draft-ietf-acme-tls-alpn-06.txt   draft-ietf-acme-tls-alpn-07.txt 
ACME Working Group R. Shoemaker ACME Working Group R. Shoemaker
Internet-Draft ISRG Internet-Draft ISRG
Intended status: Standards Track September 05, 2019 Intended status: Standards Track October 01, 2019
Expires: March 8, 2020 Expires: April 3, 2020
ACME TLS ALPN Challenge Extension ACME TLS ALPN Challenge Extension
draft-ietf-acme-tls-alpn-06 draft-ietf-acme-tls-alpn-07
Abstract Abstract
This document specifies a new challenge for the Automated Certificate This document specifies a new challenge for the Automated Certificate
Management Environment (ACME) protocol which allows for domain Management Environment (ACME) protocol that allows for domain control
control validation using TLS. validation using TLS.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on March 8, 2020. This Internet-Draft will expire on April 3, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. TLS with Application Layer Protocol Negotiation (TLS ALPN) 3. TLS with Application Layer Protocol Negotiation (TLS ALPN)
Challenge . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Challenge . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. acme-tls/1 Protocol Definition . . . . . . . . . . . . . . . 5 4. acme-tls/1 Protocol Definition . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6.1. SMI Security for PKIX Certificate Extension OID . . . . . 6 6.1. SMI Security for PKIX Certificate Extension OID . . . . . 6
6.2. ALPN Protocol ID . . . . . . . . . . . . . . . . . . . . 6 6.2. ALPN Protocol ID . . . . . . . . . . . . . . . . . . . . 6
6.3. ACME Validation Method . . . . . . . . . . . . . . . . . 6 6.3. ACME Validation Method . . . . . . . . . . . . . . . . . 7
7. Appendix: Design Rationale . . . . . . . . . . . . . . . . . 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 8. Normative References . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . 8 Appendix A. Design Rationale . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
The Automatic Certificate Management Environment (ACME) [RFC8555] The Automatic Certificate Management Environment (ACME) [RFC8555]
standard specifies methods for validating control of domain names via specification describes methods for validating control of domain
HTTP and DNS. Deployment experience has shown it is also useful to names via HTTP and DNS. Deployment experience has shown it is also
be able to validate domain control using the TLS layer alone. In useful to be able to validate domain control using the TLS layer
particular, this allows hosting providers, CDNs, and TLS-terminating alone. In particular, this allows hosting providers, CDNs, and TLS-
load balancers to validate domain control without modifying the HTTP terminating load balancers to validate domain control without
handling behavior of their backends. This separation of layers can modifying the HTTP handling behavior of their backends.
improve security and usability of ACME validation.
Early ACME drafts specified two TLS-based challenge types: TLS-SNI-01
and TLS-SNI-02. These methods were removed because they relied on
assumptions about the deployed base of HTTPS hosting providers that
proved to be incorrect. Those incorrect assumptions weakened the
security of those methods and are discussed in the "Design Rationale"
appendix.
This document specifies a new TLS-based challenge type, tls-alpn-01. This document specifies a new TLS-based challenge type, tls-alpn-01.
This challenge requires negotiating a new application-layer protocol This challenge requires negotiating a new application-layer protocol
using the TLS Application-Layer Protocol Negotiation (ALPN) Extension using the TLS Application-Layer Protocol Negotiation (ALPN) Extension
[RFC7301]. Because no existing software implements this protocol, [RFC7301]. Because this protocol does not build on a preexisting
the ability to fulfill tls-alpn-01 challenges is effectively opt-in. deployment base, the ability to fulfill tls-alpn-01 challenges is
A service provider must proactively deploy new code in order to effectively opt-in. A service provider must proactively deploy new
implement tls-alpn-01, so we can specify stronger controls in that code in order to implement tls-alpn-01, so we can specify stronger
code, resulting in a stronger validation method. controls in that code, resulting in a stronger validation method.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. TLS with Application Layer Protocol Negotiation (TLS ALPN) Challenge 3. TLS with Application Layer Protocol Negotiation (TLS ALPN) Challenge
The TLS with Application Layer Protocol Negotiation (TLS ALPN) The TLS with Application Layer Protocol Negotiation (TLS ALPN)
validation method proves control over a domain name by requiring the validation method proves control over a domain name by requiring the
client to configure a TLS server to respond to specific connection ACME client to configure a TLS server to respond to specific
attempts utilizing the ALPN extension with identifying information. connection attempts using the ALPN extension with identifying
The ACME server validates control of the domain name by connecting to information. The ACME server validates control of the domain name by
a TLS server at one of the addresses resolved for the domain name and connecting to a TLS server at one of the addresses resolved for the
verifying that a certificate with specific content is presented. domain name and verifying that a certificate with specific content is
presented.
