RFC 8002

Host Identity Protocol Certificates

📅 published October 2016, from ietf

RFC 8002: Host Identity Protocol Certificates 🎀

okay bestie, this one is all about how to carry digital certificates inside HIP packets 🦋 It's an Internet Standards Track doc from the IETF, dated October 2016, with ISSN 2070-1721. The authors are T. Heer (Albstadt-Sigmaringen University) and S. Varjonen (University of Helsinki) 💜

It updates RFC 7401 and obsoletes RFC 6253, so if you're reading old HIP stuff, this is the newer version 👑

Abstract

The Certificate (CERT) parameter is basically a container for digital certificates 📦 It carries them in Host Identity Protocol (HIP) control packets. This doc specifies the certificate parameter and the error signaling for when verification fails 🙈 It also specifies how Host Identity Tags (HITs) are represented in X.509 version 3 (v3) 🧚

The concrete stuff, like how certificates get obtained and requested and what happens after a successful or failed verification, depends on the scenario they're used in 💅 So those scenario-specific details are left to the documents that actually use the CERT parameter.

This document updates RFC 7401 and obsoletes RFC 6253.

Status of This Memo

This is an Internet Standards Track document ✨

It's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). More info on Internet Standards is in Section 2 of RFC 7841 🌸

Want the current status, any errata, or a way to send feedback? Check http://www.rfc-editor.org/info/rfc8002 🫶

Copyright Notice

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.

Table of Contents 🗺️

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
  1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
2.  CERT Parameter  . . . . . . . . . . . . . . . . . . . . . . .   3
3.  X.509 v3 Certificate Object and Host Identities . . . . . . .   5
4.  Revocation of Certificates  . . . . . . . . . . . . . . . . .   6
5.  Error Signaling . . . . . . . . . . . . . . . . . . . . . . .   7
6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
8.  Differences from RFC 6253 . . . . . . . . . . . . . . . . . .   8
9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
  9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
  9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
Appendix A.  X.509 v3 Certificate Example . . . . . . . . . . . .  11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  13
Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1. Introduction ✨

Okay so digital certificates tie a piece of info to a public key using a digital signature 🔐 That lets whoever holds the private key make statements that can be cryptographically verified. HIP [RFC7401] defines a brand new cryptographic namespace built on asymmetric cryptography. Each host's identity comes from a public key, so hosts can digitally sign data and issue certificates with their private key 🦋

This document specifies the CERT parameter, which is how digital certificates get sent in HIP. It fills the placeholder from Section 5.2 of [RFC7401], so it updates [RFC7401] 💅

1.1. 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 RFC 2119 [RFC2119] 🎀

2. CERT Parameter 📦

The CERT parameter is a container for certain types of digital certificates. It doesn't specify any certificate semantics 🙈 What it does do is define supplementary parameters that help HIP hosts send semantically grouped CERT parameters in a more systematic way ✨ How the CERT parameter gets used for different use cases is intentionally not discussed here. So the use of the CERT parameter will be defined in the documents that use it 🫶

The CERT parameter is covered and protected, when present, by the HIP SIGNATURE field. It's a non-critical parameter 💖

The CERT parameter can be used in all HIP packets. Just know that using it in the first Initiator (I1) packet is NOT RECOMMENDED 🚫 because it can increase the processing times of I1s, which can be a problem when there are processing storms of I1s 😭 Each HIP control packet MAY contain multiple CERT parameters, each carrying one certificate 🌈 These parameters MAY be related or unrelated. Related certificates are managed in CERT groups. A CERT group is a group of related CERT parameters that SHOULD be interpreted in a certain order (for example, for expressing certificate chains) 🔗 Ungrouped certificates have a unique CERT group field and set the CERT count to 1. CERT parameters with the same group number in the CERT group field indicate a logical grouping. The CERT count field tells you how many CERT parameters are in the group 🍓

CERT parameters that belong to the same CERT group MAY be contained in multiple sequential HIP control packets. You can tell this is happening when the CERT count is higher than the number of CERT parameters with matching CERT group fields in a HIP control packet 👀 The CERT parameters MUST be placed in ascending order within a HIP control packet, according to their CERT group field. CERT groups MAY only span multiple packets if the CERT group doesn't fit in the packet. And a HIP packet MUST NOT contain more than one incomplete CERT group that continues in the next HIP control packet 🧩

The CERT ID acts as a sequence number to identify the certificates in a CERT group 🔢 The numbers in the CERT ID field MUST start from 1 up to CERT count.

