Mathematical Mesh: Architecture
draft-hallambaker-mesh-architecture-00

Network Working Group                                    P. Hallam-Baker
Internet-Draft                                         Comodo Group Inc.
Intended status: Standards Track                        January 14, 2016
Expires: July 17, 2016

                    Mathematical Mesh: Architecture
                 draft-hallambaker-mesh-architecture-00

Abstract

   The Mathematical Mesh ?The Mesh? is an end-to-end secure
   infrastructure that facilitates the exchange of configuration and
   credential data between multiple user devices.  The architecture of
   the Mesh and examples of typical applications are described.

Status of This Memo

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1.  Introduction

   The Mathematical Mesh is a user centered Public Key Infrastructure
   that uses cryptography to make computers easier to use.

   The Mesh uses cryptography and an untrusted cloud service to make
   management of computer configuration data transparent to the end
   user.  Each Mesh user has a personal profile that is unique to them
   and contains a set of public keys for maintaining the user?s Mesh
   profile.

2.  Definitions

2.1.  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].

3.  Background

   Public Key Cryptography permits Internet applications to be secure
   but requires an infrastructure for key distribution.

   WebPKI has been very successful for E-commerce.  Client side PKI has
   been remarkably less successful.

   S/MIME and OpenPGP both have significant user bases but both have
   been limited to a small community.  Government for S/MIME, system
   admins and security researchers for OpenPGP.  Use of PKI for
   authentication of Web users has seen negligible use.

   One of the chief obstacles any network application has to overcome is
   the critical mass problem.  While S/MIME and OpenPGP both have
   several million users, this is a small fraction of the number of
   email users.

   It is likely that the more significant obstacle to deployment is the
   difficulty of using client side PKI applications.  While S/MIME and
   OpenPGP both claim to reduce the effort of sending secure email ?to a
   single click?, no security feature that requires the user to make a
   conscious decision to use it every time it is used can ever hope to
   achieve ubiquitous deployment.

   Attempting to automate the process of sending encrypted mail
   introduces a new problem.  The fact that a user has configured a
   client to receive encrypted mail the past does not mean that they are
   capable of receiving and decrypting such mail today.  And even if

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   they are still capable of receiving the encrypted mail today, this
   capability may be limited to a single machine that they do not
   currently have access to.

   While such objections have been repeatedly dismissed as trivial and
   ?easily solved? by protocol designers, to ordinary email users, they
   are anything but trivial.  If a change is to be made to an
   infrastructure they rely on daily, it must be completely transparent.
   An email security infrastructure that interrupts or disrupts their
   flow of work is totally unacceptable.

   Equally overlooked by application designers is the difficulty of
   configuring applications that support end-to-end security through
   cryptography.  While working on this project, the author attempted to
   configure a very popular email client to make use of the built in S/
   MIME capabilities.  Even with 25 years of experience, this took over
   half an hour and required the user to follow a procedure with 17
   different steps!

   It is important to note that this complexity is not simply a
   consequence of one poorly designed application, it is the result of
   the functions of the PKI being divided across three poorly integrated
   applications on the user?s machine compounded by a set of network
   protocols that are not designed to provide a seamless user
   experience.

   A similar problem is illustrated by the problem of configuring SSH.
   There is a simple way to configure SSH and there is a secure way and
   these are not the same.  The simple way to configure SSH is for each
   user to create a single keypair and copy it to each of the machines
   they might need terminal access to.  While this is straightforward it
   means that there is no way to mitigate the possibility of the key
   being compromised if a machine is lost or stolen.  Sharing a private
   key between machines is as bad as sharing a password between
   accounts.  But attempting to achieve cryptographic hygiene across a
   diverse collection of devices requires user effort proportional to
   the square of the number of devices.

3.1.  What it means to be user-centered

   A key principle that guides the design of the Mesh is that any set of
   instructions that can be written down and given to a user can be
   written down as code and executed by the computer.  Public key
   cryptography is used to automate the process of managing public keys.

   Traditional PKI attempted to solve the problems that were of
   paramount concern to the designers.  The designers of S/MIME were
   concerned with the problem of exchanging secure email within a

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   hierarchical organization and built a (mostly) hierarchical design.
   The designers of OpenPGP were concerned with the risk of government
   subversion of the trust infrastructure for nefarious ends.

   But what does the user care about?  What is the user?s principal
   concern?

   The biggest concern I hear from users is not the risk that someone
   else might get to see their confidential data, rather it is the risk
   that they might lose their precious data by some unintended user-
   error.

   Being user centered means considering and addressing the requirements
   that are set by users regardless of whether they are compatible with
   the designer?s view of optimal security.  In particular a user-
   centered PKI must address requirements such as:

   Guaranteeing that data loss does not happen even in the most extreme
   cases of total loss or destruction of all hardware they used to store
   their keys.

   Mitigating the consequences of user error or carelessness.

   Mitigating the consequences of devices being lost or stolen.

   Providing mechanisms that permit a user to permit access to their
   digital assets after their death.

3.2.  Eliminate unnecessary options

   Traditionally cryptographic applications give the user a bewildering
   choice of algorithms and options.  They can choose to have one RSA
   keypair used for encryption and signature or they can have separate
   keys for both, they can encrypt their messages using 3DES or AES at
   128, 192 or 256 bit security.  And so on.

   The Mesh eliminates such choices as unnecessary.  Except where
   required by an application, the Mesh always uses separate keys for
   encryption and signature operations and only uses the highest
   strength on offer.  Currently, Mesh profiles are always encrypted
   using RSA with a 2048 bit key, AES with a 256 bit key and SHA-2-512.
   (The CFRG ECC curves will be added in the near future when
   implementations become available.)

   For similar reasons, every Mesh master profile has an escrow key.
   The use of key escrow by applications is optional, but every profile
   has the capability of using it should circumstances require.

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3.3.  Why change is possible

   All four of the open standards based PKIs that have been developed in
   the IETF are based on designs that emerged in the mid-1990s.
   Performing the computations necessary for public key cryptography
   without noticeable impact on the speed of user interaction was a
   constraint for even the fastest machines of the day.  Consequently,
   PKI designs attempted to limit the number of cryptographic operations
   required to the bare minimum necessary.  There were long debates over
   the question of whether certificate chains of more than 3
   certificates were acceptable.

   Today a 32 bit computer with two processing cores running at 1.2GHz
   can be bought for $5 and public key algorithms are available that
   provide a higher level of security for less computation time.  In
   1995, the idea that a single user might need a hundred public key
   pairs and a personal PKI to manage them as an extreme scenario.
   Today when the typical user has a phone, a tablet and a laptop and
   their home is about to fill up dozens if not hundreds of network
   connected devices, the need to manage large numbers of keys for
   individual users is clear.

   Almost any information security requirement has a straightforward
   solution if you are prepared to commit the necessary resources.  In
   general, each degree of cryptographic separation that is required
   will introduce an additional layer of hierarchy.

   Traditionally PKI has focused on the problem of delegating trust from
   one party to another.  Such capabilities have been implicit in the
   model but only expressed in applications to a limited degree.

   In the WebPKI, Certificate Authorities maintain the private keys
   corresponding to their widely distributed root keys in offline
   facilities that are never connected to the Internet.  These keys are
   in turn used to sign ?intermediate root certificates? corresponding
   to the keys used to sign end entity certificates.  The CA has this
   capability but the end entity does not.  In the PKIX model it is
   assumed that if the end entity needs to change their cryptographic
   configuration, they will go back to their CA and get a new
   certificate.

   In the OpenPGP Web of trust, Alice signs the key of Bob who signs the
   key of Carol.  Since everyone is a trust provider in the OpenPGP
   model, Alice can sign a key for Alice.  This mechanism is used to
   support key rollover but the task of distributing her new keys to the
   devices where Alice needs them is a problem left to Alice.

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   While it is quite possible for a very capable and experienced PKI
   expert to configure PKIX and OpenPGP applications in a fashion that
   supports management of personal keys, such use is far beyond what can
   reasonably be expected of typical users.

   The Mesh applies PKI technology to the problem of making PKI use
   effortless.  Once an initial configuration is established, the user
   is not required to think about PKI at all.  Every PKI operation (e.g.
   key and certificate rollover) is performed automatically.

4.  Basic Concepts

4.1.  Parties

   The Mesh is a network infrastructure.  As with any such
   infrastructure it is formed not as a set of things but rather as the
   relationship between those things.

4.1.1.  User

   A Mesh user is a person or organization that has established a Mesh
   personal profile.  A Mesh personal profile describes the
   configuration of the set of devices and applications that the user
   uses.  Each Mesh profile is identified by a globally unique
   fingerprint value.

   A Mesh user MAY have multiple profiles for the purpose of
   compartmentalizing their online identity and preventing activity in
   one network context being linked to activity in another network
   context.  The extent to which such separation provides increased
   privacy is not currently understood.  From the point of view of the
   Mesh protocols, such profiles are held by separate users.

   At present the Mesh specifications are designed to support
   requirements arising from personal use such as the user transferring
   application settings from one device they own to another device they
   own.  To deploy the Mesh in an enterprise environment, features such
   as the ability to import settings provided by the IT department are
   highly desirable.

4.1.2.  Devices

   The Mesh may be used on any computer that has the ability to connect
   to a network and perform public key cryptography.

   Every device that uses the Mesh has a unique device profile that
   specifies public key pairs that are unique to that device.

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   When a device is connected to a user?s personal profile, it may be an
   Administration Device or a Connected Device depending on whether it
   has been assigned an Administration key.

      Administration device  A device that has access to an
         administration key for the user?s Mesh Personal Profile and is
         thus authorized to authorize actions such as connecting a new
         device to the profile, removing devices and creating or
         removing application profiles.

      Connected Device  A device that is connected to the Mesh Personal
         Profile that is not an administration device.

         Note that a device MAY be connected to more than one Personal
         Profile at the same time.  For example, an embedded device such
         as a thermostat might have a single device profile installed
         during manufacture.  If Alice and Bob share the same
         accommodations where the thermostat is installed, both users
         might have connected the device to their personal profile.

4.1.3.  Portal Provider

   Users do not interact with a Mesh Directly.  All interaction with the
   Mesh is mediated by a Portal Provider.  The portal provider is
   responsible for protecting the Mesh from abuse such as Denial of
   Service attacks, resource exhaustion, spam, etc.

   Users interact with a portal provider through an account which has an
   account identifier in the traditional [RFC5822] format:

   <<user>@<<domain>

   Where is an account identifier that is unique to that portal service
   and is the DNS name of the portal service.

4.1.4.  Mesh Provider

4.1.5.  InterMesh

4.2.  Technology

4.2.1.  UDF Fingerprints

   The Uniform Data Fingerprint format (UDF) [draft-hallambaker-udf] is
   used to construct names for Mesh data items.  UDF employs Base32

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   [RFC3977] encoding and the SHA-2-512 and SHA-3-512 digest functions
   to construct fingerprints of varying lengths.

   The choice of fingerprint length is a balance between security and
   compactness of the representation.  Longer fingerprints offer higher
   security but are less convenient.  The minimum fingerprint size
   recommended for use in the Mesh is 25 characters, this presents a
   work factor of 2^117 to an attacker attempting to generate a
   signature key matching a particular fingerprint, approximately the
   same work factor as RSA with 2048 bit keys.

4.2.2.  Resolving

   In contrast to the URLs resolved by the HTTP protocol which identify
   a resource by means of a location and a means of retrieval, a UDF
   fingerprint only identifies a fixed data object and the data type.

   A UDF resolution service resolves UDF fingerprints in the same manner
   that a HTTP server resolves URLs but can only provide a response for
   the set of fingerprints known to that specific server.  Unlike the
   HTTP service which the client must trust to return the correct
   resource, every response returned by a UDF resolution service may be
   validated against the fingerprint presented in the original request.
   Thus a user of a UDF resolution service is not required to trust it
   for the integrity of the result received.

4.2.3.  Signed Resources

   UDF fingerprints provide a probabilistically unique identifier for a
   static data object but do not provide a direct means of identifying
   resources that change over time.  To identify such resources, digital
   signatures are used.  A public key signature pair is created and the
   UDF fingerprint of the public key parameters serves as the
   identifier.  The private key is then used to sign either the data
   object itself or a data object containing a further public key.

   The application/pkix-keyinfo content type described in [draft-
   hallambaker-udf] is used to create identifiers for public keys.

4.2.4.  Profile

   A Mesh profile is a set of configuration settings that is bound to a
   persistent identifier (a UDF fingerprint).

   The Mesh protocols do not put any limit on the size or complexity of
   Mesh profiles but a Mesh Portal SHOULD impose such limits as are
   appropriate to avoid abuse such as denial of service attacks.

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4.2.5.  JSON Encoding

   Javascript Object Notation (JSON) [RFC7159] encoding is used to
   encode all Mesh data objects except for low level cryptographic
   formats where other encodings are already established.

4.2.6.  HTTP Web Service

   The Mesh defines two new protocols:

      Mesh Portal Protocol (mmm)  A client-server protocol that mediates
         access to a Mesh.

      Intermesh Protocol  The Intermesh protocol is used to exchange
         Mesh profile data between portals.  It is a flood fill protocol
         that applies the same principles demonstrated in NNTP
         [RFC4644].

   The DNS SRV mechanism is used for

4.2.7.  Transparency

   The principle of transparency was introduced by the Certificate
   Transparency specification [RFC6962].  Transparency is the ability to
   audit a system using only information that is available to the users
   of the system.  If the system is a public service, all the data used
   to audit the service must be public.

   The Mesh uses strong encryption and

5.  Use Scenario

5.1.  Initial Configuration

5.2.  Adding a Device

5.3.  Adding and Updating Applications

5.4.  Disaster Recovery

6.  Mesh Profiles

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6.1.  Device Profile

   Is unique to each device.  If a device has multiple accounts, each
   account would typically require a separate device profile.

   Has separate keys for encryption, authentication and signature.

   Typically generated on the device.

   Once generated, is typically constant until the device is reset.

   Used to provision application keys out to a device.

6.2.  Master Profile

   Is signed by the Master Signing Key which is in turn validated by the
   fingerprint.

   Contains a Master Signing Key, Set of Administration Keys and Set of
   Escrow Keys.

   Changes infrequently, usually only when the set of administration
   devices changes or a new escrow key is added.

6.3.  Personal Profile

   Is signed by an administration key.

   For convenience, the master profile is included as an attachment.

   Changes when there is a significant change to the configuration, the
   addition of a new device or application.

6.4.  Application Profile

   Is signed by an administration key or an application administration
   key (if specified for the application).

   Contains the application configuration data.  Is encrypted to the
   device keys.

   Changes when the application configuration is changed or when devices
   are added or removed.

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6.5.  Future Directions

   It may be desirable to partition the Application profiles so that it
   is not necessary for every device to download the whole thing.  For
   example, sign a manifest so that the portal can strip out just the
   parts of the profile that are relevant to a device.

6.5.1.  Public Profile

6.5.2.  Endorsement Statements

7.  Mesh Portal Protocol

   Not necessarily instantaneous, may be latency between an update being
   published and it being available.

8.  Intermesh Protocol

   This is not a priority at the moment.

   May be used to support local replication or replication between
   providers.

   It is anticipated that the Intermesh Protocol will operate at a
   substantially greater latency than the Mesh Portal Protocol.
   Probably resynchronizing on an hourly or even daily basis.

   Portals are not required to forward every update to the Intermesh.
   Only updates that have not been superseded within the time quanta
   need be published.

   Each Portal runs a local append only log of every transaction.  This
   is periodically closed and a new log started.  Some time after the
   log is closed, a hash structure is calculated across the log entries
   and broadcast to the other participants in the InterMesh.  After a
   quorum of hash values has been received, each participant in the
   exchange calculates a new master hash entry which will be added to
   the log before the next checkpoint occurs.

   The participants exchange log records, but this may be on a limited
   basis.  If the InterMesh has a hundred members, it is not necessary
   for every single node to have every single entry in real time.  It is
   sufficient for each node to have knowledge of a partner that can
   provide it on demand.

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9.  Transparent Audit

   Can be performed by any party that is a participant in the InterMesh
   protocol or subsequently in an offline transaction.

10.  Security Considerations

   Security Considerations are addressed in the companion document
   [draft-hallambaker-mesh-architecture]

11.  IANA Considerations

   IANA Considerations are addressed in the companion document [draft-
   hallambaker-mesh-architecture]

12.  Acknowledgements

   Comodo Group: Egemen Tas, Melhi Abdulhayo?lu, Rob Stradling, Robin
   Alden.

13.  References

13.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997.

   [RFC3977]  Feather, C., "Network News Transfer Protocol (NNTP)",
              RFC 3977, DOI 10.17487/RFC3977, October 2006.

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014.

   [RFC6962]  Laurie, B., Langley, A., and E. Kasper, "Certificate
              Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013.

   [RFC5822]  "[Reference Not Found!]".

   [draft-hallambaker-udf]
              "[Reference Not Found!]".

   [draft-hallambaker-mesh-architecture]
              "[Reference Not Found!]".

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13.2.  Informative References

   [RFC4644]  Vinocur, J. and K. Murchison, "Network News Transfer
              Protocol (NNTP) Extension for Streaming Feeds", RFC 4644,
              DOI 10.17487/RFC4644, October 2006.

Author's Address

   Phillip Hallam-Baker
   Comodo Group Inc.

   Email: philliph@comodo.com

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