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Versions: 00 01 02                                                      
Network Working Group                                       J. Paillisse
Internet-Draft                                         UPC-BarcelonaTech
Intended status: Informational                        A. Rodriguez-Natal
Expires: May 2, 2018                                          V. Ermagan
                                                                F. Maino
                                                           Cisco Systems
                                                             A. Cabellos
                                                       UPC-BarcelonaTech
                                                        October 29, 2017


 An analysis of the applicability of blockchain to secure IP addresses
                  allocation, delegation and bindings.
               draft-paillisse-sidrops-blockchain-01.txt

Abstract

   This document analyzes how blockchain technology can be used to
   secure the allocation, delegation and binding to topological
   information of the IP address space.  The main outcomes of the
   analysis are that blockchain is suitable in environments with
   multiple distrusting parties and that Proof of Stake is a potential
   candidate for a consensus algorithm.

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 http://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 2, 2018.

Copyright Notice

   Copyright (c) 2017 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



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   (http://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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   3
   3.  Blockchain in a nutshell  . . . . . . . . . . . . . . . . . .   3
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
       3.1.1.  Chain of signatures . . . . . . . . . . . . . . . . .   4
       3.1.2.  Consensus algorithm . . . . . . . . . . . . . . . . .   5
     3.2.  Features  . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Description of consensus algorithms . . . . . . . . . . .   6
       3.3.1.  Proof of Work (PoW) . . . . . . . . . . . . . . . . .   6
       3.3.2.  Proof of Stake (PoS)  . . . . . . . . . . . . . . . .   7
   4.  Blockchain for IP addresses . . . . . . . . . . . . . . . . .   8
     4.1.  Problem statement . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Analysis  . . . . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  A consensus algorithm for IP addresses  . . . . . . . . .   9
   5.  Overview of the architecture  . . . . . . . . . . . . . . . .  10
     5.1.  Pros and cons . . . . . . . . . . . . . . . . . . . . . .  13
     5.2.  Security evaluation . . . . . . . . . . . . . . . . . . .  14
       5.2.1.  Attacks against a PoS-based consensus algorithm . . .  14
       5.2.2.  Attacks against the P2P network . . . . . . . . . . .  16
   6.  Other Considerations  . . . . . . . . . . . . . . . . . . . .  17
     6.1.  Revocation  . . . . . . . . . . . . . . . . . . . . . . .  17
       6.1.1.  Expiration time . . . . . . . . . . . . . . . . . . .  18
       6.1.2.  Multi-signature transactions  . . . . . . . . . . . .  18
       6.1.3.  Revocation transaction  . . . . . . . . . . . . . . .  18
       6.1.4.  Out-of-band mechanisms  . . . . . . . . . . . . . . .  19
     6.2.  Storage management  . . . . . . . . . . . . . . . . . . .  19
     6.3.  Proof of Networking?  . . . . . . . . . . . . . . . . . .  20
     6.4.  Configuration parameters  . . . . . . . . . . . . . . . .  21
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   10. Informative References  . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23








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1.  Introduction

   Blockchain [Bitcoin] is attracting a lot of attention among the
   security community since it provides means for exchanging information
   among a set of distrusting entities without the use of digital
   certificates and centralized control.  Blockchain provides means for
   the distrusting parties to reach consensus in a distributed way.
   Formally, it is regarded as a new solution to the Byzantine Generals
   problem, well-known in fault-tolerant distributed systems.

   Although at the time of this writing the main application of
   blockchain are financial systems, their use in the field of
   networking is being explored (e.g., [Hari2016]).  Some successful
   systems exist such as [Blockstack] and [Namecoin], which aim at
   building a secure DNS.

   The main goal of this document is to represent a first step towards
   the understanding of the properties of blockchains and their
   applicability in the Internet infrastructure, specifically securing
   the allocation, delegation and bindings of IP addresses.  First, it
   introduces blockchain, then it analyzes how blockchain could be used
   to secure the delegation of IP addresses.  Finally, it presents an
   initial design for such an infrastructure.  This document also
   includes a preliminary security analysis of such system.  It is
   important to note that the goal of this document is not to provide a
   complete architecture that secures IP address allocation, delegation
   and bindings.

