Mboned                                                        J. Holland
Internet-Draft                                                   K. Rose
Intended status: Standards Track               Akamai Technologies, Inc.
Expires: January 11, 2022                                  July 10, 2021

                  Asymmetric Manifest Based Integrity


   This document defines Asymmetric Manifest-Based Integrity (AMBI).
   AMBI allows each receiver or forwarder of a stream of multicast
   packets to check the integrity of the contents of each packet in the
   data stream.  AMBI operates by passing cryptographically verifiable
   hashes of the data packets inside manifest messages, and sending the
   manifests over authenticated out-of-band communication channels.

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
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   This Internet-Draft will expire on January 11, 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of

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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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Comparison with TESLA . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Notes for Contributors and Reviewers  . . . . . . . . . .   4
       1.3.1.  Venues for Contribution and Discussion  . . . . . . .   5
       1.3.2.  Non-obvious doc choices . . . . . . . . . . . . . . .   5
   2.  Threat Model  . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Security Anchors  . . . . . . . . . . . . . . . . . . . .   6
       2.1.1.  Alternatives and Their Requirements . . . . . . . . .   7
     2.2.  System Security . . . . . . . . . . . . . . . . . . . . .   8
   3.  Protocol Operation  . . . . . . . . . . . . . . . . . . . . .   8
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  Buffering of Packets and Digests  . . . . . . . . . . . .   9
       3.2.1.  Validation Windows  . . . . . . . . . . . . . . . . .  10
       3.2.2.  Preserving Inter-packet Gap . . . . . . . . . . . . .  11
     3.3.  Packet Digests  . . . . . . . . . . . . . . . . . . . . .  11
       3.3.1.  Digest Profile  . . . . . . . . . . . . . . . . . . .  11
       3.3.2.  Pseudoheader  . . . . . . . . . . . . . . . . . . . .  13
     3.4.  Manifests . . . . . . . . . . . . . . . . . . . . . . . .  14
       3.4.1.  Manifest Layout . . . . . . . . . . . . . . . . . . .  14
     3.5.  Transitioning to Other Manifest Streams . . . . . . . . .  17
   4.  Transport Considerations  . . . . . . . . . . . . . . . . . .  18
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  18
     4.2.  HTTPS . . . . . . . . . . . . . . . . . . . . . . . . . .  18
     4.3.  TLS . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
     4.4.  DTLS  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
   6.  YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  19
     6.2.  Module  . . . . . . . . . . . . . . . . . . . . . . . . .  20
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
     7.1.  The YANG Module Names Registry  . . . . . . . . . . . . .  23
     7.2.  The XML Registry  . . . . . . . . . . . . . . . . . . . .  24
     7.3.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  24
     7.4.  URI Schemes . . . . . . . . . . . . . . . . . . . . . . .  24
       7.4.1.  TLS . . . . . . . . . . . . . . . . . . . . . . . . .  24
       7.4.2.  DTLS  . . . . . . . . . . . . . . . . . . . . . . . .  24
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
     8.1.  Predictable Packets . . . . . . . . . . . . . . . . . . .  24
     8.2.  Attacks on Side Applications  . . . . . . . . . . . . . .  25
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  25
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  26

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     10.2.  Informative References . . . . . . . . . . . . . . . . .  26
     10.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   Multicast transport poses security problems that are not easily
   addressed by the same security mechanisms used for unicast transport.

   The "Introduction" sections of the documents describing TESLA
   [RFC4082], and TESLA in SRTP [RFC4383], and TESLA with ALC and NORM
   [RFC5776] present excellent overviews of the challenges unique to
   multicast authentication for use cases like wide scale software or
   video distribution with a high data transfer rate.  The challenges
   are briefly summarized here:

   o  A MAC based on a symmetric shared secret cannot be used because
      each packet has multiple receivers that do not trust each other,
      and using a symmetric shared secret exposes the same secret to
      each receiver.

   o  Asymmetric per-packet signatures can handle only very low bit-
      rates because of the transport and computational overhead
      associated with signature transmission and verification.

   o  An asymmetric signature of a larger message comprising multiple
      packets requires reliable receipt of all such packets, something
      that cannot be guaranteed in a timely manner even for protocols
      that do provide reliable delivery, and the retransmission of which
      may anyway exceed the useful lifetime for data formats that can
      otherwise tolerate some degree of loss.

   Aymmetric Manifest-Based Integrity (AMBI) defines a method for
   receivers or middle boxes to cryptographically authenticate and
   verify the integrity of a stream of packets by comparing the data
   packets to a stream of packet "manifests" (described in Section 3.4)
   received via an out-of-band communication channel that provides
   authentication and verifiable integrity.

   Each manifest contains a message digest (described in Section 3.3)
   for each packet in a sequence of packets from the data stream,
   hereafter called a "packet digest".  The packet digest incorporates a
   cryptographic hash of the packet contents and some identifying data
   from the packet, according to a defined digest profile for the data

   Upon receipt of a packet digest inside a manifest conveyed in a
   secure channel and verification that the packet digest of a received

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   data packet matches, the receiver has proof of the integrity of the
   contents of the data packet corresponding to that digest.

   This document defines the "ietf-ambi" YANG [RFC7950] model in
   Section 6 as an extension of the "ietf-dorms" model defined in
   [I-D.draft-ietf-mboned-dorms].  Also defined are new URI schemes for
   transport of manifests over TLS or DTLS, and a new media type for
   transport of manifests over HTTPS.  The encodings for these are
   defined in Section 4.