The CERT group and CERT ID namespaces are managed locally by each host that sends CERT parameters in HIP control packets 🏠

Here's the packet layout:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  CERT group   |  CERT count   |    CERT ID    |   CERT type   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Certificate                          /
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     /                               |   Padding (variable length)   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

And here's what each field means 🎀

     Type          768
     Length        Length in octets, excluding Type, Length, and
                   Padding.
     CERT group    Group ID grouping multiple related CERT parameters.
     CERT count    Total count of certificates that are sent, possibly
                   in several consecutive HIP control packets.
     CERT ID       The sequence number for this certificate.
     CERT Type     Indicates the type of the certificate.
     Padding       Any Padding, if necessary, to make the TLV a multiple
                   of 8 bytes.  Any added padding bytes MUST be zeroed
                   by the sender, and their values SHOULD NOT be checked
                   by the receiver.

The certificates MUST use the algorithms defined in [RFC7401] as the signature and hash algorithms 🔐

These certificate types are defined 👑

          +--------------------------------+-------------+
          |          CERT format           | Type number |
          +--------------------------------+-------------+
          |            Reserved            |      0      |
          |            X.509 v3            |      1      |
          |           Obsoleted            |      2      |
          |    Hash and URL of X.509 v3    |      3      |
          |           Obsoleted            |      4      |
          |      LDAP URL of X.509 v3      |      5      |
          |           Obsoleted            |      6      |
          | Distinguished Name of X.509 v3 |      7      |
          |           Obsoleted            |      8      |
          +--------------------------------+-------------+

The next bits outline how HITs get used in X.509 v3 🧚 X.509 v3 certificates and their handling procedures are defined in [RFC5280]. The wire format for X.509 v3 is the Distinguished Encoding Rules format, as defined in [X.690] 🌸

Hash and Uniform Resource Locator (URL) encoding (3) is used as defined in Section 3.6 of [RFC7296]. Using hash and URL encodings gives you smaller HIP control packets than including the certificate(s) would, but the receiver has to resolve the URL or check a local cache against the hash 🦋

Lightweight Directory Access Protocol (LDAP) URL encoding (5) is used as defined in [RFC4516]. Using LDAP URL encoding results in smaller HIP control packets, but the receiver has to retrieve the certificate or check a local cache against the URL 💜

Distinguished Name (DN) encoding (7) is represented by the string representation of the certificate's subject DN as defined in [RFC4514]. Using the DN encoding results in smaller HIP control packets, but the receiver has to retrieve the certificate or check a local cache against the DN 🌈

X.509 v3 Certificate Object and Host Identities 🎀

okay so bestie, HITs can represent an issuer, a subject, or both in X.509 v3 🦋 and they're written as IPv6 addresses, as defined in [RFC7343] ✨. when the Host Identifier (HI) is used to sign the certificate, the HIT SHOULD go into the Issuer Alternative Name (IAN) extension, using the GeneralName form iPAddress as defined in [RFC5280] 💅. and when the certificate is issued for a HIP host (identified by a HIT and an HI), the HIT SHOULD go into the Subject Alternative Name (SAN) extension using the GeneralName form iPAddress, and the full HI gets presented as the subject's public key info as defined in [RFC5280] 🫶

here's how it looks, it's giving very clean energy 🌸

Format of X509v3 extensions:
    X509v3 Issuer Alternative Name:
        IP Address:hit-of-issuer
    X509v3 Subject Alternative Name:
        IP Address:hit-of-subject

Example X509v3 extensions:
    X509v3 Issuer Alternative Name:
        IP Address:2001:24:6cf:fae7:bb79:bf78:7d64:c056
    X509v3 Subject Alternative Name:
        IP Address:2001:2c:5a14:26de:a07c:385b:de35:60e3

Appendix A has a full example X.509 v3 certificate with HIP content 🧚

now here's a fun one 🙈 imagine a managed Public Key Infrastructure (PKI) environment where the peers have certificates anchored in (potentially different) managed trust chains. in this setup, the certificates for HIP hosts are signed by intermediate Certification Authorities (CAs) all the way up to a root CA. and the tea is that this managed PKI is neither HIP aware nor able to compute HITs and put them in the certificates 💀

so when HIP communications get set up, the HIP hosts not only need to send their identity certificates (or pointers to them) but also the chain of intermediate CAs (or pointers to the CAs) up to the root CA, or to a CA that the remote peer trusts 👑 this chain of certificates SHOULD be sent in a CERT group as specified in Section 2. the HIP peers validate each other's certificates and compute peer HITs based on the certificate public keys 💜

4. Revocation of Certificates 🥀

revocation of X.509 v3 certificates is handled as defined in Section 5 of [RFC5280], with two exceptions 🍓 first, any HIP certificate serial number that shows up on the Certificate Revocation List (CRL) is treated as invalid regardless of the reason code 😭 second, the certificateHold is not supported 🚫

5. Error Signaling 🚨

if the Initiator doesn't send all the certificates the Responder needs, the Responder MAY take actions (e.g., reject the connection) 🙅‍♀️ the Responder MAY signal this to the Initiator by sending a HIP NOTIFY message with NOTIFICATION parameter error type CREDENTIALS_REQUIRED ✨

if verification of a certificate fails, a verifier MAY signal this to the provider of the certificate by sending a HIP NOTIFY message with NOTIFICATION parameter error type INVALID_CERTIFICATE 💌

NOTIFICATION PARAMETER - ERROR TYPES     Value
------------------------------------     -----

CREDENTIALS_REQUIRED                      48

The Responder is unwilling to set up an association,
as the Initiator did not send the needed credentials.