2.  Definition of Terms

   TBC

3.  Blockchain in a nutshell

3.1.  Overview

   Conceptually, a blockchain is a distributed, secure and trustless
   database.  It can also be regarded as a state machine with rules that
   clearly state which transitions can be performed.  Participants in
   the blockchain communicate through a P2P network.  The smallest data
   unit of a blockchain is a transaction.  Users attach data to a
   transaction along with its signature and their associated public key.
   Usually, the attached data is an asset or a token, something that is
   unique and should not be replicated (e.g., coins in Bitcoin).  Then
   they broadcast this transaction to the other participants.  The rest
   of the nodes in the network store temporarily this transaction.  At
   some fixed intervals in time, one of the nodes takes a set of these
   transactions and groups them in a block.  It then broadcasts this



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   block back to the network.  When the other nodes receive this block
   they verify it, remove the transactions contained in the block from
   the temporary storage and add it after the previous block, thus
   creating a chain of blocks.  It should be noted that all nodes store
   the entire blockchain locally.  In addition, most blockchains give
   some sort of reward to nodes that add new blocks, although this is
   not strictly necessary.  Figure 1 presents an overview of the most
   common elements in a block.


   +--------+---------------+----------------+---------------+
   | Block  | Hash(Previous | Hash(All Block | Block Creator |
   | Number |     Block)    | Transactions)  |   Signature   |
   +--------+---------------+----------------+---------------+
   |                     Transaction 1                       |
   +---------------------------------------------------------+
   |                     Transaction 2                       |
   +---------------------------------------------------------+
   +                          ...                            +
   +                          ...                            +
   +---------------------------------------------------------+
   |                     Transaction N                       |
   +---------------------------------------------------------+


                  Figure 1.- Common structure of a block


   Two basic mechanisms are used to protect the chained data: a chain of
   signatures and a consensus algorithm.

3.1.1.  Chain of signatures

   The chain of signatures operates at transaction level.  Consider the
   sender and receiver of a token, each with its public-private keypair.
   To change the owner of a token, the sender signs the data and the
   receiver's public key.  It then puts together its public key, the
   signature, the data and the hash of the receiver's public key
   (Figure 2) to form a transaction.












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   +-------------+-------------------+--------+---------------+
   |   Sender    |  Signature Sender |  Data  | Hash(Receiver |
   | Public Key  |    Private Key    |        |  Public Key)  |
   +-------------+-------------------+--------+---------------+


     Figure 2.- Common transaction structure in a blockchain


   In conclusion, the rules of the blockchain enforce that:

   o  The owner of the receiver private key has total control over the
      contents of the transaction.  In Bitcoin this translates in a
      central property: only this owner can spend a coin.

   o  When an owner sends a token to the new owner, it irreversibly
      transfers the control of the contents to the new owner.

3.1.2.  Consensus algorithm

   The consensus algorithm is the central part of blockchain and it
   controls the chaining of data blocks.  The main role of the algorithm
   is to provide a set of well-defined rules so that participants agree
   on a consistent view of the database.  For this it has the following
   main functions.  First, forks (multiple chains) can exist, this may
   happen for instance due to varying network latency among
   participants.  In this case the participants must agree on which is
   the valid chain.  And second, another important function of the
   consensus algorithm is to determine which participants are allowed to
   add a new data blocks.  Section 3.3 contains more information
   regarding available consensus algorithms.

   It is important to note that regardless of the consensus algorithm,
   in blockchain data blocks are always added, never deleted nor
   modified.  This creates a tamper-proof, shared ledger among all
   participants.  Transactions can be tracked back by inspecting past
   blocks, thus enabling the verification of claims by certain parties.

3.2.  Features

   The following list tries to briefly summarize the main
   characteristics of the blockchain technology:

   Decentralized:  No central entity controls the blockchain, it is
      shared among all participants.

   No CAs:  No digital certificates, Certification Authorities or CRLs
      are needed.



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   Limited prior trust:  It is not required to trust other nodes.  It is
      worth noting that some consensus algorithms rely on some limited
      levels of trust.

   Tamper-proof:  Since data can be only added but never modified,
      attempts to alter previous records are detected.

   Non-repudiation:  All nodes share a common, immutable view on the
      status of the blockchain, and blockchain provides non-repudiation
      mechanisms.

   Censorship-resistant:  Gaining control over a transaction involves
      having access to the associated private key.

   Append-only:  Data is always added, but never modified nor deleted.

   Privacy:  Entities participating in the blockchain can achieve
      privacy using anonymous keys, i.e. randomly-generated keys not
      related to their identity.  In addition, a new keypair should be
      generated for each new transaction in order to prevent tracking
      [Bitcoin], section 10.

   Slow updates:  New transactions have to be verified, added to a block
      and received by all nodes.  This results in a delay since the
      transaction is created until it is finally available to all the
      nodes.  This delay will depend on the consensus algorithm and the
      block creation rate.

   Large storage:  The size of the blockchain keeps growing forever,
      because data blocks are always added.  This may result in
      scalability issues.

3.3.  Description of consensus algorithms

   The two more popular consensus algorithms are: Proof of Work and
   Proof of Stake.