The tls-alpn-01 ACME challenge object has the following format: The tls-alpn-01 ACME challenge object has the following format:
type (required, string): The string "tls-alpn-01" type (required, string): The string "tls-alpn-01"
token (required, string): A random value that uniquely identifies token (required, string): A random value that uniquely identifies
the challenge. This value MUST have at least 128 bits of entropy. the challenge. This value MUST have at least 128 bits of entropy.
It MUST NOT contain any characters outside the base64url alphabet It MUST NOT contain any characters outside the base64url alphabet
as described in [RFC4648] Section 5. Trailing'=' padding as described in [RFC4648] Section 5. Trailing '=' padding
characters MUST be stripped. See [RFC4086] for additional characters MUST be stripped. See [RFC4086] for additional
information on randomness requirements. information on randomness requirements.
The client prepares for validation by constructing a self-signed The client prepares for validation by constructing a self-signed
certificate which MUST contain a acmeIdentifier extension and a certificate that MUST contain an acmeIdentifier extension and a
subjectAlternativeName extension [RFC5280]. The subjectAlternativeName extension [RFC5280]. The
subjectAlternativeName extension MUST contain a single dNSName entry subjectAlternativeName extension MUST contain a single dNSName entry
where the value is the domain name being validated. The where the value is the domain name being validated. The
acmeIdentifier extension MUST contain the SHA-256 digest [FIPS180-4] acmeIdentifier extension MUST contain the SHA-256 digest [FIPS180-4]
of the key authorization [RFC8555] for the challenge. The of the key authorization [RFC8555] for the challenge. The
acmeIdentifier extension MUST be critical so that the certificate acmeIdentifier extension MUST be critical so that the certificate
isn't inadvertently used by non-ACME software. isn't inadvertently used by non-ACME software.
The acmeIdentifier extension is identified by the id-pe- The acmeIdentifier extension is identified by the id-pe-
acmeIdentifier object identifier (OID) in the id-pe arc [RFC5280]: acmeIdentifier object identifier (OID) in the id-pe arc [RFC5280]:
skipping to change at page 4, line 50 skipping to change at page 4, line 43
following steps: following steps:
1. The ACME server computes the expected SHA-256 digest of the key 1. The ACME server computes the expected SHA-256 digest of the key
authorization. authorization.
2. The ACME server resolves the domain name being validated and 2. The ACME server resolves the domain name being validated and
chooses one of the IP addresses returned for validation (the chooses one of the IP addresses returned for validation (the
server MAY validate against multiple addresses if more than one server MAY validate against multiple addresses if more than one
is returned). is returned).
3. The AMCE server initiates a TLS connection to the chosen IP 3. The ACME server initiates a TLS connection to the chosen IP
address, this connection MUST use TCP port 443. The ACME server address. This connection MUST use TCP port 443. The ACME server
MUST provide a ALPN extension with the single protocol name MUST provide an ALPN extension with the single protocol name
"acme-tls/1" and a SNI extension containing only the domain name "acme-tls/1" and an SNI extension containing only the domain name
being validated during the TLS handshake. being validated during the TLS handshake.
4. The ACME server verifies that during the TLS handshake the 4. The ACME server verifies that during the TLS handshake the
application-layer protocol "acme-tls/1" was successfully application-layer protocol "acme-tls/1" was successfully
negotiated (and that the ALPN extension contained only the value negotiated (and that the ALPN extension contained only the value
"acme-tls/1") and that the certificate returned contains: "acme-tls/1") and that the certificate returned contains:
* a subjectAltName extension containing the dNSName being * a subjectAltName extension containing the dNSName being
validated and no other entries validated and no other entries
skipping to change at page 5, line 30 skipping to change at page 5, line 24
that as ACME doesn't support Unicode identifiers all dNSNames MUST be that as ACME doesn't support Unicode identifiers all dNSNames MUST be
encoded using [RFC3492] rules. encoded using [RFC3492] rules.
