## MessageVortex Protocoldraft-gwerder-messagevortexmain-04

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Internet Engineering Task Force                                  Gwerder
Internet-Draft                                                      FHNW
Intended status: Experimental                             March 12, 2020
Expires: September 13, 2020

MessageVortex Protocol
draft-gwerder-messagevortexmain-04

Abstract

The MessageVortex (referred to as Vortex) protocol achieves different
degrees of anonymity, including sender, receiver, and third-party
anonymity, by specifying messages embedded within existing transfer
protocols, such as SMTP or XMPP, sent via peer nodes to one or more
recipients.

The protocol outperforms others by decoupling the transport from the
final transmitter and receiver.  No trust is placed into any
infrastructure except for that of the sending and receiving parties
of the message.  The creator of the routing block has full control
over the message flow.  Routing nodes gain no non-obvious knowledge
about the messages even when collaborating.  While third-party
anonymity is always achieved, the protocol also allows for either
sender or receiver anonymity.

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).  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 September 13, 2020.

Copyright Notice

Copyright (c) 2020 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document.  Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
1.2.  Protocol Specification  . . . . . . . . . . . . . . . . .   5
1.3.  Number Specification  . . . . . . . . . . . . . . . . . .   5
2.  Entities Overview . . . . . . . . . . . . . . . . . . . . . .   5
2.1.  Node  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
2.1.1.  Blocks  . . . . . . . . . . . . . . . . . . . . . . .   6
2.1.2.  NodeSpec  . . . . . . . . . . . . . . . . . . . . . .   6
2.1.2.1.  NodeSpec for SMTP nodes . . . . . . . . . . . . .   6
2.1.2.2.  NodeSpec for XMPP nodes . . . . . . . . . . . . .   6
2.2.  Peer Partners . . . . . . . . . . . . . . . . . . . . . .   7
2.3.  Encryption keys . . . . . . . . . . . . . . . . . . . . .   7
2.3.1.  Identity Keys . . . . . . . . . . . . . . . . . . . .   7
2.3.2.  Peer Key  . . . . . . . . . . . . . . . . . . . . . .   7
2.3.3.  Sender Key  . . . . . . . . . . . . . . . . . . . . .   7
2.4.  Vortex Message  . . . . . . . . . . . . . . . . . . . . .   8
2.5.  Message . . . . . . . . . . . . . . . . . . . . . . . . .   8
2.6.  Key and MAC specifications and usage  . . . . . . . . . .   9
2.6.1.  Asymmetric Keys . . . . . . . . . . . . . . . . . . .   9
2.6.2.  Symmetric Keys  . . . . . . . . . . . . . . . . . . .   9
2.7.  Transport Address . . . . . . . . . . . . . . . . . . . .  10
2.8.  Identity  . . . . . . . . . . . . . . . . . . . . . . . .  10
2.8.1.  Peer Identity . . . . . . . . . . . . . . . . . . . .  10
2.8.2.  Ephemeral Identity  . . . . . . . . . . . . . . . . .  10
2.8.3.  Official Identity . . . . . . . . . . . . . . . . . .  10
2.9.  Workspace . . . . . . . . . . . . . . . . . . . . . . . .  11
2.10. Multi-use Reply Blocks  . . . . . . . . . . . . . . . . .  11
2.11. Protocol Version  . . . . . . . . . . . . . . . . . . . .  11
3.  Layer Overview  . . . . . . . . . . . . . . . . . . . . . . .  11
3.1.  Transport Layer . . . . . . . . . . . . . . . . . . . . .  12
3.2.  Blending Layer  . . . . . . . . . . . . . . . . . . . . .  12
3.3.  Routing Layer . . . . . . . . . . . . . . . . . . . . . .  12
3.4.  Accounting Layer  . . . . . . . . . . . . . . . . . . . .  13
4.  Vortex Message  . . . . . . . . . . . . . . . . . . . . . . .  13
4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  13
4.2.  Message Prefix Block (MPREFIX)  . . . . . . . . . . . . .  13

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4.3.  Inner Message Block . . . . . . . . . . . . . . . . . . .  14
4.3.1.  Control Prefix Block  . . . . . . . . . . . . . . . .  14
4.3.2.  Control Blocks  . . . . . . . . . . . . . . . . . . .  14
4.3.2.1.  Header Block  . . . . . . . . . . . . . . . . . .  14
4.3.2.2.  Routing Block . . . . . . . . . . . . . . . . . .  15
4.3.3.  Payload Block . . . . . . . . . . . . . . . . . . . .  15
5.  General notes . . . . . . . . . . . . . . . . . . . . . . . .  15
5.1.  Supported Symmetric Ciphers . . . . . . . . . . . . . . .  16
5.2.  Supported Asymmetric Ciphers  . . . . . . . . . . . . . .  16
5.3.  Supported MACs  . . . . . . . . . . . . . . . . . . . . .  16
5.4.  Supported Paddings  . . . . . . . . . . . . . . . . . . .  16
5.5.  Supported Modes . . . . . . . . . . . . . . . . . . . . .  17
6.  Blending  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
6.1.  Blending in Attachments . . . . . . . . . . . . . . . . .  17
6.1.1.  PLAIN embedding into attachments  . . . . . . . . . .  18
6.1.2.  F5 embedding into attachments . . . . . . . . . . . .  19
6.2.  Blending into an SMTP layer . . . . . . . . . . . . . . .  19
6.3.  Blending into an XMPP layer . . . . . . . . . . . . . . .  19
7.  Routing . . . . . . . . . . . . . . . . . . . . . . . . . . .  19
7.1.  Vortex Message Processing . . . . . . . . . . . . . . . .  20
7.1.1.  Processing of incoming Vortex Messages  . . . . . . .  20
7.1.2.  Processing of Routing Blocks in the Workspace . . . .  22
7.1.3.  Processing of Outgoing Vortex Messages  . . . . . . .  23
7.2.  Header Requests . . . . . . . . . . . . . . . . . . . . .  23
7.2.1.  Request New Ephemeral Identity  . . . . . . . . . . .  23
7.2.2.  Request Message Quota . . . . . . . . . . . . . . . .  24
7.2.3.  Request Increase of Message Quota . . . . . . . . . .  24
7.2.4.  Request Transfer Quota  . . . . . . . . . . . . . . .  24
7.2.5.  Query Quota . . . . . . . . . . . . . . . . . . . . .  25
7.2.6.  Request Capabilities  . . . . . . . . . . . . . . . .  25
7.2.7.  Request Nodes . . . . . . . . . . . . . . . . . . . .  25
7.2.8.  Request Identity Replace  . . . . . . . . . . . . . .  26
7.2.9.  Request Upgrade . . . . . . . . . . . . . . . . . . .  26
7.3.  Special Blocks  . . . . . . . . . . . . . . . . . . . . .  26
7.3.1.  Error Block . . . . . . . . . . . . . . . . . . . . .  26
7.3.2.  Requirement Block . . . . . . . . . . . . . . . . . .  26
7.3.2.1.  Puzzle Requirement  . . . . . . . . . . . . . . .  27
7.3.2.2.  Payment Requirement . . . . . . . . . . . . . . .  27
7.3.2.3.  Upgrade . . . . . . . . . . . . . . . . . . . . .  27
7.4.  Routing Operations  . . . . . . . . . . . . . . . . . . .  27
7.4.1.  Mapping Operation . . . . . . . . . . . . . . . . . .  28
7.4.2.  Split and Merge Operations  . . . . . . . . . . . . .  28
7.4.3.  Encrypt and Decrypt Operations  . . . . . . . . . . .  28
7.4.4.  Add and Remove Redundancy Operations  . . . . . . . .  29
7.4.4.1.  Padding Operation . . . . . . . . . . . . . . . .  29
7.4.4.2.  Apply Matrix  . . . . . . . . . . . . . . . . . .  30
7.4.4.3.  Encrypt Target Block  . . . . . . . . . . . . . .  30
7.5.  Processing of Vortex Messages . . . . . . . . . . . . . .  30