1.1.  Comparison with TESLA

   AMBI and TESLA [RFC4082] and [RFC5776] attempt to achieve a similar
   goal of authenticating the integrity of streams of multicast packets.
   AMBI imposes a higher overhead than TESLA imposes, as measured in the
   amount of extra data required.  In exchange, AMBI relaxes the
   requirement for establishing an upper bound on clock synchronization
   between sender and receiver, and allows for the use case of
   authenticating multicast traffic before forwarding it through the
   network, while also allowing receivers to authenticate the same
   traffic.  By contrast, this is not possible with TESLA because the
   data packets can't be authenticated until a key is disclosed, so
   either the middlebox has to forward data packets without first
   authenticating them so that the receiver has them prior to key
   disclosure, or the middlebox has to hold packets until the key is
   disclosed, at which point the receiver can no longer establish their

   The other new capability is that because AMBI provides authentication
   information out of band, authentication can be retrofitted into some
   pre-existing deployments without changing the protocol of the data
   packets under some restrictions outlined in Section 8.  By contrast,
   TESLA requires a MAC to be added to each authenticated message.

1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119] and [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

1.3.  Notes for Contributors and Reviewers

   Note to RFC Editor: Please remove this section and its subsections
   before publication.

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   This section is to provide references to make it easier to review the
   development and discussion on the draft so far.

1.3.1.  Venues for Contribution and Discussion

   This document is in the Github repository at:

   https://github.com/GrumpyOldTroll/ietf-dorms-cluster [1]

   Readers are welcome to open issues and send pull requests for this

   Please note that contributions may be merged and substantially
   edited, and as a reminder, please carefully consider the Note Well
   before contributing: https://datatracker.ietf.org/submit/note-well/

   Substantial discussion of this document should take place on the
   MBONED working group mailing list (mboned@ietf.org).

   o  Join: https://www.ietf.org/mailman/listinfo/mboned [3]

   o  Search: https://mailarchive.ietf.org/arch/browse/mboned/ [4]

1.3.2.  Non-obvious doc choices

   o  TBD: we need a way to assert that we provide the full set of
      packets for an (S,G) on all UDP ports and non-UDP protocols.
      Naively authenticating UDP for specified ports and ignoring other
      ports means that an attacker could attack a separate UDP port by
      injecting traffic directed at it, potentially hitting a different
      application that listens on, so an (S,G) with legitimately
      authenticated UDP traffic on one port could be used to transport
      UDP-based attacks to apps on another port or protocol unless they
      are firewalled.  Passing traffic for an (S,G) subscription would
      open a new channel to such targets that otherwise would not be
      reachable from the internet for users behind e.g. a CPE with nat
      or connection-state-based firewalling.

   o  Dropped intent to support DTLS+FECFRAME in this spec because RFC
      6363 seems incomprehensible on a few points, most notably demux
      strategy between repair and source ADUs, which as written seems to
      require specifying another layer.  So support for this will have
      to be a later separate RFC.  However, for future extensibility
      made manifest-stream into a list instead of a leaf-list so that it
      can be an augment target for a later YANG extension with FEC
      selection from the likewise-very-confusing semi-overlapping
      registries at https://www.iana.org/assignments/rmt-fec-parameters/

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      rmt-fec-parameters.xhtml [5] defined by RFCs 5052 and 6363.  See
      also RFC 6363, RFC 6681, and RFC 6865

2.  Threat Model

   AMBI is designed to operate over the internet, under the Internet
   Threat Model described in [RFC3552].

   AMBI aims to provide Data Integrity for a multicast data stream,
   building on the security anchors described in Section 2.1 to do so.
   The aim is to enable receivers to subscribe to and receive multicast
   packets from a trusted sender without damage to the Systems Security
   (Section 2.3 of [RFC3552]) for those receivers or other entities.

   Thus, we assume there might be attackers on-path or off-path with the
   capability to inject or modify packets, but that the attackers have
   not compromised the sender or discovered any of the sender's secret
   keys.  We assume that an attacker may have compromised some receivers
   of the multicast traffic, but still aim to provide the above security
   properties for receivers that have not been compromised.

   Those sending multicast traffic to receivers that include untrusted
   receivers should avoid transmitting sensitive information that
   requires strong confidentiality guarantees, due to the risk of
   compromise from those receivers.  Since multicast transmits the same
   packets to potentially many receivers, in the presence of potentially
   compromised receivers confidentiality of the content cannot be

   However, any protocol that provides encryption of the packet data
   before generating the packet digest can provide confidentiality
   against on-path passive observers who do not possess the decryption
   key.  This level of confidentiality can be provided by any such
   protocols without impact on AMBI's operation.

2.1.  Security Anchors

   Establishing the desired security properties for the multicast data
   packets relies on secure delivery of some other information:

   o  Secured unicast connections (providing Data Integrity) to one or
      more trusted DORMS [I-D.draft-ietf-mboned-dorms] servers that use
      the AMBI extensions to the DORMS YANG model as defined in
      Section 6

   o  Secure delivery (providing Data Integrity) of a stream of
      manifests (Section 3.4)

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   The secured unicast connection to the DORMS server provides the Peer
   Entity authentication of the DORMS server that's needed to establish
   the Data Integrity of the data it sends.

