Network Working Group G. Michaelson
Internet-Draft G. Huston
Intended status: Experimental T. Harrison
Expires: September 8, 2019 APNIC
T. Bruijnzeels
M. Hoffmann
March 7, 2019

A profile for Resource Tagged Attestations (RTAs)


This document defines a Cryptographic Message Syntax (CMS) profile for a general purpose Resource Tagged Attestation (RTA), for use with the Resource Public Key Infrastructure (RPKI). The objective is to allow an attestation, in the form of an arbitrary digital object, to be signed "with resources", and for validation to provide an outcome of "valid with resources". The profile is intended to provide for the signing of an attestation with an arbitrary set of resources.

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

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This Internet-Draft will expire on September 8, 2019.

Copyright Notice

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Table of Contents

1. Introduction

This document defines a Cryptographic Message Syntax (CMS) [RFC5652] profile for a general purpose Resource Tagged Attestation (RTA), for use with the Resource Public Key Infrastructure (RPKI) [RFC6480]. An RTA allows an arbitrary digital object to be signed "with resources," and for validation of the digital signature to provide an outcome of "valid with resources." The profile is intended to provide for the signing of a arbitrary attestation with a set of resources by the duly delegated resource holder(s).

The RTA makes use of the template for RPKI Digitally Signed Objects [RFC6488], which defines a CMS wrapper for the RTA content, as well as a generic validation procedure for RPKI signed objects. However, this specification does not comply to the profile in [RFC6488] in all respects. This document describes the areas of difference to the template profile, the ASN.1 syntax for the RTA eContent, and the additional steps required to validate RTAs (in addition to the validation steps specified in [RFC6488].

An RTA is a detached signature CMS model, it leverages concepts documented in [RFC8358] and [RFC5485]. Text from these RFCs has been repurposed removing references to internet-drafts and RFCs since this is a general detached signature signing model.

2. Conventions Used In This Document

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] when they appear in ALL CAPS. These words may also appear in this document in lower case as plain English words, absent their normative meanings.

3. RTA Profile

An RTA conforms to the template for RPKI Digitally Signed Objects [RFC6488], with the exception that in order to allow for arbitrary resource sets to be used to sign an RTA, it may be necessary to use multiple signatures to sign an RTA.

The differences between this RTA profile and the profile specified by the RPKI Digitally Signed Object template are as follows:

4. The RTA ContentType

The ContentType for an RTA is defined as resourceTaggedAttestation, and has the numerical value of 1.2.840.113549.

This OID MUST appear both within the eContentType in the encapContentInfo object as well as the ContentType signed attribute in the signerInfo object (see [RFC6488]).

5. The RTA eContent

The content of an RTA indicates that an arbitrary digital object has been signed "with resources". An RTA is formally defined as:

   ResourceTaggedAttestationDefinitions DEFINITIONS ::=

     -- definition from rfc3029
    id-ct OBJECT IDENTIFIER ::= { iso(1) member-body(2)
               us(840) rsadsi(113549) pkcs(1) pkcs-9(9) id-smime(16) 1 }

    id-ct-resourceTaggedAttestation OBJECT IDENTIFIER ::=
               { id-ct(1) 36 }

     ResourceTaggedAttestation ::= SEQUENCE {
         version  [0]          INTEGER DEFAULT 0,
         subjectKeyIdentifers  SubjectKeys,
         resources             ResourceBlock,
         digestAlgorithm       AlgorithmIdentifer,
         messageDigest         OCTET STRING }

      SubjectKeys         ::= SET SIZE (1..MAX) OF SubjectKeyIdentifier
             -- defined in RFC5280

      ResourceBlock       ::= SEQUENCE {
        asID         [0]       AsList OPTIONAL,
        ipAddrBlocks [1]       IPList OPTIONAL }
            -- at least one of asID or ipAddrBlocks must be present

      AsList              ::= SEQUENCE (SIZE(1..MAX)) OF ASIdOrRange
      ASIdOrRange         ::= CHOICE {
         id                   ASId,
         range                ASRange }

      ASRange             ::= SEQUENCE {
         min                  ASId,
         max                  ASId }

