RFC 6253
Host Identity Protocol Certificates
RFC 6253: Host Identity Protocol Certificates 🎀
bestie, okay so this is RFC 6253, called Host Identity Protocol Certificates 🦋. It was written by T. Heer (COMSYS, RWTH Aachen University) and S. Varjonen (Helsinki Institute for Information Technology) and published in May 2011. It's an Experimental doc with ISSN 2070-1721, and it updates RFC 5201 💖.
Abstract ✨
So the CERT parameter is basically a container for digital certificates 📦. It's how those certs ride along in Host Identity Protocol (HIP) control packets. This doc specifies the CERT parameter and the error signaling for when a verification fails 🙈. It also covers how Host Identity Tags get represented in X.509 version 3 (v3) and Simple Public Key Infrastructure (SPKI) certificates 🔑.
Here's the tea: how certs get obtained, requested, and what happens after they verify (or don't) depends on the scenario they're used in 💅. So those scenario-specific bits are left to the documents that actually use the CERT parameter.
This document updates RFC 5201.
Status of This Memo 📝
ngl, this one is not an Internet Standards Track spec. It's published for examination, experimental implementation, and evaluation 🧪.
It defines an Experimental Protocol for the Internet community. It's a product of the Internet Engineering Task Force (IETF) and represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every IESG-approved doc is a candidate for any level of Internet Standard, so check Section 2 of RFC 5741 for that 🫶.
For info on the current status, any errata, and how to give feedback, look at http://www.rfc-editor.org/info/rfc6253 ✨.
Copyright Notice ⚖️
Copyright (c) 2011 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. Please review these documents carefully, because 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 📜.
This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English 🌈.
1. Introduction 🌸
Digital certificates bind pieces of information to a public key by means of a digital signature. That's how the holder of a private key can generate cryptographically verifiable statements 🔐. The Host Identity Protocol (HIP) [RFC5201] defines a new cryptographic namespace based on asymmetric cryptography. Each host's identity is derived 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 used to transmit digital certificates in HIP. It fills the placeholder specified in Section 5.2 of [RFC5201] and thus updates [RFC5201] 🦋.
1.1. Requirements Language
bestie, these caps words are the important ones 🙏. 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 does not specify any certificate semantics. BUT it does define supplementary parameters that help HIP hosts transmit semantically grouped CERT parameters in a more systematic way ✨. The specific use of the CERT parameter for different use cases is intentionally not discussed in this document, because it's specific to a concrete use case. So the use of the CERT parameter will be defined in the documents that use the CERT parameter 💅.
The CERT parameter is covered and protected, when present, by the HIP SIGNATURE field and is a non-critical parameter 🛡️.
The CERT parameter can be used in all HIP packets. However, using it in the first Initiator (I1) packet is NOT RECOMMENDED, because it can increase the processing times of I1s, which can be problematic when processing storms of I1s 🙈. Each HIP control packet MAY contain multiple CERT parameters. These parameters MAY be related or unrelated. Related certificates are managed in Cert groups. A Cert group specifies a group of related CERT parameters that SHOULD be interpreted in a certain order (e.g., for expressing certificate chains). For grouping CERT parameters, the Cert group and the Cert count field MUST be set. Ungrouped certificates exhibit a unique Cert group field and set the Cert count to 1. CERT parameters with the same Cert group number in the group field indicate a logical grouping. The Cert count field indicates the number of CERT parameters in the group 🧩.
CERT parameters that belong to the same Cert group MAY be contained in multiple sequential HIP control packets. This is indicated by a higher Cert count than the amount 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 does not fit the packet. 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 layout, so you can see exactly how the fields sit together 👀:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+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.The certificates MUST use the algorithms defined in [RFC5201] as the signature and hash algorithms 🔥.