   Note that DORMS provides a method for using DNS to bootstrap
   discovery of the DORMS server.  In contexts where secure DNS lookup
   cannot be provided, it's still possible to establish a secure
   connection to a trusted DORMS server as long as the trusted DORMS
   server's hostname is known to the receivers (removing the need to use
   DNS for that discovery).  Once the server name is known, the ordinary
   certificate verification of that hostname while establishing a secure
   https connection provides the needed security properties to anchor
   the rest.

   Receiving unauthenticated data packets and knowing how to generate
   packet digests from the manifest profile provided by the AMBI
   extensions in the DORMS metadata allows the receiver to generate
   packet digests based on the contents of the received packet, which
   can be compared against the packet digests that were securely

   Comparing the digests and finding the same answer then provides Data
   Integrity for the data packets that relies on one more property of
   the digest generation algorithm:

   o  the difficulty of generating a collision for the packet digests
      contained in the manifest.

   Taken together, successful validation of the multicast data packets
   proves within the above constraints that someone with control of the
   manifest URI streams provided by the DORMS server has verified the
   sending of the packets corresponding to the digests sent in that
   stream of manifests.

2.1.1.  Alternatives and Their Requirements

   Other protocols that can provide authentication could also be used
   for manifest delivery if defined later in another specification.  For
   example a protocol that asymmetrically signs each packet, as the one
   defined in Section 3 of [RFC6584] does, would be a viable candidate
   for a delivery protocol for manifests that could be delivered over a
   multicast transport, which could have some important scalability

   Other methods of securely transmitting metadata equivalent to the
   metadata provided by the "ietf-ambi" YANG model could also be used to
   provide the same security guarantees with the manifest channels.
   Defining other such possibilities is out of scope for this document.

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2.2.  System Security

   By providing the means to authenticate multicast packets, AMBI aims
   to avoid giving attackers who can inject or modify packets the
   ability to attack application vulnerabilities that might be possible
   to exercise if those applications process the attack traffic.  Many
   of the entries in the Common Vulnerabilities and Exposures (CVE) list
   at [CVE] (an extensive industry-wide database of software
   vulnerabilities) have documented a variety of system security
   problems that can result from maliciously generated UDP packets.

   TBD: Fold in a mention of how off-path attacks are possible from most
   places on the internet for interdomain multicast over AMT at an
   ingest point, and how the multicast fanout downstream of that can
   make it a good target if multicast sees more use.  A diagram plus a
   cleaned-up version of the on-list explanation here is probably
   appropriate: https://mailarchive.ietf.org/arch/msg/mboned/
   CG9FLjPwuno3MtvYvgNcD5p69I4/ [6].  Nightmare scenario is zero-day RCE
   by off-path attacker that takes over a significant number of the
   devices watching a major sports event.

   See also work-in-progress: https://squarooticus.github.io/draft-
   krose-multicast-security/draft-krose-multicast-security.html [7]

3.  Protocol Operation

3.1.  Overview

   In order to authenticate a data packet, AMBI receivers need to hold
   these three pieces of information at the same time:

   o  the data packet

   o  an authenticated manifest containing the packet digest for the
      data packet

   o  a digest profile defining the transformation from the data packet
      to its packet digest

   The manifests are delivered as a stream of manifests over an
   authenticated data channel.  Manifest contents MUST be authenticated
   before they can be used to authenticate data packets.

   The manifest stream is composed of an ordered sequence of manifests
   that each contain an ordered sequence of packet digests,
   corresponding to the original packets as sent from their origin, in
   the same order.

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   Note that a manifest contains potentially many packet digests, and
   its size can be tuned to fit within a convenient PDU (Protocol Data
   Unit) of the manifest transport stream.  By doing so, many packet
   digests for the multicast data stream can be delivered per packet of
   the manifest transport.  The intent is that even with unicast-based
   manifest transport, multicast-style efficiencies of scale can still
   be realized with only a relatively small unicast overhead, when
   manifests use a unicast transport.

3.2.  Buffering of Packets and Digests

   Using different communication channels for the manifest stream and
   the data stream introduces a possibility of desynchronization in the
   timing of the received data between the different channels, so
   receivers hold data packets and packet digests from the manifest
   stream in buffers for some duration while awaiting the arrival of
   their counterparts.

   While holding a data packet, if the corresponding packet digest for
   that packet arrives in the secured manifest stream, the data packet
   is authenticated.

   While holding an authenticated packet digest, if the corresponding
   data packet arrives with a matching packet digest, the data packet is

   Authenticating a data packet consumes one packet digest and prevents
   re-learning a digest for the same sequence number with a hold-down
   time equal to the hold time for packet digests.  The hold-down is
   necessary because a different manifest can send a duplicate packet
   digest for the same packet sequence number, either when repeating of
   packet digests is used for resilience to loss or when rotating
   authentication keys, so re-learning the packet digest could allow a
   replay of a data packet.  After authenticating a packet, the digest
   and any future digests for the same data packet remain consumed if it
   has been used to authenticate a data packet, ignoring repeated
   digests for the same sequence number until after the holddown timer

   Once the data packet is authenticated it can be further processed by
   the receiving application or forwarded through the receiving network.

   If the receiver's hold duration for a data packet expires without
   authenticating the packet, the packet SHOULD be dropped as
   unauthenticated.  If the hold duration of a manifest expires, packet
   digests last received in that manifest MUST be discarded.

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   When multiple digests for the same packet sequence number are
   received, the latest received time for an authenticated packet digest
   should be used for the expiration time.

