BIKE and SIKE Hybrid Key Exchange Cipher Suites for Transport Layer Security (TLS)
draft-campagna-tls-bike-sike-hybrid-00
| The information below is for an old version of the document |
| Document |
Type |
|
Active Internet-Draft (individual)
|
|
Authors |
|
Matt Campagna
,
Eric Crockett
|
|
Last updated |
|
2019-03-27
|
|
Stream |
|
(None)
|
|
Formats |
|
pdf
htmlized (tools)
htmlized
bibtex
|
| Stream |
Stream state |
|
(No stream defined) |
|
Consensus Boilerplate |
|
Unknown
|
|
RFC Editor Note |
|
(None)
|
| IESG |
IESG state |
|
I-D Exists
|
|
Telechat date |
|
|
|
Responsible AD |
|
(None)
|
|
Send notices to |
|
(None)
|
Internet Engineering Task Force M. Campagna
Internet-Draft E. Crockett
Intended status: Experimental AWS
Expires: September 28, 2019 March 27, 2019
BIKE and SIKE Hybrid Key Exchange Cipher Suites for Transport Layer
Security (TLS)
draft-campagna-tls-bike-sike-hybrid-00
Abstract
This document describes new hybrid key exchange schemes for the
Transport Layer Security (TLS) protocol, which are based on combining
Elliptic Curve Diffie Hellman (ECDH) with one of the Bit Flipping Key
Exchange (BIKE) or the Supersingular Isogeny Key Exchange (SIKE)
schemes. In particular, this document specifies the use of BIKE or
SIKE in combination with ECDHE as a hybrid key agreement in a TLS 1.2
handshake, together with the use of ECDSA or RSA for authentication.
Hybrid key exchange refers to executing two separate key exchanges
and subsequently feeding the two resulting shared secrets into the
existing TLS Pseudo Random Function (PRF), in order to derive a
master secret.
Context
This draft is experimental. It is intended to define hybrid key
exchanges in sufficient detail to allow independent experimentations
to interoperate. While the NIST standardization process is still a
few years away from being complete, we know that many TLS users have
highly sensitive workloads that would benefit from the speculative
additional protections provided by quantum-safe key exchanges. These
key exchanges are likely to change through the standardization
process. Early experiments serve to understand the real-world
performance characteristics of these quantum-safe schemes as well as
provide speculative additional confidentiality assurances against a
future adversary with a large-scale quantum computer.
Comments are solicited and can be sent to all authors at
mcampagna@amazon.com.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
Campagna & Crockett Expires September 28, 2019 [Page 1]
Internet-Draft Hybrid Key Exchange for TLS March 2019
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 28, 2019.
Copyright Notice
Copyright (c) 2019 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
(https://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 . . . . . . . . . . . . . . . . . . 4
2. Key Exchange Algorithms . . . . . . . . . . . . . . . . . . . 4
2.1. Key Encapsulation Method (KEM) . . . . . . . . . . . . . 5
2.2. ECDHE_BIKE_[SIG] . . . . . . . . . . . . . . . . . . . . 6
2.3. ECDHE_SIKE_[SIG] . . . . . . . . . . . . . . . . . . . . 6
3. Hybrid Premaster Secret . . . . . . . . . . . . . . . . . . . 7
3.1. Concatenated premaster secret . . . . . . . . . . . . . . 7
4. TLS Extensions for BIKE and SIKE . . . . . . . . . . . . . . 7
5. Data Structures and Computations . . . . . . . . . . . . . . 8
5.1. Client Hello Extensions . . . . . . . . . . . . . . . . . 8
5.1.1. When these extensions are sent . . . . . . . . . . . 8
5.1.2. Meaning of these extensions . . . . . . . . . . . . . 8
5.1.3. Structure of these extensions . . . . . . . . . . . . 8
5.1.4. Actions of the sender . . . . . . . . . . . . . . . . 9
5.1.5. Actions of the receiver . . . . . . . . . . . . . . . 9
5.1.6. Supported BIKE Parameter Extension . . . . . . . . . 9
5.1.7. Supported SIKE Parameter Extension . . . . . . . . . 10
5.2. Server Key Exchange . . . . . . . . . . . . . . . . . . . 11
