A Profile for Autonomous System Provider Authorization

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Table of Contents

1. Introduction

The primary purpose of the Resource Public Key Infrastructure (RPKI) is to improve routing security [RFC6480]. As part of this infrastructure, a mechanism is needed to facilitate holders of Autonomous System (AS) numbers in their capacity as Customer to authorize other ASes as their Provider(s). A Provider AS (PAS) is a network that:¶

1. offers its customers outbound (customer to Internet) data traffic connectivity and/or¶
2. further propagates in all directions (towards providers, lateral peers, and customers) any BGP Updates that the customer may send.¶

The digitally signed Autonomous System Provider Authorization (ASPA) object described in this document provides the above-mentioned authorization mechanism.¶

The ASPA object is a cryptographically signed attestation by a Customer AS (CAS) that another AS listed in the ASPA is a Provider. When the CAS has multiple Providers, all Provider ASes are listed in the ASPA including any internet exchange point (IXP) route server (RS) AS that serves the CAS.¶

The ASPA uses the template for RPKI digitally signed objects [RFC6488], which defines a Cryptographic Message Syntax (CMS) [RFC5652] wrapper for the ASPA content as well as a generic validation procedure for RPKI signed objects. As ASPAs need to be validated with RPKI certificates issued by the current infrastructure, we assume the mandatory-to-implement algorithms in [RFC6485], or its successor.¶

To complete the specification of the ASPA (see Section 4 of [RFC6488]), this document defines:¶

1. The object identifier (OID) that identifies the ASPA signed object. This OID appears in the eContentType field of the encapContentInfo object as well as the content-type signed attribute within the signerInfo structure.¶
2. The ASN.1 syntax for the ASPA content, which is the payload signed by the CAS. The ASPA content is encoded using the ASN.1 [X680] Distinguished Encoding Rules (DER) [X690].¶
3. The steps required to validate an ASPA beyond the validation steps specified in [RFC6488].¶

2. ASPA Content Type

The content-type for an ASPA is defined as id-ct-ASPA, which has the numerical value of 1.2.840.113549.1.9.16.1.49. This OID MUST appear both within the eContentType in the encapContentInfo structure as well as the content-type signed attribute within the signerInfo structure (see [RFC6488]).¶

3. ASPA eContent

The content of an ASPA identifies the Customer AS (CAS) as well as the Set of Provider ASes (SPAS) that are authorized by the CAS to be its Providers.¶

Not all route servers (RS) at internet exchange points are transparent, e.g., in some cases the AS number of the RS would be present in the AS_PATH. In this case, the RS AS is acting as a provider AS, which propagates routes between its clients (i.e., customers). Thus, a CAS MUST add both upstream providers and any connected non-transparent RS AS to its SPAS.¶

If a Customer AS is connected to multiple transit providers/non-transparent route servers, all Provider ASes MUST be registered in a single ASPA object. This rule is important to avoid possible race conditions during updates of ASPAs.¶

The eContent of an ASPA is an instance of ASProviderAttestation, formally defined by the following ASN.1 [X680] module:¶

RPKI-ASPA-2022
  { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
     pkcs-9(9) smime(16) modules(0) id-mod-rpki-aspa-2022(TBD) }

DEFINITIONS IMPLICIT TAGS ::=
BEGIN

IMPORTS
  CONTENT-TYPE
  FROM CryptographicMessageSyntax-2010  -- RFC 6268
    { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
       pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) } ;

id-ct-ASPA OBJECT IDENTIFIER ::=
  { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
    pkcs-9(9) id-smime(16) id-ct(1) 49 }

ct-ASPA CONTENT-TYPE ::=
  { TYPE ASProviderAttestation IDENTIFIED BY id-ct-ASPA }

ASProviderAttestation ::= SEQUENCE {
  version [0]   ASPAVersion DEFAULT v0,
  customerASID  ASID,
  providers     ProviderASSet }

ASPAVersion ::= INTEGER  { v0(0) }

ProviderASSet ::= SEQUENCE (SIZE(1..MAX)) OF ProviderAS

ProviderAS ::= SEQUENCE {
  providerASID  ASID,
  afiLimit      AddressFamilyIdentifier OPTIONAL }

ASID ::= INTEGER (0..4294967295)

AddressFamilyIdentifier ::= OCTET STRING (SIZE (2))

END

Note that this content appears as the eContent within the encapContentInfo as specified in [RFC6488].¶

4. ASPA Validation

Before a relying party can use an ASPA to validate a routing announcement, the relying party MUST first validate the ASPA object itself. To validate an ASPA, the relying party MUST perform all the validation checks specified in [RFC6488] as well as the following additional ASPA-specific validation steps.¶

• The Autonomous System Identifier Delegation Extension [RFC3779] MUST be present in the end-entity (EE) certificate (contained within the ASPA), and the Customer ASID in the ASPA eContent MUST be contained within the set of AS numbers specified by the EE certificate's Autonomous System Identifier Delegation Extension. The EE certificate's Autonomous System Identifier Delegation Extension MUST NOT contain any "inherit" elements.¶
• The IP Address Delegation Extension [RFC3779] MUST be absent.¶

5. IANA Considerations

Please add the id-mod-rpki-aspa-2022 to the SMI Security for S/MIME Module Identifier (1.2.840.113549.1.9.16.0) registry (https://www.iana.org/assignments/smi-numbers/smi-numbers.xml#security-smime-0) as follows:¶

    Decimal   | Description                   | Specification
    -----------------------------------------------------------
    TBD2      | id-mod-rpki-aspa-2022         | [ThisRFC]

Please add the ASPA to the SMI Security for S/MIME CMS Content Type (1.2.840.113549.1.9.16.1) registry (https://www.iana.org/assignments/smi-numbers/smi-numbers.xml#security-smime-1) as follows:¶

    Decimal   | Description                   | Specification
    -----------------------------------------------------------
    49        | id-ct-ASPA                    | [ThisRFC]

Please add Autonomous System Provider Authorization to the RPKI Signed Object registry (https://www.iana.org/assignments/rpki/rpki.xhtml#signed-objects) as follows:¶

    Name                                     | OID                         | Specification
    --------------------------------------------------------------------------------------
    Autonomous System Provider Authorization | 1.2.840.113549.1.9.16.1.49  | [ThisRFC]

Please add an item for the Autonomous System Provider Authorization file extension to the "RPKI Repository Name Scheme" registry created by [RFC6481] as follows:¶

   Filename
   Extension  RPKI Object                               Reference
   --------------------------------------------------------------------------------------
      .asa    Autonomous System Provider Authorization  [draft-ietf-sidrops-aspa-profile]

6. Security Considerations

While it is not technically enforcable, it is highly recommended that for a given Customer AS, a single ASPA object be maintained which contains all providers/route servers. Administrating all providers in a single object helps prevent race conditions during ASPA updates that might affect prefix propagation. The software that provides hosting for ASPA records SHOULD support enforcement of this rule. In the case of the transition process between different CA registries, the ASPA records SHOULD be kept identical in all registries in terms of their authorization contents.¶

8. Acknowledgments

The authors would like to thank Keyur Patel for helping kick-start the ASPA profile project, Ties de Kock & Tim Bruijnzeels for suggesting that the ProviderASSet be in a canonical form, and Kotikalapudi Sriram for review and several suggestions for improvements.¶

Authors' Addresses