The following certificate types are defined 🧁:
+--------------------------------+-------------+
| Cert format | Type number |
+--------------------------------+-------------+
| Reserved | 0 |
| X.509 v3 | 1 |
| SPKI | 2 |
| Hash and URL of X.509 v3 | 3 |
| Hash and URL of SPKI | 4 |
| LDAP URL of X.509 v3 | 5 |
| LDAP URL of SPKI | 6 |
| Distinguished Name of X.509 v3 | 7 |
| Distinguished Name of SPKI | 8 |
+--------------------------------+-------------+The next sections outline the use of Host Identity Tags (HITs) in X.509 v3 and in Simple Public Key Infrastructure (SPKI) certificates 🌷. 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]. The SPKI, its handling procedures, and its formats are defined in [RFC2693].
Hash and Uniform Resource Locator (URL) encodings (3 and 4) are used as defined in Section 3.6 of [RFC5996]. Using hash and URL encodings results in smaller HIP control packets than including the certificate(s) would, but it requires the receiver to resolve the URL or check a local cache against the hash 🔗.
Lightweight Directory Access Protocol (LDAP) URL encodings (5 and 6) are used as defined in [RFC4516]. Using LDAP URL encoding results in smaller HIP control packets, but it requires the receiver to retrieve the certificate or check a local cache against the URL 📚.
Distinguished Name (DN) encodings (7 and 8) are 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 it requires the receiver to retrieve the certificate or check a local cache against the DN 🧚.
part 1 of 2 done, part 2 is coming 🦋💜
3. X.509 v3 Certificate Object and Host Identities ✨
okay so bestie, X.509 v3 certs can carry HITs too, if they're needed 🎀 HITs get written as IPv6 addresses (the RFC4843 ORCHID prefix thing 🦋). When the Host Identifier (HI) is used to sign the certificate, the HIT MUST go into the Issuer Alternative Name (IAN) extension as a GeneralName iPAddress, per [RFC5280] 💅. And when the cert is for a HIP host, identified by a HIT and HI, the HIT MUST go into the Subject Alternative Name (SAN) extension, also as an iPAddress, and the full HI shows up as the subject's public key info 🫶
here's how it looks, with the format first:
X509v3 Issuer Alternative Name:
IP Address:hit-of-issuer
X509v3 Subject Alternative Name:
IP Address:hit-of-subjectand an example:
X509v3 Issuer Alternative Name:
IP Address:2001:14:6cf:fae7:bb79:bf78:7d64:c056
X509v3 Subject Alternative Name:
IP Address:2001:1c:5a14:26de:a07c:385b:de35:60e3Appendix B has a full X.509 v3 cert with HIP content, so go peek at that later 👀
now the managed PKI case, which is giving real-world vibes 🌸 peers have certs anchored in (maybe different) managed trust chains. The certs for HIP hosts get signed by intermediate Certification Authorities (CAs) all the way up to a root CA. This managed PKI is neither HIP aware, nor can it be set up to compute HITs and put them in the certs 😭
so when HIP comms get set up, the hosts don't just send their identity certs (or pointers to them). They ALSO send the chain of intermediate CAs (or pointers to those) up to the root CA, or to a CA the remote peer already trusts 🔥 That chain MUST be sent in a Cert group, as Section 2 says. Then the HIP peers check each other's certs and compute peer HITs from the cert public keys 🧚
4. SPKI Cert Object and Host Identities 💜
when you use SPKI certs to carry HIP host info, the HITs have to be tucked inside the certs 🎀 They can be the issuer, the subject, or both. Here we define how those identifiers look for SPKI written as S-expressions. Quick reminder: S-expressions are only the human-readable version of SPKI certs, and the full HIs live in the public key sequences of the SPKI certs 🦋
