Internet Engineering Task Force Gwerder
Internet-Draft FHNW
Intended status: Experimental November 10, 2019
Expires: May 13, 2020

MessageVortex Protocol
draft-gwerder-messagevortexmain-03

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 May 13, 2020.

Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.

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


Table of Contents

1. Introduction

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 due to the nature of the operations processed. 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.

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 1) 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 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

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

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

This representation does not support quoted local part SMTP addresses.

2.1.2.2. NodeSpec for XMPP nodes

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

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

2.2. Peer Partners

Two or more message sending or receiving entities are referred to 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.

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:

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.

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 that is designed to be small and flexible while maintaining a specific base structure.

The following key structures are available:

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.

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.

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.

2.8.3. Official Identity

An official identity may have the following items assigned.

2.9. Workspace

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

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.

3. Layer Overview

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

+------------------------------------------------------------------+
| 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 information contained in MessageVortex packets, processes them, and passes generated packets to the respective blending layer.

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

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

Figure 2: Vortex message 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.

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 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 always starts with a padding block, which guarantees that when using the same routing block multiple times, its binary structure is not repeated throughout the messages of the same routing block. The padding MUST be the first 16 bytes of the first four non-empty payload chunks (i.e., PayloadChunks). If a payload chunk is shorter than 16 bytes, then the content of the padding SHOULD be filled with zero-valued bytes (00h) from the end up to the required number of bytes. An inner message block (i.e., InnerMessageBlock) SHOULD contain at least four payload chunks with a size of 16 bytes or larger. If there are less than four payload chunks, then the padding MUST contain a random sequence of 16 bytes for those missing, and a node MUST NOT reuse random sequences.

An InnerMessageBlock contains so-called forwardSecrets, a random number that MUST be the same in the 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 if the forward secret is correct.

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 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.

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

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.

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.

5.1. Supported Symmetric Ciphers

A node MUST support the following symmetric ciphers.

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.

5.3. Supported MACs

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

A node SHOULD support the following MACs.

5.4. Supported Paddings

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

5.5. Supported Modes

A node MUST support the following modes.

A node SHOULD NOT use the following modes.

A node SHOULD support the following 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.

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 variable length unsigned integers. 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 reflects 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.

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 omited 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> ]* ")"

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

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.

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.

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.

function incomming_message(VortexMessage blendedMessage) {
  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" )
            }  
          }
        }
      }
  } catch( exception e ) {
    // Message processing failed
    throw e;
  }
}

Reflected in pseudo code, the message processing works according to the following.

7.1.2. Processing of Routing Blocks in the Workspace

A routing workspace consists of the following items.

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.

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 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 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. To accept a request without a requirement, an accepting node MUST send back a special block containing "no error." To accept a block with a requirement, an accepting node MUST send a special block containing a requirement block.

A node SHOULD NOT reply to clear-text requests if the node does not want to officially disclose its identity as a Vortex node. 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 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 officially disclose its identity as a Vortex node. 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.

7.2.8. Request Identity Replace

This request type allows a receiving node to replace an 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.

7.3. 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 where specified as a payload. 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.

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.'

To solve a puzzle posed by a node, a Vortex Message needs to be sent 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. A node calculates the MAC from the unencrypted DER encoded HeaderBlock with the algorithm specified by the node. To meet this requirement, a node adds a proofOfWork field to the HeaderBlock.

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.

7.4. 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.

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 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.

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 parameters MUST contain IV, padding or 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 output 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 choosea 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>

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 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

8.1. Accounting Operations

The accounting layer has two types of operations.

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 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.

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, 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 to not compromise a Vortex message's anonymity.