If all of the above steps succeed then the validation is successful, If all of the above steps succeed then the validation is successful,
otherwise it fails. otherwise it fails.
4. acme-tls/1 Protocol Definition 4. acme-tls/1 Protocol Definition
The "acme-tls/1" protocol MUST only be used for validating ACME tls- The "acme-tls/1" protocol MUST only be used for validating ACME tls-
alpn-01 challenges. The protocol consists of a TLS handshake in alpn-01 challenges. The protocol consists of a TLS handshake in
which the required validation information is transmitted. Once the which the required validation information is transmitted. The "acme-
handshake is completed the client MUST NOT exchange any further data tls/1" protocol does not carry application data, once the handshake
with the server and MUST immediately close the connection. is completed the client MUST NOT exchange any further data with the
server and MUST immediately close the connection. While this
protocol uses X.509 certificates, it does not use the authentication
method described in [RFC5280] and as such does not require a valid
signature on the provided certificate nor require the TLS handshake
to complete successfully. An ACME server may wish to use an off the
shelf TLS stack where it is not simple to allow these divergences in
the protocol as defined. Because of this, an ACME server MAY choose
to withhold authorization if either the certificate signature is
invalid or the handshake doesn't fully complete.
ACME servers that implement "acme-tls/1" MUST only negotiate TLS 1.2
[RFC5246] or higher when connecting to clients for validation.
5. Security Considerations 5. Security Considerations
The design of this challenge relies on some assumptions centered The design of this challenge relies on some assumptions centered
around how a server behaves during validation. around how a HTTPS server behaves during validation.
The first assumption is that when a server is being used to serve The first assumption is that when a HTTPS server is being used to
content for multiple DNS names from a single IP address that it serve content for multiple DNS names from a single IP address it
properly segregates control of those names to the users that own properly segregates control of those names to the users that own
them. This means that if User A registers Host A and User B them. This means that if User A registers Host A and User B
registers Host B the server should not allow a TLS request using a registers Host B the HTTPS server should not allow a TLS request
SNI value for Host A to be served by User B or Host B to be served by using an SNI value for Host A to be served by User B or a TLS
User A. If the server allows User B to serve this request it allows connection with a server_name extension identifying Host B to be
them to illegitimately validate control of Host A to the ACME server. answered by User A. If the HTTPS server allows User B to serve this
request it allows them to illegitimately validate control of Host A
to the ACME server.
The second assumption is that a server will not violate [RFC7301] by The second assumption is that a server will not violate [RFC7301] by
blindly agreeing to use the "acme-tls/1" protocol without actually blindly agreeing to use the "acme-tls/1" protocol without actually
understanding it. understanding it.
To further mitigate the risk of users claiming domain names used by To further mitigate the risk of users claiming domain names used by
other users on the same infrastructure hosting providers, CDNs, and other users on the same infrastructure hosting providers, CDNs, and
other service providers SHOULD NOT allow users to provide their own other service providers SHOULD NOT allow users to provide their own
certificates for the TLS ALPN validation process. If providers wish certificates for the TLS ALPN validation process. If providers wish
to implement TLS ALPN validation they SHOULD only generate to implement TLS ALPN validation they SHOULD only generate
certificates used for validation themselves and not expose this certificates used for validation themselves and not expose this
functionality to users. functionality to users.
The extensions to the ACME protocol described in this document build The extensions to the ACME protocol described in this document build
upon the Security Considerations and threat model defined in upon the Security Considerations and threat model defined in
[RFC8555] Section 10.1. [RFC8555] Section 10.1.
6. IANA Considerations 6. IANA Considerations
[[RFC Editor: please replace XXXX below by the RFC number.]] [[RFC Editor: please replace I-D.ietf-acme-tls-alpn below by the RFC
number.]]
