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The "vnc" URI Scheme
draft-warden-appsawg-vnc-scheme-00

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7869.
Authors David Warden , Iordan Iordanov
Last updated 2015-03-24
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draft-warden-appsawg-vnc-scheme-00
Applications Area Working Group                               D. Warden
Internet Draft                                         Dell Products LP
Intended status: Informational                              I. Iordanov
Expires: September 2015                                        Undatech
                                                         March 24, 2015

                           The "vnc" URI Scheme
                   draft-warden-appsawg-vnc-scheme-00.txt

Abstract

   Virtual Network Computing (VNC) software provides remote desktop
   functionality.  This document describes a Uniform Resource
   Identifier (URI) scheme enabling the launch of VNC clients from
   other applications.  The scheme specifies parameters useful in
   securely connecting clients with remote hosts.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on August 27, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document. Code Components extracted from this
   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
   2. The "vnc" URI Scheme...........................................3
      2.1. URI Scheme Syntax.........................................3
         2.1.1. URI Parameters.......................................4
         2.1.2. Data Types...........................................7
      2.2. Processing URIs...........................................9
         2.2.1. Error Handling......................................10
         2.2.2. Connection Profile Matching.........................10
      2.3. Integrated Security Types................................10
         2.3.1. The "Integrated SSH" Security Type..................10
         2.3.2. The "Secure Tunnel" Security Type...................11
   3. Security Considerations.......................................12
      3.1. Application Trust........................................13
      3.2. URI Transmission.........................................13
      3.3. Host Identification......................................14
      3.4. Connection Database Integrity............................14
   4. IANA Considerations...........................................15
      4.1. "vnc" Scheme.............................................15
      4.2. Remote Framebuffer Security Types........................15
      4.3. VNC ID Hash Algorithms...................................16
      4.4. VNC URI Parameters.......................................16
   5. References....................................................17
      5.1. Normative References.....................................17
      5.2. Informative References...................................18
   6. Acknowledgments...............................................18
   Appendix A. "vnc" URI Template...................................19

1. Introduction

   Virtual Network Computing (VNC) clients are used to support remote
   desktop connectivity based on the Remote Framebuffer (RFB) Protocol
   [RFC6143].  It is often desirable to integrate such functionality
   with other software.  However, the lack of a standard method for
   specifying VNC client parameters has limited such integration.

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   The "vnc" Uniform Resource Identifier (URI) scheme specified in this
   document facilitates the launch of VNC clients from applications in
   browser-based, desktop, and mobile environments.  Using this scheme
   users and application vendors will be able to integrate remote
   desktop capabilities without being tied to a particular client.

   Remote desktop clients often store connection profiles in a local
   connection database.  By associating connections specified in a URI
   with those stored in a database, client-specific options can be
   automatically applied to a connection launched from another
   application, even when that application is unaware of those options.

   Connections to VNC servers are often secured using mechanisms
   including Transport Layer Security/Secure Sockets Layer (TLS/SSL)
   tunneling [RFC5246] and Secure Shell (SSH) [RFC4251] tunneling which
   are outside the scope of the RFB protocol.  Defining the behavior of
   these client-integrated security options enables their use with
   "vnc" URIs.

1.1. Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

2. The "vnc" URI Scheme

2.1. URI Scheme Syntax

   The normative syntax of the "vnc" URI is defined in the <vnc-uri>
   rule in the following syntax specification.  This specification uses
   the augmented Backus-Naur Form (BNF) as described in [RFC5234].  The
   "vnc" URI conforms to the generic URI syntax specified in [RFC3986].
   The <host>, <port>, <unreserved>, and <pct-encorded> rules are
   defined in [RFC3986].

   vnc-uri = "vnc://" [ host [ ":" port ] ] [ "?" [ vnc-params ] ]

   vnc-params = param "=" value *("&" param "=" value) ["&"]

   param = 1*( param-char )

   value = *( param-char )

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   param-char = unreserved / pct-encoded / unreserved-symbols

   unreserved-symbols = ":" / "/" / "#" / "[" / "]" / "@" / "!" /

                      "$" / "'" / "(" / ")" / "*" / "," / ";"

   The "?", "=", and "&" characters are used to delimit VNC parameters
   and must be percent-encoded when representing a data octet as
   specified in [RFC3986].  Within the <vnc-params> portion of a "vnc"
   URI the <unreserved-symbols> do not have special meaning and need
   not be percent-encoded when representing a data octet.