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'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, November 1998.
[CCITT.X680.2002] International Telephone and Telegraph Consultative Committee, "Abstract Syntax Notation One (ASN.1): Specification of basic notation", November 2002.
[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", October 2001.
[FIPS-AES] Federal Information Processing Standard (FIPS), "Specification for the ADVANCED ENCRYPTION STANDARD (AES)", November 2011.
[IEEE754] IEEE, "754-2008 - IEEE Standard for Floating-Point Arithmetic", August 2008.
[ISO-10118-3] International Organization for Standardization, "ISO/IEC 10118-3:2004 -- Information technology -- Security techniques -- Hash-functions -- Part 3: Dedicated hash-functions", March 2004.
[MODES] National Institute for Standards and Technology (NIST), "Recommendation for Block Cipher Modes of Operation: Methods and Techniques", December 2001.
[RFC1423] Balenson, D., "Privacy Enhancement for Internet Electronic Mail: Part III: Algorithms, Modes, and Identifiers", RFC 1423, DOI 10.17487/RFC1423, February 1993.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC3610] Whiting, D., Housley, R. and N. Ferguson, "Counter with CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September 2003.
[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.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES) Counter Mode With IPsec Encapsulating Security Payload (ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008.
[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.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, DOI 10.17487/RFC5958, August 2010.
[RFC7253] Krovetz, T. and P. Rogaway, "The OCB Authenticated-Encryption Algorithm", RFC 7253, DOI 10.17487/RFC7253, May 2014.
[RFC8017] Moriarty, K., Kaliski, B., Jonsson, J. and A. Rusch, "PKCS #1: RSA Cryptography Specifications Version 2.2", RFC 8017, DOI 10.17487/RFC8017, November 2016.
[SEC1] Certicom Research, "SEC 1: Elliptic Curve Cryptography", May 2009.
[TWOFISH] Schneier, B., "The Twofish Encryptions Algorithm: A 128-Bit Block Cipher, 1st Edition", March 1999.
[XEP-0231] Peter, S. and P. Simerda, "XEP-0231: Bits of Binary", September 2008.

12.2. Informative References

[DeadParrot] Houmansadr, A., Burbaker, C. and V. Shmatikov, "The Parrot is Dead: Observing Unobservable Network Communications", 2013.
[KAnon] Ahn, L., Bortz, A. and N. Hopper, "k-Anonymous Message Transmission", 2003.
[MVAnalysis] Gwerder, M., "MessageVortex", 2018.
[RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3", STD 53, RFC 1939, DOI 10.17487/RFC1939, May 1996.
[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.
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595, DOI 10.17487/RFC2595, June 1999.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, DOI 10.17487/RFC5321, October 2008.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120, March 2011.

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

MessageVortex-Schema DEFINITIONS EXPLICIT TAGS ::=
BEGIN
  EXPORTS PrefixBlock, InnerMessageBlock, RoutingBlock,
          maxID;
  IMPORTS SymmetricKey, AsymmetricKey, MacAlgorithmSpec, CipherSpec
                FROM MessageVortex-Ciphers
          HeaderRequest
                FROM MessageVortex-Requests
          PayloadOperation
                FROM MessageVortex-Operations

          UsagePeriod, BlendingSpec
                FROM MessageVortex-Helpers;

  --***************************************************************
  -- Constant definitions
  --***************************************************************

  -- maximum serial number
  maxSerial                 INTEGER ::= 4294967295
  -- maximum number of administrative requests
  maxNumberOfRequests       INTEGER ::= 8
  -- maximum number of seconds which the message might be delayed
  -- in the local queue (starting from startOffset)
  maxDurationOfProcessing   INTEGER ::= 86400
  -- maximum id of an operation
  maxID                     INTEGER ::= 32767
  -- maximum number of routing blocks in a message
  maxRoutingBlocks          INTEGER ::= 127
  -- maximum number a block may be replayed
  maxNumberOfReplays        INTEGER ::= 127
  -- maximum number of payload chunks in a message
  maxPayloadBlocks          INTEGER ::= 127
  -- maximum number of seconds a proof of non revocation may be old
  maxTimeCachedProof        INTEGER ::= 86400
  -- The maximum ID of the workspace
  maxWorkspaceId            INTEGER ::= 65535
  -- The maximum number of assembly instructions per combo
  maxAssemblyInstructions   INTEGER ::= 255

