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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
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on July 17, 2016.
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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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