5.2.1. When this message is sent . . . . . . . . . . . . . . 11
5.2.2. Meaning of this message . . . . . . . . . . . . . . . 11
Campagna & Crockett Expires September 28, 2019 [Page 2]
Internet-Draft Hybrid Key Exchange for TLS March 2019
5.2.3. Structure of this message . . . . . . . . . . . . . . 11
5.2.4. Actions of the sender . . . . . . . . . . . . . . . . 13
5.2.5. Actions of the receiver . . . . . . . . . . . . . . . 13
5.3. Client Key Exchange . . . . . . . . . . . . . . . . . . . 13
5.3.1. When this message is sent . . . . . . . . . . . . . . 13
5.3.2. Meaning of the message . . . . . . . . . . . . . . . 13
5.3.3. Structure of this message . . . . . . . . . . . . . . 14
5.3.4. Actions of the sender . . . . . . . . . . . . . . . . 14
5.3.5. Actions of the receiver . . . . . . . . . . . . . . . 15
5.4. Derivation of the master secret for hybrid key agreement 15
6. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations [DRAFT] . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
10. Normative References . . . . . . . . . . . . . . . . . . . . 17
Appendix A. Additional Stuff . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
Quantum-safe (or post-quantum) key exchanges are being developed in
order to provide secure key establishment against an adversary with
access to a quantum computer. Under such a threat model, the current
key exchange mechanisms would be vulnerable. BIKE and SIKE are two
such schemes which were submitted to the NIST Call for Proposals for
Post Quantum Cryptographic Schemes. While these schemes are still
being analyzed as part of that process, there is already a need to
protect the confidentiality of today's TLS connections against a
future adversary with a quantum computer. Hybrid key exchanges are
designed to provide two parallel key exchanges: one which is
classical (e.g., ECDHE) and the other which is quantum-safe (e.g.,
BIKE or SIKE). This strategy is emerging as a method to
speculatively provide additional security to existing protocols.
This document describes additions to TLS to support BIKE and SIKE
Hybrid Key Exchanges, applicable to TLS Version 1.2 [RFC5246]. In
particular, it defines the use of the ECDH together with BIKE or
SIKE, as a hybrid key agreement method.
The remainder of this document is organized as follows. Section 2
provides an overview of BIKE- and SIKE-based key exchange algorithms
for TLS. Section 3 describes how BIKE and SIKE can be combined with
ECDHE to form a premaster secret. TLS extensions that allow a client
to negotiate the use of specific BIKE and SIKE parameters are
presented in Section 4. Section 5 specifies various data structures
needed for a BIKE- or SIKE-based hybrid key exchange handshake, their
encoding in TLS messages, and the processing of those messages.
Section 6 defines new BIKE and SIKE hybrid-based cipher suites and
Campagna & Crockett Expires September 28, 2019 [Page 3]
Internet-Draft Hybrid Key Exchange for TLS March 2019
identifies a small subset of these as recommended for all
implementations of this specification. Section 7 discusses some
security considerations. Section 8 describes IANA considerations for
the name spaces created by this document. Section 9 gives
acknowledgments.
Implementation of this specification requires familiarity with TLS
[RFC5246], TLS extensions [RFC6066], BIKE, and SIKE.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
2. Key Exchange Algorithms
This document introduces two new hybrid-based key exchange methods
for TLS. They use ECDHE with either BIKE or SIKE, in order to
compute the TLS premaster secret. The master secret derivation is
augmented to include the ClientKeyExchange message. The derivation
of the encryption/MAC keys and initialization vectors is independent
of the key exchange algorithm and not impacted by the introduction of
these hybrid key exchanges.
The table below summarizes the new hybrid key exchange schemes.
+-------------------------------+-----------------------------------+
| Hybrid Key Exchange Scheme | Description |
| Name | |
+-------------------------------+-----------------------------------+
| ECDHE_BIKE_RSA | ECDHE and BIKE with RSA |
| | signatures. |
| | |
| ECDHE_BIKE_ECDSA | ECDHE and BIKE with ECDSA |
| | signatures. |
| | |
| ECDHE_SIKE_RSA | ECDHE and SIKE with RSA |
| | signatures. |
| | |
| ECDHE_SIKE_ECDSA | ECDHE and SIKE with ECDSA |
| | signatures. |
+-------------------------------+-----------------------------------+
Table 1: BIKE and SIKE Hybrid Key Exchange Schemes
These schemes are intended to provide quantum-safe forward secrecy.
Campagna & Crockett Expires September 28, 2019 [Page 4]
Internet-Draft Hybrid Key Exchange for TLS March 2019
Client Server
------ ------
ClientHello -------->
ServerHello
Certificate
ServerKeyExchange
CertificateRequest*+
<-------- ServerHelloDone
Certificate*+
ClientKeyExchange
CertificateVerify*+
[ChangeCipherSpec]
Finished -------->
[ChangeCipherSpec]
<-------- Finished
Application Data <-------> Application Data
* message is not sent under some conditions
+ message is not sent unless client authentication
is desired
Figure 1: Message flow in a hybrid TLS handshake
Figure 1 shows the messages involved in the TLS key establishment
protocol (aka full handshake). The addition of hybrid key exchanges
has direct impact on the ClientHello, the ServerHello, the
ServerKeyExchange, and the ClientKeyExchange messages. Next, we
describe each hybrid key exchange scheme in greater detail in terms
of the content and processing of these messages. For ease of
exposition, we defer discussion of the optional BIKE- and SIKE-
specific extensions (which impact the Hello messages) until
Section 4.
2.1. Key Encapsulation Method (KEM)
A key encapsulation mechanism (KEM) is a set of three algorithms
o key generation (KeyGen)
o encapsulation (Encaps)
o decapsulation (Decaps)
and a defined key space, where
o "KeyGen()": returns a public and a secret key (pk, sk).
Campagna & Crockett Expires September 28, 2019 [Page 5]
Internet-Draft Hybrid Key Exchange for TLS March 2019
o "Encaps(pk)": takes pk as input and outputs ciphertext c and a key
K from the key space.
o "Decaps(sk, c)": takes sk and c as input, and returns a key K or
ERROR. K is called the session key.
The security of a KEM is discussed in Section 7. BIKE and SIKE are
two examples of a KEM.
2.2. ECDHE_BIKE_[SIG]
This section describes the two nearly identical hybrid key exchanges
ECDHE_BIKE_RSA and ECDHE_BIKE_ECDSA. For the remainder of this
section SIG refers to either RSA or ECDSA. The server sends its
ephemeral ECDH public key and ephemeral BIKE public key generated
using the BIKE Key Encapsulation Method (KEM) and a specification of
the corresponding curve and BIKE parameters in the ServerKeyExchange
message. These parameters MUST be signed with the signature
algorithm SIG using the private key corresponding to the public key
in the server's certificate.
The client generates an ECDHE key pair on the same curve as the
server's ephemeral ECDH key, and computes a ciphertext value based on
the BIKE public key provided by the server, and sends them in the
ClientKeyExchange message. The client computes and holds the BIKE-
encapsulated key (K) as a contribution to the premaster secret.
Both client and server perform an ECDH operation and use the
resultant shared secret (Z) as part of the premaster secret. The
server computes the BIKE decapsulation routine to compute the
encapsulated key (K), or to produce an error message in case the
decapsulation fails.
2.3. ECDHE_SIKE_[SIG]
This section describes the two nearly identical hybrid key exchanges
ECDHE_SIKE_RSA and ECDHE_SIKE_ECDSA. For the remainder of this
section SIG refers to either RSA or ECDSA. ECDHE_SIKE_[SIG] is
nearly identical to ECDHE_BIKE_[SIG]. The server sends its ephemeral
ECDH public key and ephemeral SIKE public key generated using the
SIKE Key Encapsulation Method (KEM) and a specification of the
corresponding ECDH curve and SIKE parameters in the ServerKeyExchange
message. These parameters MUST be signed with the signature
algorithm SIG using the private key corresponding to the public key
in the server's certificate.
