LURK D. Migault
Internet-Draft Ericsson
Intended status: Standards Track I. Boureanu
Expires: January 4, 2021 University of Surrey
July 03, 2020
LURK Extension version 1 for (D)TLS 1.2 Authentication
draft-mglt-lurk-tls12-03
Abstract
This document describes the LURK Extension 'tls12' which enables
interactions between a LURK Client and a LURK Server in a context of
authentication with (D)TLS 1.2.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 4, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Acronyms . . . . . . . . . . . . . . . . . . 4
3. LURK Header . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. rsa_master, rsa_master_with_poh . . . . . . . . . . . . . . . 6
4.1. Request Payload . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. Perfect Forward Secrecy . . . . . . . . . . . . . . . 8
4.2. Response Payload . . . . . . . . . . . . . . . . . . . . 9
4.3. LURK Client Behavior . . . . . . . . . . . . . . . . . . 10
4.4. LURK Server Behavior . . . . . . . . . . . . . . . . . . 10
5. rsa_extended_master, rss_extended_master_with_poh . . . . . . 11
5.1. Request Payload . . . . . . . . . . . . . . . . . . . . . 11
5.2. Response Payload . . . . . . . . . . . . . . . . . . . . 12
5.3. LURK Client Behavior . . . . . . . . . . . . . . . . . . 12
5.4. LURK Server Behavior . . . . . . . . . . . . . . . . . . 12
6. ecdhe" . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Request Payload . . . . . . . . . . . . . . . . . . . . . 13
6.2. Response Payload . . . . . . . . . . . . . . . . . . . . 15
6.3. LURK Client Behavior . . . . . . . . . . . . . . . . . . 15
6.4. LURK Server Behavior . . . . . . . . . . . . . . . . . . 15
7. capabilities . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Request Payload . . . . . . . . . . . . . . . . . . . . . 16
7.2. Response Payload . . . . . . . . . . . . . . . . . . . . 16
7.3. LURK Client Behavior . . . . . . . . . . . . . . . . . . 18
7.4. LURK Server Behavior" . . . . . . . . . . . . . . . . . . 18
8. ping . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Request Payload . . . . . . . . . . . . . . . . . . . . . 18
8.2. Response Payload . . . . . . . . . . . . . . . . . . . . 18
8.3. LURK Client Behavior . . . . . . . . . . . . . . . . . . 18
8.4. LURK Server Behavior . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9.1. RSA . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.2. ECDHE . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.3. Perfect Foward Secrecy . . . . . . . . . . . . . . . . . 21
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
12. Apendix . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
12.1. LURK Exchange for TLS RSA Master Secret with Proof of
Handshake . . . . . . . . . . . . . . . . . . . . . . . 25
12.2. LURK Exchange for TLS RSA Extended Master Secret . . . . 26
12.3. LURK Exchange for TLS RSA Extended Master Secret with
proof of handshake . . . . . . . . . . . . . . . . . . . 28
12.4. LURK Exchange for TLS ECDHE Signature . . . . . . . . . 30
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
13.1. Normative References . . . . . . . . . . . . . . . . . . 31
13.2. Informative References . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
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1. Introduction
This document describes the LURK Extension for TLS 1.2 so the LURK
Server can implement a Cryptographic Service in a TLS 1.2 [RFC5246]
and DTLS 1.2 [RFC6347] context.
More specifically, the LURK Server will be in charge of performing
the cryptographic operations associated to the private key of the TLS
Server, while other aspects of the termination of the TLS session is
handled by other services in the same administrative domain or in a
different administrative domain. Most Cryptographic Operations are
related to the TLS authentication and the current document limits the
Cryptographic Operations to the following authentication methods: RSA
and ECDHE_RSA defined in [RFC5246], [RFC6347] as well as ECDHE_ECDSA
defined in [RFC8422].
A more detailed description of some use cases foreseen in a TLS
context can be found in [I-D.mglt-lurk-tls-use-cases].
HTTPS delegation has been the main concern of the Content Delivery
Networks Interconnection (cdni) Working Group and several mechanisms
have been designed to delegate the load from an upstream entity to a
downstream entity. Entities can be of different nature and may
designated differently according to the context. Typically
designations includes Content Owner, CDN Provider, Domain Name Owner
for example. [I-D.fieau-cdni-https-delegation] provides a details
comparison of the various mechanisms applies to the CDN
Interconnection, and the remaining of this section positions these
mechanisms at a very high level view.
STAR [I-D.ietf-acme-star], [I-D.sheffer-acme-star-request] describes
a methods where the domain name owner or the content owner
orchestrates the refreshing process between a CA and the CDN
(terminating the TLS session). The CDN refreshes regularly and
automatically its certificates using [I-D.ietf-acme-acme], which
allows the use of short term certificates.
Delegated credentials [I-D.rescorla-tls-subcerts] consists having a
certificate that enables the servers to generates some "delegated
credentials".
STAR and "delegated credentials" both require some changes performed
by the CA - new certificate type for the delegated credentials and
new interfaces for the delegated and delegating entity for STAR. In
both case the TLS Client authenticates the delegated entity. While
STAR does not require changes on the TLS Client, the "delegated
credential" solution does. In both cases, the delegation is
controlled by limiting in time (7 days), which is also the limit of
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use of a stolen key or a rogue server. Such delegation provides a
high scalability of the architecture and prevents additional delays
when a TLS session is established.
The LURK Architecture [I-D.mglt-lurk-lurk] and the LURK Extension
'tls12' do not proceed to the delegation of the HTTPS delegation by
delegating the entire TLS termination. Instead, the TLS termination
is split into sub services, for example one associated to the
networking part and one associated to the cryptographic operation.