for example, a host's Host Identity Tag looks like this:
Format: (hash hit hit-of-host)
Example: (hash hit 2001:13:724d:f3c0:6ff0:33c2:15d8:5f50)Appendix A has a full SPKI cert with HIP content 💖
5. Revocation of Certificates 🥀
revoking X.509 v3 certs works exactly as Section 5 of [RFC5280] says. Revoking SPKI certs works as Section 5 of [RFC2693] says 💅
6. Error Signaling 🚨
if the Initiator doesn't send the cert the Responder needs, the Responder MAY take action, like rejecting the connection. The Responder MAY tell the Initiator about it by sending a HIP NOTIFY message with a NOTIFICATION parameter, error type CREDENTIALS_REQUIRED 🙈
if a cert fails verification, a verifier MAY tell the cert's provider by sending a HIP NOTIFY message with a NOTIFICATION parameter, error type INVALID_CERTIFICATE 😭
here are the error types:
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 n groups of 2 octets (n calculated
from the NOTIFICATION parameter length), in order Cert group and
Cert ID of the Certificate parameter that caused the failure.7. IANA Considerations 🌈
this doc defines the CERT parameter for the Host Identity Protocol [RFC5201]. It's defined in Section 2 with type 768, and that type number is also defined in [RFC5201] 🎀
the CERT parameter has an 8-bit unsigned integer field for different cert types. IANA made and now maintains a new sub-registry called "HIP Certificate Types" under the "Host Identity Protocol (HIP) Parameters" 📋 The initial values for the Certificate type registry are in Section 2. New values from the unassigned space get assigned through IETF Review ✨
in Section 6, this doc defines two new types for the "NOTIFY Message Types" sub-registry under "Host Identity Protocol (HIP) Parameters" 🍓
8. Security Considerations 🔒
okay this section is SERIOUS bestie 😭 Certificate grouping lets certs get sent across multiple consecutive packets. That might allow similar attacks to the ones IP-layer fragmentation allows. For example, sending fragments in the wrong order, or skipping some fragments, to delay or stall packet processing on the victim so they burn through resources (like CPU or memory) 💀 So hosts SHOULD implement mechanisms to discard certificate groups with outstanding certificates when state space is scarce 🛡️
checking the URL and LDAP entries might allow denial-of-service (DoS) attacks, where the target host gets hit with bogus work 🙅♀️
security considerations for SPKI certs are in [RFC2693], and for X.509 v3 they're in [RFC5280] 📚
9. Acknowledgements 🫶
the authors want to thank A. Keranen, D. Mattes, M. Komu, and T. Henderson for the fruitful conversations on this topic. D. Mattes especially contributed the non-HIP aware use case in Section 3 🌸
10. Normative References 📖
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2693] Ellison, C., Frantz, B., Lampson, B., Rivest, R., Thomas,
B., and T. Ylonen, "SPKI Certificate Theory", RFC 2693,
September 1999.
[RFC4514] Zeilenga, K., Ed., "Lightweight Directory Access Protocol
(LDAP): String Representation of Distinguished Names",
RFC 4514, June 2006.
[RFC4516] Smith, M., Ed., and T. Howes, "Lightweight Directory
Access Protocol (LDAP): Uniform Resource Locator",
RFC 4516, June 2006.
[RFC4843] Nikander, P., Laganier, J., and F. Dupont, "An IPv6 Prefix
for Overlay Routable Cryptographic Hash Identifiers
(ORCHID)", RFC 4843, April 2007.
[RFC5201] Moskowitz, R., Nikander, P., Jokela, P., Ed., and T.
Henderson, "Host Identity Protocol", RFC 5201, April 2008.