6.1. SMI Security for PKIX Certificate Extension OID 6.1. SMI Security for PKIX Certificate Extension OID
Within the SMI-numbers registry, the "SMI Security for PKIX Within the SMI-numbers registry, the "SMI Security for PKIX
Certificate Extension (1.3.6.1.5.5.7.1)" table is to be updated to Certificate Extension (1.3.6.1.5.5.7.1)" table is to be updated to
add the following entry: add the following entry:
+---------+----------------------+------------+ +---------+----------------------+------------------------+
| Decimal | Description | References | | Decimal | Description | References |
+---------+----------------------+------------+ +---------+----------------------+------------------------+
| 31 | id-pe-acmeIdentifier | RFC XXXX | | 31 | id-pe-acmeIdentifier | I-D.ietf-acme-tls-alpn |
+---------+----------------------+------------+ +---------+----------------------+------------------------+
6.2. ALPN Protocol ID 6.2. ALPN Protocol ID
Within the Transport Layer Security (TLS) Extensions registry, the Within the Transport Layer Security (TLS) Extensions registry, the
"Application-Layer Protocol Negotiation (ALPN) Protocol IDs" table is "Application-Layer Protocol Negotiation (ALPN) Protocol IDs" table is
to be updated to add the following entry: to be updated to add the following entry:
+------------+------------------------------------------+-----------+ +------------+-----------------------------+------------------------+
| Protocol | Identification Sequence | Reference | | Protocol | Identification Sequence | Reference |
+------------+------------------------------------------+-----------+ +------------+-----------------------------+------------------------+
| ACME-TLS/1 | 0x61 0x63 0x6d 0x65 0x2d 0x74 0x6c 0x73 | RFC XXXX | | acme-tls/1 | 0x61 0x63 0x6d 0x65 0x2d | I-D.ietf-acme-tls-alpn |
| | 0x2f 0x31 ("acme-tls/1") | | | | 0x74 0x6c 0x73 0x2f 0x31 | |
+------------+------------------------------------------+-----------+ | | ("acme-tls/1") | |
+------------+-----------------------------+------------------------+
6.3. ACME Validation Method 6.3. ACME Validation Method
The "ACME Validation Methods" registry is to be updated to include The "ACME Validation Methods" registry is to be updated to include
the following entry: the following entry:
+-------------+-----------------+-----------+ +-------------+-----------------+------+------------------------+
| Label | Identifier Type | Reference | | Label | Identifier Type | ACME | Reference |
+-------------+-----------------+-----------+ +-------------+-----------------+------+------------------------+
| tls-alpn-01 | dns | RFC XXXX | | tls-alpn-01 | dns | Y | I-D.ietf-acme-tls-alpn |
+-------------+-----------------+-----------+ +-------------+-----------------+------+------------------------+
7. Appendix: Design Rationale
The TLS ALPN challenge exists to replace the TLS SNI challenge
defined in the early ACME drafts. This challenge was convenient for
service providers who were either operating large TLS layer load
balancing systems at which they wanted to perform validation or
running servers fronting large numbers of DNS names from a single
host as it allowed validation purely within the TLS layer.
A security issue was discovered in the TLS SNI challenge by Frans
Rosen which allowed users of various service providers to
illegitimately validate control of the DNS names of other users of
the provider. When the TLS SNI challenge was designed it was assumed
that a user would only be able to respond to TLS traffic via SNI for
domain names they controlled (i.e. if User A registered Host A and
User B registered Host B with a service provider that User A wouldn't
be able to respond to SNI traffic for Host B). This turns out not to
be a security property provided by a number of large service
providers. Because of this users were able to respond to SNI traffic
for the SNI names used by the TLS SNI challenge validation process.
This meant that if User A and User B had registered Host A and Host B
respectively User A would be able to claim the SNI name for Host B
and when the validation connection was made that User A would be able
to answer, proving 'control' of Host B. As the SNI name used was a
subdomain of the domain name being validated, rather than the domain
name itself, it was likely to not already be registered with the
service provider for traffic routing, making it much easier for a
hijack to occur.