While micro services associated to the networking part are delegated,
the micro service associated to the cryptographic operation may not
be delegated. As a result, LURK Architecture is focused on the
protection of the Cryptographic Material and prevents leakage of the
Cryptographic Material for example by avoiding node exposed to the
Internet to host the Cryptographic Material. In addition, LURK
provides means to instantaneously suspend the delegation with a
suspicious node. On the other hand the LURK Extension 'tls12'
introduces some latency, and is not as scalable as STAR or delegated
credential solutions.
The LURK Extension 'tls12' is seen as a complementary to the STAR and
"delegated credentials". The LURK Extension 'tls12' is a backend
solution that does not require any modifications from TLS Client or
the CA. It is also aimed at protecting the Cryptographic Material.
LURK may also be deployed within an administrative domain in order to
to provide a more controlled deployment of TLS Servers.
2. Terminology and Acronyms
This document re-uses the terminology defined in
[I-D.mglt-lurk-lurk].
3. LURK Header
LURK / TLS 1.2 is a LURK Extension that introduces a new designation
"tls12". This document assumes that Extension is defined with
designation set to "tls12" and version set to 1. The LURK Extension
extends the LURKHeader structure defined in [I-D.mglt-lurk-lurk] as
follows:
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enum {
tls12 (1), (255)
} Designation;
enum {
capabilities (0), ping (1), rsa_master (2),
rsa_master_with_poh (3), rsa_extended_master (4),
rsa_extended_master_with_poh (5), ecdhe (6), (255)
}TLS12Type;
enum {
// generic values reserved or aligned with the
// LURK Protocol
request (0), success (1), undefined_error (2),
invalid_payload_format (3),
// code points for rsa authentication
invalid_key_id_type (4), invalid_key_id (5),
invalid_tls_random (6), invalid_freshness_funct (7),
invalid_encrypted_premaster (8), invalid_finished (9)
//code points for ecdhe authentication
invalid_ec_type (10), invalid_ec_curve (11),
invalid_poo_prf (12), invalid_poo (13), (255)
}TLS12Status
struct {
Designation designation = "tls12";
int8 version = 1;
} Extension;
struct {
Extension extension;
select( Extension ){
case ("tls12", 1):
TLS12Type;
} type;
select( Extension ){
case ("tls12", 1):
TLS12Status;
} status;
uint64 id;
unint32 length;
} LURKHeader;
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4. rsa_master, rsa_master_with_poh
An exchange of type "rsa_master" or "rsa_master_with_poh" enables the
LURK Client to delegate the RSA Key Exchange and authentication as
defined in [RFC5246]. The LURK Server returns the master secret.
"rsa_master" provides the necessary parameters and details to
generate the master secret, as well as to hinder replaying of old
handshake messages by a corrupt LURK Client. I.e., some attestation
of message-freshness is acquired by the LURK Server.
In addition, the"rsa_master_with_poh" provides a proof of handshake
(PoH). The proof of handshake consists in providing the Finished
message of the TLS Client to the LURK Server, so that latter can
perform more checks that in the "rsa_master" mode. Notably, herein,
the LURK Server also checks that the LURK request is performed in a
context of a TLS handshake.
While "rsa_master" and "rsa_master_with_poh" exchange have
respectively different requests, the response is the same. The
motivation for having different type is that the parameters provided
to the LURK Server are provided using different format. "rsa_master"
provides them explicitly, while "rsa_master_with_poh" provides them
via handshake messages.
4.1. Request Payload
A rsa_master request payload has the following structure:
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enum {
sha256_32 (0), (255)
}KeyPairIdType;
struct {
KeyPairIdType type;
opaque data; // length defined by the type
} KeyPairID;
enum{
sha256 (0), (255)
} FreshnessFunct
enum{
sha256 (0), sha384(1), sha512(2), (255)
} PRFHash
struct {
KeyPairID key_id;
FreshnessFunct freshness_funct;
PRFHash prf_hash;
Random client_random; // see RFC5246 section 7.4.1.2
Random server_random;
EncryptedPreMasterSecret pre_master;
// see RFC5246 section 7.4.7.1
// Length depends on the key.
}
} TLS12RSAMasterRequestPayload;
key_id The identifier of the public key. This document defines
sha256_32 format which takes the 32 first bits of the hash of the
binary ASN.1 DER representation of the public key using sha256.
The binary representation of RSA keys is described in [RFC8017].
The binary representation of ECC keys is the subjectPublicKeyInfo
structure defined in [RFC5480].
freshness_funct the one-way hash function (OWHF) used by LURK to
implement Perfect Forward Secrecy.
prf_hash the one way hash function used by the Pseudo Random
Function (PRF) to generate the master secret. PRF and hash
function are defined in {!RFC5246}} Section 5.
client_random the random value associated to the TLS Client as
defined in [RFC5246] Section 7.4.1.2.
server_random: the random value associated to the TLS Server as
defined in [RFC5246] Section 7.4.1.2.
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EncryptedPreMasterSecret : The encrypted master secret as defined in
[RFC5246] Section 7.4.7.1.
A rsa_master_with_poh request payload has the following structure:
struct {
KeyPairID key_id;
FreshnessFunct freshness_funct;
opaque handshake_messages<2...2^16-2>
// see RFC5246 section 7.4.9
Finished finished
} TLS12RSAMasterWithPoHRequestPayload;
key_id, freshness_funct are defined above
handshake_messages provides the necessary handshake messages to
compute the Finished message of the TLS Client as defined in
[RFC5246] section 7.4.9.
finished the TLS Client Finished message as defined by {{!RFC5246}
section 7.4.9.
4.1.1. Perfect Forward Secrecy
This document defines a mechanism which uses a function called
freshness_funct, to prevent an attacker to send a request to the LURK
Server in such a way that the said attacker can obtain back the
mastersecret for an old handshake. In other words, the use of this
function helps prevent a forward-secrecy attack on an old TLS
session, where the attack would make use that session's handshake-
data observed by the adversary.
This design achieves PFS with freshness_funct being a collision-
resistant hash function (CHRF). By CRHF, we mean a one-way hash
function (OWHF) which also has collision resistance; the latter means
that it is computationally infeasible to find any two inputs x1 and
x2 such that freshness_funct(x1) = freshness_funct(x2). By one-way
hash function (OWHF) we mean, as standard, a hash function
freshness_funct that satisfies preimage resistance and 2nd-preimage
resistance. That is, given a hash value y, it is computationally
infeasible to find an x such that freshness_funct(x) = y, and
respectively- given a value x1 and its hash freshness_funct(x1), it
is computationally infeasible to find another x2 such that
freshness_funct(x2) = freshness_funct(x1).
For the concrete use of our freshness_funct funtions, let S be a
fresh, randomly picked value generated by the LURK Client. The value
of server_random in the TLS exchange is then equal to
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freshness_funct(S), i.e., server_random=freshness_funct(S). Between
the TLS Client and the LURK Server only server-random is exchanged.
The LURK Client sends S to the Key Server, in the query. Note that
the latter SHOULD happen over a secure channel.
A man-in-the-middle attacker observing the (plaintext) TLS handshake
between a TLS Client and the LURK Client does not see S, but only
server_random. The preimage resistance guaranted by the
freshness_funct makes it such that this man-in-the-middle cannot
retrieve S out of the observed server-random. As such, this man-in-
the-middle attacker cannot query the S corresponding to an (old)
observed handshake to the Key Server. Moreover, the collision
resistance guaranteed by the freshness_funct makes it such that if
the aforementioned man-in-the-middle cannot find S' such that
freshness_funct(S)=freshness_funct(S').
As discussed in Section 9, PFS may be achieved in other ways (i.e.,
not using a CRHF and the aforementioned exchanges but other
cryptographic primitives and other exchanges). These may offer
better computational efficiency. These may be standardized in future
versions of the LURK extension "tls12.
The server_random MUST follow the structure of [RFC5246] section
7.4.1.2, which carries the gmt_unix_time in the first four bytes.
So, the ServerHello.random of the TLS exchange is derived from the
server_random of the LURK exchange as defined below:
gmt_unix_time = server_random[0..3];
ServerHello.random = freshness_funct( server_random + "tls12 pfs" );
ServerHello.random[0..3] = gmt_unix_time;
The operation MUST be performed by the LURK Server as well as the TLS
Server, upon receiving the master secret or the signature of the
ecdhe_params from the LURK Client.
4.2. Response Payload
The "rsa_master" response payload contains the master secret and has
the following structure:
struct {
opaque master[0..47];
} TLS12RSAMasterResponsePayload;
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4.3. LURK Client Behavior
A LURK Client initiates an rsa_master or an rsa_master_with_poh
exchange in order to retrieve the master secret. The LURK exchange
happens on the TLS Server side (Edge Server). Upon receipt of the
master_secret the Edge Server generates the session keys and finish
the TLS key exchange protocol.
A LURK Client MAY use the rsa_master_with_poh to provide the LURK
Server evidences that the LURK exchange is performed in the context
of a TLS handshake. The Proof of TLS Hanshake (POH) helps the LURK
Server to audit the context associated to the query.
The LURK Client MUST ensure that the transmitted values for
server_random is S such as server_random = freshness_funct( S ).
4.4. LURK Server Behavior
Upon receipt of a rsa_master or a rsa_master_with_poh request, the
LURK Server proceeds according to the following steps:
1. The LURK Server checks the RSA key pair is available (key_id).
If the format of the key pair identifier is not understood, an
"invalid_key_id_type" error is returned. If the designated key
pair is not available an "invalid_key_id" error is returned.
2. The LURK Server checks the freshness_funct. If it does not
support the FreshnessFunct, an "invalid_freshness_funct" error
is returned.
3. The LURK Server collects the client_random, server_random and
pre_master parameters either provided explicitly (rsa_master) or
within the handshake (rsa_master_with_poh).
4. The LURK Server MUST check the format of the server_random and
more specifically checks the gmt_unix_time associated to the
random is acceptable. Otherwise it SHOULD return an
"invalid_tls_random" error. The value of the time window is
implementation dependent and SHOULD be a configurable
parameters. The LURK Server MAY also check the client_random.
This should be considered cautiously as such check may prevent
TLS Clients to set a TLS session. client_random is generated by
the TLS Client whose clock might not be synchronized with the
one of the LURK Server or that might have a TLS implementations
that does not generate random based on gmt_unix_time.
5. The LURK Server computes the necessary ServerHello.random from
the server_random when applicable as described in Section 4.1.1.
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When option is set to "finished" the ServerHello.random in the
handshake is replaced by its new value.
6. The LURK Server checks the length of the encrypted premaster
secret and returns an "invalid_payload_format" error if the
length differs from the length of binary representation of the
RSA modulus.
7. The LURK Server decrypts the encrypted premaster secret as
described in [RFC5246] section 7.4.7.1. When a PKCS1.5 format
error is detected, or a mismatch between the TLS versions
provided as input and the one indicated in the encrypted
premaster secret, the Key Server returns a randomly generated
master secret.
8. The LURK Server generates the master secret as described in
[RFC5246] section 8.1 using the client_random, and the
server_random provided by the LURK Client.
9. With a rsa_master_with_poh, the LURK Server checks the Finished
message is checked as defined in [RFC5246] section 7.4.9. In
case of mismatch returns an "invalid_finished" error.
10. The LURK Server returns a master secret in a
TLS12RSAMasterResponsePayload.
11. Error are expected to provide the LURK Client an indication of
the cause that resulted in the error. When an error occurs the
LURK Server MAY ignore the request, or provide more generic
error codes such as "undefined_error" or "invalid_format".
5. rsa_extended_master, rss_extended_master_with_poh
A exchange of type "rsa_extended_master" enables the LURK Client to
delegate the RSA Key Exchange and authentication. The LURK Server
returns the extended master secret as defined in [RFC7627].
5.1. Request Payload
The "rsa_extended_master" request has the following structure:
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enum { sha256 (0), (255) } FreshnessFunct
enum { null(0), sha256_128(1), sha256_256(2),
(255) }POOPRF
struct {
KeyPairID key_id
FreshnessFunct freshness_funct // see RFC5246 section 6.1
opaque handshake_messages<2...2^16-2> // see RFC7627 section 4
}TLS12ExtendedMasterRSARequestPayload;
The "rsa_extended_master_with_poh" request has the following
structure:
struct {
KeyPairID key_id
FreshnessFunct freshness_funct // see RFC5246 section 6.1
opaque handshake_messages<2...2^16-2>
// see RFC5246 section 7.4.9
Finished finished
}
}TLS12ExtendedMasterRSAWithPoHRequestPayload;
key_id, freshness_funct, option, handshake, finished are defined in
Section 4.1.
handshake_messages With a the handshake message includes are those
necessary to generate a extended master secret as defined in
[RFC7627] section 4.
5.2. Response Payload
rsa_extended_master response payload has a similar structure as the
rsa_master response payload Section 4.2.
5.3. LURK Client Behavior
The LURK Client proceeds as described in {{sec-rsa-master-clt}. The
main difference is that the necessary element to generate the master
secret are included in the handshake and or not provided separately.
5.4. LURK Server Behavior
The LURK Server proceeds as described in Section 4.4 except that the
generation of the extended master is processed as described in
[RFC7627].
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6. ecdhe"
A exchange of type "ecdhe" enables the LURK Client to delegate the
ECDHE_RSA [RFC5246] or the ECDHE_ECDSA [RFC8422] authentication.
6.1. Request Payload
The "ecdhe" request payload has the following structure:
enum { null(0), sha256_128(1), sha256_256(2),
(255) }POOPRF
struct {
POOPRF poo_prf;
select( poo_prf ) {
case ( "null" ):
case ( "sha256_128" )
ECPoint vG; //RFC8422 section 5.4
opaque R[16] r;
case ( "sha256_256" ):
ECPoint vG; //RFC8422 section 5.4
opaque R[32] r;
}
} TLS12POOParams;
struct {
KeyPairID key_id;
FreshnessFunct freshness_funct;
Random client_random; // see RFC5246 section 7.4.1.2
Random server_random;
SignatureAndHashAlgorithm sig_and_hash //RFC 5246 section 4.7
ServerECDHParams ecdhe_params; // RFC8422 section 5.4
POOParams poo_params;
} TLS12ECDHERequestPayload;
key_id, freshness_funct, client_random, server_random is defined in
Section 4.1.
ecdhe_params contains as defined in [RFC8422] section 5.4, the
elliptic curve domain parameters associated with the ECDH public
key (defined by the ECParameters structure) and the ephemeral ECDH
public key (defined by the ECPoint structure). The public key is
also noted in this document bG with b is a random secret generated
by the LURK Client and G the base point of the curve.
poo_params defines the necessary parameters to provide a proof of
ownership of the ECDHE private key. This option is intended to
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prevent the LURK Server to sign bytes that do not correspond to a
ECDHE public key.
poo_prf pseudo random function used to generate the necessary
randoms to proof ownership of the private key. This document
defines sha256_128 and sha256_256 which apply the sha256 hash
function and respectively return the 128 or 256 first bits of the
resulting hash.
vG are the necessary points to generate the proof of ownership.
r necessary value to create the proof of ownership.
The proof of ownership (PoO) consists in the LURK Client proving the
knowledge of the private random b, while not disclosing b. With G
the base point, bG represents the public value. The PoO is based on
the non-interactive variant of the three-pass Schnorr identification
scheme (NIZR) also designated as the Fiat-Shamir transformation
described in [RFC8235]. More specifically, the LURK Client randomly
generates v and then derive c and r = v - b*c. The LURK Client
provides bG, vG, and r to the LURK Servers. The LURK Server first
checks bG is on the curve. Then it computes c similarly to the LURK
Client as well S = rG + (bG)c. This latest value S is compared to
vG. The equality between S and vG proves the ownership of b.
v is randomly generated by the LURK Client. v MUST remain non-
predictable with a length equivalent to the expected level of
security, that is 128 bit length (resp. 256 bit length) for a 128
(resp 256) bit security level. Given b, we RECOMMEND v to be at
least half the size of b.
c is computed by the LURK Client and the LURK Server as described in
[RFC8235]. UserID is defined by the concatenation of the
client_random and the server_random. OtherInfo is defined as the
concatenation of key_id, freshness_funct, sig_and_hash, ecdhe_params,
"tls12 poo". Each concatenated item is prefixed with a 4-byte
integer that represents the byte length of the item.
UserID = client_random || server_random
OtherInfo = key_id || freshness_funct || sig_and_hash ||
ecdhe_params || "tls12 poo"
c = poo_prf(G || vG || bG || UserID || OtherInfo)
The LURK Client provides bG in ecdhe_params and vG as well as r in
poo_params.
With X25519 or X448, b and r MUST be clamped and vG MUST use the
Curve25519 (resp. Curve448). bG MAY also use the Curve25519 or
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Curve448 representation, or the LURK Server MAY derive bG values from
the provided xlined value in ecdhe_params.
6.2. Response Payload
The "ecdhe" response payload has the following structure:
struct {
Signature signed_params; // RFC8422 section 5.4
} TLS12ECDHEResponsePayload;
signed_params signature applied to the hash of the ecdhe_params as
well as client_random and server_random as described in
[RFC8422] section 5.4.
6.3. LURK Client Behavior
The LURK Client builds the base as described in Section 4.1 and in
Section 6.1.
Upon receiving the response payload, the LURK Client MAY check the
signature. If the signature does not match an error SHOULD be
reported.
6.4. LURK Server Behavior
Upon receiving an ecdhe request, the LURK Server proceeds as follows:
1. perform steps 1 - 6 as described in Section 4.4
2. The LURK Server performs some format check of the ecdhe_params
before signing them. If the ecdhe_params does not follow the
expected structure. With the notations from [RFC8422], if
curve_type is not set to "named_curve", the LURK Server SHOULD
respond with an "invalid_ec_type" error. If the curve or
namedcurve is not supported the LURK Server SHOULD be able to
respond with an "invalid_ec_curve" error.
3. The LURK Server processes the poo_params. If the poo_prf is not
supported, the LURK Extension returns a "invalid_poo_prf" status.
If poo_prf is supported and different from "null", the LURK
Server proceeds to the proof of ownership as described in
Section 6.1. If the proof is not properly verified, the LURK
Extension returns a "invalid_poo" status.
4. The LURK Server processes the base structure as described in
Section 4.4
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5. The LURK Server generates the signed_params.
Error are expected to provide the LURK Client an indication of the
cause that resulted in the error. When an error occurs the LURK
Server MAY ignore the request, or provide more generic error codes
such as "undefined_error" or "invalid_format".
7. capabilities
A exchange of type "capabilities" enables the LURK Client to be
informed of the supported operations performed by the LURK Server.
The supported parameters are provided on a per type basis.
7.1. Request Payload
A LURK "capabilities" request has no payload.
7.2. Response Payload
The "capabilities" response payload lists for each supported type,
the supported certificates, the supported signatures and hash
associated. The "capabilities" payload has the following structure:
struct{
CertificateType certificate_type // RFC8442 section 4.4.2
select (certificate_type) {
case RawPublicKey:
/* From RFC 7250 ASN.1_subjectPublicKeyInfo */
opaque ASN1_subjectPublicKeyInfo<1..2^24-1>;
case X509:
opaque cert_data<1..2^24-1>;
};
} TypedCertificate;
struct {
KeyPairID key_id_type_list<0..255>;
TypedCertificate typed_certificate_list<0..255>
FreshnessFunctList freshness_funct_list<0..255>
CipherSuites cipher_suite_list<0..255>
PRFHash prf_hash_list<0..255>
} TLS12RSACapability;
struct {
KeyPairID key_id_type_list<0..255>;
TypedCertificate typed_certificate_list<0..255>
FreshnessFunctList freshness_funct_list<0..255>
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CipherSuites cipher_suite_list<0..255>
SignatureAndHashAlgorithm sig_and_hash_list<0..255>
NameCurve ecdsa_curves_list<0..255>;
NameCurve ecdhe_curves_list<0..255>
POOPRF poo_prf_list<0..255>
} TLS12ECDHECapability;
struct {
uint32 length;
TLS12Type type
Select( type ) {
case rsa_master : TLS12RSACapability,
case rsa_master_with_poh : TLS12RSACapability,
case rsa_extended_master : TLS12RSACapability,
case rsa_extended_master_with_poh : TLS12RSACapability,
case ecdhe : TLS12ECDHECapability
} capability ;
} TLS12Capability
struct {
TLS12Capability capability_list;
opaque state<32>;
} TLS12CapabilitiesResponsePayload;
typed_certificate enables to contain authentication credentials of
various type, such as X09 certificate or raw public key. While
different, the structure is similar of CertificateEntry defined in
[RFC8446] section 4.4.2 as well as the Certificate structure
defined in [RFC7250].
key_id_type_list the supported key_id_type.
freshness_funct_list designates the list of freshness_funct ( see
Section 4.1).
certificate_list designates the certificates associated to message
type. The format is similar but different from the
CertificateEntry defined in [RFC8446] in section 4.4.2 and
[RFC7250] section 1. The CertificateBis format enables the use of
X509 as well as Raw Public key, while the Certificate structure
defined in [RFC5246] section 7.4.2 does not.
sig_and_hash_list designates supported signature algorithms as well
as PRF used for the different operations. The format is defined
in [RFC5246] section 7.4.1.4.1.
ecdsa_curves_list the supported signatures
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ecdhe_curves_list the supported curves for ECHDE parameters.
poo_prf_list the supported message type poo_prf ( see Section 6.1.
to be used with the proof of ownership.
type_list the supported message type of the LURK extension.
state characterizes the configuration associated to 'tls12' on the
LURK Server..
7.3. LURK Client Behavior
The LURK Client performs a capability request in order to determine
the possible operations.
The LURK Client is expected to keep the state value to be able to
detect a change in the LURK Server configuration when an error
occurs.
7.4. LURK Server Behavior"
Upon receiving a capabilities request, the LURK Extension MUST return
the capabilities payload associated to a "success" status to the LURK
Server. These information are then forwarded by the LURK Server to
the LURK Client.
8. ping
A exchange of type "ping" enables the LURK Client to check the
reachability in a context of the defined LURK Extension.
8.1. Request Payload
A "ping" request has no payload.
8.2. Response Payload
A "ping" response has no payload.
8.3. LURK Client Behavior
The LURK Client sends a "ping" request to test the reachability of
the LURK Server. The reachability is performed for the tls12 LURK
Extension.
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8.4. LURK Server Behavior
Upon receiving a ping request, the LURK Extension MUST return the
ping response associated with a "success" status to the LURK Server.
These information are then forwarded by the LURK Server to the LURK
Client.
9. Security Considerations
The security considerations defined in [I-D.mglt-lurk-lurk] applies
to the LURK Extension "tls12" defined in this document.
Anti-replay mechanisms rely in part on the security of channel
between the LURK Client and the LURK Server. As such the channel
between the LURK Client and the LURK Server MUST be ensuring
confidentiality and integrity. More specifically, the exchanges
between the LURK Client and the LURK Server MUST be an encrypted with
authentication encryption, and the two parties had previously
mutually authenticated.
The LURK Extension "tls12" is expected to have response smaller that
the request or at least not significantly larger, which makes "tls12"
relatively robust to amplification attacks. This is especially
matters when LURK is using UDP. The use of an authenticated channel
reduces also the risk of amplification attacks even when UDP is being
used.
The LURK Client and the LURK Server use time in their way to generate
the server_random. Care MUST be taken so the LURK Client and LURK
Server remain synchronized.
9.1. RSA
The rsa_master and rsa_extended_master returns the master_secret
instead of the premaster. The additional hashing operation necessary
to generate the master secret is expected to improve the protection
of the RSA private key against cryptographic analysis based on the
observation of a set of clear text and corresponding encrypted text.
The standard TLS1.2 is robust against Bleichenbacher attack as it
provides no means to detect if the error comes from a TLS version
mismatch or from the premaster format. This properties remain with
LURK, and so LURK does not present vulnerabilities toward
Bleichenbacher attack, and cannot be used as a decryption oracle.
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9.2. ECDHE
A passive attacker observing the ecdhe exchange may collect a
sufficient amount of clear text and corresponding signature to
perform a cryptographic analysis or to reuse the signature for other
purposes. As a result, it remains important to encrypt the ecdhe
exchange between the LURK Client and the LURK Server. Note that this
vulnerability is present in TLS 1.2 as a TLS Client can accumulate
these data as well. The difference with LURK is by listening the
LURK Server, the accumulation is achieved for all TLS Clients.
As previously mentioned, the LURK Server may be used as signing
oracle for the specific string:
SHA(ClientHello.random + ServerHello.random +
ServerKeyExchange.params);
More specifically, the ECDHE_RSA and ECDHE_DSA mechanisms does not
associate the signature to a TLS1.2 context. As a result, an
attacker could re-used the signature in another context.
The attack may operate by collecting a large collection of clear text
and their corresponding signature. When the attacker want to provide
a signature, it checks in its database, a match occurs between the
two contents to be signed. The probability of a collision increases
with number of available hashes. The attack is related the pre-image
and collision resistance properties of the hash function.
The attacker may also given a clear text to be signed, generate a
collision such that a collision occurs which provides is related to
the second pre-image and collision resistance property of the hash
function.
The surface of attack is limited by:
o limiting the possibility of aggregating a collection of clear text
and their corresponding signatures. This could be achieved by
using multiple LURK Clients using an encrypted channel between the
LURK Client and the LURK Server.
o increasing the checks and ensure that signature is performed in a
TLS 1.2 context. For that purpose it is RECOMMENDED the LURK
Server checks the consistency of its input parameters. This
includes the proof of ownership as well as the format of the
randoms and ecdhe_params for example.
o limiting the usage of a Cryptographic material to a single usage,
in our case serving TLS 1.2.
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9.3. Perfect Foward Secrecy
This document uses sha256 as the freshness_funct, in order to achieve
PFS Section 4.1.1 as described above. By construction of the
server_random, of the output of freshness_funct we will keep only the
last 28 bytes. The PFS property is in place as long as this
truncated version of freshness_funct can be considered a CRHF and
that the 28 bytes of randomness carried by the server_random are
sufficient. Otherwise, the mechanism described in this document will
not be considered as safe.
Details on the truncation will be added. Alternatively, we could use
a hash function like SHA3 (or, more explicitly SHAKE) which considers
variable output length as part of its design. The SHAKE functions
allow arbitrary output lengths and the PFS-input S can be of
arbitrary length too. However, for SHAKE128-d, if the truncated
output is of length d as low as 224 bits (28 bytes), then one only
gets 224/2=112 bits security w.r.t. collision-resistance, > 112 bits
w.r.t. preimage resistance and 112 bits security w.r.t. second
preimage resistance.
One reason why we have the hash-based solution to is to reduce
communication costs between the LURK Client and the LURK Server,
whilst still getting more than some security w.r.t. a MiM corrupting
a LURK Client and then attempting a PFS attack.
But, if we disregard the overhaed on communication costs, we can
consider other mechanisms not based on CRHF for attaining PFS
security. See I and II below.
I. For example, as freshness_funct, one can use an instance of a
pseudo random function (PRF), keyed on a key K that the LURK Server
already shares with the LURK Client. I.e.,
server_random=freshness_funct(S;K). In this case, the mechanisms to
achieve PFS are as follows: 1. The LURK Client and the LURK Server
run a key-establishment protocol before every LURK session to
establish such a new key K for every LURK session. Alternatively,
the export this key of the key-establishment run to secure the
channel. The time-to-live of K is one session only. 2. The LURK
Server generates the value S on its side and send the server_random
to the LURK Client. 3. The LURK Client uses this server_random with
the TLS Client 4. The LURK Server checks the correctness of the use
of the said server_random when the query for the master_secret is
made, with the messages forwarded therein;
II. In fact, since the channel between the LURK Client and the LURK
Server MUST be encrypted by default, all for 2 steps in point I above
can be combined into 1 step (without the need of a specially executed
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key-establishment): a. the LURK Server sends the server_random to
the LURK Client. b. the LURK Client uses this server_random with
the TLS Client c. the LURK Server checks the correctness of the use
of the said server_random when the query for the master_secret is
made, with the messages forwarded therein;
Yet, option I and option II are more expensive on the communication
than the version achieving PFS with a hash function. I.e., in I and
II, the LURK Server needs to be involved on the first part of the TLS
handshake to produce the S or server_random for the LURK Client.
However, note that the LURK Client no longer queries S, hence the
risk of a man-in-the-middle querying an old S is eliminated by
design.
Option II above is akin to what "Content delivery over TLS: a
cryptographic analysis of keyless SSL," by K. Bhargavan, I.
Boureanu, P. A. Fouque, C. Onete and B. Richard at 2017 IEEE
European Symposium on Security and Privacy (EuroS&P), Paris, 2017,
pp. 1-16, suggested in order to amend (forward-secrecy) attacks on
Keyless SSL.
10. IANA Considerations
The requested information is defined in [I-D.mglt-lurk-lurk].
LURK Extension Designation: tls12 LURK Extension Reference: [RFD-TBD]
LURK Extension Description: RSA, ECDHE_RSA and ECDHE_ECDSA for (D)TLS
1.2.
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LURK tls12 Extension Status
Value Description Reference
---------------------------------------------------
0 - 1 Reserved [RFC-TBD-LURK]
2 undefined_error [RFC-TBD]
3 invalid_payload_format [RFC-TBD]
4 invalid_key_id_type [RFC-TBD]
5 invalid_key_id [RFC-TBD]
6 invalid_tls_random [RFC-TBD]
7 invalid_freshness_funct [RFC-TBD]
8 invalid_encrypted_premaster [RFC-TBD]
9 invalid_finished [RFC-TBD]
10 invalid_ec_type [RFC-TBD]
11 invalid_ec_curve [RFC-TBD]
12 invalid_poo_prf [RFC-TBD]
13 invalid_poo [RFC-TBD]
14 invalid_cipher_or_prf_hash [RFC-TBD]
15 - 255 UNASSIGNED
LURK tls12 Extension Type
Value Description Reference
----------------------------------------------
0 capabilities [RFC-TBD]
1 ping [RFC-TBD]
2 rsa_master [RFC-TBD]
2 rsa_master_with_poh [RFC-TBD]
3 rsa_extended_master [RFC-TBD]
3 rsa_extended_master_with_poh [RFC-TBD]
4 ecdhe [RFC-TBD]
16 - 255 UNASSIGNED
11. Acknowledgments
We would like to thank for their very useful feed backs: Yaron
Sheffer, Yoav Nir, Stephen Farrell, Eric Burger, Thomas Fossati, Eric
Rescorla, Mat Naslung, Rich Salz, Ilari Liusvaara, Scott Fluhrer.
Many ideas in this document are from [I-D.erb-lurk-rsalg].
We would also like to thank those that have supported LURK or raised
interesting discussions. This includes among others Robert Skog,
Hans Spaak, Salvatore Loreto, John Mattsson, Alexei Tumarkin, Richard
Brunner, Stephane Dault, Dan Kahn Gillmor, Joe Hildebrand, Kelsey
Cairns.
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12. Apendix
## LURK Exchange for TLS RSA Master Secret
TLS Client Edge Server Key Server
ClientHello
server_version
client_random
cipher_suite
TLS_RSA_*, ...
-------->
S = server_random
server_random = freshness_funct( S )
ServerHello
tls_version
server_random
Cipher_suite=TLS_RSA
Certificate
RSA Public Key
ServerHelloDone
<--------
ClientKeyExchange
EncryptedPremasterSecret
[ChangeCipherSpec]
Finished
-------->
TLS12 Request Header
TLS12MasterRSARequestPayload
key_id
freshness_funct
prf_hash
client_random
S
EncryptedPremasterSecret
-------->
server_random = freshness_funct( S )
master_secret = PRF(\
pre_master_secret + \
"master secret" +\
client_random +\
server_random)[0..47];
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TLS12 Response Header
TLS12MasterResponsePayload
master
<--------
[ChangeCipherSpec]
Finished
<--------
Application Data <-------> Application Data
12.1. LURK Exchange for TLS RSA Master Secret with Proof of Handshake
TLS Client Edge Server Key Server
ClientHello
server_version
client_random
cipher_suite
TLS_RSA_*, ...
-------->
S = server_random
server_random = freshness_funct( S )
ServerHello
tls_version
server_random
Cipher_suite=TLS_RSA
Certificate
RSA Public Key
ServerHelloDone
<--------
ClientKeyExchange
EncryptedPremasterSecret
[ChangeCipherSpec]
Finished
-------->
TLS12 Request Header
TLS12MasterRSAWithPoHRequestPayload
key_id
freshness_funct
handshake_messages
finished
-------->
server_random = freshness_funct( S )
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master_secret = PRF(\
pre_master_secret + \
"master secret" +\
client_random +\
server_random)[0..47];
TLS12 Response Header
TLS12MasterResponsePayload
master
<--------
[ChangeCipherSpec]
Finished
<--------
Application Data <-------> Application Data
12.2. LURK Exchange for TLS RSA Extended Master Secret
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TLS Client Edge Server Key Server
ClientHello
tls_version
cipher_suite
TLS_RSA_*, ...
Extension 0x0017
-------->
ServerHello
edge_server_version
cipher_suite=TLS_RSA
Extension 0x0017
Certificate
RSA Public Key
ServerHelloDone
<--------
ClientKeyExchange
EncryptedPremasterSecret
[ChangeCipherSpec]
Finished
-------->
TLS12 Request Header
TLS12ExtendedMasterRSARequestPayload
key_id
freshness_funct
handshake_messages
EncryptedPreMasterSecret
-------->
1. Computing Master Secret
master_secret = master_prf(
pre_master_secret +\
"extended master secret" +\
session_hash)[0..47]
TLS12 Response Header
TLS12MasterPayload
master
<--------
[ChangeCipherSpec]
Finished
<--------
Application Data <-------> Application Data
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12.3. LURK Exchange for TLS RSA Extended Master Secret with proof of
handshake
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TLS Client Edge Server Key Server
ClientHello
tls_version
cipher_suite
TLS_RSA_*, ...
Extension 0x0017
-------->
ServerHello
edge_server_version
cipher_suite=TLS_RSA
Extension 0x0017
Certificate
RSA Public Key
ServerHelloDone
<--------
ClientKeyExchange
EncryptedPremasterSecret
[ChangeCipherSpec]
Finished
-------->
TLS12 Request Header
TLS12ExtendedMasterWithPoHRequestPayload
key_id
freshness_funct
handshake_messages
finished
-------->
1. Computing Master Secret
master_secret = master_prf(
pre_master_secret +\
"extended master secret" +\
session_hash)[0..47]
TLS12 Response Header
TLS12MasterPayload
master
<--------
[ChangeCipherSpec]
Finished
<--------
Application Data <-------> Application Data
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12.4. LURK Exchange for TLS ECDHE Signature
TLS Client Edge Server Key Server
ClientHello
tls_version
client_random
cipher_suite
TLS_ECDHE_ECDSA_*, TLS_ECDHE_RSA_*, ...
Extension Supported EC, Supported Point Format
-------->
S = server_random
server_random = freshness_funct( S )
TLS12 Request Header
TLS12ECDHEInputPayload
key_id
client_random
S
ecdhe_params
-------->
server_random = freshness_funct( S )
signature = ECDSA( client_random +\
server_random + ecdhe_params )
TLS12 Response Header
TLS12DigitallySignedPayloads
signature
<--------
ServerHello
tls_version
server_random
Cipher_suite=TLS_ECDHE_ECDSA
Extension Supported EC,
Supported Point Format
Certificate
ECDSA Public Key
ServerKeyExchange
ecdhe_params
signature
ServerHelloDone
<--------
ClientKeyExchange
[ChangeCipherSpec]
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Finished
-------->
[ChangeCipherSpec]
Finished
<--------
Application Data <-------> Application Data
13. References
13.1. Normative References
[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>.
[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key
Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
<https://www.rfc-editor.org/info/rfc5480>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A.,
Langley, A., and M. Ray, "Transport Layer Security (TLS)
Session Hash and Extended Master Secret Extension",
RFC 7627, DOI 10.17487/RFC7627, September 2015,
<https://www.rfc-editor.org/info/rfc7627>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/info/rfc8017>.
[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>.
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[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
13.2. Informative References
[I-D.erb-lurk-rsalg]
Erb, S. and R. Salz, "A PFS-preserving protocol for LURK",
draft-erb-lurk-rsalg-01 (work in progress), May 2016.
[I-D.fieau-cdni-https-delegation]
Fieau, F., Emile, S., and S. Mishra, "HTTPS delegation in
CDNI", draft-fieau-cdni-https-delegation-02 (work in
progress), July 2017.
[I-D.ietf-acme-acme]
Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", draft-ietf-acme-acme-18 (work in progress),
December 2018.
[I-D.ietf-acme-star]
Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T.
Fossati, "Support for Short-Term, Automatically-Renewed
(STAR) Certificates in Automated Certificate Management
Environment (ACME)", draft-ietf-acme-star-11 (work in
progress), October 2019.
[I-D.mglt-lurk-lurk]
Migault, D., "LURK Protocol version 1", draft-mglt-lurk-
lurk-00 (work in progress), February 2018.
[I-D.mglt-lurk-tls-use-cases]
Migault, D., Ma, K., Salz, R., Mishra, S., and O. Dios,
"LURK TLS/DTLS Use Cases", draft-mglt-lurk-tls-use-
cases-02 (work in progress), June 2016.
[I-D.rescorla-tls-subcerts]
Barnes, R., Iyengar, S., Sullivan, N., and E. Rescorla,
"Delegated Credentials for TLS", draft-rescorla-tls-
subcerts-02 (work in progress), October 2017.
[I-D.sheffer-acme-star-request]
Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T.
Fossati, "Generating Certificate Requests for Short-Term,
Automatically-Renewed (STAR) Certificates", draft-sheffer-
acme-star-request-02 (work in progress), June 2018.
Migault & Boureanu Expires January 4, 2021 [Page 32]
Internet-Draft LURK/TLS 1.2 July 2020
[RFC8235] Hao, F., Ed., "Schnorr Non-interactive Zero-Knowledge
Proof", RFC 8235, DOI 10.17487/RFC8235, September 2017,
<https://www.rfc-editor.org/info/rfc8235>.
Authors' Addresses
Daniel Migault
Ericsson
8275 Trans Canada Route
Saint Laurent, QC 4S 0B6
Canada
EMail: daniel.migault@ericsson.com
Ioana Boureanu
University of Surrey
Stag Hill Campus
Guildford GU2 7XH
UK
EMail: i.boureanu@surrey.ac.uk
Migault & Boureanu Expires January 4, 2021 [Page 33]