3.2.1.  Validation Windows

   Since packet digests are usually smaller than the data packets, it's
   RECOMMENDED that senders generate and send manifests with timing such
   that the packet digests in a manifest will typically be received by
   subscribed receivers before the data packets corresponding to those
   digests are received.

   This strategy reduces the buffering requirements at receivers, at the
   cost of introducing some buffering of data packets at the sender,
   since data packets are generated before their packet digests can be
   added to manifests.

   The RECOMMENDED default hold times at receivers are:

   o  2 seconds for data packets

   o  10 seconds for packet digests

   The sender MAY recommend different values for specific data streams,
   in order to tune different data streams for different performance
   goals.  The YANG model in Section 6 provides a mechanism for senders
   to communicate the sender's recommendation for buffering durations.
   These parameters are "data-hold-time" and "digest-hold-time",
   expressed in milliseconds.

   Receivers MAY deviate from the values recommended by the sender for a
   variety of reasons, including their own memory constraints or local
   administrative configuration (for example, it might improve user
   experience in some situations to hold packets longer than the server
   recommended when there are receiver-specific delays in the manifest
   stream that exceed the server's expectations).  Decreasing the
   buffering durations recommended by the server increases the risk of
   losing packets, but can be an appropriate tradeoff for specific
   network conditions and hardware or memory constraints on some

   Receivers SHOULD follow the recommendations for hold times provided
   by the sender (including the default values from the YANG model when
   unspecified), subject to their capabilities and any administratively
   configured overrides at the receiver.

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3.2.2.  Preserving Inter-packet Gap

   It's RECOMMENDED that middle boxes forwarding buffered data packets
   preserve the inter-packet gap between packets in the same data
   stream, and that receiving libraries that perform AMBI-based
   authentication provide mechanisms to expose the network arrival times
   of packets to applications.

   The purpose for this recommendation is to preserve the capability of
   receivers to use techniques for available bandwidth detection or
   network congestion based on observation of packet times and packet
   dispersal, making use of known patterns in the sending.  Examples of
   such techniques include those described in [PathChirp], [PathRate],
   and [WEBRC].

   Note that this recommendation SHOULD NOT prevent the transmission of
   an authenticated packet because the prior packet is unauthenticated.
   This recommendation only asks implementations to delay the
   transmission of an authenticated packet to correspond to the
   interpacket gap if an authenticated packet was previously transmitted
   and the authentication of the subsequent packet would otherwise burst
   the packets more quickly.

   This does not prevent the transmission of packets out of order
   according to their order of authentication, only the timing of
   packets that are transmitted, after authentication, in the same order
   they were received.

   For receiver applications, the time that the original packet was
   received from the network SHOULD be made available to the receiving

3.3.  Packet Digests

3.3.1.  Digest Profile

   A packet digest is a message digest for a data packet, built
   according to a digest profile defined by the sender.

   The digest profile is defined by the sender, and specifies:

   1.  A cryptographically secure hash algorithm (REQUIRED)

   2.  A manifest stream identifier

   3.  Whether to hash the IP payload or the UDP payload. (see

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   The hash algorithm is applied to a pseudoheader followed by the
   packet payload, as determined by the digest profile.  The computed
   hash value is the packet digest.

   TBD: As recommended by https://tools.ietf.org/html/rfc7696#section-
   2.2 [8], a companion document containing the mandatory-to-implement
   cipher suite should also be published separately and referenced by
   this document.  Payload Type  UDP vs. IP payload validation

   When the manifest definition is at the UDP layer, it applies only to
   packets with IP protocol of UDP (0x11) and the payload used for
   calculating the packet digest includes only the UDP payload with
   length as the number of UDP payload octets, as calculated by
   subtracting the size of the UDP header from the UDP payload length.

   When the manifest definition is at the IP layer, the payload used for
   calculating the packet digest includes the full IP payload of the
   data packets in the (S,G).  There is no restriction on the IP
   protocols that can be authenticated.  The length field in the
   pseudoheader is calculated by subtracting the IP Header Length from
   the IP length, and is equal to the number of octets in the payload
   for the digest calculation.  Motivation

   Full IP payloads often aren't available to receivers without extra
   privileges on end user operating systems, so it's useful to provide a
   way to authenticate only the UDP payload, which is often the only
   portion of the packet available to many receiving applications.

   However, for some use cases a full IP payload is appropriate.  For
   example, when retrofitting some existing protocols, some packets may
   be predictable or frequently repeated.  Use of an IPSec
   Authentication Header [RFC4302] is one way to disambiguate such
   packets.  Even though the shared secret means the Authentication
   Header can't itself be used to authenticate the packet contents, the
   sequence number in the Authentication Header can ensure that specific
   packets are not repeated at the IP layer, and so it's useful for AMBI
   to have the capability to authenticate such packets.

   Another example: some services might need to authenticate the UDP
   options [I-D.ietf-tsvwg-udp-options].  When using the UDP payload,
   the UDP options would not be part of the authenticated payload, but
   would be included when using the IP payload type.

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   Lastly, since (S,G) subscription operates at the IP layer, it's
   possible that some non-UDP protocols will need to be authenticated,
   and the IP layer allows for this.  However, most user-space transport
   applications are expected to use the UDP layer authentication.