3.3.1.  Proof of Work (PoW)

   In Proof of Work nodes have to solve a complex mathematical problem
   to add a block, thus requiring some computational effort, this is
   commonly know as mining.  For example in Bitcoin the problem is to
   find a hash starting with a fixed amount of zeroes, the only known
   way to solve this problem is by brute force.  The valid chain is the
   one with most accumulated computing power, this chain is also the
   more expensive in terms of computing power to modify.  This is
   because modifying a block going N blocks back from the tip of the
   chain would require redoing the computations for all these N blocks.



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   As a result, an attacker should have more computational power than
   the power required to create the N blocks to be able to modify the
   chain.  Overall, it is commonly assumed that if more than half of the
   nodes are honest the blockchain is considered as secure.

   PoW offers relevant features, adding new blocks requires an external
   resource (CPU power) that has an economical cost.  However this also
   results in some relevant drawbacks:

   Risk of overtaking:  The security of PoW is entirely based on
      computation power.  This means that if an entity has access to
      more than half of the total blockchain's computing power it can
      control the chain.  As a result and in order to keep blockchain
      secure, the incentive of taking control of the chain must be lower
      than the cost of acquiring and operating the hardware that
      provides the equivalent to half of the participants computing
      power.  This is hard to guarantee since the economy of the
      blockchain and the economy of the required hardware are
      independent.  As an example an attacker can acquire the required
      hardware and operate it, take control of the blockchain to obtain
      an economical benefit and finally sell the hardware to reduce the
      final cost of the attack.

   Hardware dependency:  Bitcoin automatically increases -over time- the
      complexity of the mathematical problem that needs to be solved in
      order to add a block.  This is done to account for Moore's law.
      As a result the community has designed mining specific hardware
      (ASICs) that provides a competitive advantage.  In this context
      blockchain becomes less democratic, since the cost of
      participating in it increases.

   Energy inefficiency:  PoW requires large amounts of energy to perform
      the computations (e.g., [miningfarm]).

3.3.2.  Proof of Stake (PoS)

   The main idea behind Proof of Stake is that participants with more
   assets (or stake) in the blockchain are more likely to add blocks.
   With this, the control of the chain is given to entities who own more
   stake.  For each new block, a signer is selected randomly from the
   list of participants typically weighted according to their stake.  A
   fundamental assumption behind PoS is that such entities have more
   incentives for honest behaviour since they have more assets in the
   chain.

   Proof of Stake is seen as an alternative to PoW.  At the time of this
   writing major players in the blockchain environment such as
   [Ethereum] are preparing a shift towards PoS, moreover several



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   blockchains based on PoS already exist (eg.  [Peercoin]).  The main
   reason behind this paradigm shift is that PoS addresses some of PoW's
   main drawbacks:

   o  It does not require special hardware nor computationally or
      energy-expensive calculations.

   o  An attacker must get hold of a significant part of the assets in
      order to gain control of the blockchain.  As opposed to PoS the
      investment required to gain control of the chain lies within the
      chain, and does not involve using external resources.

   On the other side, Proof of Stake introduces new sources of attacks:

   o  In Proof of Stake the signer is selected randomly among the
      stakers.  In this context attackers can manipulate the source of
      randomness to sign more blocks and ultimately gain control over
      the chain.

   o  As opposed to PoW, creating forks is very inexpensive, since no
      computational power is required.  The PoS must provide means to
      select the valid chain, which is typically the longer one.

   o  Collusions of high-stakers can create alternate chains which can
      appear to be valid.

4.  Blockchain for IP addresses

4.1.  Problem statement

   The objective of this section is to analyze if an infrastructure
   using blockchain can provide a similar degree of security to
   traditional PKI-based architectures.  Specifically we aim to secure:

   o  Binding of IP address blocks to the holder (private key holder).

   o  The allocations and delegations of IP address blocks among their
      holders.

   o  Binding of IP address blocks to their topological locators (eg.
      AS numbers allocations).

   This information is public and shared among a set of distrusting
   entities over the Internet.  The architecture must be able to:

   o  Allow anyone to verify the legitimate holder of a block of
      addresses




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   o  Let participating entities allocate address blocks without
      requiring a trusted third party.

   o  Restrict the allocation of a block of addresses to only its
      legitimate holder.

   o  Prevent data modification without the consent of its holder.

4.2.  Analysis

   The main rationale behind using blockchain to secure IP address
   allocations is that IPs can be understood as coins, both concepts
   share some fundamental characteristics:

   o  They are unambiguously allocated to entities.

   o  Can be transferred between them.

   o  Cannot be assigned to two entities at the same time.

   o  Can be divided up to a certain limit.

   Such similar properties make it possible to envisage a blockchain
   that allows its participants delegate IP address blocks, similarly to
   how Bitcoin transfers coins.  For example, IANA could write a
   transaction allocating addresses to the RIRs, which in turn could
   allocate them to the LIRs, etc.  Complex management logic can be
   defined as needed for example, rejecting a transaction that allocates
   of a block of addresses originated by an entity that does not hold
   that block.  In addition, transactions accept multiple inputs and
   outputs, i.e. an arbitrary amount of public keys either as senders or
   receivers.  This means that it is possible to break and merge blocks
   of addresses as required.  Section 5 provides more detailed
   information about this architecture.

4.3.  A consensus algorithm for IP addresses

   As stated before, the consensus algorithm is a central part of a
   blockchain.  The first consensus algorithm designed for blockchain
   was PoW, and it is a common choice for new blockchain
   implementations.  However it presents several drawbacks
   (Section 3.3.1) for the IP address scenario.

   Using computing power as a means to secure blockchains has been
   proved to work in financial environments.  However, the capability to
   add new blocks and the security of the chain itself depends on the
   computing power of the participants, which is not always aligned with
   their interest in the well-being of the blockchain.  Depending on the



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   objectives of the attacker, certain attacks can become profitable.
   Namely, buying a large quantity of hardware to be able to rewrite the
   blockchain with false data (e.g., incorrect delegations of IP
   addresses).  This is because the incentives of the participants of
   the IP addresses blockchain are not linked with their computing
   power.

   In contrast, with Proof of Stake the capability to alter the
   blockchain remains within it.  This aspect is of particular
   importance in the context of securing IP addresses: it would mean
   that AS domains holding large blocks of IP addresses are more likely
   to add blocks.  These parties have a reduced incentive in tampering
   the blockchain because they would suffer the consequences: an
   insecure Internet.  Typically ASes that hold large blocks of IP
   address space have their business within the Internet and as such,
   have clear incentives in the correct operation and security of the
   Internet.

   Furthermore, in such blockchain the risk of takeover is reduced
   compared to PoW, the reason is that accumulating a large amount of IP
   addresses is typically more complex than accumulating computing
   power.  The risk of takeover is also mitigated compared to other PoS-
   based blockchains.  In this blockchain an attacker would buy tokens
   from the other parties, who receive a monetary compensation to
   participate in the attack.  However, in a blockchain for IP addresses
   this would mean buying IP addresses from other parties, who do not
   have a clear incentive to sell their blocks of addresses to the
   attacker.  Because of this, PoS appears to be a firm candidate for a
   consensus algorithm in a blockchain for securing IP addresses
   allocations and delegations.

5.  Overview of the architecture

   This architecture mimics the hierarchy of IP address allocation
   present in today's Internet, with IANA on top of it.  All nodes trust
   IANA's public key, which writes a genesis transaction assigning all
   of the address space to itself (figure 3).


   +--------------+-----------------+-----------+----------------+
   |    IANA      | Signature IANA  |  Allocate |   Hash(IANA    |
   | Public Key 1 |  Private Key 1  |  0/0      |  Public Key 2) |
   +--------------+-----------------+-----------+----------------+


                        Figure 3.- Genesis transaction





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   It then begins allocating each block of addresses to the IP address
   holders.  Each transaction allocates part of the address space to the
   legitimate holder, and the rest of space is given back to IANA using
   a new keypair (figure 4).


   +--------------+-----------------+-----------+----------------+
   |              |                 |  Rest of  |   Hash(IANA    |
   |    IANA      | Signature IANA  |  space    |  Public Key 3) |
   | Public Key 2 |  Private Key 2  +-----------+----------------+
   |              |                 |  Allocate |   Hash(APNIC   |
   |              |                 |  1/8      |  Public Key 1) |
   +--------------+-----------------+-----------+----------------+


                 Figure 4.- Example allocation transaction


   In turn, all the parties in the hierarchy allocate or delegate
   address blocks following the current allocation hierarchy.  When a
   party wants to verify the allocation of a block of addresses, it
   downloads the blockchain and verifies all the blocks and transactions
   up to the genesis block, for which it has trust.  Figure 5 presents
   an example of allocation of one prefix to each of the RIRs.



























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   +--------------+-----------------+-----------+----------------+
   |              |                 |  Rest of  |   Hash(IANA    |
   |              |                 |  space    |  Public Key 4) |
   |              |                 +-----------+----------------+
   |              |                 |  Allocate |   Hash(RIPE    |
   |              |                 |  5/8      |  Public Key 1) |
   |              |                 +-----------+----------------+
   |              |                 |  Allocate |   Hash(APNIC   |
   |     IANA     | Signature IANA  |  14/8     |  Public Key 2) |
   | Public Key 3 |  Private Key 3  +-----------+----------------+
   |              |                 |  Allocate |   Hash(ARIN    |
   |              |                 |  23/8     |  Public Key 1) |
   |              |                 +-----------+----------------+
   |              |                 |  Allocate |   Hash(AFRINIC |
   |              |                 |  102/8    |  Public Key 1) |
   |              |                 +-----------+----------------+
   |              |                 |  Allocate |   Hash(LACNIC  |
   |              |                 |  200/8    |  Public Key 1) |
   +--------------+-----------------+-----------+----------------+


           Figure 5.- Example multi-output allocation transaction


   Inside the blockchain the typical operations to manage blocks of IP
   addresses can be defined, such as the delegation of prefixes (figure
   6).  This helps to enforce the rules of IP addresses management.  For
   instance, since this transaction is marked as a delegation, if the
   new owner created an allocation transaction it would be rejected by
   the other nodes, because the parent transaction does not have the
   privileges to perform it.


   +--------------+-----------------+-----------+----------------+
   |              |                 | Rest of   |   Hash(APNIC   |
   |    APNIC     | Signature APNIC | space     |  Public Key 3) |
   | Public Key 1 |  Private Key 1  +-----------+----------------+
   |              |                 | Delegate  |  Hash(ISP A    |
   |              |                 | 1.2/16    |  Public Key 1) |
   +--------------+-----------------+-----------+----------------+


                 Figure 6.- Example delegation transaction


   Performing a key rollover is simple, because each transaction has its
   associated public key, and only depends on the previous transaction.
   In other words, rekeying means changing the public key only in the



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   holder's transaction.  This can be done adding a new transaction with
   the same data but transferring it to a new public key also controlled
   by the initial holder (figure 7).  This approach lets each entity
   decide its rekeying policies independently.


   +--------------+-----------------+-----------+----------------+
   |    ISP A     | Signature ISP A | Delegate  |  Hash(ISP A    |
   | Public Key 1 |  Private Key 1  | 1.2/16    |  Public Key 2) |
   +--------------+-----------------+-----------+----------------+


       Figure 7.- Example key rollover of a prefix delegation


   It is worth noting that this chain can define as many operations as
   required, for instance storing the binding of AS numbers to the IP
   prefixes they announce (figure 8).


   +--------------+-----------------+-----------+----------------+
   |              |    Signature    | Bind      |                |
   |    ISP A     |      ISP A      | 1.2/16    |  Hash(ISP A    |
   | Public Key 2 |  Private Key 2  | AS no.    |  Public Key 3) |
   |              |                 | 12345     |                |
   +--------------+-----------------+-----------+----------------+


              Figure 8.- Example binding of AS number to prefix


   Additional and more complex operations can be defined if the
   management logic requires it.  For instance, several signatures (from
   different parties) can be required to consider a transaction valid,
   etc.

5.1.  Pros and cons

   In this section we analyze the pros and cons of this architecture
   compared to traditional PKI infraestructures:

   Advantages:

   o  Decentralized: No central entity controls the blockchain, it is
      shared among all participants.

   o  No CAs, CRLs or certificates needed: No digital certificates,
      Certification Authorities or CRLs are needed.



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   o  Simplified rekeying: A key rollover can easily be performed by
      issuing a new transaction allocating the prefixes to a new keypair
      controlled by the same holder.  This process can be performed
      without involving any third-party.

   o  Censorship-resistant: since the control of a transaction is
      completely under the holder of the private key, the revocation of
      IP addresses without the legitimate holder's permission involves
      obtaining its private key.  Even if the private key of the
      previous owner was compromised, ownership of the current
      transaction is still preserved, as opposed to the compromise of a
      CA's private key (or a misbehaving CA).

   o  Limited prior trust: It is not required to trust other nodes.
      However, in PoS it is necessary to periodically authenticate the
      chain state out-of-band to prevent some attacks.

   o  Simplified management: since CAs are not required, their
      management overhead is avoided.

   o  Auditable: allocations and delegations can be tracked back in the
      blockchain to determine if they originate from the legitimate
      holder.

   Drawbacks:

   o  PoS does not rely on strong cryptographic guarantees: As opposed
      to PKI-based systems that rely on strong and well-established
      cryptographic mechanisms, PoS-based infraestructures ultimately
      rely on the good behaviour of the high-stakers.

   o  Costly bootstrapping: When a node is activated it has to download
      and verify the entire blockchain.

   o  Large storage required: The blockchain grows forever as more
      blocks are added, blocks cannot be removed.

5.2.  Security evaluation

5.2.1.  Attacks against a PoS-based consensus algorithm

   This section presents a list of the most relevant attacks against a
   Proof of Stake algorithm and how to mitigate them.








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5.2.1.1.  Stake grinding

   Stake grinding refers to the manipulation of the consensus algorithm
   in order to progressively obtain more stake, with the goal of signing
   blocks more frequently with the ultimate goal of taking control of
   the blockchain.  It proceeds as follows: when the attacker has to
   sign a block, it computes all the possible blocks (varying the data
   inside them) to find a combination that gives the highest possibility
   of signing another block in the future.  It then signs this block and
   sends it to the network.  This procedure is repeated for all the next
   signing opportunities.  Over time, the attacker will sign more and
   more blocks until the consensus algorithm will always select the
   attacker to sign all blocks, thereby having taken control of the
   blockchain.

   To prevent this attack, the source of randomness used to select the
   signers has to be hard to alter or to predict.

5.2.1.2.  Nothing at stake

   Nothing at stake is one of the fundamental drawbacks of Proof of
   Stake and requires careful design based on the incentives of the
   participants.  In common PoS designs, the signers of the new block
   receive an economical incentive (e.g., Ethereum).  However this does
   not hold in the IP address scenario, since participants should not
   receive any incentive.  The incentive is, as stated before, achieving
   a consistent view of the IP address space and having a secure
   Internet.

5.2.1.3.  Range attacks

   A range attack is performed by creating a fork some blocks back from
   the tip of the chain.  It is conceptually similar to the attack named
   as 'Risk of overtaking' in Section 3.3.1.  In this scenario, the
   attacker has privately fabricated a chain which (according to the
   consensus algorithm rules) will be selected over the original one.
   Benefits of this attack include gaining more stake on the blockchain
   (this attack could be part of a stake grinding attack) or rewriting
   the transaction history to erase a payment made in the original
   blockchain.

   The simplest solution to this attack is adding a revert limit to the
   blockchain, forbidding forks going back more than N blocks.  This
   provides a means to solidify the blockchain.  However, nodes that
   have been offline for more than N blocks will need an external source
   that indicates the correct chain.  It has been proposed to do this
   out of band.  This is why a PoS blockchain is not purely trustless
   and requires a small amount of trust.



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5.2.1.4.  Lack of participation

   Participants in a PoS algorithm will not always sign a block, since
   they might be offline when they are selected or lack incentives.
   Because of this, the final fraction of high-stakers that sign blocks
   can be very different from the full set of high-stakers.  The direct
   consequence of this situation is that the portion of participants
   that decide what goes into the blockchain can be a small set of
   nodes.  If this participation is low enough, it can leave the control
   of the blockchain to a small amount of people/oligarchy, thus rising
   security concerns.

5.2.2.  Attacks against the P2P network

   This section presents attacks directed towards the underlying P2P
   network used to exchange information among the participants of the
   blockchain.

5.2.2.1.  DDOS attacks

   Since blockchains are inherently based on P2P architectures, they
   present a higher degree of resistance to DDOS attacks than
   centralized server architectures, provided that the network has a
   significant number of participants.  In addition, it is always
   possible to keep an offline copy of the blockchain.

5.2.2.2.  Transaction flooding

   A special type of DDOS attack consists in creating a large amount of
   legit transactions that transfer a small amount of tokens (i.e.
   delegate a lot of small IP prefixes).  If the number of transactions
   is large enough, the addition of new transactions can be
   significantly delayed because not all of them fit into a single
   block.  The effectiveness of the attack also depends on the
   throughput of the blockchain (transactions/second).  Simple solutions
   may be to limit the granularity upon which IP addresses can be split.
   Of course, only the legitimate holder of a large amount of IP address
   can perform this attack.

5.2.2.3.  Routing attacks

   The underlying P2P network in blockchains does not typically use any
   security mechanism, e.g. node authentication or integrity of network
   protocol messages.  This enables potentially disruptive attacks.  For
   example, specially located rogue nodes could drop new transactions,
   which would block updates on the blockchain and leave legit nodes
   uncommunicated.  The effectiveness of this kind of attacks depends on




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   how the P2P algorithm selects peers and the topology of the P2P
   network.

   However, the most potentially dangerous attack of this type are
   network partitions, i.e. isolating a group of nodes from the rest of
   the network so they cannot communicate each other (e.g.,
   [Apostolaki2017]).  The consequence of this attack is that two
   versions of the blockchain are created, one at each network
   partition.  When the partition disappears and the nodes reconnect one
   of the two chains will be discarded, causing a service disruption.
   It is worth noting that Bitcoin has suffered similar attacks
   [realrouteattack].

5.2.2.4.  Transaction censorship

   When a node adds a block it chooses arbitrarily which transactions
   are added into it, i.e. no specific rules control how transactions
   are added to a block.  This enables a node to selectively add some
   transactions and intentionally exclude others, with the consequence
   that some transactions may be never added to the blockchain.  In the
   context of IP addresses, this may be performed by a competing ISP to
   prevent another ISP from executing a certain modification.  Possible
   solutions revolve around:

   o  Giving more priority to older transactions (similarly to Bitcoin).

   o  Punishing nodes that exhibit this kind of behaviour, e.g. removing
      part of their block of IP addresses or lowering their chance of
      adding blocks.

6.  Other Considerations

6.1.  Revocation

   Due to the irreversible nature of transactions, once a block of IP
   addresses has been allocated to an entity it is not possible to
   modify or remove it, as opposed to CRLs (Certificate Revocation
   Lists).  However, due to operational issues (compromised or lost
   keys, human mistake, holder misbehaviour, etc) it is critical to
   provide a way to recover a block of addresses.  Moreover, since IP
   addresses are a finite public good they cannot be lost.  Taking into
   account that a blockchain can enforce any rules its participants
   agree upon, this section presents some possible approaches to
   implement revocation, such approaches should not be considered as
   mutually exclusive.  The revocation procedure must be discussed among
   the community to achieve consensus between the relevant players
   (IANA, RIRs, ISPs, institutions, etc).




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   All these mechanisms present different balances of power between the
   current holder and the entity whose asset is being revoked.  Behind
   all these mechanisms there is a fundamental tradeoff between trusting
   an upstream provider of the addresses and retaining full control of
   the block of addresses.

   Regardless of the revocation policy and as opposed to traditional PKI
   systems, each IP prefix delegation only depends on the private key of
   the holder of such IP block.  As such, it does not need to trust a CA
   or a chain of certificates.  Only by means of this private key the IP
   delegation can be altered.

6.1.1.  Expiration time

   A simple approach to allow revocation is adding a lease time (i.e,
   time-to-live) to the blocks of addresses.  After the lease ends, the
   new holder of the address block automatically becomes the previous
   one, or addresses are transferred to a default holder.  As stated
   before, this revocation procedure should be enforced by the rules of
   the blockchain, this means that participants would not recognise
   expired allocations as valid.

6.1.2.  Multi-signature transactions

   A multi-signature transaction is a transaction that admits more than
   one authorized signer.  In other words, a transaction is considered
   valid if it has, for instance, 2 out of 5 valid signatures.  This
   way, 3 keys can be lost but with the renaming 2 keys the block of
   addresses can be recovered.  This approach exemplifies the
   aforementioned tradeoff in trust, since the holder of the block of
   addresses must trust the owners of the keys participating in the
   multi-signature transaction.

6.1.3.  Revocation transaction

   A simpler approach than multi-signature transactions is creating a
   'revocation' transaction.  When a block of address is required to be
   reassigned without the consent of the current holder, a revocation
   transaction (specifying the new holder) is inserted in the
   blockchain.  This transaction should be issued either by a
   consensuated authority or by a disputing entity.  The revocation
   transaction should be resolved by either accepting the revocation
   transaction automatically when issued by the accepted authority or by
   means of out-of-band mechanisms when issued by a disputing party.







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6.1.4.  Out-of-band mechanisms

   Disputes regarding transactions can be resolved by means of out-of-
   band mechanisms, e.g, discussion, court, etc.  In order to reflect
   the decision of this out-of-band mechanism the blockchain must be
   modified.  Since this represents a deviation from the rules, it must
   be done through a hard blockchain fork.  Although cumbersome and
   complex, this is feasible from a technical standpoint.

6.2.  Storage management

   The never ending size of the blockchain presents a potential
   scalability issue.  At the time of this writing, mature blockchains
   like Bitcoin require more than 100 GB of storage.  Simply deleting or
   summarizing old transactions degrades the security of PoW-based
   chains, since their security relies on the computing power required
   to generate them.  The longer they are, the harder they are to
   attack.

   However, PoS-based chains do not rely on computing power and hence,
   space-saving strategies do not degrade the security.  For instance a
   simple solution could be to, once the PoS-based chain reaches a
   certain storage size, summarize a subset of the older transactions.
   In what follows we overview this strategy:



























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   +-----+-----+-----+-----+-----------------+-----+-----+-----+
   |  0  |  1  |  2  |  3  |      .....      |47832|47833|47834|
   +-----+-----+-----+-----+-----------------+-----+-----+-----+


   9.1 Old blockchain


   +-----+-----+-----+-----+-----+
   | r0  | r1  | r2  | r3  | r4  |
   +-----+-----+-----+-----+-----+


   9.2 Write present state to special reset blocks


   +-----+-----+-----+-----+-----+-----+-----+
   | r0  | r1  | r2  | r3  | r4  |  0  |  1  | ...
   +-----+-----+-----+-----+-----+-----+-----+


   9.3 Continue working after the reset blocks


   Figure 9.- A simple technique to reduce blockchain storage


   This approach reduces bootstrapping cost, it is worth noting that
   this strategy requires trust on the reset blocks, such blocks can be
   obtained with an out-of-band mechanism (see Section 5.2.1.3 for
   further information).

6.3.  Proof of Networking?

   In this section we speculate how one could design an equivalent of
   Proof-of-Work (PoW) for networks.  Conceptually, PoW is a proof of
   computational resources, can we devise a proof of networking
   resources?  It could be thought that a PoW equivalent may exist in
   the context of networks, i.e., an equivalent to spending computer
   cycles in a network.  Some resources unique to networks are
   bandwidth, computation of checksums, number of BGP peers, etc.
   Hence, we could envisage a blockchain secured by the resources
   inherent to its participating computer networks.  As long as half of
   the resources were controlled by honest members, security is
   guaranteed.  For example, bandwidth could be a potential candidate;
   however it does not satisfy two key features present in PoW:





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   o  Asymmetry: the proof has to be hard to generate but fast to
      verify.

   o  Verifiability: it has to be possible to embed the proof in the
      block in order to account for the spending of resources.

   In this context, Proof-of-Networking is an open research issue .

6.4.  Configuration parameters

   Configuration parameters refer to a set of values:

   o  Block creation rate

   o  Maximum block size

   o  Other parameters related to the consensus algorithm

   These parameters, beyond regulating the operation of the blockchain
   also have an influence on its performance.  For example, a small
   block size increases propagation speed (thus consensus can be reached
   faster) but reduces the number of transactions per second that the
   blockchain can handle.  As an example, in Bitcoin, the 10-minute
   block creation rate seeks to balance fast confirmation times and
   reduced probability of forks [Antonopoulos2015].  Experimental
   deployments and operational requirements should help tuning such
   parameters.

7.  Security Considerations

   This document aims to understand the security implications of using
   the blockchain technology to secure IP addresses allocation.

8.  IANA Considerations

   This memo includes no request to IANA.

9.  Acknowledgements

   The authors wish to thank Jordi Herrera-Joancomarti, Andreu
   Rodriguez-Donaire and Jordi Baylina for their helpful discussions
   about Bitcoin and blockchain technology, as well as Leo Vegoda for
   his insights regarding revocation mechanisms.








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10.  Informative References

   [Antonopoulos2015]
              Antonopoulos, A., "Mastering Bitcoin, available online:
              http://chimera.labs.oreilly.com/books/1234000001802/
              index.html", 2015.

   [Apostolaki2017]
              Apostolaki, M., Zohar, A., and L. Vanbever, "Hijacking
              Bitcoin: Routing Attacks on Cryptocurrencies. 2017 IEEE
              Symposium on Security and Privacy (SP).", 2017.

   [Bitcoin]  Nakamoto, S., "Bitcoin: A Peer-to-Peer Electronic Cash
              System. https://bitcoin.org/bitcoin.pdf", 2008.

   [Blockstack]
              Ali, et al., M., "Blockstack : A Global Naming and Storage
              System Secured by Blockchains, USENIX Annual Technical
              Conference", 2016.

   [Ethereum]
              The Ethereum project, "https://www.ethereum.org/", 2016.

   [Hari2016]
              Hari, A. and T. Lakshman, "The Internet Blockchain: A
              Distributed, Tamper-Resistant Transaction Framework for
              the Internet. Fifteenth ACM Workshop on Hot Topics in
              Networks", 2016.

   [miningfarm]
              Inside a mining farm, "http://www.bbc.com/future/
              story/20160504-we-looked-inside-a-secret-chinese-bitcoin-
              mine", 2016.

   [Namecoin]
              Namecoin, "https://namecoin.org/", 2011.

   [Peercoin]
              The Peercoin cryptocurrency, "https://peercoin.net/",
              2016.

   [realrouteattack]
              Hacker Redirects Traffic From 19 Internet Providers to
              Steal Bitcoins, "https://www.wired.com/2014/08/isp-
              bitcoin-theft/", 2014.






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Authors' Addresses

   Jordi Paillisse
   UPC-BarcelonaTech
   c/ Jordi Girona 1-3
   Barcelona, Catalonia  08034
   Spain

   Email: jordip@ac.upc.edu


   Alberto Rodriguez-Natal
   Cisco Systems
   170 Tasman Drive
   San Jose, CA
   USA

   Email: natal@cisco.com


   Vina Ermagan
   Cisco Systems
   170 Tasman Drive
   San Jose, CA
   USA

   Email: vermagan@cisco.com


   Fabio Maino
   Cisco Systems
   170 Tasman Drive
   San Jose, CA
   USA

   Email: fmaino@cisco.com


   Albert Cabellos
   UPC-BarcelonaTech
   c/ Jordi Girona 1-3
   Barcelona, Catalonia  08034
   Spain

   Email: acabello@ac.upc.edu






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