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8.  Accounting  . . . . . . . . . . . . . . . . . . . . . . . . .  30
8.1.  Accounting Operations . . . . . . . . . . . . . . . . . .  31
8.1.1.  Time-Based Garbage Collection . . . . . . . . . . . .  31
8.1.2.  Time-Based Routing Initiation . . . . . . . . . . . .  31
8.1.3.  Routing Based Quota Updates . . . . . . . . . . . . .  31
8.1.4.  Routing Based Authorization . . . . . . . . . . . . .  31
8.1.5.  Ephemeral Identity Creation . . . . . . . . . . . . .  31
9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  32
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  32
11. Security Considerations . . . . . . . . . . . . . . . . . . .  32
12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
12.1.  Normative References . . . . . . . . . . . . . . . . . .  34
12.2.  Informative References . . . . . . . . . . . . . . . . .  36
Appendix A.  The ASN.1 schema for Vortex messages . . . . . . . .  37
A.1.  The main VortexMessageBlocks  . . . . . . . . . . . . . .  37
A.2.  The VortexMessage Ciphers Structures  . . . . . . . . . .  37
A.3.  The VortexMessage Request Structures  . . . . . . . . . .  37
A.4.  The VortexMessage Replies Structures  . . . . . . . . . .  37
A.5.  The VortexMessage Requirements Structures . . . . . . . .  37
A.6.  The VortexMessage Helpers Structures  . . . . . . . . . .  37
A.7.  The VortexMessage Additional Structures . . . . . . . . .  37
Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  38

1.  Introduction

Anonymisation is hard to achieve.  Most previous attempts relied on
either trust in a dedicated infrastructure or a specialized
networking protocol.

Instead of defining a transport layer, Vortex piggybacks on other
transport protocols.  A blending layer embeds Vortex messages
(VortexMessage) into ordinary messages of the respective transport
protocol.  This layer picks up the messages, passes them to a routing
layer, which applies local operations to the messages, and resends
the new message chunks to the next recipients.

A processing node learns as little as possible from the message or
the network utilized.  The operations have been designed to be
sensible in any context.  The 'onionized' structure of the protocol
makes it impossible to follow the trace of a message without having
control over the processing node.

MessageVortex is a protocol which allows sending and receiving
messages by using a routing block instead of a destination address.
With this approach, the sender has full control over all parameters
of the message flow.

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A message is split and reassembled during transmission.  Chunks of
the message may carry redundant information to avoid service
interruptions during transit.  Decoy and message traffic are not
differentiable as the nature of the addRedundancy operation allows
each generated portion to be either message or decoy.  Therefore, any
routing node is unable to distinguish between message and decoy
traffic.

After processing, a potential receiver node knows if the message is
destined for it (by creating a chunk with ID 0) or other nodes.  Due
to missing keys, no other node may perform this processing.

This RFC begins with general terminology (see Section 2) followed by
an overview of the process (see Section 3).  The subsequent sections
describe the details of the protocol.

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 [RFC2119].

1.2.  Protocol Specification

Appendix A specifies all relevant parts of the protocol in ASN.1 (see
[CCITT.X680.2002] and [CCITT.X208.1988]).  The blocks are DER
encoded, if not otherwise specified.

1.3.  Number Specification

All numbers within this document are, if not suffixed, decimal
numbers.  Numbers suffixed with a small letter 'h' followed by two
hexadecimal digits are octets written in hexadecimal.  For example, a
blank ASCII character (' ') is written as 20h and a capital 'K' in
ASCII as 4Bh.

2.  Entities Overview

The following entities used in this document are defined below.

2.1.  Node

The term 'node' describes any computer system connected to other
nodes, which support the MessageVortex Protocol.  A 'node address' is
typically an email address, an XMPP address or other transport
protocol identity supporting the MessageVortex protocol.  Any address
SHOULD include a public part of an 'identity key' to allow messages

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to transmit safely.  One or more addresses MAY belong to the same
node.

2.1.1.  Blocks

A 'block' represents an ASN.1 sequence in a transmitted message.  We
embed messages in the transport protocol, and these messages may be
of any size.

2.1.2.  NodeSpec

A nodeSpec block, as specified in Appendix A.6, expresses an
addressable node in a unified format.  The nodeSpec contains a
reference to the routing protocol, the routing address within this
protocol, and the keys required for addressing the node.  This RFC
specifies transport layers for XMPP and SMTP.  Additional transport
layers will require an extension to this RFC.

2.1.2.1.  NodeSpec for SMTP nodes

An alternative address representation is defined that allows a
standard email client to address a Vortex node.  A node SHOULD
support the smtpAlternateSpec (its specification is noted in ABNF as
in [RFC5234]).  For applications with QR code support, an
implementation SHOULD use the smtpUrl representation.

localPart         = <local part of address>
domain            = <domain part of address>
email             = localPart "@" domain
keySpec           = <BASE64 encoded AsymmetricKey [DER encoded]>
smtpAlternateSpec = localPart ".." keySpec ".." domain "@localhost"
smtpUrl           = "vortexsmtp://" smtpAlternateSpec

This representation does not support quoted local part SMTP
addresses.

2.1.2.2.  NodeSpec for XMPP nodes

Typically, a node specification follows the ASN.1 block NodeSpec.
For support of XMPP clients, an implementation SHOULD support the
jidAlternateSpec (its specification is noted in ABNF as in
[RFC5234]).

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localPart         = <local part of address>
domain            = <domain part of address>
resourcePart      = <resource part of the address>
jid               = localPart "@" domain [ "/" resourcePart ]
keySpec           = <BASE64 encoded AsymmetricKey [DER encoded]>;
jidAlternateSpec  = localPart ".." keySpec ".."
domain "@localhost" [ "/" resourcePart ]
jidUrl            = "vortexxmpp://" jidAlternateSpec

2.2.  Peer Partners

This document refers to two or more message sending or receiving
entities as peer partners.  One partner sends a message, and all
others receive one or more messages.  Peer partners are message
specific, and each partner always connects directly to a node.

2.3.  Encryption keys

Several keys are required for a Vortex message.  For identities and
ephemeral identities (see below), we use asymmetric keys, while
symmetric keys are used for message encryption.

2.3.1.  Identity Keys

Every participant of the network includes an asymmetric key, which
SHOULD be either an EC key with a minimum length of 384 bits or an
RSA key with a minimum length of 2048 bits.

The public key must be known by all parties writing to or through the
node.

2.3.2.  Peer Key

Peer keys are symmetrical keys transmitted with a Vortex message and
are always known to the node sending the message, the node receiving
the message, and the creator of the routing block.

A peer key is included in the Vortex message as well as the building
instructions for subsequent Vortex messages (see RoutingCombo in
Appendix A).

2.3.3.  Sender Key

The sender key is a symmetrical key protecting the identity and
routing block of a Vortex message.  It is encrypted with the
receiving peer key and prefixed to the identity block.  This key
further decouples the identity and processing information from the
previous key.

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A sender key is known to only one peer of a Vortex message and the
creator of the routing block.

2.4.  Vortex Message

The term 'Vortex message' represents a single transmission between
two routing layers.  A message adapted to the transport layer by the
blending layer is called a 'blended Vortex message' (see Section 3).