3.3.2.  Pseudoheader

   When calculating the hash for the packet digest, the hash algorithm
   is applied to a pseudoheader followed by the payload from the packet.
   The complete sequence of octets used to calculate the hash is
   structured as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |         Source Address (32 bits IPv4/128 bits IPv6)           |
   |                             ...                               |
   |       Destination Address (32 bits IPv4/128 bits IPv6)        |
   |                             ...                               |
   |     Zeroes    |   Protocol    |            Length             |
   |          Source Port          |        Destination Port       |
   |                     Manifest Identifier                       |
   |                        Payload Data                           |
   |                             ...                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  Source Address

   The IPv4 or IPv6 source address of the packet.  Destination Address

   The IPv4 or IPv6 destination address of the packet.  Zeroes

   All bits set to 0.  Protocol

   The IP Protocol field from IPv4, or the Next Header field for IPv6.
   When using UDP-layer authentication, this value is always UDP (0x11)
   but for IP-layer authentication it can vary per-packet.

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   The length in octets of the Payload Data field, expressed as an
   unsigned 16-bit integer.  Source Port

   The source port of the packet.  Zeroes if using IP-layer
   authentication for a non-UDP protocol.  Destination Port

   The UDP destination port of the packet.  Zeroes if using IP-layer
   authentication for a non-UDP protocol.  Manifest Identifier

   The 32-bit identifier for the manifest stream.  Payload Data

   The payload data includes either the IP payload or the UDP payload,
   as indicated by the digest profile.

3.4.  Manifests

3.4.1.  Manifest Layout

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                  Manifest Stream Identifier                   |
   |                   Manifest sequence number                    |
   |                 First packet sequence number                  |
   |T|      Packet Digest Count    | TLV Space (present iff T set) |
   |       ... TLVs (Length=TLV Space or 0 if T unset) ...         |
   |                      ... Packet Digests ...                   |

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   A 32-bit unsigned integer chosen by the sender.  This value MUST be
   equal to the "id" field in the manifest-stream in the "ietf-ambi"
   model.  If a manifest is seen that does not have the expected value
   from the metadata provided for the manifest, the receiver MUST stop
   processing this manifest and disconnect from this manifest stream.
   It MAY reconnect with an exponential backoff starting at 1s, or it
   MAY connect to an alternative manifest stream if one is known.  Manifest Sequence Number

   A monotonically increasing 32-bit unsigned integer.  Each manifest
   sent by the sender increases this value by 1.  On overflow it wraps
   to 0.

   It's RECOMMENDED to expire the manifest stream and start a new stream
   for the data packets before a sequence number wrap is necessary.  First Packet Sequence Number

   A monotonically increasing 32-bit unsigned integer.  Each packet in
   the data stream increases this value by 1.

   It's RECOMMENDED to expire the manifest stream and start a new stream
   for the data packets before a sequence number wrap is necessary.

   Note: for redundancy, especially if using a manifest stream with
   unreliable transport, successive manifests MAY provide duplicates of
   the same packet digest with the same packet sequence number, using
   overapping sets of packet sequence numbers.  When received, these
   reset the hold timer for the listed packet digests.  T bit (TLVs Present)

   If 1, this indicates the TLV Length and TLV space fields are present.
   If 0, this indicates neither field is present.  Packet Digest Count

   A 15-bit unsigned integer equal to the count of packet digests in the
   manifest.  TLV Space

   A 16-bit unsigned integer with the length of the TLVs section.

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   These are Type-Length-Value blocks, back to back.  These may be
   extended by future specifications.

   These are composed of 3 fields:

   o  Type: an 8-bit unsigned integer indicating the type.  Type values
      in 0-127 have an 8-bit length, and type values in 128-255 have a
      16-bit length.

   o  Length: a 8-bit or 16-bit unsigned integer indicating the length
      of the value

   o  Value: a value with semantics defined by the Type field.

   Defined values:

   | Type | Name     | Value                                           |
   | 0    | Pad      | Length can be 0-255. Value is filled with 0 and |
   |      |          | ignored by receiver.                            |
   |      |          |                                                 |
   | 128  | Refresh  | Length MUST be 2.  Value is a 16-bit unsigned   |
   |      | Deadline | integer number of seconds.  When this field is  |
   |      |          | absent or zero, it means the current digest     |
   |      |          | profile for the current manifest stream is      |
   |      |          | stable.  A nonzero value means the              |
   |      |          | authentication is transitioning to a new        |
   |      |          | manifest stream, and the set of digest profiles |
   |      |          | SHOULD be refreshed by receivers before this    |
   |      |          | much time has elapsed in order to avoid a       |
   |      |          | disruption.  See Section 3.5.                   |

   1-120 and 129-248 are unassigned 121-127 and 249-255 are reserved for

   Any unknown values MUST be skipped and ignored by the receiver, using
   the Length field to skip.

   The total size of the manifest in octets is exactly equal to:

   Size of digests * packet count + 14 if T is 0 Size of digests *
   packet count + 16 + TLV Length if T is 1

   The total size of the TLV space is exactly equal to:

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   (2 + Length) summed for each TLV

   The total size of the TLV space MUST exactly equal TLV Length.  If
   the TLV space exceeds the TLV Length, the receiver MUST disconnect,
   and behave as if the Manifest Stream Identifier was wrong.  This
   state indicates a failed decoding of the TLV space.  Packet Digests

   Packet digests appended one after the other, aligned to 8-bit
   boundaries with 0-bit padding at the end if the bit length of the
   digests are not multiples of 8 bits.