  --***************************************************************
  -- Block Definitions
  --***************************************************************
  PrefixBlock ::= SEQUENCE {
    forwardsecret   ChainSecret,
    key             SymmetricKey,
	version			INTEGER OPTIONAL
  }

  IdentityBlock ::= SEQUENCE {
    -- Public key of the identity representing this transmission
    identityKey         AsymmetricKey,
    -- serial identifying this block
    serial              INTEGER (0..maxSerial),
    -- number of times this block may be replayed (Tuple is
    -- identityKey, serial while UsagePeriod of block)
    maxReplays          INTEGER (0..maxNumberOfReplays),
    -- subsequent Blocks are not processed before valid time.
    -- Host may reject too long retention. Recomended validity
    -- support >=1Mt.
    valid               UsagePeriod,
    -- represents the chained secret which has to be found in
    -- subsequent blocks
    -- prevents reassembly attack
    forwardSecret       ChainSecret,
    --  contains the MAC-Algorithm used for signing
    signAlgorithm       MacAlgorithmSpec,
    -- contains administrative requests such as quota requests
    requests            SEQUENCE (SIZE (0..maxNumberOfRequests))
                        OF HeaderRequest ,
    -- Reply Block for the requests
    requestReplyBlock   RoutingCombo,
    -- padding and identitifier required to solve the cryptopuzzle
    identifier  [12201] PuzzleIdentifier OPTIONAL,
    -- This is for solving crypto puzzles
    proofOfWork [12202] OCTET STRING OPTIONAL
  }

  InnerMessageBlock ::= SEQUENCE {
    padding   OCTET STRING,
    prefix    CHOICE {
        plain           [11011] PrefixBlock,
        -- contains prefix encrypted with receivers public key
        encrypted       [11012] OCTET STRING
    },
    identity  CHOICE  {
      -- debug/internal use only
      plain     [11021] IdentityBlock,
      -- contains encrypted identity block
      encyrpted [11022] OCTET STRING
    },
    -- contains signature of Identity [as stored in
    -- HeaderBlock; signed unencrypted HeaderBlock without Tag]
    identitySignature OCTET STRING,
    -- contains routing information (next hop) for the payloads
    routing     CHOICE {
      plain     [11031] RoutingBlock,
      -- contains encrypted routing block
      encyrpted [11032] OCTET STRING
    },
    -- contains the actual payload
    payload     SEQUENCE (SIZE (0..maxPayloadBlocks))
                OF OCTET STRING
  }

  RoutingBlock ::= SEQUENCE {
    -- contains the prefix to be used
    routing    CHOICE {
      -- debug/internal use only
      plain             [331] SEQUENCE (SIZE (0..maxRoutingBlocks))
                              OF RoutingCombo,
      encrypted         [332] SEQUENCE (SIZE (0..maxRoutingBlocks))
                              OF OCTET STRING
    },
    -- contains the secret of the header block
    forwardSecret     ChainSecret,
    -- contains a routing block which may be used when sending
    -- error messages back to the quota owner
    -- this routing block may be cached for future use
    replyBlock [131]   SEQUENCE {
         murb           RoutingCombo,
         maxReplay      INTEGER,
         validity       UsagePeriod
    } OPTIONAL
  }