INVALID_CERTIFICATE                       50

Sent in response to a failed verification of a certificate.
Notification Data MAY contain a CERT group and CERT ID octet
(in this order) of the CERT parameter that caused the
failure.

6. IANA Considerations 📋

this document defines the CERT parameter for HIP [RFC7401] ✨ the CERT parameter type number (768) is defined in [RFC7401] 🔢

the CERT parameter has an 8-bit unsigned integer field for different certificate types, and IANA has created and maintains a subregistry called "HIP Certificate Types" under "Host Identity Protocol (HIP) Parameters" 🗂️ values for the "HIP Certificate Types" registry are given in Section 2 🌈 new values for the Certificate types from the unassigned space get assigned through IETF Review 🧐

in Section 5, this document defines two types for the "NOTIFY Message Types" subregistry under "Host Identity Protocol (HIP) Parameters" 🎯

as this document obsoletes [RFC6253], references to [RFC6253] in IANA registries have been replaced by references to this document 🔄 this document changes the "HIP Certificate Types" registry in Section 2 💫

the following updates to the "HIP Certificate Types" registry have been made 💖

the references have been updated from [RFC6253] to this document.
this document obsoleted the type numbers "2", "4", "6", and "8" for the Simple Public Key Infrastructure (SPKI) certificates.

7. Security Considerations 🚨🔐

okay this section is SERIOUS bestie, so pay attention 😤

certificate grouping lets the certificates get sent across multiple consecutive packets. this might allow similar attacks to the ones IP-layer fragmentation allows 😱 for example, sending fragments in the wrong order and skipping some fragments to delay or stall packet processing by the victim, so they burn through resources (e.g., CPU or memory) 🔥 hence, hosts SHOULD implement mechanisms to discard certificate groups with outstanding certificates if state space is scarce 🛡️

although the CERT parameter is allowed in the I1 packet, it is NOT RECOMMENDED because it can increase the processing times of I1s, which can be a problem when there are processing storms of I1s 🌪️ furthermore, the Initiator has to keep in mind that the Responder can drop the CERT parameter in I1 without processing it 👀

checking the URL and LDAP entries might allow denial-of-service (DoS) attacks, where the target host gets subjected to bogus work 💀

security considerations for X.509 v3 are discussed in [RFC5280] 📚

8. Differences from RFC 6253 🔍

this section summarizes the technical changes made from [RFC6253] 🍰 this section is informational and is meant to help implementors of the previous protocol version 🧠 if any text in this section contradicts text in other portions of this specification, the text found outside of this section should be considered normative 📜

the following change has been made 🎀

support for SPKI certificates has been removed.

9. References 📚

9.1. 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, <http://www.rfc-editor.org/info/rfc2119>.

[RFC4514] Zeilenga, K., Ed., "Lightweight Directory Access Protocol (LDAP): String Representation of Distinguished Names", RFC 4514, DOI 10.17487/RFC4514, June 2006, <http://www.rfc-editor.org/info/rfc4514>.

[RFC4516] Smith, M., Ed. and T. Howes, "Lightweight Directory Access Protocol (LDAP): Uniform Resource Locator", RFC 4516, DOI 10.17487/RFC4516, June 2006, <http://www.rfc-editor.org/info/rfc4516>.

[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, DOI 10.17487/RFC5280, May 2008, <http://www.rfc-editor.org/info/rfc5280>.

[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014, <http://www.rfc-editor.org/info/rfc7296>.

[RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay Routable Cryptographic Hash Identifiers Version 2 (ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September 2014, <http://www.rfc-editor.org/info/rfc7343>.

[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. Henderson, "Host Identity Protocol Version 2 (HIPv2)", RFC 7401, DOI 10.17487/RFC7401, April 2015, <http://www.rfc-editor.org/info/rfc7401>.

[X.690] ITU-T, , "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 | ISO/IEC 8825-1, August 2015.

9.2. Informative References 🌷

[RFC6253] Heer, T. and S. Varjonen, "Host Identity Protocol Certificates", RFC 6253, DOI 10.17487/RFC6253, May 2011, <http://www.rfc-editor.org/info/rfc6253>.