      ASId                ::= INTEGER

      IPList              ::= SEQUENCE (SIZE(1..MAX)) OF IPAddressFamily

      IPAddressFamily     ::= SEQUENCE {    -- AFI & optional SAFI --
         addressFamily        OCTET STRING (SIZE (2..3)),
         addressesOrRanges    SEQUENCE OF IPAddressOrRange }

      IPAddressOrRange    ::= CHOICE {
         addressPrefix        IPAddress,
         addressRange         IPAddressRange }

      IPAddressRange      ::= SEQUENCE {
         min                  IPAddress,
         max                  IPAddress }

      IPAddress           ::= BIT STRING

      -- imported from [@!RFC5280]
      AlgorithmIdentifer  ::= SEQUENCE {
         algorithm            OBJECT IDENTIFIER,
         parameters           ANY DEFINED BY algorithm OPTIONAL }

Note that this content appears as the eContent within the encapContentInfo (see [RFC6488]).

[TODO: this needs some work. The AttestationSet is from prior pre-00 state. What is this referring to?]

Note that AttestationSet is a SET OF EncapsulatedContentInfo from [RFC5485]

5.1. version

The version number of the ResourceTaggedAttestation MUST be 0.

5.2. subjectKeyIdentifiers

The subjectKeyIdentifiers MUST be the set of SubjectKeyIdentifier values contained in each of the EE certificates carried in the CMS certificates field.

5.3. resources

The resources contained here are the resources used to tag the attestation, and MUST match the set of resources listed by the set of EE certificates carried in the CMS certificates field.

The ordering of resources is defined in [RFC3779].

5.4. digestAlgorithm

The digest algorithm used to create the message digest of the attested digital object. This algorithm MUST be a hashing algorithm defined in [RFC7935].

5.5. messageDigest

The message digest of the attested digital object using the algorithm specified in the digestAlgorithm field.

5.6. attestations

The SET OF EncapsulatedContentInfo [RFC5485] which form the individual digital signatures, made by each signing party. For each instance in the set, one of the subjectKeyIdentifiers MUST identify a certificate which can validate the signature. This means that there will be an instance of a SignedData and SignerInfo for that subjectKeyIdentifier (SignerInfo.sid)

The eContentType is id-ct-anyContentType, which refers to the ASN.1 ANY octet sequence.

6. RTA Validation

To validate an RTA the relying party MUST perform all the validation checks specified in [RFC6488] as well as the following additional RTA-specific validation steps.

[TODO more text needed about CRL/CRLDP and handling expired CRLS]

7. Need for Canonicalization

As in [RFC5485] and [RFC8358] there is a need for canonicalization.

The following text is based on section 4 of [RFC8358] with changes to remove references to internet-drafts and RFCs.

In general, the content is treated like a single octet string for the generation of the digital signature. Unfortunately, text and HTML files require canonicalization to avoid signature validation problems. The primary concern is the manner in which different operating systems indicate the end of a line of text. Some systems use a single new-line character, other systems use the combination of the carriage-return character followed by a line-feed character, and other systems use fixed-length records padded with space characters. For the digital signature to validate properly, a single convention must be employed.

7.1. ASCII, UTF-8, and HTML File Canonicalization

The canonicalization procedure follows the conventions used for text files in the File Transfer Protocol (FTP) [FTP]. Such files must be supported by FTP implementations, so code reuse seems likely.

The canonicalization procedure converts the data from its internal character representation to the standard 8-bit NVT-ASCII representation (see TELNET [TELNET]). In accordance with the NVT standard, the <CRLF> sequence MUST be used to denote the end of a line of text. Using the standard NVT-ASCII representation means that data MUST be interpreted as 8-bit bytes.

Trailing space characters MUST NOT appear on a line of text. That is, the space character must not be followed by the <CRLF> sequence.

Thus, a blank line is represented solely by the <CRLF> sequence.

The form-feed nonprintable character (0x0C) is expected.

Other non-printable characters, such as tab and backspace, are not expected, but they do occur. Non-printable or non-ASCII characters (ones outside the range 0x20 to 0x7E) MUST NOT be changed in any way not covered by the rules for end-of-line handling in the previous paragraph.

Trailing blank lines MUST NOT appear at the end of the file. That is, the file must not end with multiple consecutive <CRLF> sequences.

In some environments, a Byte Order Mark (BOM) (U+FEFF) is used at the beginning of a file to indicate that it contains non-ASCII characters. In UTF-8 or HTML files, a BOM at the beginning of the file is not considered to be part of the file content. One or more consecutive leading BOMs, if present, MUST NOT be processed by the digital signature algorithm.