[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.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[X.690] ITU-T, "Recommendation X.690 (2002) | ISO/IEC 8825-1:2002,
Information Technology - ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", July 2002.Appendix A. SPKI Certificate Example 🧾
this section shows an SPKI cert with encoded HITs. The example has been indented so it's easier to read 👀
(sequence
(public_key
(rsa-pkcs1-sha1
(e #010001#)
(n |yDwznOwX0w+zvQbpWoTnfWrUPLKW2NFrpXbsIcH/QBSLb
k1RKTZhLasFwvtSHAjqh220W8gRiQAGIqKplyrDEqSrJp
OdIsHIQ8BQhJAyILWA1Sa6f5wAnWozDfgdXoKLNdT8ZNB
mzluPiw4ozc78p6MHElH75Hm3yHaWxT+s83M=|
)
)
)
(cert
(issuer
(hash hit 2001:15:2453:698a:9aa:253a:dcb5:981e)
)
(subject
(hash hit 2001:12:ccd6:4715:72a3:2ab1:77e4:4acc)
)
(not-before "2011-01-12_13:43:09")
(not-after "2011-01-22_13:43:09")
)
(signature
(hash sha1 |h5fC8HUMATTtK0cjYqIgeN3HCIMA|)
|u8NTRutINI/AeeZgN6bngjvjYPtVahvY7MhGfenTpT7MCgBy
NoZglqH5Cy2vH6LrQFYWx0MjWoYwHKimEuBKCNd4TK6hrCyAI
CIDJAZ70TyKXgONwDNWPOmcc3lFmsih8ezkoBseFWHqRGISIm
MLdeaMciP4lVfxPY2AQKdMrBc=|
)
)Appendix B. X.509 v3 Certificate Example 🎀
this section shows an X.509 v3 cert with encoded HITs 💅
Certificate:
Data:
Version: 3 (0x2)
Serial Number: 0 (0x0)
Signature Algorithm: sha1WithRSAEncryption
Issuer: CN=Example issuing host, DC=example, DC=com
Validity
Not Before: Mar 11 09:01:39 2011 GMT
Not After : Mar 21 09:01:39 2011 GMT
Subject: CN=Example subject host, DC=example, DC=com
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
RSA Public Key: (1024 bit)
Modulus (1024 bit):
00:c0:db:38:50:8e:63:ed:96:ea:c6:c4:ec:a3:36:
62:e2:28:e9:74:9c:f5:2f:cb:58:0e:52:54:60:b5:
fa:98:87:0d:22:ab:d8:6a:61:74:a9:ee:0b:ae:cd:
18:6f:05:ab:69:66:42:46:00:a2:c0:0c:3a:28:67:
09:cc:52:27:da:79:3e:67:d7:d8:d0:7c:f1:a1:26:
fa:38:8f:73:f5:b0:20:c6:f2:0b:7d:77:43:aa:c7:
98:91:7e:1e:04:31:0d:ca:94:55:20:c4:4f:ba:b1:
df:d4:61:9d:dd:b9:b5:47:94:6c:06:91:69:30:42:
9c:0a:8b:e3:00:ce:49:ab:e3
Exponent: 65537 (0x10001)
X509v3 extensions:
X509v3 Issuer Alternative Name:
IP Address:2001:13:8d83:41c5:dc9f:38ed:e742:7281
X509v3 Subject Alternative Name:
IP Address:2001:1c:6e02:d3e0:9b90:8417:673e:99db
Signature Algorithm: sha1WithRSAEncryption
83:68:b4:38:63:a6:ae:57:68:e2:4d:73:5d:8f:11:e4:ba:30:
a0:19:ca:86:22:e9:6b:e9:36:96:af:95:bd:e8:02:b9:72:2f:
30:a2:62:ac:b2:fa:3d:25:c5:24:fd:8d:32:aa:01:4f:a5:8a:
f5:06:52:56:0a:86:55:39:2b:ee:7a:7b:46:14:d7:5d:15:82:
4d:74:06:ca:b7:8c:54:c1:6b:33:7f:77:82:d8:95:e1:05:ca:
e2:0d:22:1d:86:fc:1c:c4:a4:cf:c6:bc:ab:ec:b8:2a:1e:4b:
04:7e:49:9c:8f:9d:98:58:9c:63:c5:97:b5:41:94:f7:ef:93:
57:29Authors' Addresses 💌
Tobias Heer Chair of Communication and Distributed Systems - COMSYS RWTH Aachen University Ahornstrasse 55 Aachen Germany
Phone: +49 241 80 20 776 EMail: heer@cs.rwth-aachen.de URI: http://www.comsys.rwth-aachen.de/team/tobias-heer/
Samu Varjonen Helsinki Institute for Information Technology Gustaf Haellstroemin katu 2b Helsinki Finland
EMail: samu.varjonen@hiit.fi URI: http://www.hiit.fi
📦 where this page comes from
- ietf: rfc6253 2011-05
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms