Internet DRAFT - draft-zubov-snif
draft-zubov-snif
Network Working Group J. Zubov
Internet-Draft VESvault Corp
Intended status: Experimental 16 February 2022
Expires: 20 August 2022
Deploying Publicly Trusted TLS Servers on IoT Devices Using SNI-based
End-to-End TLS Forwarding (SNIF)
draft-zubov-snif-04
Abstract
This document proposes a solution, referred as SNIF, that provides
the means for any Internet connected device to:
* allocate a globally unique anonymous hostname;
* obtain and maintain a publicly trusted X.509 certificate issued
for the allocated hostname;
* accept incoming TLS connections on specific TCP ports of the
allocated hostname from any TLS clients that are capable of
sending Server Name Indication.
The private key associated with the X.509 certificate is securely
stored on the TLS terminating device, and is never exposed to any
other party at any step of the process.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-zubov-snif.
Information can be found at https://snif.host.
Source for this draft and an issue tracker can be found at
https://github.com/vesvault/snif-i-d.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Zubov Expires 20 August 2022 [Page 1]
Internet-Draft SNIF February 2022
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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 20 August 2022.
Copyright Notice
Copyright (c) 2022 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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. SNIF CA Proxy Protocol . . . . . . . . . . . . . . . . . . . 4
3.1. Protocol Variables . . . . . . . . . . . . . . . . . . . 5
3.2. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . 5
3.3. CN Allocation Request . . . . . . . . . . . . . . . . . . 7
3.4. CSR Submission Request . . . . . . . . . . . . . . . . . 7
3.5. Certificate Download Request . . . . . . . . . . . . . . 8
4. SNIF Relay Protocol Suite . . . . . . . . . . . . . . . . . . 9
4.1. SNIF Messages . . . . . . . . . . . . . . . . . . . . . . 9
4.2. SNIF Control Connection Protocol . . . . . . . . . . . . 9
4.3. SNIF Service Connection Protocol . . . . . . . . . . . . 12
4.4. SNIF Client Connection Protocol . . . . . . . . . . . . . 13
4.5. SNIF IPC FIFO Protocol . . . . . . . . . . . . . . . . . 14
4.6. Abuse Management . . . . . . . . . . . . . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Normative References . . . . . . . . . . . . . . . . . . 19
Zubov Expires 20 August 2022 [Page 2]
Internet-Draft SNIF February 2022
7.2. Informative References . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
A typical Internet-of-Things (IoT) device connects to the Internet
using a dynamic IP address, and is usually unable to accept incoming
connections to TCP ports. A dedicated trusted relay is needed to
facilitate the communications between the IoT device and its intended
users. While all communications are recommended to be TLS encrypted,
the trusted relay will terminate each TLS connection and therefore
have access to unencrypted traffic between IoT devices and user
clients, which may pose undesirable security risk.
Designing a dedicated relay that works in end-to-end encrypted mode,
where the TLS tunnel is established between the IoT device and the
client, and is passed by the relay in an encrypted form, raises
additional challenges. Clients expect to be able to verify the
authenticity of the TLS certificate presented by the IoT device they
are connecting to. Public certificate authorities requite to
validate the ownership of the hostname the certificate is being
requested for, using certain challenge mechanisms. Therefore, the
IoT device needs to allocate a unique hostname, and to be able to
complete the CA challenge in order to acquire a trusted certificate.
Alternatively, the client may decide to use a different certificate
trust scheme, not based on publicly trusted root CAs. In this case,
the client is limited to specifically built software with custom
trust rules, or the system trust root on the client device needs to
be customized.
This document proposes a solution, referred as SNIF, that allows any
common TLS client with standard root CAs, such as a web browser, to
establish a trusted end-to-end TLS connection with an IoT device
using the unique hostname permanently allocated to the device, via a
dedicated relay.
While this document focuses on IoT devices, SNIF is applicable to any
physical or virtual device or software that can benefit from
accepting trusted TLS connections to an anonymous hostname.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Zubov Expires 20 August 2022 [Page 3]
Internet-Draft SNIF February 2022
2. Overview
_SNIF CA Proxy_ is a combination of web-based services and background
processes that run on a publicly accessible server, normally on the
same physical server as SNIF Relay. SNIF CA Proxy allocates
hostnames for SNIF Connectors and facilitates issuing and renewing
X.509 certificates [RFC5280] without having access to the Connectors'
private keys. The functions of SNIF CA Proxy are described in
Section 3.
_SNIF Relay_ is a process that runs on a publicly accessible server,
normally on the same physical server as SNIF CA Proxy. SNIF Relay
facilitates end-to-end TLS connections, [RFC8446] or older versions,
between SNIF Clients and SNIF Connectors. The functions of SNIF
Relay are described in Section 4.
_SNIF Connector_ is a software process that runs on an IoT device, or
on other type of device that intends to provide TLS-based services
that can be accessed by general purpose TLS clients using SNIF Relay.
SNIF Connector can be implemented as a standalone process that
communicates with the TLS server processes over local filesystem and
sockets, or as an integral part of a TLS server process.
_SNIF Client_ is any common TLS-compatible client with SNI capability
[RFC6066], such as a web browser or an email client, that connects to
a SNIF hostname provided by a specific SNIF Connector. SNIF Client
does not need any awareness of SNIF, or of any protocols described in
this document.
_Certificate Authority (CA)_ is a service that issues public trusted
TLS Certificates to specific hostnames when requested by the hostname
owner, upon validating the ownership of the hostname. CA does not
need any awareness of SNIF, except for a working relationship with
the SNIF CA Proxy that requests certificates using protocols
supported by the CA.
_SNIF Peripheral Process_ is any kind of additional service that
extends or supplements functions of SNIF, in a way not defined within
the scope of this document.
3. SNIF CA Proxy Protocol
SNIF CA Proxy Protocol is designed for securely acquiring and
maintaining a publicly trusted TLS/SSL X.509 certificate issued by a
Certificate Authority to a uniquely allocated hostname, by an agent
that has no direct control over that hostname, or over a server the
hostname is pointing to.
Zubov Expires 20 August 2022 [Page 4]
Internet-Draft SNIF February 2022
SNIF CA Proxy accepts requests from SNIF Connectors via HTTP / HTTPS.
SNIF CA Proxy interacts with the CA using protocols supported by the
CA, such as ACME [RFC8555], not covered by this document.
3.1. Protocol Variables
Each SNIF Connector MUST be configured with an initiation URL
({initUrl}), which is specific to the SNIF CA Proxy server the
Connector intends to work with. Depending on the CA Proxy rules,
{initUrl} might be unique for each Connector, or common for multiple
Connectors.
The canonical name {cn} is received by a SNIF Connector in response
to the CN Allocation Request (Section 3.3), and might be either a
single hostname or a wildcard starting with "*.", depending on the CA
Proxy rules.
{cn_host} is a hostname derived from the {cn} - it is identical to
{cn} in case of a single-host CN, or is the {cn} with truncated
initial "*." in case of a wildcard CN. Note that {cn_host} is
different than the SNIF hostname in case of a wildcard CN.
Each SNIF Connector MAY be configured with an API URL base -
{apiUrl}. If configured, the {apiUrl} SHOULD be HTTPS.
In case if {apiUrl} is not configured - the SNIF Connector MUST
derive {apiUrl} from the {cn_host}, upon allocating the CN, as
following:
{apiUrl} := http://{cn_host}/snif-cert/
3.2. Protocol Flow
Upon the initial start or after a hard reset, the Connector SHALL
generate a Private Key, which needs to be securely permanently stored
by the Connector. Any key algorithm acceptable by the CA can be
used, the choice of the algorithm should be made according to the CA
guidelines and industry practices.
The Connector SHALL send a CN Allocation Request using the {initUrl}.
Having the canonical name {cn}, the Connector SHALL generate a CSR
[RFC2986] using the Private Key, the subject containing the {cn}. The
CSR subject may or may not have other fields besides {cn}, according
to the specific requirements of the CA.
Zubov Expires 20 August 2022 [Page 5]
Internet-Draft SNIF February 2022
The Connector SHALL issue a CSR Submission Request to send the CSR to
the CA Proxy.
Once the CSR is submitted, the Connector MUST permanently store the
{cn} by some means - to minimize the storage compartments it might be
practical to generate and store a dummy self-signed certificate with
the {cn} in the subject until it gets replaced with a trusted
certificate issued by the CA.
A this point, the Connector will normally know the SNIF hostname it
will be using with the SNIF Relay - it matches the {cn} in case of a
single host CN, or is a one sub-level down from a wildcard {cn}, the
name being derived by the Connector in a way that is not
deterministically derivable from the {cn} and the public key, e.g. a
hash of the Private Key.
The Connector can now send a Certificate Download Request, and MUST
verify the returned Certificate. If the Certificate is valid - the
Connector MUST permanently store it.
If the Certificate Download Request fails - the Connector SHOULD
repeat the request after certain delay. In case if the response was
401 and the {authUrl} is returned in a header, and the Connector has
the means of communicating with the device user - the Connector also
SHOULD alert the user and bring {authUrl} to their attention by some
means, so the user can complete the required authorization steps. If
the Connector has no means of alerting the user, which is often the
case with IoT devices - the user MUST be provided with some external
means of authorizing with the CA Proxy, not covered by this
domcument.
Once the Certificate is validated and stored, the Connector is
capable of terminating SNIF connections, and may proceed launching a
SNIF Control Connection (Section 4.2). The Connector SHOULD
communicate its SNIF hostname by some means to the SNIF Clients that
will be accessing the Connector. The means of such communication are
not covered by this document.
The Connector SHOULD watch for the expiration of the stored
Certificate. If the Certificate is about to expire in 7 days or
less, or has already expired - the Connector SHOULD send a
Certificate Download Requests, and repeat with appropriate delays
until the renewed Certificate is successfully downloaded and
verified.
At any stage of the flow, if the Connector receives unexpected volume
of rejections or inconsistent responses from the CA Proxy, the
Connector MAY decide to hard reset the storage and start the flow
Zubov Expires 20 August 2022 [Page 6]
Internet-Draft SNIF February 2022
over from the beginning. In such case, the Connector will have to
re-send its new SNIF hostname to any concerned SNIF Clients, the
means of such communication is not covered by this document.
3.3. CN Allocation Request
Connection from: SNIF Connector
Connection to: SNIF CA Proxy
Protocol: https or http
GET {initUrl}
Response 200: Canonical Name (CN) is successfully allocated. The
response headers MUST include X-SNIF-CN: with the value of the
allocated {cn}, either a wildcard starting with "*.", or a single
hostname, depending on the CA Proxy rules. The Relay MUST NOT ever
return a CN that's been previously returned by another CN Allocation
Request. The Connector SHOULD ignore the response body.
Any other response: Error, try again later.
3.4. CSR Submission Request
Connection from: SNIF Connector
Connection to: SNIF CA Proxy
Protocol: https or http
PUT {apiUrl}{cn_host}.csr
Content-Type: application/pkcs10
The request body MUST contain a PEM encoded PKCS#10 CSR [RFC5967],
the newlines are either <CR><LF> or <LF>, the length of the body
SHOULD NOT exceed 16384 bytes.
Note that a CSR for the specific allocated CN can be submitted to the
CA Proxy once in a lifetime. In case of an incorrect submission the
Connector SHOULD hard reset the storage and restart the flow from the
beginning, including allocating a new CN.
Response 201: the CSR is successfully submitted. The response
headers MAY include X-SNIF-AuthUrl: with the value of an {authUrl},
that SHOULD, if possible, be communicated to the user to authorize
the certificate issuance.
Zubov Expires 20 August 2022 [Page 7]
Internet-Draft SNIF February 2022
Response 403: the CSR for this CN has already been submitted, or is
denied by the CA Proxy rules. If the Connector receives 403, is
SHOULD hard reset the storage and restart the CA Proxy flow from the
beginning.
Response 404: the CN was not allocated.
Any other response: Error, try again later.
3.5. Certificate Download Request
Connection from: SNIF Connector
Connection to: SNIF CA Proxy
Protocol: https or http
GET {apiUrl}{cn_host}.crt
The CA Proxy SHOULD check for a cached previously generated
Certificate chain for the {cn}. If the cached Certificate chain is
found and if it expires in more that 10 days in the future - the
cached Certificate chain SHOULD be returned with status 200.
Otherwise, if the {cn} has a valid CSR and a proper authorization to
issue a certificate - the CA Proxy SHOULD return status 503 and
SHOULD launch a background process that communicates with the CA to
issue or renew the certificate, and caches the issued Certificate
chain for subsequent Certificate Download Requests.
Response 200: the Certificate chain is returned. The Content-Type of
such response SHOULD be "application/x-x509-ca-cert". The response
body MUST be a PEM encoded X.509 certificate chain, the issued
certificate being the first member, the newlines are either <CR><LF>
or <LF>, the length of the body SHOULD NOT exceed 65535 bytes.
Response 503: the Certificate is being issued, try later.
Response 401: Certificate issuance authorization is required. The
response headers MAY include X-SNIF-AuthUrl: with the value of an
{authUrl}, that SHOULD, if possible, be communicated to the user to
authorize the certificate issuance. If the CA Proxy expects to work
with Connectors that cannot communicate with the user, it MUST
include external means of the authorization, not covered by this
document.
Response 404: the CN was not allocated, or the CSR was not submitted.
Any other response: Error, try again later.
Zubov Expires 20 August 2022 [Page 8]
Internet-Draft SNIF February 2022
4. SNIF Relay Protocol Suite
Except for SNIF Client Connection, all protocols mentioned below
involve sending and receiving asynchronous SNIF Messages over a
specific type of stream connection.
_SNIF Control Connection Protocol_ defines communications between
SNIF Relay and SNIF Connector that runs on an IoT device, or other
type of device that provides TLS-based services through SNIF.
_SNIF Service Connection Protocol_ defines secondary communications
between SNIF Relay and SNIF Connector that include end-to-end TLS
traffic forwarded by the Relay.
_SNIF Client Connection Protocol_ defines TLS communications between
SNIF Relay and a Client, where the Relay acts as a transparent end-
to-end forwarder.
_SNIF IPC FIFO Protocol_ defines communications between nodes of a
SNIF Relay cluster, and/or between SNIF Relay and SNIF Peripheral
Processes.
4.1. SNIF Messages
A SNIF Message consists of a 1 or more ASCII characters excluding
special characters, terminated by <CR><LF>.
The total length of a SNIF Message, including the terminal <CR><LF>,
SHOULD NOT exceed 4096 bytes.
8-bit characters are discouraged. If 8-bit characters are used, they
SHOULD comply to UTF-8 [RFC3629].
The receiving party SHOULD silently ignore any invalid or malformed
SNIF message.
4.2. SNIF Control Connection Protocol
Protocol name: snif
Connection from: SNIF Connector
Connection to: SNIF Relay
To be able to open a SNIF Control Connection, the SNIF Connector MUST
have a valid trusted TLS/SSL certificate, the CN hostname DNS
pointing to the SNIF Relay or a wildcard CN having a sub-host DNS
pointing to the SNIF Relay, and a Private Key that matches the
Zubov Expires 20 August 2022 [Page 9]
Internet-Draft SNIF February 2022
Certificate. Normally, the SNIF Connector will generate the Private
Key and use SNIF CA Proxy Protocol (Section 3) to obtain and maintain
the Certificate, although other means can be used.
To initiate the Control Connection, the SNIF Connector opens a TCP
connection to the hostname matching the Certificate's CN, that points
to the Relay.
Upon accepting the incoming TCP connection, the SNIF Relay MUST
initiate a reversed TLS session as a client peer. If the Relay
expects connections from Connectors that have been configured with
{apiUrl} (Section 3.1) - it MAY supply a trusted client TLS
certificate issued to a host matching such {apiUrl}.
The SNIF Connector MUST initiate the TLS as a server peer, using the
Certificate and the Private Key.
Upon successful TLS negotiation, the SNIF Relay MUST validate the
SNIF Connector's certificate. If the certificate is not trusted, the
SNIF Relay MUST shut down the TLS session and the TCP socket
immediately.
If the certificate is accepted, both SNIF Relay and SNIF Connector
are ready to accept SNIF Messages from each other over the TLS
connection, as following.
SNIF LISTEN {hostname}
Sent by: SNIF Connector
The SNIF LISTEN message informs the Relay that the Connector is ready
to accept incoming TLS connections to {hostname} through the Relay.
{hostname} MUST specify a single host (no wildcards), and MUST match
the CN of the Connector's TLS certificate - either match a wildcard
CN, or exactly match a single host CN.
The SNIF LISTEN message SHOULD be sent only once per the Control
Connection. The Relay SHOULD ignore any invalid or subsequent SNIF
LISTEN messages.
SNIF CONNECT {conn_id} {dst_host}:{dst_port} {fwd_host}:{fwd_port} {cln_addr}:{cln_port}
Sent by: SNIF Relay
The SNIF CONNECT message informs the Connector of an incoming TLS
connection from a Client to the Connector's {dst_host}, TCP port
{dst_port}.
Zubov Expires 20 August 2022 [Page 10]
Internet-Draft SNIF February 2022
{conn_id} is a unique alphanumeric connection identifier assigned by
the Relay, {cln_addr}:{cln_port} are the Client's remote IPv4/IPv6
address and TCP port, {cln_addr} is supplied in "[" brackets "]".
The Relay sends the SNIF CONNECT message to Connectors with
{dst_host} matching the {hostname} the Connector is listening to.
The Connector doesn't need to verify {dst_host}.
If the Connector decides to accept the connection - it MUST launch a
SNIF Service Connection to {fwd_host}:{fwd_port}. It also SHOULD send
any SNIF message back to the Relay over the Control Connection to
update the keep-alive timer, a copy of the SNIF ACCEPT message that
is sent over the Service Connection can be used.
In case of a rejection - the Connector SHOULD send SNIF CLOSE with
matching {conn_id}.
SNIF CLOSE {conn_id}
Sent by: SNIF Connector
The SNIF CLOSE message instructs the Relay to terminate the Client
connection with matching {conn_id}.
For SNIF CLOSE received from a Connector, the Relay MUST validate
that the connection was targeted at the Connector's {hostname},
otherwise ignore the message.
SNIF ABUSE {conn_id} {abuse_score}
Sent by: SNIF Connector
The SNIF ABUSE message instructs the Relay to increase the DoS
protection abuse counter for the Client that initiated the connection
{conn_id} by {abuse score}.
{abuse score} SHOULD be an integer from 1 to 255, 1 is the score for
a normal non-abusive connection.
For SNIF ABUSE received from a Connector, the Relay MUST validate
that the connection was targeted at the Connector's {hostname},
otherwise ignore the message.
SNIF MSG {hostname} {content}
Sent by: SNIF Connector or SNIF Relay
Zubov Expires 20 August 2022 [Page 11]
Internet-Draft SNIF February 2022
The SNIF MSG message is relayed between the Connector and the SNIF
Peripheral Processes attached to the Relay.
{content} SHOULD NOT contain whitespaces or special characters. Its
semantics is specific to the targeted Peripheral Process, and is not
covered by this document.
For SNIF MSG received by the Relay from a Connector, the Relay MUST
verify that the {hostname} matches the one associated with the
Connector, forward the message to all IPC FIFOs if matched, ignore
otherwise.
For SNIF MSG received by the Relay from an IPC FIFO, the Relay SHOULD
forward the message to the Connector(s) with the matching {hostname},
ignore the message if none are found.
Note that in certain uncommon circumstances a SNIF MSG send by a
Connector might come back to the Connector through a different
Control Connection. The Connector SHOULD be aware of this fact to
avoid a potential message storm.
NOOP
Sent by: SNIF Connector or SNIF Relay
The NOOP message is not associated with any explicit action, except
that the Relay receiving NOOP from the connector SHOULD promply send
NOOP or any other message back to the Connector. Therefore, the
Connector may use NOOP as a keep-alive ping.
4.3. SNIF Service Connection Protocol
Protocol name: snif-srv
Connection from: SNIF Connector
Connection to: SNIF Relay
The SNIF Connector opens a TCP connection to the
{fwd_host}:{fwd_port} in response to a SNIF CONNECT message received
from the Relay over the Control Connection.
The Connector MUST immediately send a SNIF ACCEPT message over the
Service Connection as a plain TCP:
SNIF ACCEPT {conn_id}
Zubov Expires 20 August 2022 [Page 12]
Internet-Draft SNIF February 2022
The {conn_id} is the one that was received in the SNIF CONNECT
message over the Control Connection.
Upon sending the SNIF ACCEPT message, the Connector MUST immediately
assign further control and bi-directional traffic of the SNIF Service
Connection to the matching TLS server process.
If the Relay decides to reject the connection, either because of
invalid message or {conn_id}, or because of reaching the abuse
threshold - the Relay SHOULD terminate the TCP connection
immediately.
Otherwise, the Relay SHOULD link the Service Connection to the
matched Client Connection, forward to the Service Connection all
buffered TLS data previously received from the Client, and start bi-
directional forwarding between the Client Connection and the Service
Connection.
When either Client or Service Connection is shut down, or an
inactivity timeout is reached, the Relay SHOULD shut down both the
Client Connection and the Service Connection.
Once the Relay has linked the Client Connection matching the
{conn_id} to the Service Connection, any further SNIF ACCEPT messages
with the same {conn_id} on other Service Connections MUST be
rejected.
4.4. SNIF Client Connection Protocol
Protocol name: snif-cln
Connection from: Any TLS enabled software, such as a web browser or
an email client
Connection to: SNIF Relay
From the Client's perspective, a SNIF Client Connection functions as
a direct TLS connection to the IoT Device.
The ports the Relay is listening to, can be any well-known ports for
services with persistent TLS, such as https or imaps, or can be any
custom ports agreed among the Relay, the Connectors and the Clients.
The Relay accepts an incoming TCP connection, receives and buffers
the incoming initial data from the client, and attempts to interpret
the received data as a TLS handshake.
Zubov Expires 20 August 2022 [Page 13]
Internet-Draft SNIF February 2022
If the received data is not recognized as a TLS handshake, does not
contain an SNI record in a supported format, or the SNI hostname does
not meet rules defined for the Relay - the Relay SHOULD immediately
reject the TLS session with an appropriate error status, and shut
down the Client Connection.
If the SNI hostname is found acceptable - the Relay allocates a
unique {conn_id}, checks if there are current Control Connections
that match the SNI hostname, and sends a SNIF CONNECT message over
those connections.
If there are no active applicable Control Connections, or if the
Relay doesn't receive a response from a SNIF Connector within a
specified timeframe - the Relay SHOULD forward the same SNIF CONNECT
message over IPC FIFOs (if any are open) to alert cluster peer Relays
and Peripheral processes of the incoming Client Connection.
A Service Connection with a matching SNIF ACCEPT establishes an end-
to-end TLS circuit with the Client Connection. Once established, the
Relay bi-directionally forwards all traffic between the Client and
the Service Connection until either of the connections is closed or
is timed out due to inactivity.
Upon receiving a matching SNIF CLOSE - the Relay MUST terminate the
Client Connection. If a Service Connection has already been linked
it MUST be terminated too, otherwise the Relay SHOULD attempt to
gracefully reject TLS on the Client Connection with an appropriate
status prior to shutting down TCP.
4.5. SNIF IPC FIFO Protocol
Protocol name: snif-fifo
Connection from: SNIF Relay or SNIF Peripheral Service
Connection to: SNIF Relay or SNIF Peripheral Service
SNIF IPC FIFO is a permanent trusted connection between the SNIF
Relay and a SNIF Peripheral Process, or between a pair of nodes in a
SNIF Relay cluster. An IPC FIFO is usually unidirectional, but a
bidirectional connection can serve as a pair of FIFOs. An IPC FIFO
can be implemented as a Unix FIFO pipe, a TCP socket, an SSH tunnel
or by other means. The mechanism of establishing and maintaining IPC
FIFOs is implementation specific and is not covered by this document.
The following SNIF Messages are defined over an IPC FIFO from the
perspective of a SNIF Relay:
Zubov Expires 20 August 2022 [Page 14]
Internet-Draft SNIF February 2022
SNIF CONNECT {conn_id} {dst_host}:{dst_port} {fwd_host}:{fwd_port} {cln_addr}:{cln_port}
Direction: Send or Receive
(see SNIF Control Connection, Section 4.2).
The SNIF CONNECT message is sent by a Relay over an IPC FIFO in case
if the Relay failed to reach the respective Connector through Control
Connections. SNIF CONNECT sent by a Relay MUST be followed up by one
of SNIF CLEAR or SNIF CLOSE to inform the Peripheral Processes of the
further outcome.
When a SNIF CONNECT message is received by a Relay, the Relay SHOULD
forward it to any matching open Control Connections, or ignore it
otherwise.
SNIF CLEAR {conn_id}
Direction: Send
The SNIF CLEAR message SHOULD be sent by a Relay only as a followup
to SNIF CONNECT with a matching {conn_id}, in case if the Client
Connection that triggered SNIF CONNECT was accepted by a Service
Connection.
The purpose of SNIF CLEAR is to advice Peripheral Processes to cease
further attempts of reaching the Connector by external means, not
specified within this document.
SNIF CLOSE {conn_id}
Direction: Send or Receive
(see SNIF Control Connection, Section 4.2).
The SNIF CLOSE message SHOULD be sent by a Relay only as a followup
to SNIF CONNECT with a matching {conn_id}, in case if the Client
Connection that triggered SNIF CONNECT was closed without being
accepted.
When the SNIF CLOSE is received by a Relay, the Relay SHOULD
immediately close the matching Client and/or Service Connection if
any found, ignore the message otherwise.
SNIF ABUSE {conn_id} {abuse_score}
Direction: Receive
Zubov Expires 20 August 2022 [Page 15]
Internet-Draft SNIF February 2022
(see SNIF Control Connection, Section 4.2).
SNIF MSG {hostname} {content}
Direction: Send or Receive
(see SNIF Control Connection, Section 4.2).
SNIF CTL {ctl_fd} {hostname} {remote_addr}:{remote_port}
SNIF CTL {ctl_fd}
Direction: Send
The SNIF CTL message is sent by a Relay to inform Peripheral
Processes about Control Connections. The first version is sent for
each opening Control Connection, and is followed up by the second
version with the matching {ctl_fd} when the Control Connection is
closed. {ctl_fd} is a numeric descriptor which is unique for open
connections, but can be reused after a connection is closed.
4.6. Abuse Management
SNIF Relay SHOULD implement basic protection from denial of service.
A separate abuse count SHOULD be assigned to each remote address,
incremented by 1 on every incoming connection from the address,
incremented by a specified score on every received SNIF ABUSE
message, and periodically decremented or reset at regular time
intervals.
If the abuse counter for a certain remote address reaches a specific
threshold, the Relay SHOULD drop any further TCP connections from
that address until the abuse counter goes below the threshold. The
Relay MAY allow some grace above the threshold to incoming SNIF
Service Connections, to minimize stalled Client Connections.
SNIF Connector MAY implement basic protection from denial of service
by limiting the number of accepted connections per period of time
and/or the total number of open connections, and reject connections
over the limit.
5. Security Considerations
Requests to CA Proxy (Section 3) sent over plain unencrypted HTTP,
including a PKCS#10 CSR in the CSR Submission Request payload, do not
contain senstive information.
Zubov Expires 20 August 2022 [Page 16]
Internet-Draft SNIF February 2022
The response to the CN Allocation Request, if sent over plain HTTP,
is a randomly generated hostname or wildcard, that will also be
publicly exposed through Certificate Transparency once the
Certificate is issued. Any attempt by an intruder to submit an
alternate CSR for the issued CN prior to the legitimate Connector,
will result in a certificate that doesn't match the Connector's
private key, therefore the Connector will need to hard reset and redo
the initialization. If the intruder alters the X-SNIF-CN: response
sent to the Connector, the CSR submission for a bad CN will be
rejected by the CA Proxy, which will also require to hard reset the
Connector.
The content of the Certificate Download Request response is an X.509
certificate which is safe to be exposed to any parties. If the
intruder alters the HTTP response to the CSR Submission Request or to
the Certificate Download request, the Connector won't receive a valid
certificate and will need a hard reset.
SNIF Connector SHOULD NOT send its hostname to any parties until it
downloads and successfully validates the Certificate from the CA
Proxy.
To mitigate request flooding potentially resulting in denial of
service, it is RECOMMENDED for SNIF CA Proxy to require a Certificate
issuance authorization. For SNIF Connectors that have a means of
interacting with the user such as a built-in web browser, the CA
Proxy SHOULD implement an interactive authorization mechanism not
described in this document, and return {authUrl} to the Connector
(Section 3.5), and the Connector SHOULD open {authUrl} in the browser
for the user to complete the process.
Zubov Expires 20 August 2022 [Page 17]
Internet-Draft SNIF February 2022
For a SNIF CA Proxy that intends to work with devices that have
limited capabilities of interacting with their user, some non-
interactive Certificate issuance authorization mechanism SHOULD be
implemented. As an example of such mechanism, each SNIF Connector
can have a unique {initUrl} that MUST be HTTPS to avoid possible
interception, and each device is supplied with a unique setup URL
presented to the user, the CA Proxy properly mapping each setup URL
to the mathing {initUrl}, and using the setup URL to authorize the
certificate issuance and to communicate the SNIF Connector's hostname
to the user's browser. Such mechanism MUST have a means of alerting
the user about misrouted setup, when some other agent other than the
legitimate user has used the same setup URL during the device setup
process, in such case the user MUST be instructed to immediately hard
reset the device and repeat the setup. Such mechanism is RECOMMENDED
to use an HTTPS {apiUrl} (Section 3.1); otherwise it MUST provide a
means to prevent or detect intercepted setup when an intruder alters
a submitted CSR, such as status lights on the device to indicate the
completion of SNIF setup. The details of such mechanism are not
covered by this document.
Since each certificate issued by a CA remains on the certificate
transparency public records, it is RECOMMENDED for SNIF CA Proxy to
only issue Certificates with a wildcard CN. This way, the actual
Connector's hostname (Section 3.2) will not be listed on the public
records.
SNIF Control Connection Protocol communicates all sensitive
information over a TLS connection with a trusted certificate supplied
by the SNIF Connector. In high security settings, the SNIF Relay
SHOULD provide a trusted client certificate when initiating the
Control Connection, and the Connector SHOULD be configured with an
HTTPS {apiUrl} (Section 3.1). If the client certificate is not valid
for the {apiUrl} - the Connector SHOULD immediately terminate the
Control Connection. In case if the Connector doesn't validate a
client certificate from the Relay - the Connector MUST NOT send any
sensitine information in SNIF MSG messages, and MUST NOT consider any
messages received from the Relay to be trusted.
Zubov Expires 20 August 2022 [Page 18]
Internet-Draft SNIF February 2022
SNIF Service Connection Protocol communicates a randomly generated
{conn_id} over an unsecure TCP connection. Except if used over a
trusted SNIF IPC FIFO, the {conn_id} can be used only once to accept
the Client's TLS connection, which in turn can only be successfully
negotiated by the targeted SNIF Connector. All further
communications are comprised of end-to-end encrypted TLS traffic.
The security of the TLS encrypted content between the Client and the
Connector is specific to the protocols involved. The underlying
protocol SHOULD require proper authentication specific to the
protocol before communicating any sensitive information. Negotiation
of the credentials for such authentication is not covered by this
document.
SNIF Client Connection is a TLS session with a trusted certificate.
The security of the TLS encrypted content between the Client and the
Connector is specific to the protocols involved.
SNIF IPC FIFO connections SHOULD only be established between mutually
trusted parties, and need to be secured by external means specific to
the implementation, such as filesystem permissions, TLS or SSH
tunnels etc. The security of such external means cannot be assessed
within the scope of this document.
A compromised SNIF CA Proxy can potentially issue certificates to any
hostnames allocated by the Relay, including a catch-all wildcard,
using an alternative private key, and thus allow a man-in-the-middle
attack on any SNIF Connectors associated with the Relay. This
vulnerability can be mitigated by constant monitoring of public TLS
Transparency logs, such as [RFC6962]. At least one independent party
SHOULD continuously monitor TLS Transparency logs for each deployed
SNIF CA Proxy and Relay. Once any duplicate or overlapping
certificates are detected - the corresponding SNIF Relay MUST be
permanently deemed compromised.
6. IANA Considerations
Service Names "snif", "snif-srv", "snif-cln" and "snif-fifo" are
registered with IANA.
TCP port 7123 is registered with IANA for service "snif".
7. References
7.1. Normative References
Zubov Expires 20 August 2022 [Page 19]
Internet-Draft SNIF February 2022
[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>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
7.2. Informative References
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967,
DOI 10.17487/RFC5967, August 2010,
<https://www.rfc-editor.org/info/rfc5967>.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
<https://www.rfc-editor.org/info/rfc6962>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>.
Zubov Expires 20 August 2022 [Page 20]
Internet-Draft SNIF February 2022
Author's Address
Jim Zubov
VESvault Corp
Email: jz@vesvault.com
URI: https://snif.host
Zubov Expires 20 August 2022 [Page 21]
