shoemaker-acme-ip-00.txt

Internet DRAFT - draft-shoemaker-acme-ip

draft-shoemaker-acme-ip

Last Version:	draft-shoemaker-acme-ip-00.txt	Tracker Entry
Date:	`28-Mar-2017`
Disposition:	.draft-ietf-acme-ip

Network Working Group R. Shoemaker
Internet-Draft ISRG
Intended status: Standards Track March 27, 2017
Expires: September 28, 2017

ACME IP Identifier Validation Extension
draft-shoemaker-acme-ip-00

Abstract

This document specifies identifiers and challenges required to enable
the Automated Certificate Management Environment (ACME) to issue
certificates for IP addresses.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on September 28, 2017.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. IP Identifier . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Identifier Validation Challenges . . . . . . . . . . . . . . 3
4.1. Reverse DNS . . . . . . . . . . . . . . . . . . . . . . . 3
4.2. Existing Challenges . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.1. Identifier Types . . . . . . . . . . . . . . . . . . . . 5
5.2. Challenge Types . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6.1. Certificate Lifetime . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6

1. Introduction

The Automatic Certificate Management Environment (ACME)
[I-D.ietf-acme-acme] only defines challenges for validating control
of DNS host name identifiers which limits its use to being used for
issuing certificates for these identifiers. In order to allow
validation of IPv4 and IPv6 identifiers for inclusion in X.509
certificates this document defines a new challenge type and specifies
how challenges defined in the original ACME specification can be used
to validate IP identifiers.

2. Terminology

In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
[RFC2119] and indicate requirement levels for compliant ACME-Wildcard
implementations.

3. IP Identifier

ACME only defines the identifier type "dns" which is used to refer to
fully qualified domain names. If a ACME server wishes to request
proof that a user controls a IPv4 or IPv6 address it MUST create an
authorization with the identifier type "ip". The value field of the
identifier MUST contain the textual form of the address as defined in
RFC 1123 [RFC1123] Section 2.1 for IPv4 and in RFC 4291 [RFC4291]
Section 2.2 for IPv6.

An identifier for the IPv6 address 2001:db8::1 would be formatted
like so:

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{"type": "ip", "value": "2001:db8::1"}

4. Identifier Validation Challenges

When creating an authorization for a identifier with the type "ip"
the following challenge types MAY be used to perform validation.

4.1. Reverse DNS

With Reverse DNS validation the client proves control of an IP
address by provisioning a TXT resource record containing a designated
value for a specific validation domain name constructed using the
value of the PTR record for the reverse mapping of the address.

type (required, string): The string "reverse-dns-01".

token (required, string): A random value that uniquely identifies
the challenge. This value MUST have at least 128 bits of entropy,
in order to prevent an attacker from guessing it. It MUST NOT
contain any characters outside the base64url [RFC4648] alphabet,
including padding characters ("=").

GET /acme/authz/1234/2 HTTP/1.1
Host: example.com

HTTP/1.1 200 OK
{
"type": "reverse-dns-01",
"url": "https://example.com/acme/authz/1234/2",
"status": "pending",
"token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
}

A client responds to this challenge by constructing a key
authorization from the "token" value provided in the challenge and
the client's ACME account key. The client then computes the SHA-256
digest [FIPS180-4] of the key authorization. The record provisioned
to the authoritative DNS server is the base64url encoding of this
digest.

The client constructs the validation domain name by prepending the
label "_acme-challenge" to the domain name referenced in the PTR
resource record for the IN-ADDR.ARPA [RFC1034] or IP6.ARPA [RFC3596]
reverse mapping of the IP address. The client then provisions a TXT
record with the digest for this name.

For example, if the IP address being validated is 2001:db8::1 and its
IP6.ARPA mapping had the following PTR record:

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1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. 300 IN PTR example.com

then the client would provision the following DNS record:

_acme-challenge.example.com. 300 IN TXT "gfj9Xq...Rg85nM"

The response to the Reverse DNS challenge provides the computed key
authorization to acknowledge that the client is ready to fulfill this
challenge.

keyAuthorization (required, string): The key authorization for this
challenge.

POST /acme/authz/1234/2
Host: example.com
Content-Type: application/jose+json

{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/1",
"nonce": "JHb54aT_KTXBWQOzGYkt9A",
"url": "https://example.com/acme/authz/1234/2"
}),
"payload": base64url({
"keyAuthorization": "evaGxfADs...62jcerQ"
}),
"signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4"
}

On receiving a response, the server MUST verify that the key
authorization in the response matches the "token" value in the
challenge and the client's ACME account key. If they do not match,
then the server MUST return an HTTP error in response to the POST
request in which the client sent the challenge.

To validate a DNS challenge, the server performs the following steps:

1. Compute the SHA-256 digest of the key authorization

2. Query for a PTR record for the IP identifiers relevant reverse
mapping based on its version

3. Query for TXT records for the computed validation domain name

4. Verify that the contents of one of the TXT records matches the
digest value

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If all of the above verifications succeed, then the validation is
successful. If no PTR or TXT DNS records are found, or the returned
TXT records do not contain the expected key authorization digest,
then the validation fails.

4.2. Existing Challenges

IP identifiers MAY be used with the existing "http-01" and "tls-sni-
02" challenges from RFC XXXX Sections XXX and XXX respectively. To
use IP identifiers with these challenges their initial DNS resolution
step MUST be skipped and the address used for validation MUST be the
value of the identifier.

The existing "dns-01" challenge MUST NOT be used to validate IP
identifiers.

5. IANA Considerations

5.1. Identifier Types

Adds a new type to the Identifier list defined in Section XXX of RFC
XXXX with the label "ip" and reference RFC XXXX.

5.2. Challenge Types

Adds a new type to the Challenge list defined in Section XXX of RFC
XXXX with the label "reverse-dns-01", identifier type "ip", and
reference RFC XXXX.

Add the value "ip" to the identifier type column for the "http-01"
and "tls-sni-02" challenges.

6. Security Considerations

6.1. Certificate Lifetime

Given the often short delegation periods for IP addresses provided by
various service providers CAs MAY want to impose shorter lifetimes
for certificates which contain IP identifiers. They MAY also impose
restrictions on IP identifiers which are in CIDRs known to be
assigned to service providers who dynamically assign addresses to
users for indeterminate periods of time.

7. Normative References

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[FIPS180-4]
Department of Commerce, National., "NIST FIPS 180-4,
Secure Hash Standard", March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>.

[I-D.ietf-acme-acme]
Barnes, R., Hoffman-Andrews, J., and J. Kasten, "Automatic
Certificate Management Environment (ACME)", draft-ietf-
acme-acme-06 (work in progress), March 2017.

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.

[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123, DOI 10.17487/
RFC1123, October 1989,
<http://www.rfc-editor.org/info/rfc1123>.

[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>.

[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", RFC 3596, DOI
10.17487/RFC3596, October 2003,
<http://www.rfc-editor.org/info/rfc3596>.

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>.

[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<http://www.rfc-editor.org/info/rfc4648>.

Author's Address

Roland Bracewell Shoemaker
Internet Security Research Group

Email: roland@letsencrypt.org

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