Network Working Group J. Paillisse
Internet-Draft UPC-BarcelonaTech
Intended status: Informational A. Rodriguez-Natal
Expires: December 30, 2018 V. Ermagan
F. Maino
Cisco Systems
L. Vegoda
Individual
A. Cabellos
UPC-BarcelonaTech
June 28, 2018
An analysis of the applicability of blockchain to secure IP addresses
allocation, delegation and bindings.
draft-paillisse-sidrops-blockchain-02
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
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This Internet-Draft will expire on December 30, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3
3. Blockchain in a nutshell . . . . . . . . . . . . . . . . . . 3
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Chain of signatures . . . . . . . . . . . . . . . . . 4
3.1.2. Consensus algorithm . . . . . . . . . . . . . . . . . 5
3.2. Features . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Description of consensus algorithms . . . . . . . . . . . 7
3.3.1. Proof of Work (PoW) . . . . . . . . . . . . . . . . . 7
3.3.2. Proof of Stake (PoS) . . . . . . . . . . . . . . . . 8
4. Blockchain for IP addresses . . . . . . . . . . . . . . . . . 9
4.1. Problem statement . . . . . . . . . . . . . . . . . . . . 9
4.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . . 9
4.3. A consensus algorithm for IP addresses . . . . . . . . . 10
5. Overview of the architecture . . . . . . . . . . . . . . . . 11
5.1. Support for IPv6 and AS numbers . . . . . . . . . . . . . 13
5.2. Pros and cons . . . . . . . . . . . . . . . . . . . . . . 14
5.3. Security evaluation . . . . . . . . . . . . . . . . . . . 16
5.3.1. Attacks against a PoS-based consensus algorithm . . . 16
5.3.2. Attacks against the P2P network . . . . . . . . . . . 17
6. Revocation . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1. Expiration time . . . . . . . . . . . . . . . . . . . . . 20
6.2. Multi-signature transactions . . . . . . . . . . . . . . 20
6.3. Revocation transaction . . . . . . . . . . . . . . . . . 20
6.4. Heartbeat transaction . . . . . . . . . . . . . . . . . . 20
6.5. Out-of-band mechanisms . . . . . . . . . . . . . . . . . 21
6.6. A simple revocation protocol . . . . . . . . . . . . . . 21
7. Other Considerations . . . . . . . . . . . . . . . . . . . . 21
7.1. Storage management . . . . . . . . . . . . . . . . . . . 21
7.2. Proof of Networking? . . . . . . . . . . . . . . . . . . 22
7.3. Configuration parameters . . . . . . . . . . . . . . . . 23
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7.4. PoS algorithm design particularities . . . . . . . . . . 23
7.5. Candidate PoS consensus algorithms . . . . . . . . . . . 24
7.6. Privacy concerns . . . . . . . . . . . . . . . . . . . . 25
7.7. Governance . . . . . . . . . . . . . . . . . . . . . . . 26
8. Implementations . . . . . . . . . . . . . . . . . . . . . . . 26
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
12. Informative References . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
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
[Byzantine].
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 naming system, providing a similar functionality to
that of DNSSEC.
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
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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 temporarily store 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
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
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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.
+-------------+-------------------+--------+---------------+
| 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 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.
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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.
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.
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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, requiring some computational effort. This is
commonly known 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.
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 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 takeover: 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. On the other hand, several ASIC-
resistant algorithms are in use in various cryptocurrencies. This
is usually achieved with memory-intensive calculations or
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frequently changing the mining algorithm. Although they appear to
be a promising alternative, vendors react by developing a silicon
implementation of the algorithm. In this situation, the
developers usually change the algorithm by means of a hard fork
[monero]. Ultimately, this becomes an arms-race.
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 pseudo-randomly selected 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
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.
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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
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
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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
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 entities 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 entities that hold large blocks of the 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
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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
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
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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
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,
restrict permissions for customer sub-delegations, etc.
5.1. Support for IPv6 and AS numbers
The allocation and delegation of IPv6 addresses and AS numbers is
equivalent to that of IPv4, maintaining the IANA -> RIR -> LIR
hierarchy. For example, for IPv6:
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+--------------+------------------+-----------+----------------+
| IANA v6 | Signature IANA | Allocate | Hash(IANA v6 |
| Public Key 1 | v6 Private Key 1 | 0::/0 | Public Key 2) |
+--------------+------------------+-----------+----------------+
+--------------+------------------+-----------+----------------+
| | | Rest of | Hash(IANA v6 |
| IANA v6 | Signature IANA | space | Public Key 3) |
| Public Key 2 | v6 Private Key 2 +-----------+----------------+
| | | Allocate | Hash(IANA v6 |
| | | 2000::/3 | Public Key 4) |
+--------------+------------------+-----------+----------------+
+--------------+------------------+------------+------------------+
| | | Rest of | Hash(IANA v6 |
| IANA v6 | Signature IANA | space | Public Key 5) |
| Public Key 4 | v6 Private Key 2 +------------+------------------+
| | | Allocate | Hash(AFRINIC v6 |
| | | 2c00::/12 | Public Key 1) |
+--------------+------------------+------------+------------------+
+--------------+-------------------+-----------+-----------------+
| | | Rest of | Hash(AFRINIC v6 |
| AFRINIC v6 | Signature AFRINIC | space | Public Key 2) |
| Public Key 1 | v6 Private Key 1 +-----------+-----------------+
| | | Allocate | Hash(ISP A v6 |
| | | 2c0c::/15 | Public Key 1) |
+--------------+-------------------+-----------+-----------------+
Figure 9.- IPv6 allocation transactions. From top to bottom:
genesis transaction, global unicast allocation, AFRINIC allocation
and LIR allocation.