  RoutingCombo ::= SEQUENCE {
    -- contains the period when the payload should be processed
    -- Router might refuse to long queue retention
    -- Recommended support for retention >=1h
    minProcessTime INTEGER (0..maxDurationOfProcessing),
    maxProcessTime INTEGER (0..maxDurationOfProcessing),
    -- The message key to encrypt the message
    messageKey    [401] SymmetricKey OPTIONAL,
    -- contains the next recipient
    recipient     [402] BlendingSpec OPTIONAL,
    -- PrefixBlock encrypted with message key
    mPrefix       [403] OCTET STRING OPTIONAL,
    -- PrefixBlock encrypted with sender key
    cPrefix       [404] OCTET STRING OPTIONAL,
    -- HeaderBlock encrypted with sender key
    header        [405] OCTET STRING OPTIONAL,
    -- RoutingBlock encrypted with sender key
    routing       [406] OCTET STRING OPTIONAL,
    -- contains information for building messages (when used as MURB
    -- ID 0 denotes original message; ID 1-maxPayloadBlocks denotes
    -- target message; 32768-maxWorkspaceId shared workspace for all
    -- blocks of this identity)
    assembly      [407] SEQUENCE (SIZE (0..maxAssemblyInstructions))
                  OF PayloadOperation,
    validity      [408] UsagePeriod,
    -- optional - to identify the sender of a message when received
    id            [409] INTEGER OPTIONAL
  }

  PuzzleIdentifier          ::= OCTET STRING ( SIZE(0..16) )

  ChainSecret ::= INTEGER (0..4294967295)

END

A.2. The VortexMessage Ciphers Structures

MessageVortex-Ciphers DEFINITIONS EXPLICIT TAGS ::=
BEGIN
  EXPORTS SymmetricKey, AsymmetricKey, MacAlgorithmSpec, 
          MacAlgorithm, CipherSpec, PRNGType;

  CipherSpec ::= SEQUENCE {
      asymmetric [16001] AsymmetricAlgorithmSpec OPTIONAL,
      symmetric  [16002] SymmetricAlgorithmSpec OPTIONAL,
      mac        [16003] MacAlgorithmSpec OPTIONAL,
      cipherUsage[16004] CipherUsage
  }

  CipherUsage ::= ENUMERATED {
    sign     (200),
    encrypt  (210)
  }

  SymmetricAlgorithmSpec  ::=  SEQUENCE  {
    algorithm               [16101]SymmetricAlgorithm,
    -- if ommited: pkcs1
    padding                 [16102]CipherPadding OPTIONAL,
    -- if ommited: cbc
    mode                    [16103]CipherMode OPTIONAL,
    parameter               [16104]AlgorithmParameters OPTIONAL
  }

  AsymmetricAlgorithmSpec  ::=  SEQUENCE  {
    algorithm               AsymmetricAlgorithm,
    parameter               AlgorithmParameters OPTIONAL
  }

  MacAlgorithmSpec  ::=  SEQUENCE  {
    algorithm               MacAlgorithm,
    parameter               AlgorithmParameters
  }

  PRNGAlgorithmSpec ::= SEQUENCE {
    type                    PRNGType,
    seed                    OCTET STRING
  }

  PRNGType ::= ENUMERATED {
    mrg32k3a        (1000),
    blumMicali      (1001)
  }

  SymmetricAlgorithm ::= ENUMERATED {
    aes128          (1000),  -- required
    aes192          (1001),  -- optional support
    aes256          (1002),  -- required
    camellia128     (1100),  -- required
    camellia192     (1101),  -- optional support
    camellia256     (1102),  -- required
    twofish128      (1200),  -- optional support
    twofish192      (1201),  -- optional support
    twofish256      (1202)   -- optional support
  }

  CipherMode ::= ENUMERATED {
    -- ECB is a really bad choice. Do not use unless really
    -- necessary
    ecb             (10000),
    cbc             (10001),
    eax             (10002),
    ctr             (10003),
    ccm             (10004),
    gcm             (10005),
    ocb             (10006),
    ofb             (10007),
    none            (10100)
  }

  CipherPadding ::= ENUMERATED {
    none            (1000),
    pkcs1           (1001),
    pkcs7           (1002)
  }

  AsymmetricAlgorithm ::= ENUMERATED {
    rsa             (2000),
    dsa             (2100),
    ec              (2200),
    ntru            (2300)
  }

  MacAlgorithm ::= ENUMERATED {
    sha3-256        (3000),
    sha3-384        (3001),
    sha3-512        (3002),
    ripemd160       (3100),
    ripemd256       (3101),
    ripemd320       (3102)
  }

  ECCurveType ::= ENUMERATED{
    secp384r1       (2500),
    sect409k1       (2501),
    secp521r1       (2502)
  }

  AlgorithmParameters ::= SEQUENCE {
    keySize              [10000] INTEGER (0..65535) OPTIONAL,
    curveType            [10001] ECCurveType   OPTIONAL,
    initialisationVector [10002] OCTET STRING  OPTIONAL,
    nonce                [10003] OCTET STRING  OPTIONAL,
    mode                 [10004] CipherMode    OPTIONAL,
    padding              [10005] CipherPadding OPTIONAL,
    n                    [10010] INTEGER       OPTIONAL,
    p                    [10011] INTEGER       OPTIONAL,
    q                    [10012] INTEGER       OPTIONAL,
    k                    [10013] INTEGER       OPTIONAL,
    t                    [10014] INTEGER       OPTIONAL
  }

  -- Symmetric key
  SymmetricKey ::= SEQUENCE {
    keyType SymmetricAlgorithm,
    parameter AlgorithmParameters,
    key     OCTET STRING (SIZE(16..512))
  }

  -- Asymmetric Key
  AsymmetricKey ::= SEQUENCE {
    keyType       AsymmetricAlgorithm,
	-- private key encoded as PKCS#8/PrivateKeyInfo
    publicKey     [2] OCTET STRING,
	-- private key encoded as X.509/SubjectPublicKeyInfo
    privateKey    [3] OCTET STRING OPTIONAL
  }

END

A.3. The VortexMessage Request Structures

MessageVortex-Requests DEFINITIONS EXPLICIT TAGS ::=
BEGIN
  EXPORTS HeaderRequest;
  IMPORTS RequirementBlock
                FROM MessageVortex-Requirements
          UsagePeriod, NodeSpec
                FROM MessageVortex-Helpers;

  HeaderRequest ::= CHOICE {
    identity      [0] HeaderRequestIdentity,
    capabilities  [1] HeaderRequestCapability,
    messageQuota  [2] HeaderRequestIncreaseMessageQuota,
    transferQuota [3] HeaderRequestIncreaseTransferQuota,
    quotaQuery    [4] HeaderRequestQuota,
    nodeQuery     [5] HeaderRequestNodes,
    replace       [6] HeaderRequestReplaceIdentity
  }

  HeaderRequestIdentity ::= SEQUENCE {
    period UsagePeriod
  }

  HeaderRequestReplaceIdentity ::= SEQUENCE {
	old			   NodeSpec,
	new            NodeSpec
  }

  HeaderRequestQuota ::= SEQUENCE {
  }

  HeaderRequestNodes ::= SEQUENCE {
    numberOfNodes   INTEGER (0..255)
  }

  HeaderRequestIncreaseMessageQuota ::= SEQUENCE {
    messages INTEGER (0..4294967295)
  }

  HeaderRequestIncreaseTransferQuota ::= SEQUENCE {
    size     INTEGER (0..4294967295)
  }

  HeaderRequestCapability ::= SEQUENCE {
    period UsagePeriod
  }


END

A.4. The VortexMessage Replies Structures

MessageVortex-Replies DEFINITIONS EXPLICIT TAGS ::=
BEGIN
  EXPORTS SpecialBlock;
  IMPORTS BlendingSpec, NodeSpec
                FROM MessageVortex-Helpers
          RequirementBlock
                FROM MessageVortex-Requirements
          CipherSpec, PRNGType, MacAlgorithm
                FROM MessageVortex-Ciphers;

  SpecialBlock ::= CHOICE {
    capabilities  [1]  ReplyCapability,
    requirement   [2]  SEQUENCE (SIZE (1..127))
                       OF RequirementBlock,
    quota         [4]  ReplyCurrentQuota,
    nodes         [5]  ReplyNodes,
    status        [99] StatusBlock
  }

  StatusBlock ::= SEQUENCE {
    code            StatusCode
  }

  StatusCode ::= ENUMERATED {

    -- System messages
    ok                          (2000),
    quotaStatus                 (2101),
    puzzleRequired              (2201),

    -- protocol usage failures
    transferQuotaExceeded       (3001),
    messageQuotaExceeded        (3002),
    requestedQuotaOutOfBand     (3003),
    identityUnknown             (3101),
    messageChunkMissing         (3201),
    messageLifeExpired          (3202),
    puzzleUnknown               (3301),

    -- capability errors
    macAlgorithmUnknown         (3801),
    symmetricAlgorithmUnknown   (3802),
    asymmetricAlgorithmUnknown  (3803),
    prngAlgorithmUnknown        (3804),
    missingParameters           (3820),
    badParameters               (3821),

    -- Mayor host specific errors
    hostError                   (5001)
  }

  ReplyNodes ::= SEQUENCE {
      node   SEQUENCE (SIZE (1..5))
             OF NodeSpec
  }

  ReplyCapability ::= SEQUENCE {
    -- supported ciphers
    cipher            SEQUENCE (SIZE (2..256)) OF CipherSpec,
    -- supported mac algorithms
    mac               SEQUENCE (SIZE (2..256)) OF MacAlgorithm,
    -- supported PRNGs
    prng              SEQUENCE (SIZE (2..256)) OF PRNGType,
    -- maximum number of bytes to be transferred (outgoing bytes in vortex message without blending)
    maxTransferQuota  INTEGER (0..4294967295),
    -- maximum number of messages to process for this identity
    maxMessageQuota   INTEGER (0..4294967295),
    -- maximum simultaneously tracked header serials
    maxHeaderSerials  INTEGER (0..4294967295),
    -- maximum simultaneously valid build operations in workspace
    maxBuildOps       INTEGER (0..4294967295),
    -- maximum header lifespan in seconds
    maxHeaderLive     INTEGER (0..4294967295), 
    
    supportedBlendingIn SEQUENCE OF BlendingSpec
  }

  ReplyCurrentQuota ::= SEQUENCE {
    messages INTEGER (0..4294967295),
    size     INTEGER (0..4294967295)
  }

END

A.5. The VortexMessage Requirements Structures

MessageVortex-Requirements DEFINITIONS EXPLICIT TAGS ::=
BEGIN
  EXPORTS RequirementBlock;
  IMPORTS MacAlgorithmSpec
                FROM MessageVortex-Ciphers
          UsagePeriod, UsagePeriod
                FROM MessageVortex-Helpers;

  RequirementBlock ::= CHOICE {
    puzzle  [1] RequirementPuzzleRequired,
    payment [2] RequirementPaymentRequired
  }

  RequirementPuzzleRequired ::= SEQUENCE {
    -- bit sequence at beginning of hash from encrypted identity
    -- block
    challenge     BIT STRING,
    mac           MacAlgorithmSpec,
    valid         UsagePeriod,
    identifier    INTEGER (0..4294967295)
  }

  RequirementPaymentRequired ::= SEQUENCE {
    account       OCTET STRING,
    ammount       REAL,
    currency      Currency
  }

  Currency ::= ENUMERATED {
    btc      (8001),
    eth      (8002),
    zec      (8003)
  }

END

A.6. The VortexMessage Helpers Structures

MessageVortex-Helpers DEFINITIONS EXPLICIT TAGS ::=
BEGIN
  EXPORTS UsagePeriod, BlendingSpec, NodeSpec;
  IMPORTS AsymmetricKey, SymmetricKey
                FROM MessageVortex-Ciphers;

  -- the maximum number of parameters that might be embedded
  maxNumberOfParameter      INTEGER ::= 127

  UsagePeriod ::= SEQUENCE {
    notBefore       [0]     GeneralizedTime OPTIONAL,
    notAfter        [1]     GeneralizedTime OPTIONAL
  }

  -- contains a node spec of a routing point
  -- At the moment either smtp:<email> or xmpp:<jabber>
  BlendingSpec ::= SEQUENCE {
    target            [1] NodeSpec,
    blendingType      [2] IA5String,
    parameter         [3] SEQUENCE ( SIZE (0..maxNumberOfParameter) )
                          OF BlendingParameter
  }

  BlendingParameter ::= CHOICE {
    offset          [1] INTEGER,
    symmetricKey    [2] SymmetricKey,
    asymmetricKey   [3] AsymmetricKey,
    passphrase      [4] OCTET STRING
  }

  NodeSpec ::= SEQUENCE {
    transportProtocol [1] Protocol,
    recipientAddress  [2] IA5String,
    recipientKey      [3] AsymmetricKey OPTIONAL
  }

  Protocol ::= ENUMERATED {
    smtp  (100),
    xmmp  (110)
  }

END

A.7. The VortexMessage Additional Structures

-- States: Tuple()=Value() [vallidity; allowed operations] {Store}
-- - Tuple(identity)=Value(messageQuota,transferQuota,sequence of
--   Routingblocks for Error Message Routing) [validity; Requested
--   at creation; may be extended upon request] {identityStore}
-- - Tuple(Identity,Serial)=maxReplays ['valid' from Identity
--   Block; from First Identity Block; may only be reduced]
--   {IdentityReplayStore}

MessageVortex-NonProtocolBlocks DEFINITIONS EXPLICIT TAGS ::=
BEGIN
  IMPORTS PrefixBlock, InnerMessageBlock, RoutingBlock, maxID
                FROM MessageVortex-Schema
          UsagePeriod, NodeSpec, BlendingSpec
                FROM MessageVortex-Helpers
          AsymmetricKey
                FROM MessageVortex-Ciphers
          RequirementBlock
                FROM MessageVortex-Requirements;

  -- maximum size of transfer quota in bytes of an identity
  maxTransferQuota          INTEGER ::= 4294967295
  -- maximum size of message quota in messages of an identity
  maxMessageQuota           INTEGER ::= 4294967295

  -- do not use these blocks for protocol encoding (internal only)
  VortexMessage ::= SEQUENCE {
    prefix        CHOICE {
        plain           [10011] PrefixBlock,
        -- contains prefix encrypted with receivers public key
        encrypted       [10012] OCTET STRING
    },
    innerMessage  CHOICE {
        plain     [10021] InnerMessageBlock,
        -- contains inner message encrypted with Symmetric key from
        -- Prefix
        encrypted [10022] OCTET STRING
    }
  }

  MemoryPayloadChunk ::= SEQUENCE {
    id                        INTEGER (0..maxID),
    payload                   [100] OCTET STRING,
    validity                  UsagePeriod
  }

  IdentityStore ::= SEQUENCE {
    identities SEQUENCE (SIZE (0..4294967295))
               OF IdentityStoreBlock
  }

  IdentityStoreBlock ::= SEQUENCE {
    valid               UsagePeriod,
    messageQuota        INTEGER (0..maxMessageQuota),
    transferQuota       INTEGER (0..maxTransferQuota),
    -- if omitted this is a node identity
    identity            [1001] AsymmetricKey OPTIONAL,
    -- if ommited own identity key
    nodeAddress         [1002] NodeSpec      OPTIONAL,
    -- Contains the identity of the owning node;
    -- May be ommited if local node
    nodeKey             [1003] SEQUENCE OF AsymmetricKey OPTIONAL,
    routingBlocks       [1004] SEQUENCE OF RoutingBlock OPTIONAL,
    replayStore         [1005] IdentityReplayStore,
    requirement         [1006] RequirementBlock OPTIONAL
  }

  IdentityReplayStore ::= SEQUENCE {
    replays   SEQUENCE (SIZE (0..4294967295))
              OF IdentityReplayBlock
  }

  IdentityReplayBlock ::= SEQUENCE {
    identity            AsymmetricKey,
    valid               UsagePeriod,
    replaysRemaining  INTEGER (0..4294967295)
  }

END

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