Any end-of-file marker used by an operating system is not considered to be part of the file content. When present, such end-of-file markers MUST NOT be processed by the digital signature algorithm.

Note: This text file canonicalization procedure is consistent with the NVT-ASCII definition offered in Appendix B of RFC 5198 [UFNI].

7.2. XML File Canonicalization

Utilities that produce XML files are expected to follow the guidance provided by the World Wide Web Consortium (W3C) in Section 2.11 of [R20081126]. If this guidance is followed, no canonicalization is needed.

A robust signature generation process MAY perform canonicalization to ensure that the W3C guidance has been followed. This guidance says that a <LF> character MUST be used to denote the end of a line of text within an XML file. Therefore, any two-character <CRLF> sequence and any <CR> that is not followed by <LF> are to be translated to a single <LF> character.

7.3. No Canonicalization of Other File Formats

No canonicalization is needed for file formats currently used or planned other than ASCII, UTF-8, HTML, and XML files. Other file formats, including PDF [PDF], PostScript [PS], and EPUB [EPUB] are treated as a simple sequence of octets by the digital signature algorithm.

8. Standalone Use

An RTA MAY include the set of certificates and CRL which permit the RTA and the object which has been signed to be validated cryptographically given a set of applicable trust anchors. The set of certificates and CRLs must form a complete path from a trust anchor to each end-entity certificate used to sign.

No publication protocol is specified, or expected. RTA objects are standalone, and intended to be exchanged freely as attachments to email or lodged in the web, or other mechanisms.

The EE certificates generated and used to sign MAY omit the Subject Information Access (SIA) extension mandated by RFC 6487 as that extension requires an rsync URI for the accessLocation form and the RTA method does not require repository access via rsync.

An RTA and its associated EE certificates MAY appear on an RPKI Manifest and MAY be published in a repository.

9. IANA Considerations

IANA is entirely off the hook on this one.

10. Security Considerations

Security is explicitly a consideration in the whole of this draft.

The intent is to make testable digital signatures over data to associate the data with specific INR.

11. Acknowledgments

Russ Housely advised informally on the use of CMS signed objects around 2012.

Russ's work on CMS signed internet drafts in [RFC8358] and [RFC5485] has been re-purposed here to apply to arbitrary signed objects, not just internet-drafts and text documents.

An early implementation of RTA was coded by Robert Loomans and Gary Kennedy at APNIC before 2011 which used simpler ASN.1 semantics to specify the signed object.

Jamie Gillespie (APNIC) provided valuable feedback and critique of the 00 draft.

12. Revision history

13. 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.
[RFC3779] Lynn, C., Kent, S. and K. Seo, "X.509 Extensions for IP Addresses and AS Identifiers", RFC 3779, DOI 10.17487/RFC3779, June 2004.
[RFC5485] Housley, R., "Digital Signatures on Internet-Draft Documents", RFC 5485, DOI 10.17487/RFC5485, March 2009.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009.
[RFC6488] Lepinski, M., Chi, A. and S. Kent, "Signed Object Template for the Resource Public Key Infrastructure (RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012.
[RFC7935] Huston, G. and G. Michaelson, "The Profile for Algorithms and Key Sizes for Use in the Resource Public Key Infrastructure", RFC 7935, DOI 10.17487/RFC7935, August 2016.
[RFC8358] Housley, R., "Update to Digital Signatures on Internet-Draft Documents", RFC 8358, DOI 10.17487/RFC8358, March 2018.

Authors' Addresses

George G. Michaelson Asia Pacific Network Information Centre 6 Cordelia St South Brisbane, QLD 4101 Australia EMail:
Geoff Huston Asia Pacific Network Information Centre 6 Cordelia St South Brisbane, QLD 4101 Australia EMail:
Tom Harrison Asia Pacific Network Information Centre 6 Cordelia St South Brisbane, QLD 4101 Australia EMail:
Tim Bruijnzeels Open Netlabs B.V. Science Park 400 Amsterdam, 1098 XH The Netherlands EMail:
Martin Hoffmann Open Netlabs B.V. Science Park 400 Amsterdam, 1098 XH The Netherlands EMail: