Internet DRAFT - draft-cragie-tls-ecjpake
draft-cragie-tls-ecjpake
tls R. Cragie
Internet-Draft ARM Ltd.
Intended status: Informational F. Hao
Expires: November 12, 2016 Newcastle University (UK)
May 11, 2016
Elliptic Curve J-PAKE Cipher Suites for Transport Layer Security (TLS)
draft-cragie-tls-ecjpake-00
Abstract
This document defines new cipher suites based on an Elliptic Curve
Cryptography (ECC) variant of Password Authenticated Key Exchange by
Juggling (J-PAKE) for the Transport Layer Security (TLS) and Datagram
Transport Layer Security (DTLS) protocols.
Status of This Memo
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This Internet-Draft will expire on November 12, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. ECJ-PAKE Based AES-CCM Cipher Suites . . . . . . . . . . . . 4
3. Notations . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Elliptic Curve Points . . . . . . . . . . . . . . . . . . 5
3.2. Integers . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Octet Strings . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Integer to Octet String Conversion . . . . . . . . . . . 6
3.5. Octet String to Integer Conversion . . . . . . . . . . . 7
4. Handshake . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Failure processing . . . . . . . . . . . . . . . . . . . . . 7
6. ECJ-PAKE TLS Extensions and Modification . . . . . . . . . . 7
6.1. New Structure Definitions . . . . . . . . . . . . . . . . 8
6.1.1. Public Key and Schnorr ZKP Pair . . . . . . . . . . . 8
6.1.2. Schnorr ZKP . . . . . . . . . . . . . . . . . . . . . 8
6.2. ClientHello and ServerHello TLS Extensions . . . . . . . 9
6.2.1. Existing Extensions . . . . . . . . . . . . . . . . . 9
6.2.2. Additional Extensions . . . . . . . . . . . . . . . . 9
6.3. ServerKeyExchange . . . . . . . . . . . . . . . . . . . . 10
6.4. ClientKeyExchange . . . . . . . . . . . . . . . . . . . . 10
7. Calculations . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. User Identity Selection . . . . . . . . . . . . . . . . . 11
7.2. Schnorr ZKP Hash Calculation . . . . . . . . . . . . . . 11
7.3. Shared Secret . . . . . . . . . . . . . . . . . . . . . . 12
7.3.1. Example . . . . . . . . . . . . . . . . . . . . . . . 13
7.4. ClientHello and ServerHello Calculations . . . . . . . . 13
7.4.1. Public Key Generation . . . . . . . . . . . . . . . . 13
7.4.2. Schnorr ZKP Generation . . . . . . . . . . . . . . . 14
7.4.3. Schnorr ZKP Verification . . . . . . . . . . . . . . 14
7.5. ServerKeyExchange Calculations . . . . . . . . . . . . . 15
7.5.1. Public Key Generation . . . . . . . . . . . . . . . . 15
7.5.2. Schnorr ZKP Generation . . . . . . . . . . . . . . . 16
7.5.3. Schnorr ZKP Verification . . . . . . . . . . . . . . 17
7.6. ClientKeyExchange Calculations . . . . . . . . . . . . . 17
7.6.1. Public Key Generation . . . . . . . . . . . . . . . . 17
7.6.2. Schnorr ZKP Generation . . . . . . . . . . . . . . . 18
7.6.3. Schnorr ZKP Verification . . . . . . . . . . . . . . 19
7.7. Premaster Secret Generation . . . . . . . . . . . . . . . 20
7.7.1. Server Premaster Secret Generation . . . . . . . . . 20
7.7.2. Client Premaster Secret Generation . . . . . . . . . 20
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9.1. Transport Layer Security (TLS) Parameters . . . . . . . . 21
9.1.1. TLS Cipher Suite Registry . . . . . . . . . . . . . . 21
9.2. Transport Layer Security (TLS) Extensions . . . . . . . . 21
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9.2.1. ExtensionType Values . . . . . . . . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10.1. Security Proof . . . . . . . . . . . . . . . . . . . . . 21
10.2. Counter Reuse . . . . . . . . . . . . . . . . . . . . . 22
10.3. Password . . . . . . . . . . . . . . . . . . . . . . . . 22
10.4. Rate Limiting . . . . . . . . . . . . . . . . . . . . . 22
10.5. Usage Restrictions . . . . . . . . . . . . . . . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . 22
11.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
This document defines new cipher suites based on an Elliptic Curve
Cryptography (ECC) variant of Password Authenticated Key Exchange by
Juggling (J-PAKE) for version 1.2 of Transport Layer Security (TLS)
protocol [RFC5246] as well as version 1.2 of the Datagram Transport
Layer Security (DTLS) protocol [RFC6347]. The cipher suites are AEAD
cipher suites using AES-CCM [CCM] based on the cipher suites defined
in [RFC7251], using ECJ-PAKE as an alternative key establishment
mechanism.
The existing set of TLS cipher suites are typically aimed at more
traditional client-server interactions, for example, a web browser to
web server. However, TLS and DTLS are increasingly being specified
for use in Internet-of-Things (IoT) standards for peer-to-peer
application layer interaction. For example, DTLS is specified as a
binding to provide security for the CoAP protocol [RFC7252], which is
widely used in IoT applications.
J-PAKE is a balanced password-authenticated key exchange (PAKE)
protocol resistant to off-line dictionary attack designed by Feng Hao
and Peter Ryan in 2008 [HR08]. The use of a PAKE for IoT devices is
highly appropriate as it allows a simple method of commissioning IoT
devices onto a network without requiring certificates to be issued
and maintained for each device. An ECC variant of J-PAKE [J-PAKE] is
particularly suited to IoT devices, which are often constrained with
regard to memory and processing power. The cipher suite
TLS_ECJPAKE_WITH_AES_128_CCM_8 as defined in this document is
currently being used in the Thread protocol [THREAD].
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 [RFC2119].
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1.2. Terminology
AEAD
Authenticated Encryption with Associated Data.
ECJ-PAKE
Elliptic Curve Cryptography (ECC) variant of Password
Authenticated Key Exchange by Juggling (J-PAKE).
ZKP
Zero-knowledge proof.
2. ECJ-PAKE Based AES-CCM Cipher Suites
The cipher suites defined in this document are based on the AES-CCM
Authenticated Encryption with Associated Data (AEAD) algorithms
AEAD_AES_128_CCM and AEAD_AES_256_CCM described in [RFC5116]. The
following cipher suites are defined:
TLS_ECJPAKE_WITH_AES_128_CCM = {0xTBD, 0xTBD}
TLS_ECJPAKE_WITH_AES_256_CCM = {0xTBD, 0xTBD}
TLS_ECJPAKE_WITH_AES_128_CCM_8 = {0xTBD, 0xTBD}
TLS_ECJPAKE_WITH_AES_256_CCM_8 = {0xTBD, 0xTBD}
These cipher suites make use of the AEAD capability in TLS 1.2
[RFC5246]. Cipher suites ending with "8" use eight-octet
authentication tags; the other cipher suites have 16-octet
authentication tags. The HMAC truncation option described in
Section 7 of [RFC6066] (which negotiates the "truncated_hmac" TLS
extension) does not have an effect on the cipher suites defined in
this document, because they do not use HMAC to protect TLS records.
The "nonce" input to the AEAD algorithm is as defined in [RFC6655].
These cipher suites make use of the default TLS 1.2 Pseudorandom
Function (PRF), which uses HMAC with the SHA-256 hash function.
The following stipulations apply to the use of elliptic curves:
o Curves with a cofactor equal to one SHOULD be used; this
simplifies their use.
o The uncompressed point format MUST be supported. Other point
formats MAY be used.
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o Fundamental ECC algorithms [RFC6090] MAY be used as an
implementation method.
3. Notations
This section describes the notations used in this document.
3.1. Elliptic Curve Points
The generator (base point) of an elliptic curve is represented by the
letter 'G':
G
A modified generator is represented by the letter 'G' concatenated
with a single uppercase character:
GB
Elliptic curve points are represented using a single uppercase
character or a single uppercase character concatenated with a single
lowercase character or decimal digit, for example:
X
Xc
X2
Conversion to and from elliptic curve points to octet strings is as
specified in Sections 2.3.3 and 2.3.4 of [SEC1].
Point multiplication is shown as an elliptic curve point multiplied
by a scalar integer using the '*' operator, for example:
G*x
Point addition or subtraction is shown as the addition or subtraction
of elliptic curve points or scalar multiplied elliptic curve points
using the '+' and '-' operators respectively, for example:
X1 + X3 + X4
X*h + G*r
Xs - X4*x2*s
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3.2. Integers
Integers are represented using a single lowercase character or a
single lowercase character followed by a single lowercase character
or decimal digit, for example:
x
xc
x2
Where expressed, integers are shown in hexadecimal and/or decimal
form. Hexadecimal numbers have an '0x' prefix. For example:
0x12ab34cd
3132110061
Integer multiplication is shown as two integers multiplied together
using the '*' operator:
x*s
Integer addition or subtraction is shown as the addition or
subtraction of integers or multiplied integers using the '+' and '-'
operators respectively:
v - x*h
3.3. Octet Strings
Octet strings are expressed in a hexadecimal form, with no '0x'
prefix and with a space separator, first octet leftmost, for example:
12 ab 34 cd
3.4. Integer to Octet String Conversion
Integer to octet string conversion SHALL be performed as stated in
Section 2.3.7 of [SEC1]. It is represented as follows:
M = str(mlen, x)
where x, mlen, and M are the parameters as stated in Section 2.3.7 of
[SEC1].
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3.5. Octet String to Integer Conversion
Octet string to integer conversion SHALL be as stated in section
2.3.8 of [SEC1]. It is represented as follows:
x = int(mlen, M)
where x, mlen, and M are the parameters as stated in Section 2.3.8 of
[SEC1].
4. Handshake
The TLS-ECJ-PAKE handshake is as follows, augmented with parameters
in braces to show the ECJ-PAKE material conveyed in each case:
Client Server
------ ------
ClientHello -------->
{(X1,ZKP(X1)),
(X2,ZKP(X2))} ServerHello
{(X3, ZKP(X3)),
(X4, ZKP(X4))}
ServerKeyExchange
{Xs, ZKP(Xs)}
<-------- ServerHelloDone
ClientKeyExchange
{Xc, ZKP(Xc)}
[ChangeCipherSpec]
Finished -------->
[ChangeCipherSpec]
<-------- Finished
Application Data <-------> Application Data
Figure 1: Message flow in a TLS-ECJ-PAKE handshake
5. Failure processing
If there are failures for any reason on client or server side, for
example, Schnorr ZKP verification or missing extensions, the
handshake SHALL abort immediately and send a TLS Error Alert message
to the peer, using code 40 (handshake_failure) (see Section 7.2 of
[RFC5246]).
6. ECJ-PAKE TLS Extensions and Modification
This section describes existing and newly-defined extensions required
for ECJ-PAKE-TLS.
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6.1. New Structure Definitions
TLS-ECJ-PAKE requires new structure definitions for:
o Public key and Schnorr ZKP pair
o Schnorr ZKP
6.1.1. Public Key and Schnorr ZKP Pair
The TLS structure is as follows:
struct {
ECPoint X;
ECSchnorrZKP zkp;
} ECJPAKEKeyKP;
X
Public key represented as an elliptic curve point. ECPoint is
defined in [RFC4492].
zkp
ECSchnorrZKP is defined in Section 6.1.2.
6.1.2. Schnorr ZKP
The TLS structure is as follows:
struct {
ECPoint V;
opaque r<1..2^8-1>;
} ECSchnorrZKP;
V
Ephemeral public key represented as an elliptic curve point.
ECPoint is defined in [RFC4492].
r
Schnorr signature.
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6.2. ClientHello and ServerHello TLS Extensions
6.2.1. Existing Extensions
The following TLS extensions defined in Section 4 of [RFC4492] SHALL
be present in ClientHello:
o Supported Elliptic Curves Extension (NamedCurve,
EllipticCurveList)
o Supported Point Formats Extension (ECPointFormat,
ECPointFormatList)
and the following TLS extension defined in Section 4 of [RFC4492]
SHALL be present in ServerHello:
o Supported Point Formats Extension (ECPointFormat,
ECPointFormatList)
6.2.2. Additional Extensions
The following extension SHALL additionally be present in both
ClientHello and ServerHello:
enum { ecjpake_key_kp_pair(TBC) } ExtensionType;
struct {
opaque identity<0..2^16-1>;
ECJPAKEKeyKP ecjpake_key_kp_pair_list[2];
} ECJPAKEKeyKPPairList;
identity
MAY be included if the Client or Server needs to uniquely identify
themselves to the other party. An identity is used in the Schnorr
ZKP hash calculation (see Section 7.2).
ecjpake_key_kp_pair_list
The list is precisely two elements long. The list in a
ClientHello extension conveys public keys X1 and X2 and the list
in a ServerHello extension conveys public keys X3 and X4, with
associated Schnorr ZKPs.
Note: When used in conjunction with DTLS and denial-of-service
countermeasures as described in Section 4.2.1 of [RFC6347], the
ECJPAKEKeyKPPairList in the subsequent ClientHello message SHALL be
the same as the ECJPAKEKeyKPPairList in initial ClientHello message,
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i.e. the public keys X1 and X2 and associated Schnorr ZKPs SHALL be
the same.
6.3. ServerKeyExchange
ServerKeyExchange is extended as follows:
enum { ecjpake } KeyExchangeAlgorithm;
ecjpake
Indicates the ServerKeyExchange message contains
ServerECJPAKEParams.
ServerKeyExchange for ecjpake SHALL be formatted as follows:
struct {
ECParameters curve_params;
ECJPAKEKeyKP ecjpake_key_kp;
} ServerECJPAKEParams;
select (KeyExchangeAlgorithm) {
case ecjpake:
ServerECJPAKEParams params;
} ServerKeyExchange;
6.4. ClientKeyExchange
ClientKeyExchange is extended as follows:
enum { ecjpake } KeyExchangeAlgorithm;
ecjpake
Indicates the ClientKeyExchange message contains
ClientECJPAKEParams.
ClientKeyExchange for ecjpake SHALL be formatted as follows:
struct {
ECJPAKEKeyKP ecjpake_key_kp;
} ClientECJPAKEParams;
select (KeyExchangeAlgorithm) {
case ecjpake:
ClientECJPAKEParams params;
} ClientKeyExchange;
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7. Calculations
This section describes the calculations required to populate the data
conveyed between Client and Server and also calculations required to
verify knowledge proofs.
The following notation is used throughout this section:
Order of the base point: n
7.1. User Identity Selection
The Schnorr ZKP hash calculation requires non-confidential user
identities. These identities need to be unique in the context of a
transaction and be different for each party. In a peer-to-peer
transaction where there is no ambiguity of identity, the identities
can be a simple string representing the Client and Server
respectively:
+------------+----------+-------------------+--------------------+
| Originator | Name | Identity | Length of identity |
+------------+----------+-------------------+--------------------+
| Client | "client" | 63 6c 69 65 6e 74 | 6 |
| Server | "server" | 73 65 72 76 65 72 | 6 |
+------------+----------+-------------------+--------------------+
Table 1: Simple Client and Server identities
In a multi-party transaction, each party SHOULD additionally provide
an identity in the ClientHello and/or ServerHello to uniquely
distinguish their user identity.
7.2. Schnorr ZKP Hash Calculation
The hash calculation is defined as follows:
+-------------------+-----------------------------------+
| Public Key | Calculation |
+-------------------+-----------------------------------+
| X1, X2, X3 and X4 | h = SHA-256(G, V, X, ID) mod n |
| Xs | h = SHA-256(GB, V, Xs, IDs) mod n |
| Xc | h = SHA-256(GA, V, Xc, IDc) mod n |
+-------------------+-----------------------------------+
Table 2: Schnorr ZKP Hash Calculation
Each item in the hash calculation is prepended with its length in
octets represented an octet (length 4), formed by applying integer to
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octet string conversion as defined in Section 3.4. For example, the
length of an uncompressed octet string representation of a public key
is 65 (decimal) therefore the octet string (length 4) representation
of 65 in hexadecimal is:
o 00 00 00 41
Each public key (elliptic curve point) is first converted to an octet
string according to Section 2.3.3 of [SEC1].
The concatentation order of the hash is as follows:
1. G (or GA, GB): Generator
2. V: ZKP ephemeral public key
3. X (or Xs, Xc): Public key to be verified
4. ID (or IDc, IDs): User ID (see Section 7.1)
The hash is therefore performed on the concatenation as follows:
o H = SHA-256(lenG || G || lenV || V || lenX || X || lenID || ID)
An integer representation of the hash (see Section 3.5) is produced:
o h = int(H)
7.3. Shared Secret
The shared secret for the ServerKeyExchange and ClientKeyExchange
calculations is required to be an integer in the range 1 to n-1.
This section shows an example of how this could be practically
accomplished using an initial password. The initial password is
usually represented visually as a variable length character string
using a subset of internationally recognized characters from the
UTF-8 character set, which prevents the possibility of the resulting
shared secret having the value 0. The initial password is then be
converted into an octet string <password> using UTF-8 conversion.
The integer shared secret calculation is thus defined as follows,
using the function defined in Section 3.5:
s = int(<password>) mod n
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7.3.1. Example
Password:
"d45yj8e"
Equivalent octet string M using UTF-8 conversion (no null
termination):
64 34 35 79 6a 38 65
Length mlen:
7
Shared secret:
0x643435796a3865
28204901945981028 (decimal)
7.4. ClientHello and ServerHello Calculations
The structure ECJPAKEKeyKPPairList conveys the public key and
associated Schnorr ZKP for ClientHello (X1 and X2) and ServerHello
(X3 and X4).
7.4.1. Public Key Generation
For X1, X2, X3 and X4, the value for the public key part X of the
ECJPAKEKeyKP structure is generated as follows:
The inputs are:
o Base point: G
o Order of the base point: n
The public key of the key pair is calculated as follows:
1. A random integer in the range 1 to n-1 is assigned to private key
x.
2. A public key associated with x is generated and assigned to X:
X = G*x
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3. X is assigned to the public key part X of the ECJPAKEKeyKP
structure.
7.4.2. Schnorr ZKP Generation
For X1, X2, X3 and X4, the values for the ZKP part zkp.V and zkp.r of
the ECJPAKEKeyKP structure are generated as follows:
The inputs are:
o Base point: G
o Order of the base point: n
o Identity of originator: ID (IDc or IDs depending on context)
o Key pair to provide a ZKP of: (X,x) (public key: X, private key:
x), where X is X1, X2, X3, or X4 and x is x1, x2, x3, or x4,
depending on context
The ZKP is generated as follows:
1. A random integer in the range 1 to n-1 is assigned to ephemeral
private key v.
2. An ephemeral public key associated with v is generated and
assigned to V:
V = G*v
3. An integer representation of a hash (see Section 7.2) is
generated and assigned to h:
h = int(SHA-256(G, V, X, ID)) mod n
4. A signature is generated and assigned to r:
r = v - x*h mod n
5. V and r are assigned to the ZKP part zkp.V and zkp.r of the
ECJPAKEKeyKP structure respectively.
7.4.3. Schnorr ZKP Verification
For X1, X2, X3 and X4, the ECJPAKEKeyKP structure is verified as
follows:
The inputs are:
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o Base point: G
o Order of the base point: n
o Identity of originator: ID (IDc or IDs depending on context)
o Public key to be verified: X (X1, X2, X3, or X4 depending on
context)
o ZKP ephemeral public key: V
o ZKP signature: r
The ZKP is verified as follows:
1. An integer representation of a hash (see Section 7.2) is
generated and assigned to h:
h = int(SHA-256(G, V, X, ID)) mod n
2. A check point is generated and assigned to V':
V'= X*h + G*r
3. The points V' and V are compared. If equal then the ZKP
verifies, otherwise it does not verify.
7.5. ServerKeyExchange Calculations
The structure ECJPAKEKeyKP conveys the public key and associated
Schnorr ZKP for Xs.
7.5.1. Public Key Generation
For Xs, the value for the public key part X of the ECJPAKEKeyKP
structure is generated as follows:
The inputs are:
o Public keys: X1, X2 and X3
o Private key: x4
o Shared secret: s (integer format, see Section 7.3)
o Order of the base point: n
The public key of the key pair is calculated as follows:
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1. A new generator is generated and assigned to GB:
GB = X1 + X2 + X3
2. A private key is generated and assigned to xs:
xs = x4*s mod n
3. A public key associated with xs is generated and assigned to Xs:
Xs = GB*xs
4. Xs is assigned to the public key part X of the ECJPAKEKeyKP
structure.
7.5.2. Schnorr ZKP Generation
For Xs, the values for the ZKP part zkp.V and zkp.r of the
ECJPAKEKeyKP structure are generated as follows:
The inputs are:
o New generator: GB
o Order of the base point: n
o Identity of originator: IDs
o Key pair to provide a ZKP of: (Xs,xs) (public key: Xs, private
key: xs)
The ZKP is generated as follows:
1. A random integer in the range 1 to n-1 is assigned to ephemeral
private key v.
2. An ephemeral public key associated with v is generated and
assigned to V:
V = GB*v
3. An integer representation of a hash (see Section 7.2) is
generated and assigned to h:
h = int(SHA-256(GB, V, Xs, IDs)) mod n
4. A signature is generated and assigned to r:
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r = v - xs*h mod n
5. V and r are assigned to the ZKP part zkp.V and zkp.r of the
ECJPAKEKeyKP structure respectively.
7.5.3. Schnorr ZKP Verification
For Xs, the ECJPAKEKeyKP structure is verified as follows:
The inputs are:
o New generator: GB
o Order of the base point: n
o Identity of originator: IDs
o Public key to be verified: Xs
o ZKP ephemeral public key: V
o ZKP signature: r
The ZKP is verified as follows:
1. An integer representation of a hash (see Section 7.2) is
generated and assigned to h:
h = int(SHA-256(GB, V, Xs, IDs)) mod n
2. A check point is generated and assigned to V':
V'= X*h + GB*r
3. The points V' and V are compared. If equal then the ZKP
verifies, otherwise it does not verify.
7.6. ClientKeyExchange Calculations
The structure ECJPAKEKeyKP conveys the public key and associated
Schnorr ZKP for Xc.
7.6.1. Public Key Generation
For Xc, the value for the public key part X of the ECJPAKEKeyKP
structure is generated as follows:
The inputs are:
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o Public keys: X1, X3 and X4
o Private key: x2
o Shared secret: s (integer format, see Section 7.3)
o Order of the base point: n
The public key of the key pair is calculated as follows:
1. A new generator is generated and assigned to GA:
GA = X1 + X3 + X4
2. A private key is generated and assigned to xc:
xc = x2*s mod n
3. A public key associated with xs is generated and assigned to Xc:
Xc = GA*xc
4. Xc is assigned to the public key part X of the ECJPAKEKeyKP
structure.
7.6.2. Schnorr ZKP Generation
For Xc, the values for the ZKP part zkp.V and zkp.r of the
ECJPAKEKeyKP structure are generated as follows:
The inputs are:
o New generator: GA
o Order of the base point: n
o Identity of originator: IDc
o Key pair to provide a ZKP of: (Xc,xc) (public key: Xc, private
key: xc)
The ZKP is generated as follows:
1. A random integer in the range 1 to n-1 is assigned to ephemeral
private key v.
2. An ephemeral public key associated with v is generated and
assigned to V:
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V = GA*v
3. An integer representation of a hash (see Section 7.2) is
generated and assigned to h:
h = int(SHA-256(GA, V, Xc, IDc)) mod n
4. A signature is generated and assigned to r:
r = v - xc*h mod n
5. V and r are assigned to the ZKP part zkp.V and zkp.r of the
ECJPAKEKeyKP structure respectively.
7.6.3. Schnorr ZKP Verification
For Xc, the ECJPAKEKeyKP structure is verified as follows:
The inputs are:
o New generator: GA
o Order of the base point: n
o Identity of originator: IDc
o Public key to be verified: Xc
o ZKP ephemeral public key: V
o ZKP signature: r
The ZKP is verified as follows:
1. An integer representation of a hash (see Section 7.2) is
generated and assigned to h:
h = int(SHA-256(GA, V, Xc, IDc)) mod n
2. A check point is generated and assigned to V':
V'= X*h + GA*r
3. The points V' and V are compared. If equal then the ZKP
verifies, otherwise it does not verify.
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7.7. Premaster Secret Generation
The TLS-ECJ-PAKE handshake relies on the generation of identical
premaster secrets at the client and server to verify the key
establishment. The use of the protected Finished messages is
therefore used for key confirmation purposes and to verify the
handshake.
7.7.1. Server Premaster Secret Generation
The inputs are:
o Public key of the client: Xc
o Public key: X2
o Private key: x4
o Shared secret: s (integer format, see Section 7.3)
The premaster secret is generated as follows:
1. Compute PMSK:
PMSK = (Xc - X2*x4*s)*x4
2. Compute PMS:
PMS = SHA-256(str(32, X coordinate of PMSK))
3. The master secret and key expansion is generated according to
Section 8.1 and Section 6.3 of [RFC5246].
7.7.2. Client Premaster Secret Generation
The inputs are:
o Public key of the server: Xs
o Public key: X4
o Private key: x2
o Shared secret: s (integer format, see Section 7.3)
The premaster secret is generated as follows:
1. Compute PMSK:
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PMSK = (Xs - X4*x2*s)*x2
2. Compute PMS:
PMS = SHA-256(str(32, X coordinate of PMSK))
3. The master secret and key expansion is generated according to
Section 8.1 and Section 6.3 of [RFC5246].
8. Acknowledgements
The authors would like to thank Sorin Aliciuc, Richard Kelsey,
Maurizio Nanni, Manuel Pegourie-Gonnard and Martin Turon for their
helpful comments and assistance.
9. IANA Considerations
9.1. Transport Layer Security (TLS) Parameters
9.1.1. TLS Cipher Suite Registry
IANA is requested to add the following entries in the TLS Cipher
Suite Registry:
TLS_ECJPAKE_WITH_AES_128_CCM = {0xTBD, 0xTBD}
TLS_ECJPAKE_WITH_AES_256_CCM = {0xTBD, 0xTBD}
TLS_ECJPAKE_WITH_AES_128_CCM_8 = {0xTBD, 0xTBD}
TLS_ECJPAKE_WITH_AES_256_CCM_8 = {0xTBD, 0xTBD}
9.2. Transport Layer Security (TLS) Extensions
9.2.1. ExtensionType Values
IANA is requested to add the following entries in the ExtensionType
Values:
ecjpake_key_kp_pair = TBD
10. Security Considerations
10.1. Security Proof
An independent study that proves security of J-PAKE in a model with
algebraic adversaries and random oracles can be found in [ABM15].
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10.2. Counter Reuse
The cipher suites described in this document are AES-CCM-based AEAD
cipher suites, therefore the security considerations for counter
reuse described in [RFC6655] also apply to these cipher suites.
10.3. Password
The password forming the basis of the shared secret SHOULD be
distributed in a secure out-of-band channel. In the specific case of
[THREAD], this is achieved by the user enabling the use of the
password only through a commissioning session where the user is in
control of adding details of devices they wish to add to the Thread
network.
10.4. Rate Limiting
An attacker could attempt to engage repeatedly with a ECJ-PAKE server
in an attempt to guess the password. Servers SHOULD take steps to
ensure the opportunity for repeated contact is limited.
10.5. Usage Restrictions
The cipher suites described in this document have primarily been
developed to enable authentication and authorization for network
access for IoT devices, as described in [THREAD]. It is therefore
RECOMMENDED that the use of these cipher suite is restricted to
similar uses and SHOULD NOT be used in conjunction with web servers
and web browsers unless consideration is given to secure entry of
passwords in a browser.
11. References
11.1. Normative References
[CCM] National Institute of Standards and Technology,
"Recommendation for Block Cipher Modes of Operation: The
CCM Mode for Authentication and Confidentiality", SP
800-38C, May 2004, <http://csrc.nist.gov/publications/
nistpubs/800-38C/SP800-38C_updated-July20_2007.pdf>.
[SEC1] Standards for Efficient Cryptography Group, "Standards for
Efficient Cryptography: SEC 1: Elliptic Curve
Cryptography", SECG SEC1-v2, May 2004,
<http://www.secg.org/sec1-v2.pdf>.
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[THREAD] Thread Group, "Thread Commissioning", July 2015,
<http://threadgroup.org/Portals/0/documents/whitepapers/
Thread%20Commissioning%20white%20paper_v2_public.pdf>.
[HR08] Hao, F. and P. Ryan, "Password Authenticated Key Exchange
by Juggling", 16th Workshop on Security Protocols
(SPW'08), May 2008,
<http://grouper.ieee.org/groups/1363/Research/
contributions/hao-ryan-2008.pdf>.
[ABM15] Abdalla, M., Benhamouda, F., and P. MacKenzie, "Security
of the J-PAKE Password-Authenticated Key Exchange
Protocol", IEEE Symposium on Security and Privacy, May
2015,
<https://www.normalesup.org/~fbenhamo/files/publications/
SP_AbdBenMac15.pdf>.
[J-PAKE] Hao, F., "J-PAKE: Password Authenticated Key Exchange by
Juggling", draft-hao-jpake-03 (work in progress), February
2016, <http://tools.ietf.org/id/draft-hao-jpake-03.txt>.
[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>.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492,
DOI 10.17487/RFC4492, May 2006,
<http://www.rfc-editor.org/info/rfc4492>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<http://www.rfc-editor.org/info/rfc5116>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>.
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[RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
Transport Layer Security (TLS)", RFC 6655,
DOI 10.17487/RFC6655, July 2012,
<http://www.rfc-editor.org/info/rfc6655>.
[RFC7251] McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES-
CCM Elliptic Curve Cryptography (ECC) Cipher Suites for
TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014,
<http://www.rfc-editor.org/info/rfc7251>.
11.2. Informative References
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090,
DOI 10.17487/RFC6090, February 2011,
<http://www.rfc-editor.org/info/rfc6090>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
Authors' Addresses
Robert Cragie
ARM Ltd.
110 Fulbourn Road
Cambridge CB1 9NJ
UK
Email: robert.cragie@arm.com
Feng Hao
Newcastle University (UK)
Claremont Tower, School of Computing Science, Newcastle University
Newcastle upon Tyne NE1 7RU
UK
Email: feng.hao@ncl.ac.uk
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