   A "vnc" URI has the general form:

      vnc://host:port?parm1=value1&param2=value2...

   The host information and each parameter value specify information
   used in establishing or operating the remote desktop session as
   specified in Section 2.1.1.

   For example:

      vnc://10.0.0.1:5901?VncPassword=secret&SecurityType=2

   Indicates a vnc connection to the host at IP "10.0.0.1" on port
   "5901" with VNC password "secret" using VNC security.

2.1.1. URI Parameters

   A description of host information and URI parameters is provided in
   this section.  Information on the constraints of various data types
   is provided in Section 2.1.2.  All parameters are considered
   optional, however a client will not be able to connect without
   sufficient information.

   The <host> and <port> values in the "vnc" URI specify the address of
   the VNC server on the remote host:

   +------------+------------+-----------------------------+----------+
   | Name       | Type       | Description                 | Default  |
   +------------+------------+-----------------------------+----------+
   | host       | string     | VNC server hostname or IP   |          |
   +------------+------------+-----------------------------+----------+
   | port       | ushort     | VNC server port             | 5900     |
   +------------+------------+-----------------------------+----------+

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   The "vnc" URI parameter values specify remote desktop connection or
   session properties, including aspects of client operation,
   usability, and security as specified in the table below:

   +---------------+---------+-----------------------------+----------+
   | Name          | Type    | Description                 | Default  |
   +---------------+---------+-----------------------------+----------+
   |ConnectionName | string  | Name of connection profile  |          |
   +---------------+---------+-----------------------------+----------+
   |VncUsername    | string  | VNC server username         |          |
   +---------------+---------+-----------------------------+----------+
   |VncPassword    | string  | VNC server password         |          |
   +---------------+---------+-----------------------------+----------+
   |SecurityType   | enum    | VNC security type used      | 2        |
   |               | <vncsec>|                             |(VNC Auth)|
   +---------------+---------+-----------------------------+----------+
   |SshHost        | string  | SSH server hostname or IP   | <host>   |
   +---------------+---------+-----------------------------+----------+
   |SshPort        | ushort  | SSH server port             | 22       |
   +---------------+---------+-----------------------------+----------+
   |SshUsername    | string  | SSH username                |          |
   +---------------+---------+-----------------------------+----------+
   |SshPassword    | string  | SSH password                |          |
   +---------------+---------+-----------------------------+----------+
   |IdHashAlgorithm| enum    | Hash algorithm used with    | 2        |
   |               | <idhash>| "IdHash" parameter          | (SHA1)   |
   +---------------+---------+-----------------------------+----------+
   |IdHash         | string  | Expected hash of remote     |          |
   |               | <hex>   | public key or certificate   |          |
   +---------------+---------+-----------------------------+----------+
   |ColorModel     | enum    | Client color depth/mode     | 7        |
   |               | <cmodel>|                             | (24-bit) |
   +---------------+---------+-----------------------------+----------+
   |ViewOnly       | boolean | Client is view only         | false    |
   +---------------+---------+-----------------------------+----------+
   |SaveConnection | boolean | Store connection info       | true     |
   +---------------+---------+-----------------------------+----------+
   |LaunchKey      | string  | Caller identification       |          |
   +---------------+---------+-----------------------------+----------+

   o  ConnectionName, SaveConnection

      The "ConnectionName" is used to identify a connection profile in
      both the launching application and VNC client.  Profiles are
      applied as described in Section 2.2.2.  If omitted, the client
      MAY generate a name based on the host, port, and/or other
      parameters.  The VNC client MAY normalize the name as required.

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      If true, "SaveConnection" indicates a connection profile should
      be created or updated and stored in the client connection
      database.  If false, no profile should be updated or persisted.

   o  VncUsername, VncPassword, SecurityType

      The SecurityType parameter indicates which RFB security type
      applies to the connection.  VNC security types are recorded in
      the IANA "Remote Framebuffer Security Types" registry created by
      [RFC6143].  The VNC client will use this information to determine
      which parameters are required and establish the connection.

      The "VncUsername" and "VncPassword" are used when applicable to
      authenticate to the VNC server using the specified
      "SecurityType".

   o  SshHost, SshPort, SshUsername, SshPassword

      The SSH parameters are intended for use with the "Integrated SSH"
      security type described in Section 2.3.1. These parameters can
      also be used with any future SSH-based security types.

   o  IdHashAlgorithm, IdHash

      The "IdHashAlgorithm" and "IdHash" values are used to verify the
      expected identity of the remote system based on its public key or
      certificate.  Use of these values in the context of the
      "Integrated SSH" and "Secure Tunnel" security types is provided
      in Section 2.3.

   o  ColorModel

      The "ColorModel" parameter specifies the color model to use for
      data transfer and display as specified in Section 2.1.2.  If the
      requested color model is unsupported, the VNC client SHOULD
      select the supported color model closest to the requested model
      among those having higher color fidelity.  If no supported models
      have higher fidelity, it SHOULD select the model having the
      highest fidelity available.

   o  ViewOnly

      If true, the VNC client should operate in a display-only mode and
      refrain from sending input data including KeyEvent, PointerEvent,
      and ClientCutText messages specified in Section 7.5 of [RFC6143].

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   o  LaunchKey

      If provided, the launch key MAY be used by a client to enable
      licensed features.  The key can help identify a launching
      application for greater security, however if used to enable
      security-sensitive parameters, the VNC client SHOULD perform
      additional verification.

   Parameter names and values shall be interpreted in a case sensitive
   manner, unless otherwise noted.

   Additional parameters likely to be useful with multiple VNC clients
   can be added to the "VNC URI Parameters" registry as specified in
   Section 4.4 of this document.  Individual clients MAY support
   parameters specific to that client. VNC Clients supporting
   application-specific parameters SHOULD include a distinguishing
   prefix within the parameter name, such as the name of the
   application package specified in source code.  For example:

      vnc://?com.dell.vncclient.ScreenMode=2&

   It can also be expected that clients will maintain backward
   compatibility with legacy URI formats and parameters.

2.1.2. Data Types

   As "vnc" URIs may be percent-encoded as specified in [RFC3986] and
   must be decoded.  After decoding, the following type constraints and
   semantics apply:

   o  string

      Values of "string" type are UTF-encoded strings as specified in
      [RFC3629].

      The "string<hex>" subtype used in the "IdHash" consists of colon-
      delimited ":" octets displayed in hexadecimal. For example:

         5D:D2:39:57

      Comparison of "string<hex>" values shall be case-insensitive,
      however the uppercase notation is preferred for readability.

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   o  enum

      The "enum" types consist of specific enumerated subtypes and are
      represented by their decimal index value.

      The "enum<vncsec>" values represent a VNC security type included
      in the IANA "Remote Framebuffer Security Types" registry created
      by [RFC6143].

      Values of the "enum<idhash>" parameter represent secure hash
      algorithms in the "VNC Hash Algorithms" registry created by
      Section 4.3 of this document.  The initial values include:

         Value     Description
         --------  ------------
         1         MD5
         2         SHA1
         4         SHA256

      The MD5 algorithm is described in [RFC1321]. The SHA1 and SHA256
      algorithms are described in [SHS].

      Values of the "enum<cmodel>" subtype represent a color model. In
      the table below, the columns have the meaning specified in
      Section 7.4 of [RFC6143]:

         BPP = bits-per-pixel
         TC = true-color-flag
         RM = red-max
         GM = green-max
         BM = blue-max
         RS = red-shift
         GS = green-shift
         BS = blue-shift

      The values are:

         Value  Description      BPP Depth TC RM   GM   BM   RS GS BS
         -----  ---------------  --- ----- -- ---- ---- ---- -- -- --
         1      Black and White  8   3     t  1    1    1    2  1  0
         2      Greyscale        8   6     t  3    3    3    4  2  0
         3      8 Colors         8   3     t  1    1    1    2  1  0
         4      64 Colors        8   6     t  3    3    3    4  2  0
         5      256 Colors       8   8     t  7    7    3    0  3  6
         6      16-bit Color     16  16    t  31   63   31   11 5  0
         7      24-bit Color     32  24    t  255  255  255  16 8  0
         8      30-bit Color     32  30    t  1023 1023 1023 0  10 20

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      A value of "t" indicates the true-color-flag should be set, the
      big-endian-flag should be set as required for the system.

   o  ushort

      The "ushort" values represent unsigned 16-bit integers expressed
      in decimal digits with value between 0-65535 inclusive.

   o  boolean

      "boolean" values represent conditions that are true or false and
      are represented as either "true" or "false" respectively.  For
      maximum compatibility, clients SHOULD accept the value "1" as
      representing true values and "0" as representing false values.
      Clients SHOULD perform parsing of "boolean" values in a case
      insensitive manner.

   An example "vnc" URI including several of these data types is:

      vnc://localhost:5900?ConnectionName=Server&SecurityType=2&
         IdHash=0D:3A:72:08:57:EA:4D:30&SaveConnection=false&

2.2. Processing URIs

   In general, when a VNC client receives a "vnc" URI it will initiate
   an RFB protocol remote desktop connection using the specified host
   information and parameter values.  Initiating the connection using
   an integrated security mechanism such as those specified in Section
   2.3 may require processing prior to establishing the RFB connection.
   To best integrate with other applications the VNC client SHOULD
   initiate the connection with minimal or no user intervention,
   whenever sufficient information is available and adequate security
   is preserved.

   Host information and parameter values may be provided through
   connection profiles.  When a parameter value is not available from
   either a URI or a connection profile described in Section 2.2.2, the
   default value specified in Section 2.1.1 should be applied.  If
   available parameters are not sufficient to establish a connection,
   the VNC client SHOULD present a session initiation data-entry
   screen. Canceling the dialog or ending the session SHOULD terminate
   the application.

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2.2.1. Error Handling

   If an error prevents a session from being established, the VNC
   client MUST present an error message to the user.  When the message
   is acknowledged, the console application MAY show a session
   initiation data-entry screen populated with available session
   parameters or it MAY terminate.  If an error occurs after a session
   is successfully established which terminates the connection, the VNC
   client MUST present a termination notification to the user.  When
   the termination notification is acknowledged, the client MAY present
   a reconnection prompt or MAY terminate.

2.2.2. Connection Profile Matching

   VNC clients MAY store remote desktop session settings in connection
   profiles.  If the client is able to uniquely identify and associate
   a connection request with a connection profile based on the
   "ConnectionName" parameter value, remote host IP address, or
   hostname/fully-qualified domain name, the VNC client SHOULD apply
   profile values for those settings which do not have values supplied
   in the "vnc" URI.  When profile data is unavailable, the VNC client
   MAY apply global application defaults for settings not supplied in
   the URI and for which the scheme does not specify a default value.
   The VNC client MUST NOT override supplied parameters with profile
   values or global defaults.

   When the "SaveConnection" parameter value is true, a connection
   profile SHOULD be created or updated with the values supplied in the
   "vnc" URI.  Profile updates and storage should be consistent with
   the recommendations in Section 3.4.

2.3. Integrated Security Types

2.3.1. The "Integrated SSH" Security Type

   The "Integrated SSH" security type is establishes an SSH connection
   to a host, authenticates with SSH password authentication,
   establishes a secure tunnel to the VNC host/port, and then connects
   to the VNC server using "VNC Authentication".  The secure tunnel
   will provide encryption and data integrity, while verifying the
   public key authenticates the server.  The SSH architecture is
   specified in [RFC4251].  The steps are detailed below:

   1. The VNC client initiates a transport-level connection to the
      "SshHost" on the "SshPort" specified in the parameter values with
      a key exchange as described in [RFC4253].

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   2. When the VNC client receives the server key (or certificate), the
      hash of the key (or certificate) is computed using the algorithm
      corresponding to the "IdHashAlgorithm" parameter value and
      compared with the expected "IdHash" value (if available).  If the
      certificate hash cannot be verified, the client MUST alert the
      user.  The alert MUST provide the remote system's identifying
      information including the hash value and allow the user to
      terminate the connection. The alert MAY allow the user to accept
      the key and continue establishing the connection.

   3. The SSH client authenticates the user using the "SshUsername" and
      "SshPassword" parameter values according to the "password"
      authentication mechanism described in [RFC4252].

   4. The SSH client opens a TCP/IP channel as specified in [RFC4254]
      from the local system to the system indicated by the <host> and
      <port> information values.

   5. The VNC client establishes a RFB connection to the VNC server
      over the channel and authenticates using VNC Security as
      described in [RFC6143] and the "VncPassword" parameter.

   The VNC client MAY establish the connection described in this
   section using an external SSH client, by launching the client and
   then connecting to a secure tunnel created between a local port and
   the VNC server.

   If the VNC client is supplied with additional parameters outside the
   scope of this document, it MAY perform a variation of these steps
   consistent with the underlying protocols, for example by using
   "publickey" SSH client authentication [RFC4252] or providing another
   form of authentication to the VNC server.

   While the SHA1 hash algorithm is the default, many SSH clients
   present key hashes using MD5 and it can be expected that launching
   applications MAY specify the hash be displayed in the manner its
   users are familiar with.

2.3.2. The "Secure Tunnel" Security Type

   The "Secure Tunnel" security type establishes a TLS connection with
   a remote server using certificate authentication, over which a
   connection to the VNC server is established using "VNC
   Authentication".  The secure tunnel will provide encryption and data
   integrity, while verifying the certificate authenticates the server.
   The TLS protocol is specified in [RFC5246].  The steps are detailed
   below:

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   1. The VNC client initiates the TLS Handshake Protocol with a system
      indicated by the <host> and <port> information values.

   2. When the server certificate is received, the hash of the key
      certificate is computed using the algorithm corresponding to the
      "IdHashAlgorithm" parameter value and compared with the expected
      "IdHash" value (if available).  If the certificate hash cannot be
      verified, the client MUST alert the user.  The alert MUST provide
      the remote system's identifying information and allow the user to
      terminate the connection. The alert MAY allow the user to accept
      the key and continue establishing the connection.

      When providing identifying information of a host identified by an
      X509 certificate [x.509], the certificate subject, issuer,
      validity period, and certificate hash MUST be included.  The VNC
      client MAY give users the option of verifying the certificate
      name, certificate authority, certificate revocation list, and
      validity period.  If information on the validity of a certificate
      is not displayed, the console application MUST include a
      statement indicating such information has not been verified.

   3. The client finishes establishing the TLS tunnel.

   4. The VNC client establishes a RFB connection to the VNC server
      over the channel and authenticates using VNC Security as
      described in [RFC6143] and the "VncPassword" parameter.