Campagna & Crockett Expires September 28, 2019 [Page 6]
Internet-Draft Hybrid Key Exchange for TLS March 2019
3. Hybrid Premaster Secret
This section defines new hybrid key exchanges for TLS 1.2 [RFC5246].
Here, both the server and the client compute two shared secrets: the
previously defined ECDHE shared secret Z from RFC 6066, and another
shared secret K from the underlying BIKE or SIKE key encapsulation
method.
To simplify the text when we speak about BIKE or SIKE interchangeably
we will simply denote this as [KEM].
3.1. Concatenated premaster secret
Form the premaster secret for ECDHE_[KEM]_[SIG] hybrid key exchanges
as the concatenation of the ECDHE shared secret Z with the KEM key K
to form the opaque data value "premaster_secret = Z || K".
4. TLS Extensions for BIKE and SIKE
Two new TLS extensions are defined in this specification:
1. the Supported BIKE Parameters Extension, and
2. the Supported SIKE Parameters Extension.
These allow negotiating the use of specific [KEM] parameter sets
during a handshake starting a new session. These extensions are
especially relevant for constrained clients that may only support a
limited number of [KEM] parameter sets. They follow the general
approach outlined in RFC 6066; message details are specified in
Section 5. The client enumerates the BIKE and SIKE parameters it
supports by including the appropriate extensions in its ClientHello
message.
A TLS client that proposes [KEM] cipher suites in its ClientHello
message SHOULD include these extensions. Servers implementing a
[KEM] cipher suite MUST support these extensions, and when a client
uses these extensions, servers MUST NOT negotiate the use of a [KEM]
parameter set unless they can complete the handshake while respecting
the choice of parameters specified by the client. This eliminates
the possibility that a negotiated hybrid handshake will be
subsequently aborted due to a client's inability to deal with the
server's [KEM] key.
The client MUST NOT include these extensions in the ClientHello
message if it does not propose any [KEM] cipher suites. That is, if
a client does not support BIKE, it must not include the BIKE
parameters extension, and if the client does not support SIKE, it
Campagna & Crockett Expires September 28, 2019 [Page 7]
Internet-Draft Hybrid Key Exchange for TLS March 2019
must not include the SIKE parameter extension. A client that
proposes a [KEM] scheme may choose not to include these extensions.
In this case, the server is free to choose any one of the parameter
sets listed in Section 5. That section also describes the structure
and processing of these extensions in greater detail.
In the case of session resumption, the server simply ignores the
Supported [KEM] Parameter Extension appearing in the current
ClientHello message. These extensions only play a role during
handshakes negotiating a new session.
5. Data Structures and Computations
This section specifies the data structures and computations used by
[KEM] hybrid-key agreement mechanisms specified in Sections 2, 3, and
4. The presentation language used here is the same as that used in
TLS 1.2 [RFC5246].
5.1. Client Hello Extensions
This section specifies two TLS extensions that can be included with
the ClientHello message as described in RFC 6066, and the Supported
[KEM] Parameters Extension.
5.1.1. When these extensions are sent
The extensions SHOULD be sent along with any ClientHello message that
proposes the associated [KEM] cipher suites.
5.1.2. Meaning of these extensions
These extensions allow a client to enumerate the BIKE or SIKE
parameters sets it supports.
5.1.3. Structure of these extensions
The general structure of TLS extensions is described in RFC 6066, and
this specification adds two new types to ExtensionType.
enum {
bike_parameters(0xFE01),
sike_parameters(0xFE02)
} ExtensionType;
where
o "bike_parameters" (Supported BIKE Parameters Extension): Indicates
the set of BIKE parameters supported by the client. For this
Campagna & Crockett Expires September 28, 2019 [Page 8]
Internet-Draft Hybrid Key Exchange for TLS March 2019
extension, the opaque extension_data field contains
BIKEParameterList. See Section 5.1.6 for details.
o "sike_parameters" (Supported SIKE Parameters Extension): Indicates
the set of SIKE parameters supported by the client. For this
extension, the opaque extension_data field contains
SIKEParameterList. See Section 5.1.7 for details.
5.1.4. Actions of the sender
A client that proposes a [KEM] hybrid key exchange cipher suites in
its ClientHello message appends these extensions (along with any
others), enumerating the parameters it supports. Clients SHOULD send
the Supported BIKE Parameters Extension if it supports a BIKE hybrid
key exchange cipher suite, and it SHOULD send the Supported SIKE
Parameters Extension if it supports a SIKE hybrid key exchange cipher
suite.
5.1.5. Actions of the receiver
A server that receives a ClientHello containing one or both of these
extensions MUST use the client's enumerated capabilities to guide its
selection of an appropriate cipher suite. One of the proposed [KEM]
cipher suites must be negotiated only if the server can successfully
complete the handshake while using the [KEM] parameters supported by
the client (cf. Section 5.1.6 and Section 5.1.7.)
If a server does not understand the Supported [KEM] Parameters
Extension, or is unable to complete the [KEM] handshake while
restricting itself to the enumerated parameters, it MUST NOT
negotiate the use of the corresponding [KEM] cipher suite. Depending
on what other cipher suites are proposed by the client and supported
by the server, this may result in a fatal handshake failure alert due
to the lack of common cipher suites.
5.1.6. Supported BIKE Parameter Extension
enum {
BIKE1r1-Level1 (1),
BIKE1r1-Level3 (2),
BIKE1r1-Level5 (3),
BIKE2r1-Level1 (4),
BIKE2r1-Level3 (5),
BIKE2r1-Level5 (6),
BIKE3r1-Level1 (7),
BIKE3r1-Level3 (8),
BIKE3r1-Level5 (9)
} NamedBIKEKEM (2^8-1);
Campagna & Crockett Expires September 28, 2019 [Page 9]
Internet-Draft Hybrid Key Exchange for TLS March 2019
"BIKE1r1-Level1", etc: Indicates support of the corresponding BIKE
parameters defined in BIKE, the round 1 candidate to the NIST Post
Quantum Cryptography Standardization Process.
struct {
NamedBIKEKEM bike_parameter_list <1..2^8-1>
} BIKEParameterList;
Items in "bike_parameter_list" are ordered according to the client's
preferences (favorite choice first).
As an example, a client that only supports BIKE1r1-Level1 ( value 1 =
0x01) and BIKE2-Level1 ( value 4 = 0x04) and prefers to use
BIKE1r1-Level1 would include a TLS extension consisting of the
following octets:
FE 01 00 03 02 01 04
Note that the first two octets indicate the extension type (Supported
BIKE Parameter Extension), the next two octets indicates the length
of the extension (00 03), and the next octet indicates the length of
enumerated values (02).
5.1.7. Supported SIKE Parameter Extension
enum {
SIKEp503r1-KEM (1),
SIKEp751r1-KEM (2),
SIKEp964r1-KEM (3)
} NamedSIKEKEM (2^8-1);
SIKEp503r1-KEM, etc.: Indicates support of the corresponding SIKE
parameters defined in SIKE, the round 1 candidate to the NIST Post
Quantum Cryptography Standardization Process.
struct {
NamedSIKEKEM sike_parameter_list <1,..., 2^8 - 1>
} SIKEParameterList;
Items in sike_parameter_list are ordered according to the client's
preferences (favorite choice first).
As an example, a client that only supports SIKEp503r1-KEM ( value 1 =
0x01) and SIKEp751r1-KEM ( value 2 = 0x02) and prefers to use
SIKEp503r1-KEM would include a TLS extension consisting of the
following octets:
FE 02 00 03 02 01 02
Campagna & Crockett Expires September 28, 2019 [Page 10]
Internet-Draft Hybrid Key Exchange for TLS March 2019
Note that the first two octets indicate the extension type (Supported
SIKE Parameter Extension), the next two octets indicates the length
of the extension (00 03), and the next octet indicates the length of
enumerated values (02).
5.2. Server Key Exchange
5.2.1. When this message is sent
This message is sent when using the ECDHE_[KEM]_ECDSA and
ECDHE_[KEM]_RSA hybrid key exchange algorithms.
5.2.2. Meaning of this message
This message is used to convey the server's ephemeral ECDH and BIKE
or SIKE public key to the client.