A complete Vortex message contains the following items:

o  The peer key, which is encrypted with the host key of the node and
stored in a prefixBlock, protects the inner Vortex message
(innerMessageBlock).

o  The sender key, also encrypted with the host key of the node,
protects the identity and routing block.

o  The identity block, protected by the sender key, contains
information about the ephemeral identity of the sender, replay
protection information, header requests (optional), and a
requirement reply (optional).

o  The routing block, protected by the sender key, contains
information on how subsequent messages are processed, assembled,
and blended.

o  The payload block, protected by the peer key, contains payload
chunks for processing.

2.5.  Message

A message is content to be transmitted from a single sender to a
recipient.  The sender uses a routing block either built itself or
provided by the receiver to perform the transmission.  While a
message may be anonymous, there are different degrees of anonymity as
described by the following.

o  If the sender of a message is not known to anyone else except the
sender, then this degree is referred to as 'sender anonymity.'

o  If the receiver of a message is not known to anyone else except
the receiver, then the degree is 'receiver anonymity.'

o  If an attacker is unable to determine the content, original
sender, and final receiver, then the degree is considered 'third-
party anonymity.'

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o  If a sender or a receiver may be determined as one of a set of <k>
entities, then it is referred to as k-anonymity[KAnon].

A message is always MIME encoded as specified in [RFC2045].

2.6.  Key and MAC specifications and usage

MessageVortex uses a unique encoding for keys.  This encoding is
designed to be small and flexible while maintaining a specific base
structure.

The following key structures are available:

o  SymmetricKey

o  AsymmetricKey

MAC does not require a complete structure containing specs and
values, and only a MacAlgorithmSpec is available.  The following
sections outline the constraints for specifying parameters of these
structures where a node MUST NOT specify any parameter more than
once.

If a crypto mode is specified requiring an IV, then a node MUST
provide the IV when specifying the key.

2.6.1.  Asymmetric Keys

Nodes use asymmetric keys for identifying peer nodes (i.e.,
identities) and encrypting symmetric keys (for subsequent
de-/encryption of the payload or blocks).  All asymmetric keys MUST
contain a key type specifying a strictly-normed key.  Also, they MUST
contain a public part of the key encoded as an X.509 container and a
private key specified in PKCS#8 wherever possible.

RSA and EC keys MUST contain a keySize parameter.  All asymmetric
keys SHOULD contain a padding parameter, and a node SHOULD assume
PKCS#1 if no padding is specified.

NTRU specification MUST provide the parameters "n", "p", and "q".

2.6.2.  Symmetric Keys

Nodes use symmetric keys for encrypting payloads and control blocks.
These symmetric keys MUST contain a key type specifying a key, which
MUST be in an encoded form.

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A node MUST provide a keySize parameter if the key (or, equivalently,
the block) size is not standardized or encoded in the name.  All
symmetric key specifications MUST contain a mode and padding
parameter.  A node MAY list multiple padding or mode parameters in a
ReplyCapability block to offer the recipient a free choice.

2.7.  Transport Address

The term 'transport address' represents the token required to address
the next immediate node on the transport layer.  An email transport
layer would have SMTP addresses, such as 'vortex@example.com,' as the
transport address.

2.8.  Identity

2.8.1.  Peer Identity

The peer identity may contain the following information of a peer
partner:

o  A transport address (always) and the public key of this identity,
given there is no recipient anonymity.

o  A routing block, which may be used to contact the sender.  If
striving for recipient anonymity, then this block is required.

o  The private key, which is only known by the owner of the identity.

2.8.2.  Ephemeral Identity

Ephemeral identities are temporary identities created on a single
node.  These identities MUST NOT relate to another identity on any
other node so that they allow bookkeeping for a node.  Each ephemeral
identity has a workspace assigned, and may also have the following
items assigned.

o  An asymmetric key pair to represent the identity.

o  A validity time of the identity.

2.8.3.  Official Identity

An official identity may have the following items assigned.

o  Routing blocks used to reply to the node.

o  A list of assigned ephemeral identities on all other nodes and
their projected quotas.

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o  A list of known nodes with the respective node identity.

2.9.  Workspace

Every official or ephemeral identity has a workspace, which consists
of the following elements.

o  Zero or more routing blocks to be processed.

o  Slots for a payload block sequentially numbered.  Every slot:

*  MUST contain a numerical ID identifying the slot.

*  MAY contain payload content.

*  If a block contains a payload, then it MUST contain a validity
period.

2.10.  Multi-use Reply Blocks

'Multi-use reply blocks' (MURB) are a special type routing block sent
to a receiver of a message or request.  A sender may use such a block
one or several times to reply to the sender linked to the ephemeral
identity, and it is possible to achieve sender anonymity using MURBs.

A vortex node MAY deny the use of MURBs by indicating a maxReplay
equal to zero when sending a ReplyCapability block.  An unobservable
node SHOULD deny the use of MURBs.

2.11.  Protocol Version

This Document describes the version 1 of the protocol.  The message
PrefixBlock contains an optional version indicator.  If absent
protocol version 1 should be assumed.

3.  Layer Overview

The protocol is designed in four layers as shown in Figure 1.

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+------------------------------------------------------------------+
| Vortex Node                                                      |
| +--------------------------------------------------------------+ |
| |                       Accounting                             | |
| |______________________________________________________________| |
|                                                                  |
| +--------------------------------------------------------------+ |
| |                         Routing                              | |
| |______________________________________________________________| |
|                                                                  |
| +---------------------------+ +--------------------------------+ |
| |           Blending        | |             Blending           | |
| |___________________________| |________________________________| |
|__________________________________________________________________|
+---------------------------+ +--------------+ +---------------+
|          Transport        | | Transport in | | Transport out |
|___________________________| |______________| |_______________|

Figure 1: Layer overview

Every participating node MUST implement the layer's blending,
routing, and accounting.  There MUST be at least one incoming and one
outgoing transport layer available to a node.  All blending layers
SHOULD connect to the respective transport layers for sending and
receiving packets.

3.1.  Transport Layer

The transport layer transfers the blended Vortex messages to the next
vortex node and stores it until the next blending layer picks up the
message.

The transport layer infrastructure SHOULD NOT be specific to
anonymous communication and should contain significant portions of
non-Vortex traffic.

3.2.  Blending Layer

The blending layer embeds blended Vortex Message into the transport
layer data stream and extracts the packets from the transport layer.

3.3.  Routing Layer

The routing layer expands the information contained in MessageVortex
packets, processes them, and passes generated packets to the
respective blending layer.

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3.4.  Accounting Layer

The accounting layer tracks all ephemeral identities authorized to
use a MessageVortex node and verifies the available quotas to an
ephemeral identity.

4.  Vortex Message

4.1.  Overview

Figure 2 shows a Vortex message.  The enclosed sections denote
encrypted blocks, and the three or four-letter abbreviations denote
the key required for decryption.  The abbreviation k_h stands for the
asymmetric host key, and sk_p is the symmetric peer key.  The
receiving node obtains this key by decrypting MPREFIX with its host
key k_h.  Then, sk_s is the symmetric sender key.  When decrypting
the MPREFIX block, the node obtains this key.  The sender key
protects the header and routing blocks by guaranteeing the node
assembling the message does not know about upcoming identities,
operations, and requests.  The peer key protects the message,
including its structure, from third-party observers.

+-+---+-+-+---+-+---+-+-+---+-+-+---+-+-------+-+
| |   | | | | C | | |   | | | R | |       | |
| |   | | | | P | | | H | | | O | |       | |
| | M | | | | R | | | E | | | U | |   P   | |
| | P | | | | E | | | A | | | T | |   A   | |
| | R | | | | F | | | D | | | I | |   Y   | |
| | E | | | | I | | | E | | | N | |   L   | |
| | F | | | | X | | | R | | | G | |   O   | |
| | I | | | +---+ | |___| | |___| |   A   | |
| | X | | |  k_h  | sk_s  | sk_s  |   D   | |
| |___| | |_______|_______|_______|_______| |
|  k_h  |                sk_p               |
|_______|___________________________________|

Figure 2: Vortex message overview

4.2.  Message Prefix Block (MPREFIX)

The PrefixBlock contains a symmetrical key as defined in Appendix A.1
and is encrypted using the host key of the receiving peer host.  The
symmetric key utilized MUST be from the set advertised by a
CapabilitiesReplyBlock (see Section 7.2.6).  A node MAY choose any
parameters omitted in the CapabilitiesReplyBlock freely unless stated
otherwise in Section 7.2.6.  A node SHOULD avoid sending unencrypted
PrefixBlocks, and a prefix block MUST contain the same forward-secret
as the other prefix as well as the routing and header blocks.  A host

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MAY reply to a message with an unencrypted message block, but any
reply to a message SHOULD be encrypted.

The sender MUST choose a key which may be encrypted with the host key
in the respective PrefixBlock using the padding advertised by the
CapabilitiesReplyBlock.

4.3.  Inner Message Block

A node MUST always encrypt an InnerMessageBlock with the symmetric
key of the PrefixBlock to hide the inner structure of the message.
The InnerMessageBlock SHOULD always accommodate four or more payload
chunks.

An InnerMessageBlock contains so-called forwardSecrets, a random
number that MUST be the same in the PrefixBlock, HeaderBlock,
RoutingBlock, and PrefixBlock.  Nodes receiving messages containing
non-matching forwardSecrets MUST discard these messages and SHOULD
NOT send an error message.  If a node receives too many messages with
illegal forward secrets, then the node SHOULD delete this identity.
A node receiving a message with a broken forwardSecret SHOULD treat
the block as a replayed block and discard it regardless of a valid
forwardSecret.  Any replay within the replay protection time MUST be
discarded regardless of a correct forward secret.

4.3.1.  Control Prefix Block

Control prefix (CPREFIX) and MPREFIX blocks share the same structure
and logic as well as containing the sender key sk_s.  If an MPREFIX
block is unencrypted, a node MAY omit the CPREFIX block.  An omitted
CPREFIX block results in unencrypted control blocks (e.g., the
HeaderBlock and RoutingBlock).

A prefix block MUST contain the same forwardSecret as the other
prefix, the routing block, and the header block.

4.3.2.  Control Blocks

The control blocks of the HeaderBlock and a RoutingBlock contain the
core information to process the payload.

4.3.2.1.  Header Block

The header block (see HeaderBlock in Appendix A) contains the
following information.

o  It MUST contain the local ephemeral identity of the routing block
builder.

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o  It MAY contain header requests.

o  It MAY contain the solution to a PuzzleRequired block previously
opposed in a header request.

The list of header requests MAY be one of the following.

o  Empty.

o  Contain a single identity create request (HeaderRequestIdentity).

o  Contain a single increase quota request.

If a header block violates these rules, then a node MUST NOT reply to
any header request.  The payload and routing blocks SHOULD still be
added to the workspace and processed if the message quota is not
exceeded.

4.3.2.2.  Routing Block

The routing block (see RoutingBlock in Appendix A) contains the
following information.

o  It MUST contain a serial number uniquely identifying the routing
block of this user.  The serial number MUST be unique during the
lifetime of the routing block.

o  It MUST contain the same forward secret as the two prefix blocks
and the header block.

o  It MAY contain assembly and processing instructions for subsequent
messages.

o  It MAY contain a reply block for messages assigned to the owner of
the identity.

4.3.3.  Payload Block

Each InnerMessageBlock with routing information SHOULD contain at
least four PayloadChunks.

5.  General notes

The MessageVortex protocol is a modular protocol that allows the use
of different encryption algorithms.  For its operation, a Vortex node
SHOULD always support at least two distinct types of algorithms,
paddings or modes such that they rely on two mathematical problems.

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5.1.  Supported Symmetric Ciphers

A node MUST support the following symmetric ciphers.

o  AES128 (see [FIPS-AES] for AES implementation details).

o  AES256.

o  CAMELLIA128 (see [RFC3657] Chapter 3 for Camellia implementation
details).

o  CAMELLIA256.

A node SHOULD support any standardized key larger than the smallest
key size.

A node MAY support Twofish ciphers (see [TWOFISH]).

5.2.  Supported Asymmetric Ciphers

A node MUST support the following asymmetric ciphers.

o  RSA with key sizes greater or equal to 2048 ([RFC8017]).

o  ECC with named curves secp384r1, sect409k1 or secp521r1 (see
[SEC1]).

5.3.  Supported MACs

A node MUST support the following Message Authentication Codes (MAC).

o  SHA3-256 (see [ISO-10118-3] for SHA implementation details).

o  RipeMD160 (see [ISO-10118-3] for RIPEMD implementation details).

A node SHOULD support the following MACs.

o  SHA3-512.

o  RipeMD256.

o  RipeMD512.

5.4.  Supported Paddings

A node MUST support the following paddings specified in [RFC8017].

o  PKCS1 (see [RFC8017]).

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o  PKCS7 (see [RFC5958]).

5.5.  Supported Modes

A node MUST support the following modes.

o  CBC (see [RFC1423]) such that the utilized IV must be of equal
length as the key.

o  EAX (see [EAX]).

o  GCM (see [RFC5288]).

o  NONE (only used in special cases, see Section 11).

A node SHOULD NOT use the following modes.

o  NONE (except as stated when using the addRedundancy function).

o  ECB.

A node SHOULD support the following modes.

o  CTR ([RFC3686]).

o  CCM ([RFC3610]).

o  OCB ([RFC7253]).

o  OFB ([MODES]).

6.  Blending

Each node supports a fixed set of blending capabilities, which may be
different for incoming and outgoing messages.

The following sections describe the blending mechanism.  There are
currently two blending layers specified with one for the Simple Mail
Transfer Protocol (SMTP, see [RFC5321]) and the second for the
Extensible Messaging and Presence Protocol (XMPP, see [RFC6120]).
All nodes MUST at least support "encoding=plain:0,256".

6.1.  Blending in Attachments

There are two types of blending supported when using attachments.

o  Plain binary encoding with offset (PLAIN).

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o  Embedding with F5 in an image (F5).

A node MUST support PLAIN blending for reasons of interoperability
whereas a node MAY support blending using F5.

6.1.1.  PLAIN embedding into attachments

A blending layer embeds a VortexMessage in a carrier file with an
offset for PLAIN blending.  For replacing a file start, a node MUST
use the offset 0.  The routing node MUST choose the payload file for
the message, and SHOULD use a credible payload type (e.g., MIME type)
with high entropy.  Furthermore, it SHOULD prefix a valid header
structure to avoid easy detection of the Vortex message.  Finally, a
routing node SHOULD use a valid footer, if any, to a payload file to
improve blending.

The blended Vortex message is embedded in one or more message chunks,
each starting with two unsigned integers of variable length.  The
integer starts with the LSB, and if bit 7 is set, then there is
another byte following.  There cannot be more than four bytes where
the last, fourth byte is always 8 bit.  The three preceding bytes
have a payload of seven bits each, which results in a maximum number
of 2^29 bits.  The first of the extracted numbers reflect the number
of bytes in the chunk after the length descriptors.  The second
contains the number of bytes to be skipped to reach the next chunk.
There exists no "last chunk" indicator.  A chunk or the gap MAY
surpass the end of the file.

position:00h   02h   04h   06h   08h ... 400h  402h  404h  406h  408h  40Ah
value:   01 02 03 04 05 06 07 08 09  ... 01 05 0A 0B 0C 0D 0E 0F f0 03 12 13

Embedding: "(plain:1024)"

Result:  0A 13 (+ 494 omitted bytes; then skip 12 bytes to next chunk)

A node SHOULD offer at least one PLAIN blending method and MAY offer
multiple offsets for incoming Vortex messages.

A plain blending is specified as the following.

plainEncoding = "("plain:" <numberOfBytesOfOffset>
[ "," <numberOfBytesOfOffset> ]* ")"

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6.1.2.  F5 embedding into attachments

For F5, a blending layer embeds a Vortex message into a jpeg file
according to [F5].  The password for blending may be public, and a
routing node MAY advertise multiple passwords.  The use of F5 adds
approximately tenfold transfer volume to the message.  A routing
block building node SHOULD only use F5 blending where appropriate.

A blending in F5 is specified as the following.

f5Encoding = "(F5:" <passwordString> [ "," <PasswordString> ]* ")"

Commas and backslashes in passwords MUST be escaped with a backslash
whereas closing brackets are treated as normal password characters
unless they are the final character of the encoding specification
string.

6.2.  Blending into an SMTP layer

Email messages with content MUST be encoded with Multipurpose
Internet Mail Extensions (MIME) as specified in [RFC2045].  All nodes
MUST support BASE64 encoding and MUST test all sections of a MIME
message for the presence of a VortexMessage.

A vortex message is present if a block containing the peer key at the
known offset of any MIME part decodes correctly.

A node SHOULD support SMTP blending for sending and receiving.  For
sending SMTP, the specification in [RFC5321] must be used.  TLS
layers MUST always be applied when obtaining messages using POP3 (as
specified in [RFC1939] and [RFC2595]) or IMAP (as specified in
[RFC3501]).  Any SMTP connection MUST employ a TLS encryption when
passing credentials.

6.3.  Blending into an XMPP layer

For interoperability, an implementation SHOULD provide XMPP blending.

Blending into XMPP traffic is performed using the [XEP-0231]
extension of the XMPP protocol.

PLAIN and F5 blending are acceptable for this transport layer.

7.  Routing

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7.1.  Vortex Message Processing

7.1.1.  Processing of incoming Vortex Messages

An incoming message is considered initially unauthenticated.  A node
should consider a VortexMessage as authenticated as soon as the
ephemeral identity is known and is not temporary.

For an unauthenticated message, the following rules apply.

o  A node MUST ignore all Routing blocks.

o  A node MUST ignore all Payload blocks.

o  A node SHOULD accept identity creation requests in unauthenticated
messages.

o  A node MUST ignore all other header requests except identity
creation requests.

o  A node MUST ignore all identity creation requests belonging to an
existing identity.

A message is considered authenticated as soon as the identity used in
the header block is known and not temporary.  A node MUST NOT treat a
message as authenticated if the specified maximum number of replays
is reached.  For authenticated messages, the following rules apply.

o  A node MUST ignore identity creation requests.

o  A node MUST replace the current reply block with the reply block
provided in the routing block (if any).  The node MUST keep the
reply block if none is provided.

o  A node SHOULD process all header requests.

o  A node SHOULD add all routing blocks to the workspace.

o  A node SHOULD add all payload blocks to the workspace.

A routing node MUST decrement the message quota by one if a received
message is authenticated, valid, and contains at least one payload
block.  If a message is identified as duplicate according to the
reply protection, then a node MUST NOT decrement the message quota.

The message processing works according pseudo-code shown below.

function incomming_message(VortexMessage blendedMessage) {

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try{
msg = unblend( blendedMessage );
if( not msg ) {
// Abort processing
throw exception( "no embedded message found" )
} else {
hdr = get_header( msg )
if( not known_identity( hdr.identity ) {
if( get_requests( hdr ) contains HeaderRequestIdentity ) {
create_new_identity( hdr ).set_temporary( true )
send_message( create_requirement( hdr )  )
} else {
// Abort processing
throw exception( "identity unknown" )
}
} else {
if( is_duplicate_or_replayed( msg ) ) {
// Abort processing
throw exception "duplicate or replayed message" )
} else {
if( get_accounting( hdr.identity ).is_temporary() ) {
if( not verify_requirement( hdr.identity, msg ) ) {
get_accounting( hdr.identity ).set_temporary( false )
}
}
if( get_accounting( hdr ).is_temporary() ) {
throw exception( "no processing on temporary identity" )
}

// Message authenticated
get_accounting( hdr.identity ).register_for_replay_protection( msg )
if( not verify_mtching_forward_secrets( msg ) ) {
throw exception( "forward secret missmatch" )
}
if( contains_payload( msg ) ) {
if( get_accounting( hdr.identity ).decrement_message_quota() ) {
while index,nextPayloadBlock = get_next_payload_block( msg ) {
add_workspace( header.identity, index, nextPayloadBlock )
}
while nextRoutingBlock = get_next_routing_block( msg ) {
add_workspace( hdr.identity, add_routing( nextRoutingBlock ) )
}
process_reserved_mapping_space( msg )
while nextRequirement = get_next_requirement( hdr ) {
add_workspace( hdr.identity, nextRequirement )
}
} else {
throw exception( "Message quota exceeded" )

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}
}
}
}
} catch( exception e ) {
// Message processing failed
throw e;
}
}

7.1.2.  Processing of Routing Blocks in the Workspace

A routing workspace consists of the following items.

o  The identity linked to, which determines the lifetime of the
workspace.

o  The linked routing combos (RoutingCombo).

o  A payload chunk space with the following multiple subspaces
available:

*  ID 0 represents a message to be embedded (when reading) or a
message to be extracted to the user (when written).

*  ID 1 to ID maxPayloadBlocks represent the payload chunk slots
in the target message.

*  All blocks between ID maxPayloadBlocks + 1 to ID 32767 belong
to a temporary routing block-specific space.

*  All blocks between ID 32768 to ID 65535 belong to a shared
space available to all operations of the identity.

The accounting layer typically triggers processing and represents
either a cleanup action or a routing event.  A cleanup event deletes
the following information from all workspaces.

o  All processed routing combos.

o  All routing combos with expired usagePeriod.

o  All payload chunks exceeding the maxProcess time.

o  All expired objects.

o  All expired puzzles.

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o  All expired identities.

o  All expired replay protections.

Note that maxProcessTime reflects the number of seconds since the
arrival of the last octet of the message at the transport layer
facility.  A node SHOULD NOT take additional processing time (e.g.,
for anti-UBE or anti-virus) into account.

The accounting layer triggers routing events occurring at least the
minProcessTime after the last octet of the message arrived at the
routing layer.  A node SHOULD choose the latest possible moment at
which the peer node receives the last octet of the assembled message
before the maxProcessTime is reached.  The calculation of this last
point in time where a message may be set SHOULD always assume that
the target node is working.  A sending node SHOULD choose the time
within these bounds randomly.  An accounting layer MAY trigger
multiple routing combos in bulk to further obfuscate the identity of
a single transport message.

First, the processing node escapes the payload chunk at ID 0 if
needed (e.g., a non-special block is starting with a backslash).
Next, it executes all processing instructions of the routing combo in
the specified sequence.  If an instruction fails, then the block at
the target ID of the operation remains unchanged.  The routing layer
proceeds with the subsequent processing instructions by ignoring the
error.  For a detailed description of the operations, see
Section 7.4.  If a node succeeds in building at least one payload
chunk, then a VortexMessage is composed and passed to the blending
layer.

7.1.3.  Processing of Outgoing Vortex Messages

The blending layer MUST compose a transport layer message according
to the specification provided in the routing combo.  It SHOULD choose
any decoy message or steganographic carrier in such a way that the
dead parrot syndrome, as specified in [DeadParrot], is avoided.

7.2.  Header Requests

Header requests are control requests for the anonymization system.
Messages with requests or replies only MUST NOT affect any quota.

7.2.1.  Request New Ephemeral Identity

Requesting a new ephemeral identity is performed by sending a message
containing a header block with the new identity and an identity

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creation request (HeaderRequestIdentity) to a node.  The node MAY
send an error block (see Section 7.3.1) if it rejects the request.

If a node accepts an identity creation request, then it MUST send a
reply.  A node accepting a request without a requirement MUST send
back a special block containing "no error".  A node accepting a
request under the precondition of a requirement to be fulfilled MUST
send a special block containing a requirement block.

A node SHOULD NOT reply to any clear-text requests if the node does
not want to disclose its identity as a Vortex node officially.  A
node MUST reply with an error block if a valid identity is used for
the request.

7.2.2.  Request Message Quota

Any valid ephemeral identity may request an increase of the current
message quota to a specific value at any time.  The request MUST
include a reply block in the header and may contain other parts.  If
a requested value is lower than the current quota, then the node
SHOULD NOT refuse the quota request and SHOULD send a "no error"
status.

A node SHOULD reply to a HeaderRequestIncreaseMessageQuota request
(see Appendix A) of a valid ephemeral identity.  The reply MUST
include a requirement, an error message or a "no error" status
message.

7.2.3.  Request Increase of Message Quota

A node may request to increase the current message quota by sending a
HeaderRequestIncreaseMessageQuota request to the routing node.  The
value specified within the node is the new quota.
HeaderRequestIncreaseMessageQuota requests MUST include a reply
block, and a node SHOULD NOT use a previously sent MURB to reply.

If the requested quota is higher than the current quota, then the
node SHOULD send a "no error" reply.  If the requested quota is not
accepted, then the node SHOULD send a requestedQuotaOutOfBand reply.

A node accepting the request MUST send a RequirementBlock or a "no
error block."

7.2.4.  Request Transfer Quota

Any valid ephemeral identity may request to increase the current
transfer quota to a specific value at any time.  The request MUST
include a reply block in the header and may contain other parts.  If

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a requested value is lower than the current quota, then the node
SHOULD NOT refuse the quota request and SHOULD send a "no error"
status.

A node SHOULD reply to a HeaderRequestIncreaseTransferQuota request
(see Appendix A) of a valid ephemeral identity.  The reply MUST
include a requirement, an error message or a "no error" status
message.

7.2.5.  Query Quota

Any valid ephemeral identity may request the current message and
transfer quota.  The request MUST include a reply block in the header
and may contain other parts.

A node MUST reply to a HeaderRequestQueryQuota request (see
Appendix A), which MUST include the current message quota and the
current message transfer quota.  The reply to this request MUST NOT
include a requirement.

7.2.6.  Request Capabilities

Any node MAY request the capabilities of another node, which include
all information necessary to create a parseable VortexMessage.  Any
node SHOULD reply to any encrypted HeaderRequestCapability.

A node SHOULD NOT reply to clear-text requests if the node does not
want to disclose its identity as a Vortex node officially.  A node
MUST reply if a valid identity is used for the request, and it MAY
reply to unknown identities.

7.2.7.  Request Nodes

A node may ask another node for a list of routing node addresses and
keys, which may be used to bootstrap a new node and add routing nodes
to increase the anonymization of a node.  The receiving node of such
a request SHOULD reply with a requirement (e.g.,
RequirementPuzzleRequired).

A node MAY reply to a HeaderRequest request (see Appendix A) of a
valid ephemeral identity, and the reply MUST include a requirement,
an error message or a "no error" status message.  A node MUST NOT
reply to an unknown identity, and SHOULD always reply with the same
result set to the same identity.

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7.2.8.  Request Identity Replace

This request type allows a receiving node to replace an existing
identity with the identity provided in the message, and is required
if an adversary manages to deny the usage of a node (e.g., by
deleting the corresponding transport account).  Any sending node may
recover from such an attack by sending a valid authenticated message
to another identity to provide the new transport and key details.

A node SHOULD reply to such a request from a valid known identity,
and the reply MUST include an error message or a "no error" status
message.

7.2.9.  Request Upgrade

This request type allows a node to request a new version of the
software in an anonymous, unliked manor.  The identifier MUST
identify the software product uniquely.  The version MUST reflect the
version tag of the currently installed version or a similarly usable
tag.

7.3.  Special Blocks

Special blocks are payload messages that reflect messages from one
node to another and are not visible to the user.  A special block
starts with the character sequence '\special' (or 5Ch 73h 70h 65h 63h
69h 61h 6Ch) followed by a DER encoded special block (SpecialBlock).
Any non-special message decoding to ID 0 in a workspace starting with
this character sequence MUST escape all backslashes within the
payload chunk with an additional backslash.

7.3.1.  Error Block

An error block may be sent as a reply contained in the payload
section.  The error block is embedded in a special block and sent
with any provided reply block.  Error messages SHOULD contain the
serial number of the offending header block and MAY contain human-
readable text providing additional messages about the error.

7.3.2.  Requirement Block

If a node is receiving a requirement block, then it MUST assume that
the request block is accepted, is not yet processed, and is to be
processed if it meets the contained requirement.  A node MUST process
a request as soon as the requirement is fulfilled, and MUST resend
the request as soon as it meets the requirement.

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A node MAY reject a request, accept a request without a requirement,
accept a request upon payment (RequirementPaymentRequired), or accept
a request upon solving a proof of work puzzle
(RequirementPuzzleRequired).

7.3.2.1.  Puzzle Requirement

If a node requests a puzzle, then it MUST send a
RequirementPuzzleRequired block.  The puzzle requirement is solved if
the node receiving the puzzle is replying with a header block that
contains the puzzle block, and the hash of the encoded block begins
with the bit sequence mentioned in the puzzle within the period
specified in the field 'valid.'

A node solving a puzzle requires sending a VortexMessage to the
requesting node, which MUST contain a header block that includes the
puzzle block and MUST have a MAC fingerprint starting with the bit
sequence as specified in the challenge.  The receiving node
calculates the MAC from the unencrypted DER encoded HeaderBlock with
the algorithm specified by the node.  The sending node may achieve
the requirement by adding a proofOfWork field to the HeaderBlock
containing any content fulfilling the criteria.  The sending node
SHOULD keep the proofOfWork field as short as possible.

7.3.2.2.  Payment Requirement

If a node requests a payment, then it MUST send a
RequirementPaymentRequired block.  As soon as the requested fee is
paid and confirmed, the requesting node MUST send a "no error" status
message.  The usage period 'valid' describes the period during which
the payment may be carried out.  A node MUST accept the payment if
occurring within the 'valid' period but confirmed later.  A node
SHOULD return all unsolicited payments to the sending address.

7.3.2.3.  Upgrade

If a node requests an upgrade a ReplyUpgrade block MAY be sent.  The
block must contain the identifier and version of the most recent
software version.  The blob MAY contain the software if there is a
newer one available.

7.4.  Routing Operations

Routing operations are contained in a routing block and processed
upon arrival of a message or when compiling a new message.  All
operations are reversible, and no operation is available for
generating decoy traffic, which may be used through encryption of an
unpadded block or the addRedundancy operation.

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All payload chunk blocks inherit the validity time from the message
routing combos as arrival time + max(maxProcessTime).

When applying an operation to a source block, the resulting target
block inherits the expiration of the source block.  When multiple
expiration times exist, the one furthest in the future is applied to
the target block.  If the operation fails, then the target expiration
remains unchanged.

7.4.1.  Mapping Operation

The straightforward mapping operation is used in inOperations of a
routing block to map the routing block's specific blocks to a
permanent workspace.

7.4.2.  Split and Merge Operations

The split and merge operations allow splitting and recombining
message chunks.  A node MUST adhere to the following constraints.

o  The operation must be applied at an absolute (measuring in bytes)
or relative (measured as a float value in the range 0>value>100)
position.

o  All calculations must be performed according to IEEE 754 [IEEE754]
and in 64-bit precision.

o  If a relative value is a non-integer result, then a floor
operation (i.e., cutting off all non-integer parts) determines the
number of bytes.

o  If an absolute value is negative, then the size represents the
number of bytes counted from the end of the message chunk.

o  If an absolute value is greater than the number of bytes in a
block, then all bytes are mapped to the respective target block,
and the other target block becomes a zero byte-sized block.

An operation MUST fail if relative values are equal to, or less than,
zero.  An operation MUST fail if a relative value is equal to, or
greater than, 100.  All floating-point operations must be performed
according to [IEEE754] and in 64-bit precision.

7.4.3.  Encrypt and Decrypt Operations

Encryption and decryption are executed according to the standards
mentioned above.  An encryption operation encrypts a block
symmetrically and places the result in the target block.  The

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parameters MUST contain IV, padding, and cipher modes.  An encryption
operation without a valid parameter set MUST fail.

7.4.4.  Add and Remove Redundancy Operations

The addRedundancy and removeRedundancy operations are core to the
protocol.  They may be used to split messages and distribute message
content across multiple routing nodes.  The operation is separated
into three steps.

1.  Pad the input block to a multiple of the key block size in the
resulting output blocks.

2.  Apply a Vandermonde matrix with the given sizes.

3.  Encrypt each resulting block with a separate key.

The following sections describe the order of the operations within an
addRedundancy operation.  For a removeRedundancy operation, invert
the functions and order.  If the removeRedundancy has more than the
required blocks to recover the information, then it should take only
the required number beginning from the smallest.  If a seed and PRNG
are provided, then the removeRedundancy operation MAY test any
combination until recovery is successful.

7.4.4.1.  Padding Operation

A processing node calculates the final length of all payload blocks,
including redundancy.  This is done by L=roof((<input block size in
bytes>+4)/<encryption block size in bytes>)*<encryption block size in
bytes>.  The block is prepended with a 32-bit unit length indicator
in bytes (little-endian).  This length indicator, i, is calculated by
i=<input block size in bytes>*randominteger\cdot L.  The remainder of
the input block, up to length L, is padded with random data.  A
routing block builder should specify the value of the
$randomInteger$. If not specified the routing node may choose a
random positive integer value.  A routing block builder SHOULD
specify a PRNG and a seed used for this padding.  If GF(16) is
applied, then all numbers are treated as little-endian
representations.  Only GF(8) and GF(16) are allowed fields.

For padding removal, the padding i at the start is first removed as a
little-endian integer.  Second, the length of the output block is
calculated by applying <output block size in bytes>=i mod <input
block size in bytes>

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This padding guarantees that each resulting block matches the block
size of the subsequent encryption operation and does not require
further padding.

7.4.4.2.  Apply Matrix

Next, the input block is organized in a data matrix D of dimensions
(inrows, incols) where incols=(<number of data blocks>-<number of
redundancy blocks>) and inrows=L/(<number of data blocks>-<number of
redundancy blocks>).  The input block data is first distributed in
this matrix across, and then down.

Next, the data matrix D is multiplied by a Vandermonde matrix V with
its number of rows equal to the incols calculated and columns equal
to the <number of data blocks>.  The content of the matrix is formed
by v(i,j)=pow(i,j), where i reflects the row number starting at 0,
and j reflects the column number starting at 0.  The calculations
described must be carried out in the GF noted in the respective
operation to be successful.  The completed operation results in
matrix A.

7.4.4.3.  Encrypt Target Block

Each row vector of A is a new data block encrypted with the
corresponding encryption key noted in the keys of the
addRedundancyOperation.  If there are not enough keys available, then
the keys used for encryption are reused from the beginning after the
final key is used.  A routing block builder SHOULD provide enough
keys so that all target blocks may be encrypted with a unique key.
All encryptions SHOULD NOT use padding.

7.5.  Processing of Vortex Messages

The accounting layer triggers processing according to the information
contained in a routing block in the workspace.  All operations MUST
be executed in the sequence provided in the routing block, and any
failing operation must leave the result block unmodified.

All workspace blocks resulting in IDs of 1 to maxPayloadBlock are
then added to the message and passed to the blending layer with
appropriate instructions.

8.  Accounting

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8.1.  Accounting Operations

The accounting layer has two types of operations.

o  Time-based (e.g., cleanup jobs and initiation of routing).

o  Routing triggered (e.g., updating quotas, authorizing operations,
and pickup of incoming messages).

Implementations MUST provide sufficient locking mechanisms to
guarantee the integrity of accounting information and the workspace
at any time.

8.1.1.  Time-Based Garbage Collection

The accounting layer SHOULD keep a list of expiration times.  As soon
as an entry (e.g., payload block or identity) expires, the respective
structure should be removed from the workspace.  An implementation
MAY choose to remove expired items periodically or when encountering
them during normal operation.

8.1.2.  Time-Based Routing Initiation

The accounting layer MAY keep a list of when a routing block is
activated.  For improved privacy, the accounting layer should use a
slotted model where, whenever possible, multiple routing blocks are
handled in the same period, and the requests to the blending layers
are mixed between the transactions.

8.1.3.  Routing Based Quota Updates

A node MUST update quotas on the respective operations.  For example,
a node MUST decrease the message quota before processing routing
blocks in the workspace and after the processing of header requests.

8.1.4.  Routing Based Authorization

The transfer quota MUST be checked and decreased by the number of
data bytes in the payload chunks after an outgoing message is
processed and fully assembled.  The message quota MUST be decreased
by one on each routing block triggering the assembly of an outgoing
message.

8.1.5.  Ephemeral Identity Creation

Any packet may request the creation of an ephemeral identity.  A node
SHOULD NOT accept such a request without a costly requirement since
the request includes a lifetime of the ephemeral identity.  The costs

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for creating the ephemeral identity SHOULD increase if a longer
lifetime is requested.

9.  Acknowledgments

Thanks go to my family who supported me with patience and countless
hours as well as to Mark Zeman for his feedback challenging my
thoughts and peace.

10.  IANA Considerations

This memo includes no request to IANA.

Additional encryption algorithms, paddings, modes, blending layers or
puzzles MUST be added by writing an extension to this or a subsequent
RFC.  For testing purposes, IDs above 1,000,000 should be used.

11.  Security Considerations

The MessageVortex protocol should be understood as a toolset instead
of a fixed product.  Depending on the usage of the toolset, anonymity
and security are affected.  For a detailed analysis, see
[MVAnalysis].

The primary goals for security within this protocol rely on the
following focus areas.

o  Confidentiality

o  Integrity

o  Availability

o  Anonymity

*  Third-party anonymity

*  Sender anonymity

*  Receiver anonymity

These aspects are affected by the usage of the protocol, and the
following sections provide additional information on how they impact
the primary goals.

The Vortex protocol does not rely on any encryption of the transport
layer since Vortex messages are already encrypted.  Also,

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confidentiality is not affected by the protection mechanisms of the
transport layer.

If a transport layer supports encryption, then a Vortex node SHOULD
use it to improve the privacy of the message.

Anonymity is affected by the inner workings of the blending layer in
many ways.  A Vortex message cannot be read by anyone except the peer
nodes and routing block builder.  The presence of a Vortex node
message may be detected through the typical high entropy of an
encrypted file, broken structures of a carrier file, a meaningless
content of a carrier file or the contextless communication of the
transport layer with its peer partner.  A blending layer SHOULD
minimize the possibility of simply detection by minimizing these
effects.

A blending layer SHOULD use carrier files with high compression or
encryption.  Carrier files SHOULD NOT have inner structures such that
the payload is comparable to valid content.  To achieve
undetectability by a human reviewer, a routing block builder should
use F5 instead of PLAIN blending.  This approach, however, increases
the protocol overhead by approximately tenfold.

The two layers of 'routing' and 'accounting' have the deepest insight
into a Vortex message's inner working.  Each knows the immediate peer
sender and the peer recipients of all payload chunks.  As decoy
traffic is generated by combining chunks and applying redundancy
calculations, a node can never know if a malfunction (e.g., during a
recovery calculation) was intended.  Therefore, a node is unable to
distinguish a failed transaction from a terminated transaction as
well as content from decoy traffic.

A routing block builder SHOULD follow the following rules not to
compromise a Vortex message's anonymity.

o  All operations applied SHOULD be credibly involved in a message
transfer.

o  A sufficient subset of the result of an addRedundancy operation
should always be sent to peers to allow recovery of the data
built.

o  The anonymity set of a message should be sufficiently large to
avoid legal prosecution of all jurisdictional entities involved,
even if a certain amount of the anonymity set cooperates with an
adversary.

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o  Encryption and decryption SHOULD follow normal usage whenever
possible by avoiding the encryption of a block on a node with one
key and decrypting it with a different key on the same or adjacent
node.

o  Traffic peaks SHOULD be uniformly distributed within the entire
anonymity set.

o  A routing block SHOULD be used for a limited number of messages.
If used as a message block for the node, then it should be used
only once.  A block builder SHOULD use the
HeaderRequestReplaceIdentity block to update the reply to routing
blocks regularly.  Implementers should always remember that the
same routing block is identifiable by its structure.

An active adversary cannot use blocks from other routing block
builders.  While the adversary may falsify the result by injecting an
incorrect message chunk or not sending a message, such message
disruptions may be detected by intentionally routing information to
the routing block builder (RBB) node.  If the Vortex message does not
carry the information expected, then the node may safely assume that
one of the involved nodes is misbehaving.  A block building node MAY
calculate reputation for involved nodes over time and MAY build
redundancy paths into a routing block to withstand such malicious
nodes.

Receiver anonymity is at risk if the handling of the message header
and content is not done with care.  An attacker might send a bugged
message (e.g., with a DKIM or DMARC header) to deanonymize a
recipient.  Careful attention is required when handling anything
other than local references when processing, verifying, or rendering
a message.

12.  References

12.1.  Normative References

[CCITT.X208.1988]
International Telephone and Telegraph Consultative
Committee, "Specification of Abstract Syntax Notation One
(ASN.1)", CCITT Recommendation X.208, 11 1998.

[CCITT.X680.2002]
International Telephone and Telegraph Consultative
Committee, "Abstract Syntax Notation One (ASN.1):
Specification of basic notation", 11 2002.

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[EAX]      Bellare, M., Rogaway, P., and D. Wagner, "The EAX mode of
operation", 2011.

[F5]       Westfeld, A., "F5 - A Steganographic Algorithm - High
Capacity Despite Better Steganalysis", 10 2001.

[FIPS-AES]
Federal Information Processing Standard (FIPS),
"Specification for the ADVANCED ENCRYPTION STANDARD
(AES)", 11 2011.

[IEEE754]  IEEE, "754-2008 - IEEE Standard for Floating-Point
Arithmetic", 08 2008.

[ISO-10118-3]
International Organization for Standardization, "ISO/IEC
10118-3:2004 -- Information technology -- Security
techniques -- Hash-functions -- Part 3: Dedicated hash-
functions", 3 2004.

[MODES]    National Institute for Standards and Technology (NIST),
"Recommendation for Block Cipher Modes of Operation:
Methods and Techniques", 12 2001.

[RFC1423]  Balenson, D., "Privacy Enhancement for Internet Electronic
Mail: Part III: Algorithms, Modes, and Identifiers",
RFC 1423, DOI 10.17487/RFC1423, February 1993,
<https://www.rfc-editor.org/info/rfc1423>.

[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>.

[RFC3610]  Whiting, D., Housley, R., and N. Ferguson, "Counter with
CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September
2003, <https://www.rfc-editor.org/info/rfc3610>.

[RFC3657]  Moriai, S. and A. Kato, "Use of the Camellia Encryption
Algorithm in Cryptographic Message Syntax (CMS)",
RFC 3657, DOI 10.17487/RFC3657, January 2004,
<https://www.rfc-editor.org/info/rfc3657>.

[RFC3686]  Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004,
<https://www.rfc-editor.org/info/rfc3686>.

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[RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.

[RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
DOI 10.17487/RFC5288, August 2008,
<https://www.rfc-editor.org/info/rfc5288>.

[RFC5958]  Turner, S., "Asymmetric Key Packages", RFC 5958,
DOI 10.17487/RFC5958, August 2010,
<https://www.rfc-editor.org/info/rfc5958>.

[RFC7253]  Krovetz, T. and P. Rogaway, "The OCB Authenticated-
Encryption Algorithm", RFC 7253, DOI 10.17487/RFC7253, May
2014, <https://www.rfc-editor.org/info/rfc7253>.

[RFC8017]  Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/info/rfc8017>.

[SEC1]     Certicom Research, "SEC 1: Elliptic Curve Cryptography",
05 2009.

[TWOFISH]  Schneier, B., "The Twofish Encryptions Algorithm: A
128-Bit Block Cipher, 1st Edition", 03 1999.

[XEP-0231]
Peter, S. and P. Simerda, "XEP-0231: Bits of Binary", 09
2008, <https://xmpp.org/extensions/xep-0231.html>.

12.2.  Informative References

[DeadParrot]
Houmansadr, A., Burbaker, C., and V. Shmatikov, "The
Parrot is Dead: Observing Unobservable Network
Communications", 2013,
<https://people.cs.umass.edu/~amir/papers/parrot.pdf>.

[KAnon]    Ahn, L., Bortz, A., and N. Hopper, "k-Anonymous Message
Transmission", 2003.

[MVAnalysis]
Gwerder, M., "MessageVortex", 2018,
<https://messagevortex.net/devel/messageVortex.pdf>.

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[RFC1939]  Myers, J. and M. Rose, "Post Office Protocol - Version 3",
STD 53, RFC 1939, DOI 10.17487/RFC1939, May 1996,
<https://www.rfc-editor.org/info/rfc1939>.

[RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>.

[RFC2595]  Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, DOI 10.17487/RFC2595, June 1999,
<https://www.rfc-editor.org/info/rfc2595>.

[RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
<https://www.rfc-editor.org/info/rfc3501>.

[RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008,
<https://www.rfc-editor.org/info/rfc5321>.

[RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
March 2011, <https://www.rfc-editor.org/info/rfc6120>.

Appendix A.  The ASN.1 schema for Vortex messages

The following sections contain the ASN.1 modules specifying the
MessageVortex Protocol.

A.1.  The main VortexMessageBlocks

A.2.  The VortexMessage Ciphers Structures

A.3.  The VortexMessage Request Structures

A.4.  The VortexMessage Replies Structures

A.5.  The VortexMessage Requirements Structures

A.6.  The VortexMessage Helpers Structures

A.7.  The VortexMessage Additional Structures

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Author's Address

Martin Gwerder
University of Applied Sciences of Northwestern Switzerland
Bahnhofstrasse 5
Windisch, AG  5210
Switzerland

Phone: +41 56 202 76 81
Email: rfc@messagevortex.net

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