8. Acknowledgements 7. Acknowledgements
The author would like to thank all those whom have provided design The author would like to thank all those whom have provided design
insights and editorial review of this document, including Richard insights and editorial review of this document, including Richard
Barnes, Ryan Hurst, Adam Langley, Ryan Sleevi, Jacob Hoffman-Andrews, Barnes, Ryan Hurst, Adam Langley, Ryan Sleevi, Jacob Hoffman-Andrews,
Daniel McCarney, Marcin Walas, Martin Thomson and especially Frans Daniel McCarney, Marcin Walas, Martin Thomson and especially Frans
Rosen who discovered the vulnerability in the TLS SNI method which Rosen, who discovered the vulnerability in the TLS SNI method that
necessitated the writing of this specification. necessitated the writing of this specification.
9. Normative References 8. Normative References
[FIPS180-4] [FIPS180-4]
Department of Commerce, National., "NIST FIPS 180-4, Department of Commerce, National., "NIST FIPS 180-4,
Secure Hash Standard", March 2012, Secure Hash Standard", March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/ <http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>. fips-180-4.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
skipping to change at page 8, line 37 skipping to change at page 8, line 19
[RFC4343] Eastlake 3rd, D., "Domain Name System (DNS) Case [RFC4343] Eastlake 3rd, D., "Domain Name System (DNS) Case
Insensitivity Clarification", RFC 4343, Insensitivity Clarification", RFC 4343,
DOI 10.17487/RFC4343, January 2006, DOI 10.17487/RFC4343, January 2006,
<https://www.rfc-editor.org/info/rfc4343>. <https://www.rfc-editor.org/info/rfc4343>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>. <https://www.rfc-editor.org/info/rfc4648>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011, DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>. <https://www.rfc-editor.org/info/rfc6066>.
skipping to change at page 9, line 27 skipping to change at page 9, line 18
<https://www.itu.int/ITU-T/studygroups/com17/languages/ <https://www.itu.int/ITU-T/studygroups/com17/languages/
X.680-0207.pdf>. X.680-0207.pdf>.
[X.690] International Telecommunication Union, ., "Information [X.690] International Telecommunication Union, ., "Information
Technology -- ASN.1 encoding rules: Specification of Basic Technology -- ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", 2015, Distinguished Encoding Rules (DER)", 2015,
<https://www.itu.int/ITU-T/studygroups/com17/languages/ <https://www.itu.int/ITU-T/studygroups/com17/languages/
X.690-0207.pdf>. X.690-0207.pdf>.
Appendix A. Design Rationale
The TLS ALPN challenge exists to iterate on the TLS SNI challenge
defined in the early ACME drafts. The TLS SNI challenge was
convenient for service providers who were either operating large TLS
layer load balancing systems at which they wanted to perform
validation or running servers fronting large numbers of DNS names
from a single host as it allowed validation purely within the TLS
layer. The value provided by the TLS SNI challenge was considered
large enough that this document was written in order to provide a new
challenge type that addressed the existing security concerns.
A security issue in the TLS SNI challenge was discovered by Frans
Rosen, which allowed users of various service providers to
illegitimately validate control of the DNS names of other users of
the provider. When the TLS SNI challenge was designed it was assumed
that a user would only be able to respond to TLS traffic via SNI for
domain names they had registered with a service provider (i.e., if a
user registered 'a.example' they would only be able to respond to SNI
requests for 'a.example' and not for SNI requests for 'b.example').
It turns out that a number of large service providers do not honor
this property. Because of this, users were able to respond to SNI
requests for the names used by the TLS SNI challenge validation
process. This meant that if User A and User B had registered Host A
and Host B, respectively, User A would be able to claim the
constructed SNI challenge name for Host B and when the validation
connection was made that User A would be able to answer, proving
'control' of Host B. As the SNI name used was a subdomain of the
domain name being validated, rather than the domain name itself, it
was likely to not already be registered with the service provider for
traffic routing, making it much easier for a hijack to occur.
Author's Address Author's Address
Roland Bracewell Shoemaker Roland Bracewell Shoemaker
Internet Security Research Group Internet Security Research Group
Email: roland@letsencrypt.org Email: roland@letsencrypt.org
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