Appendix A. X.509 v3 Certificate Example ✨

Okay so this section shows an X.509 v3 certificate with the HITs encoded inside it 🎀 Here's the whole thing, dump and all:

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 12705268244493839545 (0xb0522e27291b2cb9)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: DC=Example, DC=com, CN=Example issuing host
        Validity
            Not Before: Feb 25 11:28:29 2016 GMT
            Not After : Feb 24 11:28:29 2017 GMT
        Subject: DC=Example, DC=com, CN=Example issuing host
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:c9:b0:85:94:af:1f:3a:77:39:c9:d5:81:a5:ee:
                    d2:b5:6b:72:91:5d:22:2c:1e:59:e5:06:29:bd:a2:
                    19:f6:ac:ca:eb:f7:88:d8:54:55:41:01:58:d8:87:
                    64:d8:c8:cf:6e:c2:38:81:22:1a:ae:e9:a6:80:22:
                    03:ee:f3:1b:7e:68:11:e3:f4:7b:98:33:28:bf:40:
                    ec:4f:19:e8:10:8a:8b:07:60:f7:9f:e4:82:f8:a7:
                    58:04:3d:42:07:c8:34:ca:99:6d:11:eb:73:c1:d9:
                    96:93:55:e5:c7:ed:80:4f:8a:f2:1a:6f:83:c8:15:
                    a4:8f:b8:6a:fe:f3:4f:49:1a:5c:1f:89:bb:30:e6:
                    98:bc:ce:a3:a2:37:85:b1:79:1c:26:e6:44:0c:b9:
                    3e:d8:37:81:46:f4:02:25:46:a2:ea:da:25:5c:46:
                    a2:a3:c5:58:80:53:1f:c5:e5:11:a0:da:d8:f2:ad:
                    d6:98:d4:ce:55:35:cc:0b:d3:5b:09:48:ef:57:65:
                    80:cb:65:79:fd:cb:4d:5b:b3:8d:1a:ff:2a:58:3e:
                    96:65:10:3e:04:81:78:2b:d5:ca:89:78:ea:28:5c:
                    bc:02:4a:54:cd:aa:a9:99:8d:d6:39:e9:5e:a9:73:
                    1a:5d:93:55:39:9b:72:1a:c2:a0:1f:e3:4c:b0:41:
                    98:97
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Alternative Name:
                IP Address:2001:27:DCFC:CB8:F885:D53F:4E63:48B7
            X509v3 Issuer Alternative Name:
                IP Address:2001:2D:F878:64C1:67E3:9716:88BD:68E4

    Signature Algorithm: sha256WithRSAEncryption
         6d:e6:a9:a6:30:c4:ab:3e:86:39:1e:de:76:4d:4e:a4:2d:63:
         4d:bb:41:bf:d3:0c:66:13:8b:4d:b2:50:59:36:fc:ae:42:9e:
         c8:a0:41:1a:1c:94:56:05:28:82:34:4e:63:75:87:31:25:67:
         36:a6:1a:0f:b8:f7:db:03:e7:dd:a6:9a:26:c4:68:e2:cf:59:
         54:e6:ee:cc:a7:ce:fb:56:bf:31:60:f4:cb:e7:f0:0e:50:f8:
         b7:c5:3c:1a:de:74:d0:aa:83:e5:15:25:b1:bf:be:a4:7f:af:
         0a:de:08:09:0e:13:1d:2a:3b:1a:99:d9:af:10:fc:08:92:5f:
         d8:d0:10:d6:b9:0c:86:da:85:3b:44:b5:97:90:10:02:4f:5a:
         1f:ae:07:30:6b:f5:e6:12:93:72:e2:10:c9:8e:2c:00:8b:d6:
         f0:05:c3:ff:91:24:69:6d:5b:5a:0c:40:28:01:f2:5b:45:b8:
         9b:ae:9e:73:e9:dd:83:e0:85:d7:ad:6c:b1:81:ac:a0:30:37:
         9d:60:bd:92:3b:d2:a1:21:87:8b:c4:d9:5a:5c:21:56:3e:02:
         7e:f3:6f:a5:de:40:75:80:f5:41:68:5c:b2:61:fb:1d:9a:a5:
         97:a8:d4:a9:82:45:86:79:3c:63:76:3d:fd:86:a0:f8:14:84:
         55:c1:8c:fa

And here's the same certificate in PEM form 💜

Acknowledgments 🫶

The authors wanna give a huge shoutout to A. Keranen, D. Mattes, M. Komu, and T. Henderson for the fruitful conversations on the subject ✨ D. Mattes most notably contributed the non-HIP-aware use case in Section 3 💅

Authors' Addresses 🦋

Here are the authors and how to reach them, bestie 💌

Tobias Heer
Albstadt-Sigmaringen University
Poststr. 6
72458 Albstadt
Germany

Email: heer@hs-albsig.de

Samu Varjonen
University of Helsinki
Gustaf Haellstroemin katu 2b
00560 Helsinki
Finland

Email: samu.varjonen@helsinki.fi

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