5.2.3. Structure of this message
struct {
opaque public_key <1,...,2^16 - 1>;
} BIKEKEMPublicKey;
public_key: This is a byte string representation of the BIKE public
key following the conversion defined by the BIKE implementation.
struct {
NamedBIKEKEM bike_params;
BIKEKEMPublicKey public;
} ServerBIKEKEMParams;
struct {
opaque public_key <1,...,2^16 - 1>;
} SIKEKEMPublicKey;
where
o "public_key": This is a byte string representation of the SIKE
public key following the conversion routines of Section 1.2.9 of
the SIKE specification [SIKE].
struct {
NamedSIKEKEM sike_params;
SIKEKEMPublicKey public;
} ServerSIKEKEMParams;
The ServerKeyExchange message is extended as follows:
Campagna & Crockett Expires September 28, 2019 [Page 11]
Internet-Draft Hybrid Key Exchange for TLS March 2019
enum {
ecdh_bike,
ecdh_sike
} KeyExchangeAlgorithm;
"ecdh_bike": Indicates the ServerKeyExchange message contains an ECDH
public key and the server's BIKE parameters. "ecdh_sike": Indicates
the ServerKeyExchange message contains an ECDH public key and the
server's SIKE parameters.
select (KeyExchangeAlgorithm) {
case ecdh_bike:
ServerECDHParams ecdh_params;
ServerBIKEKEMParams bike_params;
Signature signed_params;
case ecdh_sike:
ServerECDHParams ecdh_params;
ServerSIKEKEMParams sike_params;
Signature signed_params;
} ServerKeyExchange;
where
o "ecdh_params": Specifies the ECDH public key and associated domain
parameters.
o "bike_params": Specifies the BIKE public key and associated
parameters.
o "sike_params": Specifies the SIKE public key and associated
parameters.
o "signed_params": a signature over the server's key exchange
parameters. The private key corresponding to the certified public
key in the server's Certificate message is used for signing.
digitally-signed struct {
opaque client_random[32];
opaque server_random[32];
ServerDHParams ecdh_params;
select (KeyExchangeAlgorithm) {
case ecdh_bike:
ServerBIKEKEMParams bike_params;
case ecdh_sike:
ServerSIKEKEMParams sike_params;
} signed_params;
Campagna & Crockett Expires September 28, 2019 [Page 12]
Internet-Draft Hybrid Key Exchange for TLS March 2019
The parameters are hashed as part of the signing algorithm as
follows, where H is the hash function used for generating the
signature:
For ECDHE_[KEM]_[SIG]:
"H( client_random[32] + server_random[32] + ecdh_params +
[KEM]_params)."
NOTE: SignatureAlgorithm is "rsa" for the ECDHE_[KEM]_RSA and hybrid
key exchange schemes. These cases are defined for TLS 1.2 [RFC5246].
SignatureAlgorithm is "ecdsa" for ECDHE_[KEM]_ECDSA. ECDSA
signatures are generated and verified as described in RFC 8422.
5.2.4. Actions of the sender
The server selects elliptic curve domain parameters and an ephemeral
ECDH public key corresponding to these parameters according to
RFC 8422. The server selects BIKE or SIKE parameters and an
ephemeral public key corresponding to the parameters according to
BIKE or SIKE respectively. It conveys this information to the client
in the ServerKeyExchange message using the format defined above.
5.2.5. Actions of the receiver
The client verifies the signature and retrieves the server's elliptic
curve domain parameters and ephemeral ECDH public key and the [KEM]
parameters and public key from the ServerKeyExchange message.
A possible reason for a fatal handshake failure is that the client's
capabilities for handling elliptic curves and point formats are
exceeded (see RFC 8422), the [KEM] parameters are not supported (see
Section 5.1), or the signature does not verify.
5.3. Client Key Exchange
5.3.1. When this message is sent
This message is sent in all key exchange algorithms. In the key
exchanges defined in this document, it contains the client's
ephemeral ECDH public key and the [KEM] ciphertext value.
5.3.2. Meaning of the message
This message is used to convey ephemeral data relating to the key
exchange belonging to the client (such as its ephemeral ECDH public
key and the [KEM] ciphertext value).