3.5.  Transitioning to Other Manifest Streams

   It's possible for multiple manifest streams authenticating the same
   data stream to be active at the same time.  The different manifest
   streams can have different hash algorithms, manifest ids, and current
   packet sequence numbers for the same data stream.  These result in
   different sets of packet digests for the same data packets, one
   digest per packet per digest profile.

   It's necessary sometimes to transition gracefully from one manifest
   stream to another.  The Refresh Deadline TLV from the manifest is
   used to signal to receivers the need to transition.

   When a receiver gets a nonzero refresh deadline in a manifest the
   sender SHOULD have an alternate manifest stream ready and available,
   and the receiver SHOULD learn the alternate manifest stream, join the
   new one, and leave the old one before the number of seconds given in
   the refresh deadline.  After the refresh deadline has expired, a
   manifest stream MAY stop transmitting and close connections from the
   server side.  When multiple manifest-streams are provided in the
   metadata, all or all but one SHOULD contain an expire-time, and new
   or refreshing receivers SHOULD choose a manifest stream without an
   expire-time, or with the latest expire-time if all manifests have an

   The receivers SHOULD start the refresh after a random time delay
   between now and one half the number of seconds in the deadline field
   after the first manifest they receive containing a nonzero refresh
   deadline.  This time delay is to desynchronize the refresh attempts
   in order to spread the spike of load on the DORMS server while
   changing manifest profiles during a large multicast event.

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4.  Transport Considerations

4.1.  Overview

   AMBI manifests MUST be authenticated, but any transport protocol
   providing authentication can be used.  This section discusses several
   viable options for the use of an authenticating transport, and some
   associated design considerations.

   TBD: add ALTA to the list when and if it gets further along
   [I-D.draft-krose-mboned-alta].  Sending an authenticatable multicast
   stream (instead of the below unicast-based proposals) is a worthwhile
   goal, else a 1% unicast authentication overhead becomes a new unicast
   limit to the scalability.

   TBD: probably should add quic also?  Or maybe https is sufficient?

   TBD: add a recommendation about scalability, like with DORMS, when
   using a unicast hash stream.  CDN or other kind of fanout solution
   that can scale the delivery, and still generally hit the time window.

4.2.  HTTPS

   This document defines a new media type 'application/ambi' for use
   with HTTPS.  URIs in the manifest-transport list with the scheme
   'https' use this transport.

   An HTTPS stream carrying the 'application/ambi' media type is
   composed of a sequence of binary AMBI manifests, sent back to back in
   the payload body (payload body is defined in Section 3.3 of

   Complete packet digests from partially received manifests MAY be used
   by the receiver for authentication of data packets from the multicast
   channel, even if the full manifest is not yet delivered.

4.3.  TLS

   This document defines the new uri scheme 'ambi+tls' for use with TLS
   [RFC8446].  URIs in the manifest-transport list with the scheme
   'ambi+tls' use this transport.

   A TLS stream carrying AMBI manifests is composed of a sequence of
   binary AMBI manifests, transmitted back to back.

   Complete packet Digests from partially received manifests MAY be used
   by the receiver for authentication, even if the full manifest is not
   yet delivered.

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4.4.  DTLS

   This document defines the new uri scheme 'ambi+dtls' for use with
   DTLS [RFC6347].

   Manifests transported with DTLS have the tradeoff (relative to TLS or
   HTTPS) that they might be lost and not retransmitted or reordered,
   but they will not cause head-of-line blocking or delay in processing
   data packets that arrived later.  For some applications this is a
   worthwhile tradeoff.

   Note that loss of a single DTLS packet can result in the loss of
   multiple packet digests, which can mean failure to authenticate
   multiple data packets.

   DTLS transport for manifests supports one manifest per packet.  It's
   OPTIONAL to provides for some redundancy in packet digests by
   providing overlap in the packet sequence numbers across different
   manifests, thereby sending some or all packet digests multiple times
   to avoid loss.

   Future extensions might define extensions that can provide more
   efficient redundancy via FEC.  Those future extensions will require a
   different URI scheme.

5.  Examples

   TBD: walk through some examples as soon as we have a build running.
   Likely to need some touching up of the spec along the way...

6.  YANG Module

6.1.  Tree Diagram

   The tree diagram below follows the notation defined in [RFC8340].

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   module: ietf-ambi

     augment /dorms:dorms/dorms:metadata/dorms:sender/dorms:group
       +--rw ambi
          +--rw manifest-stream* [id]
             +--rw id                  uint32
             +--rw manifest-stream* [uri]
             |  +--rw uri    inet:uri
             +--rw hash-algorithm      iha:hash-algorithm-type
             +--rw data-hold-time?     uint32
             +--rw digest-hold-time?   uint32
             +--rw expiration?         yang:date-and-time
     augment /dorms:dorms/dorms:metadata/dorms:sender/dorms:group:
       +--rw ambi
          +--rw manifest-stream* [id]
             +--rw id                  uint32
             +--rw manifest-stream* [uri]
             |  +--rw uri    inet:uri
             +--rw hash-algorithm      iha:hash-algorithm-type
             +--rw data-hold-time?     uint32
             +--rw digest-hold-time?   uint32
             +--rw expiration?         yang:date-and-time

