Token Binding Working Group G. Mandyam
Internet-Draft L. Lundblade
Intended status: Standards Track J. Azen
Expires: March 9, 2018 Qualcomm Technologies Inc.
September 5, 2017
Attested TLS Token Binding
draft-mandyam-tokbind-attest-02
Abstract
Token binding allows HTTP servers to bind bearer tokens to TLS
connections. In order to do this, clients or user agents must prove
possession of a private key. However, proof-of-possession of a
private key becomes truly meaningful to a server when accompanied by
an attestation statement. This specification describes extensions to
the existing token binding protocol to allow for attestation
statements to be sent along with the related token binding messages.
Status of This Memo
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This Internet-Draft will expire on March 9, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Attestation Enhancement to TLS Token Binding Message . . . . 3
3. Example - Platform Attestation for Anomaly Detection . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Normative References . . . . . . . . . . . . . . . . . . 4
5.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
[I-D.ietf-tokbind-protocol] and [I-D.ietf-tokbind-negotiation]
describe a framework whereby servers can leverage cryptographically-
bound authentication tokens to verify TLS connections. This is
useful for prevention of man-in-the-middle attacks on TLS sessions,
and provides a mechanism by which identity federation systems can be
leveraged by a relying party to verify a client based on proof-of-
possession of a private key.
Once the use of token binding is negotiated as part of the TLS
handshake, an application layer message (the Token Binding message)
may be sent from the client to the relying party whose primary
purpose is to encapsulate a signature over a value associated with
the current TLS session (Exported Key Material, i.e. EKM - see
[I-D.ietf-tokbind-protocol]).
Proof-of-possession of a private key is useful to a relying party,
but the associated signature in the Token Binding message does not
provide an indication as to how the private key is stored and in what
kind of environment the associated cryptographic operation takes
place. This information may be required by a relying party in order
to satisfy requirements regarding client platform integrity.
Therefore, attestations are sometimes required by relying parties in
order for them to accept signatures from clients. As per the
definition in [I-D.birkholz-tuda], "remote attestation describes the
attempt to determine the integrity and trustworthiness of an endpoint
-- the attestee -- over a network to another endpoint -- the verifier
-- without direct access." Attestation statements are therefore
widely used in any server verification operation that leverages
client cryptography.
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TLS token binding can therefore be enhanced with remote attestation
statements. The attestation statement can be used to augment Token
Binding message. This could be used by a relying party for several
different purpose, including (1) to determine whether to accept token
binding messages from the associated client, or (2) require an
additional mechanism for binding the TLS connection to an
authentication operation by the client.
2. Attestation Enhancement to TLS Token Binding Message
The attestation statement can be processed 'in-band' as part of the
Token Binding Message itself. This document leverages the
TokenBinding.extensions field of the Token Binding Message as
described in Section 3.4 of [I-D.ietf-tokbind-protocol], where the
extension data conforms to the guidelines of Section 6.3 of the same
document. The extension data takes the form of a CBOR (compact
binary object representation) Data Definition Language construct,
i.e. CDDL.
extension_data = {attestation}
attestation = (
attestation_type: tstr,
attestation_data: bstr,
)
The attestation data is determined according to the attestation type.
In this document, the following types are defined: "packed" (where
the corresponding attestation data defined in [Webauthn]) and "TPM"
(where the corresponding attestation data defined in [TPM]).
Additional attestation types may be accepted by the token binding
implementation.
3. Example - Platform Attestation for Anomaly Detection
An example of where a platform-based attestation is useful can be for
remote attestation based on client traffic anomaly detection. Many
network infrastructure deployments employ network traffic monitors
for anomalous pattern detection. Examples of anomalous patterns
detectable in the TLS handshake could be unexpected cipher suite
negotiation for a given source/destination pairing. In this case, it
may be desirable for a client-enhanced attestation reflecting for
instance that an expected offered cipher suite in the client hello
message is present or the originating browser integrity is intact
(e.g. through a hash over the browser application package). If the
network traffic monitor can interpret the atttestation included in
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the token binding message, then it can verify the attestation and
potentially emit alerts based on an unexpected attestation.
4. IANA Considerations
This memo includes no request to IANA.
5. References
5.1. Normative References
[I-D.greevenbosch-appsawg-cbor-cddl]
Vigano, C. and H. Birkholz, "CBOR data definition language
(CDDL): a notational convention to express CBOR data
structures", draft-greevenbosch-appsawg-cbor-cddl-09 (work
in progress), September 2016.
[I-D.ietf-tokbind-https]
Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
Hodges, "Token Binding over HTTP", draft-ietf-tokbind-
https-05 (work in progress), July 2016.
[I-D.ietf-tokbind-negotiation]
Popov, A., Nystrom, M., Balfanz, D., and A. Langley,
"Transport Layer Security (TLS) Extension for Token
Binding Protocol Negotiation", draft-ietf-tokbind-
negotiation-03 (work in progress), July 2016.
[I-D.ietf-tokbind-protocol]
Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
Hodges, "The Token Binding Protocol Version 1.0", draft-
ietf-tokbind-protocol-08 (work in progress), July 2016.
[TPM] The Trusted Computing Group, "Trusted Platform Module
Library, Part 1: Architecture", October 2014.
[Webauthn]
The Worldwide Web Consortium, "Web Authentication: An API
for accessing Scoped Credentials",
<https://www.w3.org/TR/webauthn/>.
5.2. Informative References
[I-D.birkholz-tuda]
Fuchs, A., Birkholz, H., McDonald, I., and C. Bormann,
"Time-Based Uni-Directional Attestation", draft-birkholz-
tuda-02 (work in progress), July 2016.
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Authors' Addresses
Giridhar Mandyam
Qualcomm Technologies Inc.
5775 Morehouse Drive
San Diego, California 92121
USA
Phone: +1 858 651 7200
Email: mandyam@qti.qualcomm.com
Laurence Lundblade
Qualcomm Technologies Inc.
5775 Morehouse Drive
San Diego, California 92121
USA
Phone: +1 858 658 3584
Email: llundbla@qti.qualcomm.com
Jon Azen
Qualcomm Technologies Inc.
5775 Morehouse Drive
San Diego, California 92121
USA
Phone: +1 858 651 9476
Email: jazen@qti.qualcomm.com
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