Validation

Before a relying party can use a signed object, the relying party
MUST validate the signed object by verifying that all of the
following conditions hold. A relying party may perform these checks
in any order. Note that these checks are necessary, but not
sufficient. In general, further validation MUST be performed based
on the specific type of signed object.

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1. The signed object syntax complies with this specification. In
particular, each of the following is true:

a. The content-type of the CMS object is SignedData (OID
1.2.840.113549.1.7.2)

b. The version of the SignedData object is 3.

c. The certificates field in the SignedData object is present and
contains one EE certificate, the SubjectKeyIdentifier field of
which matches the sid field of the SignerInfo object.

d. The crls field in the SignedData object is omitted.

e. The version of the SignerInfo is 3.

f. The signedAttrs field in the SignerInfo object is present and
contains both the content-type attribute (OID
1.2.840.113549.1.9.3) and the message-digest attribute (OID
1.2.840.113549.1.9.4).

g. The signedAttrs field in the SignerInfo object does not
contain any attributes other than the following four: the
content-type attribute (OID 1.2.840.113549.1.9.3), the
message-digest attribute (OID 1.2.840.113549.1.9.4), the
signing-time attribute (OID 1.2.840.113549.1.9.5), and the
binary-signing-time attribute (OID
1.2.840.113549.1.9.16.2.46). Note that the signing-time and
binary-signing-time attributes MAY be present, but they are
not required.

h. The eContentType in the EncapsulatedContentInfo is an OID that
matches the attrValues in the content-type attribute.

i. The unsignedAttrs field in the SignerInfo object is omitted.

j. The digestAlgorithm in the SignedData and SignerInfo objects
conforms to the RPKI Algorithms and Key Size Profile
specification [RFC6485].

k. The signatureAlgorithm in the SignerInfo object conforms to
the RPKI Algorithms and Key Size Profile specification
[RFC6485].

l. The signed object is DER encoded.

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2. The public key of the EE certificate (contained within the CMS
signed-data object) can be used to successfully verify the
signature on the signed object.

3. The EE certificate (contained within the CMS signed-data object)
is a valid EE certificate in the RPKI as specified by [RFC6487].
In particular, a valid certification path from a trust anchor to
this EE certificate exists.

If the above procedure indicates that the signed object is invalid,
then the signed object MUST be discarded and treated as though no
signed object were present. If all of the conditions above are true,
then the signed object may be valid. The relying party MUST then
perform any additional validation steps required for the particular
type of signed object.

Note that a previously valid signed object will cease to be valid
when the associated EE certificate ceases to be valid (for example,
when the end of the certificate's validity period is reached, or when
the certificate is revoked by the authority that issued it). See
[RFC6487] for a complete specification of resource certificate
validity.

4. Definition of Specific Signed Objects

Each RPKI signed object MUST be defined in an Internet Standards
Track document based on this profile, by specifying the following
data elements and validation procedure:

1. eContentType: A single OID to be used for both the eContentType
field and the content-type attribute. This OID uniquely
identifies the type of signed object.

2. eContent: Define the syntax for the eContent field in
encapContentInfo. This is the payload that contains the data
specific to a given type of signed object.

3. Additional Validation: Define a set of additional validation
steps for the specific signed object. Before using this specific
signed object, a relying party MUST perform both the generic
validation steps in Section 3 above, as well as these additional
steps.

5. Security Considerations

There is no assumption of confidentiality for the data in an RPKI
signed object. The integrity and authenticity of each signed object
is based on the verification of the object's digital signature, and

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RFC 6488 RPKI Signed Object Template February 2012

the validation of the EE certificate used to perform that
verification. It is anticipated that signed objects will be stored
in repositories that will be publicly accessible.

Since RPKI signed objects make use of CMS as an encapsulation format,
the security considerations for CMS apply [RFC5652].

6. IANA Considerations

IANA has created a registry of "RPKI Signed Objects" types that
utilize the template defined in this document. This registry
contains three fields: an informal name for the signed object, the
OID for the eContentType of the signed object, and a specification
pointer that references the RFC in which the signed object is
specified. The entries in this registry are managed by IETF
Standards Action.

The registry has been initially populated with the following two
entries.

Name | OID | Specification
----------------------------------------------------------------
ROA | 1.2.840.113549.1.9.16.1.24 | RFC 6482
Manifest | 1.2.840.113549.1.9.16.1.26 | RFC 6486

7. Acknowledgements

The authors wish to thank Charles Gardiner, Russ Housley, and Derek
Kong for their help and contributions. Additionally, the authors
would like to thank Rob Austein, Roque Gagliano, Danny McPherson,
Sean Turner, and Sam Weiler for their careful reviews and helpful
comments.

8. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.

[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.

[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, September 2009.

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RFC 6488 RPKI Signed Object Template February 2012

[RFC6485] Huston, G., "The Profile for Algorithms and Key Sizes for
Use in the Resource Public Key Infrastructure (RPKI)", RFC
6485, February 2012.

[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", RFC 6487, February
2012.

[X.208-88] CCITT. Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1), 1988.

[X.509-88] CCITT. Recommendation X.509: The Directory Authentication
Framework, 1988.

9. Informative References

[RFC6019] Housley, R., "BinaryTime: An Alternate Format for
Representing Date and Time in ASN.1", RFC 6019, September
2010.

[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, February 2012.

[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482, February 2012.

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RFC 6488 RPKI Signed Object Template February 2012

Authors' Addresses

Matt Lepinski
BBN Technologies
10 Moulton Street
Cambridge MA 02138

EMail: [email protected]

Andrew Chi
BBN Technologies
10 Moulton Street
Cambridge MA 02138

EMail: [email protected]

Stephen Kent
BBN Technologies
10 Moulton Street
Cambridge MA 02138

EMail: [email protected]

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