6.2.  Module

   <CODE BEGINS> file ietf-ambi@2021-07-11.yang
   module ietf-ambi {
     yang-version 1.1;

     namespace "urn:ietf:params:xml:ns:yang:ietf-ambi";
     prefix "ambi";

     import ietf-dorms {
       prefix "dorms";
       reference "I-D.jholland-mboned-dorms";

     import ietf-inet-types {
       prefix "inet";
       reference "RFC6991 Section 4";

     import iana-hash-algs {
       prefix "iha";
       reference "draft-ietf-netconf-crypto-types";

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     import ietf-yang-types {
       prefix "yang";
       reference "RFC 6991: Common YANG Data Types";

     organization "IETF";

         "Author:   Jake Holland

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

      Redistribution and use in source and binary forms, with or
      without modification, is permitted pursuant to, and subject to
      the license terms contained in, the Simplified BSD License set
      forth in Section 4.c of the IETF Trust's Legal Provisions
      Relating to IETF Documents

      This version of this YANG module is part of RFC XXXX
      (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
      for full legal notices.

      The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
      'MAY', and 'OPTIONAL' in this document are to be interpreted as
      described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
      they appear in all capitals, as shown here.

      This module contains the definition for the AMBI data types.
      It provides metadata for authenticating SSM channels as an
      augmentation to DORMS.";

     revision 2021-07-08 {
       description "Draft version.";

     grouping manifest-stream-definition {
           "This grouping specifies a manifest stream for
            authenticating a multicast data stream with AMBI";
       leaf id {

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         type uint32;
         mandatory true;
             "The Manifest ID referenced in a manifest.";
       list manifest-stream {
         key uri;
         leaf uri {
           type inet:uri;
           mandatory true;
               "The URI for a stream of manifests.";
         description "A URI that provides a location for the
             manifest stream";
       leaf hash-algorithm {
         type iha:hash-algorithm-type;
         mandatory true;
             "The hash algorithm for the packet hashes within
              manifests in this stream.";
       leaf data-hold-time {
         type uint32;
         default 2000;
         units "milliseconds";
             "The number of milliseconds to hold data packets
              waiting for a corresponding digest before
       leaf digest-hold-time {
         type uint32;
         default 10000;
         units "milliseconds";
             "The number of milliseconds to hold packet
              digests waiting for a corresponding data packet
              before discarding";
       leaf expiration {
         type yang:date-and-time;
             "The time after which this manifest stream may
              stop providing authentication for the data stream.
              When not present or empty there is no known expiration.";

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         "dorms:udp-stream" {
       description "AMBI extensions for securing UDP multicast.";

       container ambi {
         description "UDP-layer AMBI container for DORMS extension.";
         list manifest-stream {
           key id;
           description "Manifest stream definition list.";
           uses manifest-stream-definition;

         "/dorms:dorms/dorms:metadata/dorms:sender/dorms:group" {
       description "AMBI extensions for securing IP multicast.";

       container ambi {
         description "IP-layer AMBI container for DORMS extension.";
         list manifest-stream {
           key id;
           description "Definition of a manifest stream.";
           uses manifest-stream-definition;

7.  IANA Considerations

7.1.  The YANG Module Names Registry

   This document adds one YANG module to the "YANG Module Names"
   registry maintained at <https://www.iana.org/assignments/yang-
   parameters>.  The following registrations are made, per the format in
   Section 14 of [RFC6020]:

         name:      ietf-ambi
         namespace: urn:ietf:params:xml:ns:yang:ietf-ambi
         prefix:    ambi
         reference: I-D.draft-jholland-mboned-ambi

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7.2.  The XML Registry

   This document adds the following registration to the "ns" subregistry
   of the "IETF XML Registry" defined in [RFC3688], referencing this

          URI: urn:ietf:params:xml:ns:yang:ietf-ambi
          Registrant Contact: The IESG.
          XML: N/A, the requested URI is an XML namespace.

7.3.  Media Type

   TBD: Register 'application/ambi' according to advice from:
   https://www.iana.org/form/media-types [9]

   TBD: check guidelines in https://tools.ietf.org/html/rfc5226 [10]

7.4.  URI Schemes

7.4.1.  TLS

   TBD: register 'ambi+tls' as a uri scheme according to advice from:
   https://datatracker.ietf.org/doc/html/rfc7595 [11]

7.4.2.  DTLS

   TBD: register 'ambi+dtls' as a uri scheme according to advice from:
   https://datatracker.ietf.org/doc/html/rfc7595 [12]

8.  Security Considerations

8.1.  Predictable Packets

   Protocols that have predictable packets run the risk of offline
   attacks for hash collisions against those packets.  When
   authenticating a protocol that might have predictable packets, it's
   RECOMMENDED to use a hash function secure against such attacks or to
   add content to the packets to make them unpredictable, such as an
   Authentication Header ([RFC4302]), or the addition of an ignored
   field with random content to the packet payload.

   TBD: explain attack from generating malicious packets and then
   looking for collisions, as opposed to having to generate a collision
   on packet contents that include a sequence number and then hitting a

   TBD: follow the rest of the guidelines: https://tools.ietf.org/html/

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8.2.  Attacks on Side Applications

   A multicast receiver subscribes to an (S,G) and if it's a UDP
   application, listens on a socket with a port number for packets to

   UDP applications sometimes bind to an "unspecified" address ("::" or
   "") for a particular UDP port, which will make the appliction
   receive and process any packet that arrives on said port.

   Forwarding multicast traffic opens a new practical attack surface
   against receivers that have bound sockets using the "unspecified"
   address and were operating behind a firewall and/or NAT.  Such
   applications will receive traffic from the internet only after
   sending an outbound packet, and usually only for return packets with
   the reversed source and destination port and IP addresses.

   Multicast subscription and routing operates at the IP layer, so when
   a multicst receive application subscribes to a channel, traffic with
   the IP addresses for that channel will start arriving.  There is no
   selection for the UDP port at the routing layer that prevents
   multicast IP traffic from arriving.

   When an insecure application with a vulnerability is listening to a
   UDP port on an unspecified address, it will receive multicast packets
   arriving at the device and with that destination UDP port.  Although
   the primary problem lies in the insecure application, accepting
   multicast subscriptions increases the attack scope against those
   applications to include attackers who can inject a packet into a
   properly subscribed multicast stream.

   It's RECOMMENDED that senders using AMBI to secure their traffic
   include all IP traffic that they send in their DORMS metadata
   information, and that firewalls using AMBI to provide secure access
   to multicast traffic block multicast traffic destined to unsecured
   UDP ports on (S,G)s that have AMBI-based security for any traffic.
   This mitigation prevents new forwarding of multicast traffic from
   providing attackers with a packet inject capability access to new
   attack surfaces from pre-existing insecure apps.

9.  Acknowledgements

   Many thanks to Daniel Franke, Eric Rescorla, Christian Worm
   Mortensen, Max Franke, and Albert Manfredi for their very helpful
   comments and suggestions.

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10.  References

10.1.  Normative References

              Holland, J., "Discovery Of Restconf Metadata for Source-
              specific multicast", draft-ietf-mboned-dorms-01 (work in
              progress), October 2020.

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

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

10.2.  Informative References

   [CVE]      MITRE, "Common Vulnerabilities and Exposures", September
              1999, <https://cve.mitre.org/>.

              Rose, K. and J. Holland, "Asymmetric Loss-Tolerant
              Authentication", draft-krose-mboned-alta-01 (work in
              progress), July 2019.

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              Touch, J., "Transport Options for UDP", draft-ietf-tsvwg-
              udp-options-12 (work in progress), May 2021.

              Ribeiro, V., Riedi, R., Baraniuk, R., Navratil, J.,
              Cottrell, L., Department of Electrical and Computer
              Engineering Rice University, and SLAC/SCS-Network
              Monitoring, Stanford University, "pathChirp: Efficient
              Available Bandwidth Estimation for Network Paths", 2003.

              Dovrolis, C., Ramanathan, P., and D. Moore, "Packet
              dispersion techniques and a capacity estimation
              methodology", IEEE/ACM Transactions on Networking, Volume
              12, Issue 6, pp. 963-977. , December 2004.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              DOI 10.17487/RFC3552, July 2003,

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,

   [RFC4082]  Perrig, A., Song, D., Canetti, R., Tygar, J., and B.
              Briscoe, "Timed Efficient Stream Loss-Tolerant
              Authentication (TESLA): Multicast Source Authentication
              Transform Introduction", RFC 4082, DOI 10.17487/RFC4082,
              June 2005, <https://www.rfc-editor.org/info/rfc4082>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,

   [RFC4383]  Baugher, M. and E. Carrara, "The Use of Timed Efficient
              Stream Loss-Tolerant Authentication (TESLA) in the Secure
              Real-time Transport Protocol (SRTP)", RFC 4383,
              DOI 10.17487/RFC4383, February 2006,

   [RFC5776]  Roca, V., Francillon, A., and S. Faurite, "Use of Timed
              Efficient Stream Loss-Tolerant Authentication (TESLA) in
              the Asynchronous Layered Coding (ALC) and NACK-Oriented
              Reliable Multicast (NORM) Protocols", RFC 5776,
              DOI 10.17487/RFC5776, April 2010,

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   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,

   [RFC6584]  Roca, V., "Simple Authentication Schemes for the
              Asynchronous Layered Coding (ALC) and NACK-Oriented
              Reliable Multicast (NORM) Protocols", RFC 6584,
              DOI 10.17487/RFC6584, April 2012,

   [WEBRC]    Luby, M. and V. Goyal, "Wave and Equation Based Rate
              Control Using Multicast Round Trip Time: Extended Report",
              Digital Fountain Technical Report no. DF2002-07-001 ,
              September 2002.

10.3.  URIs

   [1] https://github.com/GrumpyOldTroll/ietf-dorms-cluster

   [2] https://datatracker.ietf.org/submit/note-well/

   [3] https://www.ietf.org/mailman/listinfo/mboned

   [4] https://mailarchive.ietf.org/arch/browse/mboned/

   [5] https://www.iana.org/assignments/rmt-fec-parameters/rmt-fec-

   [6] https://mailarchive.ietf.org/arch/msg/mboned/

   [7] https://squarooticus.github.io/draft-krose-multicast-security/

   [8] https://tools.ietf.org/html/rfc7696#section-2.2

   [9] https://www.iana.org/form/media-types

   [10] https://tools.ietf.org/html/rfc5226

   [11] https://datatracker.ietf.org/doc/html/rfc7595

   [12] https://datatracker.ietf.org/doc/html/rfc7595

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Authors' Addresses

   Jake Holland
   Akamai Technologies, Inc.
   150 Broadway
   Cambridge, MA 02144
   United States of America

   Email: jakeholland.net@gmail.com

   Kyle Rose
   Akamai Technologies, Inc.
   150 Broadway
   Cambridge, MA 02144
   United States of America

   Email: krose@krose.org

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