Campagna & Crockett Expires September 28, 2019 [Page 13]
Internet-Draft Hybrid Key Exchange for TLS March 2019
5.3.3. Structure of this message
The TLS ClientKeyExchange message is extended as follows.
struct {
opaque ciphertext <1,..., 2^16 - 1>;
} BIKEKEMCiphertext;
where
o "ciphertext": This is a byte string representation of the BIKE
ciphertext of the KEM construction. Since the underlying calling
convention of the KEM API handles the ciphertext byte string
directly it is sufficient to pass this as single byte string array
in the protocol.
struct {
opaque ciphertext <1,..., 2^16 - 1>;
} SIKEKEMCiphertext;
where
o "ciphertext": This is a byte string representation of the SIKE
ciphertext of the KEM construction. It is the concatenation of a
public_key with a fixed-length masked secret value. Since the
underlying calling convention of the KEM API handles the
ciphertext byte string directly it is sufficient to pass this as
single byte string array in the protocol.
struct {
select (KeyExchangeAlgorithm) {
case ecdh_bike:
ClientECDiffieHellmanPublic ecdh_public;
BIKEKEMCiphertext ciphertext;
case ecdh_sike:
ClientECDiffieHellmanPublic ecdh_public;
SIKEKEMCiphertext ciphertext;
} exchange_keys;
} ClientKeyExchange;
5.3.4. Actions of the sender
The client selects an ephemeral ECDH public key corresponding to the
parameters it received from the server according to RFC 8422 and
[KEM] ciphertexts according to BIKE or SIKE respectively. It conveys
this information to the client in the ClientKeyExchange message using
the format defined above.
Campagna & Crockett Expires September 28, 2019 [Page 14]
Internet-Draft Hybrid Key Exchange for TLS March 2019
5.3.5. Actions of the receiver
The server retrieves the client's ephemeral ECDH public key and the
[KEM] ciphertext from the ClientKeyExchange message and checks that
it is on the same elliptic curve as the server's ECDH key, and that
the [KEM] ciphertexts conform to the domain parameters selected by
the server.
In the case of BIKE there is a decapsulation failure rate no greater
than 10^(-7). In the case of a decapsulation failure, an
implementation MUST abort the handshake.
5.4. Derivation of the master secret for hybrid key agreement
This section defines a new hybrid master secret derivation. It is
defined under the assumption that we use the concatenated premaster
secret defined in Section 3.1 (Section 3.1). Recall in this case the
premaster_secret = Z || K, where Z it the ECDHE shared secret, and K
is the KEM shared secret.
We define the master secret as follows:
master_secret[48] = TLS-PRF(secret, label, seed)
where
o "secret": the premaster_secret,
o "label": the string "hybrid master secret", and
o "seed": the concatenation of ClientHello.random ||
ServerHello.random || ClientKeyExchange
6. Cipher Suites
The table below defines new hybrid key exchange cipher suites that
use the key exchange algorithms specified in Section 2 (Section 2).
Campagna & Crockett Expires September 28, 2019 [Page 15]
Internet-Draft Hybrid Key Exchange for TLS March 2019
+-------------------------------------------------------------------+
| Ciphersuite |
+-------------------------------------------------------------------+
| CipherSuite TLS_ECDHE_BIKE_ECDSA_WITH_AES_128_GCM_SHA256 = { |
| 0xFF, 0x01 } |
| |
| CipherSuite TLS_ECDHE_BIKE_ECDSA_WITH_AES_256_GCM_SHA384 = { |
| 0xFF, 0x02 } |
| |
| CipherSuite TLS_ECDHE_BIKE_RSA_WITH_AES_128_GCM_SHA256 = { |
| 0xFF, 0x03 } |
| |
| CipherSuite TLS_ECDHE_BIKE_RSA_WITH_AES_256_GCM_SHA384 = { |
| 0xFF, 0x04 } |
| |
| CipherSuite TLS_ECDHE_SIKE_ECDSA_WITH_AES_128_GCM_SHA256 = { |
| 0xFF, 0x05 } |
| |
| CipherSuite TLS_ECDHE_SIKE_ECDSA_WITH_AES_256_GCM_SHA384 = { |
| 0xFF, 0x06 } |
| |
| CipherSuite TLS_ECDHE_SIKE_RSA_WITH_AES_128_GCM_SHA256 = { |
| 0xFF, 0x07 } |
| |
| CipherSuite TLS_ECDHE_SIKE_RSA_WITH_AES_256_GCM_SHA384 = { |
| 0xFF, 0x08 } |
+-------------------------------------------------------------------+
Table 2: TLS hybrid key exchange cipher suites
The key exchange method, cipher, and hash algorithm for each of these
cipher suites are easily determined by examining the name. Ciphers
and hash algorithms are defined in RFC 5288.