   If the VNC client is supplied with additional parameters, it may
   perform a variation of these steps consistent with the underlying
   protocols, for example by providing another form of authentication
   to the VNC server.

   Since the TLS protocol provides backwards compatibility with SSLv3,
   and SSL tunnel MAY be used if supported.

3. Security Considerations

   General security concerns involving URI schemes are discussed in
   [RFC3986].  In implementing support for the "vnc" URI scheme, areas
   for particular consideration include application trust, URI
   transmission, host identification, and connection database security.

   Remote desktop connectivity requires the transmission of security
   credentials, which may be included in a URI.  If those credentials
   are not kept secure, an attacker may gain access to any systems
   using those credentials.  Host addresses and connection parameters

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   may also be considered sensitive, as such information can be used in
   planning an attack.

   URIs can also contain host identification information.  It is
   important to securely identify the remote host system connected to.
   If a user connects to an attacker's system, user data, including
   credentials, may be exposed.

   Note that the RFB protocol itself does not encrypt data.  To protect
   data in transit, RFB should be tunneled over TLS [RFC5246], SSH
   [RFC4251], or another secure protocol.

   Some VNC systems can be used without authentication. To protect the
   remote host, strong passwords or other authentication mechanisms
   should be used.

3.1. Application Trust

   A malicious application receiving VNC credentials via URI or other
   means can obviously misuse those credentials.  To protect against
   this, users should only install applications from trusted sources.
   The integrity of application packages can be verified through
   digital signatures.

   Applications launching VNC clients MAY wish to launch only
   particular trusted clients, and can specify those clients through
   platform-specific mechanisms.  Package integrity can be verified
   programmatically by querying the package manager for digital
   signatures or other platform-specific means.

   The risk to a VNC client from a launching application is generally
   much lower, since the launching application will not receive
   credentials or data from the client.  A VNC client MAY verify its
   caller thorough platform-specific means.

   VNC clients SHOULD NOT accept potentially destructive parameters
   from untrusted launching applications without explicit user
   confirmation.  For example, a client-specific parameter that runs an
   arbitrary command upon establishing a SSH connection used for VNC
   tunneling is potentially destructive and high risk.

3.2. URI Transmission

   Within a mobile or desktop environment, application launch will
   typically involve in-memory URI data transmission facilitated and
   secured by the OS.

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   If sensitive URI information is exchanged across a network, for
   example by providing a list of connection URIs in a web page, the
   data should be encrypted in transit and only be accessible to
   authorized users.

3.3. Host Identification

   In the absence of verifiable host identification, a VNC client
   application is vulnerable to spoofing and man-in-the-middle attacks
   which capture VNC or host OS credentials and user data.  To prevent
   such attacks, administrators SHOULD secure their VNC communications
   with TLS [RFC5246] or SSH [RFC4251] tunnels or other connection
   mechanisms identifying remote hosts via certificate or public key.
   VNC clients MUST verify the respective certificates or public keys
   to confirm the remote host's identity.

   An application launching a VNC client via URI MAY provide a
   certificate hash or public key hash identifying the remote host.
   VNC clients maintaining a connection database MAY also store
   certificate or public key data suitable for validating a host's
   identity.

   If connecting to a system identified by certificate or public key
   and a remote system ID hash cannot be matched to available
   identifying data, the VNC client MUST alert the user.  The alert
   MUST provide the remote system's identifying information and allow
   the user to terminate the connection.  The alert MAY allow the user
   to accept the information and continue establishing the connection.

   When providing identifying information of a host identified by an
   X509 certificate [x.509], the certificate subject, issuer, validity
   period, and certificate hash MUST be included.  The VNC client MAY
   give users the option of verifying the certificate name, certificate
   authority, certificate revocation list, and validity period.  If
   information on the validity of a certificate is not displayed, the
   console application MUST include a statement indicating such
   information has not been verified.

   Identifying information of a host identified by public key, such as
   the endpoint of an SSH connection using a raw key, MUST include a
   hash of the key.

3.4. Connection Database Integrity

   A VNC client application and/or launching application MAY maintain a
   connection database containing remote host information, credentials,
   and/or connection parameters.  Applications MUST NOT store

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   credentials unless the credentials are stored in an encrypted format
   with a decryption process requiring user-supplied or device-specific
   data.  If supported, an application SHOULD have a setting disabling
   storage of credentials.

   If available, the VNC client connection database SHOULD store
   certificate or public key data used to verify host identification.
   To prevent a malicious URI from overriding the database, if
   identification information in the URI conflicts with information in
   the database, the user MUST be prompted to accept the new
   information prior to updating the database.

4. IANA Considerations

   The "vnc" scheme should be registered in the URI schemes registry.

   The IANA "Remote Framebuffer Security Types", "VNC ID Hash
   Algorithms", and "VNC URI Parameters" registries support elements of
   the scheme.  Future assignments to these registries should be made
   through the "Expert Review" or "IESG Approval" process described in
   [RFC5226].

4.1. "vnc" Scheme

   The "vnc" scheme should be listed in the URI schemes registry with
   description "Remote Framebuffer Protocol" and reference to this
   document.  A registration template is provided in Appendix A.

4.2. Remote Framebuffer Security Types

   This document references the existing IANA "Remote Framebuffer
   Security Types" registry in specifying security type options.  The
   registry includes entries for the "Secure Tunnel" and "Integrated
   SSH" security types described in this document and should refer to
   this document.

   Future RFB security types will be supported in "vnc" URIs.  Any new
   security mechanism integrated with a VNC client which alters the
   process by which a connection is established should also be
   reflected in the registry to avoid overlapping numeric assignments.

   This applies even if the mechanism does not involve a change to the
   VNC server implementation or RFB protocol itself.  For example, the
   "Secure Tunnel" security type does not require RFB modification, but
   indicates to the client that it must establish a TLS tunnel prior to
   initiating RFB communications.  Without inclusion in the registry, a

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   URI-launched client will be unable to distinguish future client-
   initiated and protocol-based security mechanisms.

4.3. VNC ID Hash Algorithms

   The ID hash algorithms should be maintained in a "VNC ID Hash
   Algorithms" sub-registry within the "Remote Framebuffer (RFB)"
   protocol registry.  The registry should include the enumeration
   value, description, and reference document/contact person.

   The initial hash algorithms specified are a subset of the algorithms
   contained in the "TLS HashAlgorithm Registry". The initial contents
   of the registry are:

   Value     Description   Reference
   --------  ------------  ---------------
   1         MD5           (this document)
   2         SHA1          (this document)
   4         SHA256        (this document)

4.4. VNC URI Parameters

   The URI parmeters should be maintained in a "VNC URI Parameters"
   sub-registry within the "Remote Framebuffer (RFB)" protocol
   registry.

   The initial contents are described in this document. They are:

   +-----------------+-----------------------------+-----------------+
   | Name            | Description                 | Reference       |
   +-----------------+-----------------------------+-----------------+
   | ConnectionName  | Name of connection profile  | (this document) |
   +-----------------+-----------------------------+-----------------+
   | VncUsername     | VNC server username         | (this document) |
   +-----------------+-----------------------------+-----------------+
   | VncPassword     | VNC server password         | (this document) |
   +-----------------+-----------------------------+-----------------+
   | SecurityType    | VNC security type used      | (this document) |
   +-----------------+-----------------------------+-----------------+
   | SshHost         | SSH server hostname or IP   | (this document) |
   +-----------------+-----------------------------+-----------------+
   | SshPort         | SSH server port             | (this document) |
   +-----------------+-----------------------------+-----------------+
   | SshUsername     | SSH username                | (this document) |
   +-----------------+-----------------------------+-----------------+
   | SshPassword     | SSH password                | (this document) |
   +-----------------+-----------------------------+-----------------+

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   +-----------------+-----------------------------+-----------------+
   | IdHashAlgorithm | Hash algorithm used with    | (this document) |
   |                 | "IdHash" parameter          |                 |
   +-----------------+-----------------------------+-----------------+
   | IdHash          | Expected hash of remote     | (this document) |
   |                 | public key or certificate   |                 |
   +-----------------+-----------------------------+-----------------+
   | ColorModel      | Client color depth/mode     | (this document) |
   +-----------------+-----------------------------+-----------------+
   | ViewOnly        | Client is view only         | (this document) |
   +-----------------+-----------------------------+-----------------+
   | SaveConnection  | Store connection info       | (this document) |
   +-----------------+-----------------------------+-----------------+
   | LaunchKey       | Caller identification       | (this document) |
   +-----------------+-----------------------------+-----------------+

5. References

5.1. Normative References

   [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
             April 1992.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3629] Yergeau, F., "UTF-8, a transformation format of
             ISO 10646", STD 63, RFC 3629, November 2003.

   [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
             Resource Identifier (URI): Generic Syntax", STD 66, RFC
             3986, January 2005.

   [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
             Protocol Architecture", RFC 4251, January 2006.

   [RFC4252] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
             Authentication Protocol", RFC 4252, January 2006.

   [RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
             Transport Layer Protocol", RFC 4253, January 2006.

   [RFC4254] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
             Connection Protocol", RFC 4254, January 2006.

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   [RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
             Syntax Specifications: ABNF", STD 68, RFC 5234, January
             2008.

   [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
             (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC6143] Richardson, T., and J. Levine, "The Remote Framebuffer
             Protocol", RFC 6143, March 2011.

   [SHS]     NIST FIPS PUB 180-2, "Secure Hash Standard", National
             Institute of Standards and Technology, U.S. Department of
             Commerce, August 2002.

   [X.509]   ITU-T Recommendation X.509 (2005) | ISO/IEC 9594-8:2005,
             Information technology - Open Systems Interconnection -
             The Directory: Public-key and attribute certificate
             frameworks.

5.2. Informative References

   [RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
             Registration Procedures for New URI Schemes", BCP 35, RFC
             4395, February 2006.

   [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", BCP 26, RFC 5226,
             May 2008.

6. Acknowledgments

   RFB and VNC are registered trademarks of RealVNC Ltd. in the U.S.
   and in other countries.

   This document was prepared using 2-Word-v2.0.template.dot.

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Appendix A.                 "vnc" URI Template

   This template is provided for registration of the VNC URI in the
   IANA URI schemes registry as specified in [RFC4395].

   URI Scheme name: vnc

   Status: Permanent

   URI scheme syntax: See Section 2 of this document.

   Encoding considerations: See Section 2 of this document.

   Applications/protocols that use this URI scheme name: Virtual
   Network Computing (VNC) remote desktop applications use vnc URIs.
   VNC applications use the Remote Framebuffer (RFB) protocol.

   Interoperability considerations: Legacy software applications
   respond to vnc URIs in different ways and may fail to behave as
   expected. It is advisable to test vnc URIs with specific
   applications or consult application-specific documentation.

   Security considerations: See Section 3 of this document.

   Contact: IETF Applications Area Directors <app-ads@tools.ietf.org>

   Author/Change Controller: See the Authors of this document. Change
   control is through the IESG on behalf of the IETF iesg@ietf.org.

   References: This document.

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Authors' Addresses

   David Warden
   Dell Products LP
   200 Dell Way
   Round Rock, Texas 78682
   U.S.A.

   Phone: 512-728-0380
   Email: David_Warden@dell.com
   URI:   http://www.dell.com

   Iordan Iordanov
   Undatech
   260 Scarlet Road, Apt. 503
   Toronto, ON M6N 4X6
   CANADA

   Email: iiordanov@gmail.com

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