RFC6488

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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.

                       2.1.6.4.4. Binary-Signing-Time Attribute ...8

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.

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).

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.

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.

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].

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.

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.

version

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

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.

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.

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

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.

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.

crls

The crls field MUST be omitted.

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 }
version

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

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.

digestAlgorithm

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

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.

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.

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.

signatureAlgorithm

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

signature

The signature value is defined as:

     SignatureValue ::= OCTET STRING

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

unsignedAttrs

unsignedAttrs MUST be omitted.

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.

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.

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.

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.

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

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.

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

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.

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.

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.

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.

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]