Network Working Group                                           J. Zubov
Internet-Draft                                             VESvault Corp
Intended status: Experimental                            31 January 2022
Expires: 4 August 2022


 Deploying Publicly Trusted TLS Servers on IoT Devices Using SNI-based
                    End-to-End TLS Forwarding (SNIF)
                          draft-zubov-snif-00

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 [RFC5280]
      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 [RFC6066]

   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-00 .

   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 4 August 2022                 [Page 1]


Internet-Draft                    SNIF                      January 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 4 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 Summary  . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Protocol Flow . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  CN Allocation Request . . . . . . . . . . . . . . . . . .   6
     3.4.  CSR Submission Request  . . . . . . . . . . . . . . . . .   7
     3.5.  Certificate Download Request  . . . . . . . . . . . . . .   8
   4.  SNIF Relay Protocol Suite . . . . . . . . . . . . . . . . . .   8
     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 . . . . . . . . . . . . . . . . . . . . .  17
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  17



Zubov                     Expires 4 August 2022                 [Page 2]


Internet-Draft                    SNIF                      January 2022


     7.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18

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 4 August 2022                 [Page 3]


Internet-Draft                    SNIF                      January 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 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 between SNIF Clients with 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, 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 4 August 2022                 [Page 4]


Internet-Draft                    SNIF                      January 2022


3.1.  Protocol Summary

   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.

   Each SNIF Connector is configured with a specific 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.

3.2.  Protocol Flow

   Upon the initial start or after a hard reset, the Connector MUST
   generate a Private Key, which needs to be securely permanently stored
   by the Connector.  Any key algorithm acceptable by the CA can be
   used, generally RSA-4096 is recommended.

   The Connector MUST send a CN Allocation Request using the {initUrl}.

   Having the {cn}, the Connector MUST 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.

   The Connector MUST 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 SHOULD communicate the
   hostname by some means to the SNIF Clients that will be accessing the
   Connector.  The means of such communication is not covered by this
   document.






Zubov                     Expires 4 August 2022                 [Page 5]


Internet-Draft                    SNIF                      January 2022


   The Connector can now send a Certificate Download Request, and SHOULD
   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 should be provided with some
   external means of authorizing with the CA Proxy, not covered by this
   domcument.

   Once the Certificate is stored, the Connector is capable of
   terminating SNIF connections, and may proceed launching a SNIF
   Control Connection (Section 4.2).

   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
   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}









Zubov                     Expires 4 August 2022                 [Page 6]


Internet-Draft                    SNIF                      January 2022


   Response 200: 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 response content type SHOULD be "text/plain",
   the response body SHOULD include the copy of the allocated {cn},
   optionally padded with newlines or spaces on the right.

   Any other response: Error, try again later.

3.4.  CSR Submission Request

   Connection from:  SNIF Connector

   Connection to:    SNIF CA Proxy

   Protocol:         http

      PUT http://{cn_host}/snif-cert/{cn_host}.csr
      Content-Type: application/pkcs10

   {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.

   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.

   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.





Zubov                     Expires 4 August 2022                 [Page 7]


Internet-Draft                    SNIF                      January 2022


3.5.  Certificate Download Request

   Connection from:  SNIF Connector

   Connection to:    SNIF CA Proxy

   Protocol:         http

      GET http://{cn_host}/snif-cert/{cn_host}.crt

   {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.

   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 Connector cannot
   communicate with the user, the CA Proxy should 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.

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.



Zubov                     Expires 4 August 2022                 [Page 8]


Internet-Draft                    SNIF                      January 2022


   _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

   Default port:     TCP 7123

   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
   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.




Zubov                     Expires 4 August 2022                 [Page 9]


Internet-Draft                    SNIF                      January 2022


   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.

   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 send 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}.

   {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 "]".






Zubov                     Expires 4 August 2022                [Page 10]


Internet-Draft                    SNIF                      January 2022


   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

   The SNIF MSG message is relayed between the Connector and the SNIF
   Peripheral Processes attached to the Relay.






Zubov                     Expires 4 August 2022                [Page 11]


Internet-Draft                    SNIF                      January 2022


   {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

   Default port:     TCP 7120 (unofficial)

   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}

   The {conn_id} is the one that was received in the SNIF CONNECT
   message over the Control Connection.



Zubov                     Expires 4 August 2022                [Page 12]


Internet-Draft                    SNIF                      January 2022


   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

   Default port:     N/A

   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 4 August 2022                [Page 13]


Internet-Draft                    SNIF                      January 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

   Default port:     N/A

   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.





Zubov                     Expires 4 August 2022                [Page 14]


Internet-Draft                    SNIF                      January 2022


   The following SNIF Messages are defined over an IPC FIFO from the
   perspective of a SNIF Relay:

   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.  When sent by a Relay, SNIF CONNECT 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}



Zubov                     Expires 4 August 2022                [Page 15]


Internet-Draft                    SNIF                      January 2022


   Direction:        Receive

   (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

   All information communicated to/from SNIF CA Proxy over plain
   unencrypted HTTP is safe to be exposed to third parties or to
   intruders without compromising any private information.




Zubov                     Expires 4 August 2022                [Page 16]


Internet-Draft                    SNIF                      January 2022


   SNIF Control Connection Protocol communicates all sensitive
   information over a TLS connection with a trusted certificate.

   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 authentification 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 continuosly 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

   Protocols "snif", "snif-srv", "snif-cln" and "snif-fifo" are
   registered with IANA.

   TCP port 7123 is registered with IANA for protocol "snif".

7.  References

7.1.  Normative References




Zubov                     Expires 4 August 2022                [Page 17]


Internet-Draft                    SNIF                      January 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>.

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>.

Author's Address






Zubov                     Expires 4 August 2022                [Page 18]


Internet-Draft                    SNIF                      January 2022


   Jim Zubov
   VESvault Corp

   Email: jz@vesvault.com
   URI:   https://snif.host














































Zubov                     Expires 4 August 2022                [Page 19]