It is recommended that any implementation of this specification
include at least one of
o CipherSuite TLS_ECDHE_BIKE_RSA_WITH_AES_256_GCM_SHA384 = { 0xFF,
0x04 }
o CipherSuite TLS_ECDHE_SIKE_RSA_WITH_AES_256_GCM_SHA384 = { 0xFF,
0x08 }
using the parameters BIKE1r1-Level1 or SIKEp503r1-KEM.
Campagna & Crockett Expires September 28, 2019 [Page 16]
Internet-Draft Hybrid Key Exchange for TLS March 2019
7. Security Considerations [DRAFT]
The security considerations in TLS 1.2 [RFC5246] and RFC 8422 apply
to this document as well. In addition, as described in RFC 5288 and
RFC 5289, these cipher suites may only be used with TLS 1.2 or
greater.
The description of a KEM is provided in Section 2.1. The security of
the KEM is defined through the indistinguishability K against a
chosen-plaintext (IND-CPA) and against a chosen-ciphertext (IND-CCA)
adversary. We are focused here on the IND-CPA security of the KEM.
In the IND-CPA experiment of KEMs, an oracle generates keys (sk, pk)
with "KeyGen()", computes (c, K) with "Encaps(pk)", and draws
uniformly at random a value R from the key space, and a random bit b.
The adversary is an algorithm A that is given (pk, c, K) if b=1, and
(pk, c, R) if b=0. Algorithm A outputs a bit b' as a guess for b,
and wins if b' = b.
8. IANA Considerations
This document describes three new name spaces for use with the TLS
protocol:
9. Acknowledgements
10. Normative References
[BIKE] Misoczki, R., Aragon, N., Barreto, P., Bettaieb, S.,
Bidoux, L., Blazy, O., Deneuville, J., Gaborit, P.,
Gueron, S., Guneysu, T., Melchor, C., Persichetti, E.,
Sendrier, N., Tillich, J., and G. Zemor, "BIKE: Bit
Flipping Key Encapsulation", March 2018,
<http://http://bikesuite.org/files/BIKE.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
Campagna & Crockett Expires September 28, 2019 [Page 17]
Internet-Draft Hybrid Key Exchange for TLS March 2019
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
DOI 10.17487/RFC5288, August 2008,
<https://www.rfc-editor.org/info/rfc5288>.
[RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
DOI 10.17487/RFC5289, August 2008,
<https://www.rfc-editor.org/info/rfc5289>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
Curve Cryptography (ECC) Cipher Suites for Transport Layer
Security (TLS) Versions 1.2 and Earlier", RFC 8422,
DOI 10.17487/RFC8422, August 2018,
<https://www.rfc-editor.org/info/rfc8422>.
[SIKE] Jao, D., Azarderakhsh, R., Campagna, M., Costello, C., De
Feo, L., Hess, B., Jalali, A., Koziel, B., LaMacchia, B.,
Longa, P., Naehrig, M., Renes, J., Soukharev, V., and D.
Urbanik, "Supersingular Isogeny Key Encapsulation",
November 2017, <https://sike.org/files/SIDH-spec.pdf>.
Appendix A. Additional Stuff
This becomes an Appendix.
Authors' Addresses
Matt Campagna
AWS
Email: campagna@amazon.com
Eric Crockett
AWS
Email: ericcro@amazon.com
Campagna & Crockett Expires September 28, 2019 [Page 18]