The process is equivalent for AS numbers. Besides, in the context of
a multi-signature scheme, it is also possible to ask the holder of
the AS number to confirm the binding of its AS number to a particular
prefix.
5.2. Pros and cons
In this section we analyze the pros and cons of this architecture
compared to traditional PKI infraestructures:
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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.
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.
o Limited legal liability: since users control their private keys,
Internet Registries cannot be held legally responsible of their
loss. In turn, this can foster the creation of a unified registry
instead of the current five. Ultimately, this would ease cross-
registry resource transfers.
o No single point of failure: again, due to the fact that each user
controls its private key, the compromise of a user's key does not
compromise the entire system. This starkly contrasts with the
compromise of a CA, which can potentially invalidate all
downstream certificates.
o Simplified state update: PKIs need specific subsystems to update
its state (e.g. issue/revoke certificates). On the other hand,
in a blockchain all these operations are embedded in it thanks to
its transactional nature.
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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.
5.3. Security evaluation
5.3.1. 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.
5.3.1.1. 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.
5.3.1.2. 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.
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5.3.1.3. 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 takeover' 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.
5.3.1.4. Monopolies
A monopoly refers to a single party controlling enough IP addresses
so it can sign a significant proportion of new blocks, thus being
able to decide which information is written in the chain (e.g., a 51
% attack in Bitcoin). However and in this use-case, this is of less
concern since parties do not have a clear incentive to alter normal
chain operation. In order to successfully launch this attack a party
should control more than 50% of the IP blocks, while this is
difficult to achieve and participants do not have a clear incentive
to sell/give away blocks of IPs, the attacker would also impact its
own infrastructure, making the Internet less secure. Section 7.4
contains more details regarding monopolies.
5.3.1.5. 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.
5.3.2. Attacks against the P2P network
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This section presents attacks directed towards the underlying P2P
network used to exchange information among the participants of the
blockchain.
5.3.2.1. 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.
5.3.2.2. 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.
5.3.2.3. 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
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].
5.3.2.4. Transaction censorship
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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. 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).
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.
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6.1. 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.
6.2. Multi-signature transactions
A multi-signature transaction is a transaction with more than one
associated public key. 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. For instance, if some of these keys are
owned by IANA or an Internet Registry, we can return part of the
control over the allocation to them.
6.3. 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.
6.4. Heartbeat transaction
Another approach involves issuing a heartbeat transaction every N
days, signalling to the network that the holder still owns the key
associated with that particular resource. If the holder fails to
issue this transaction, the blockchain considers that the resource is
automatically returned to the registry.
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6.5. 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.
6.6. A simple revocation protocol
Here we present a simple revocation protocol to handle accidental key
loss:
1. On detecting the key loss, the holder notifies the registry, e.g.
via e-mail.
2. The registry issues a revocation transaction, similar to the one
in section Section 6.3.
3. The current holder has a fixed period of time to issue a
transaction re-claiming the resource. This transaction must be
signed by the private key associated with the claimed resource.
4. If the holder issues the transaction, it retains the resource.
5. Otherwise, after the fixed time interval, the blockchain
considers that the resource is returned to the registry, so it
can be re-allocated.
This protocol combines two of the aforementioned techniques, and
allows to balance power between resource holders and registries.
Registries can revoke lost or unclaimed resources, while address
holders can retain them if the registry misbehaves or its key is
compromised. However, it should be noted that this protocol does not
protect from stolen keys.
The time interval can be different depending on the nature of the
revocating entity. For example, IANA -> RIR allocations could wait a
couple of weeks, whereas RIR -> LIR allocations could go faster with
a 72 hours notification period.
7. Other Considerations
7.1. Storage management
The never ending size of the blockchain presents a potential
scalability issue. At the time of this writing, mature blockchains
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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:
+-----+-----+-----+-----+-----------------+-----+-----+-----+
| 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 10.- 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 5.3.1.3 for
further information).
7.2. Proof of Networking?
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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:
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 .
7.3. 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.
7.4. PoS algorithm design particularities
The particular use case of IP addresses presents some characteristics
that the PoS algorithm should take into account:
Monopoly prevention: As described in section Section 5.3.1.4,
monopolies can pose a threat to a PoS blockchain. In order to
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prevent a small number of large-stakers from controlling the
chain, we can design the PoS algorithm to have a smart mapping of
IP prefixes to the weight of the random selection. A potential
solution could be fine-tuning the weighting of IP addresses
(slightly biasing the choice towards medium-sized holders), in
order to reduce the power of high stakers. This can provide an
upper-bound of the maximum number of addresses that a party can
hold to avoid monopolies (ideally as high as possible).
IPv6 support: Large parts of the IPv6 address space remain
unallocated and still owned by IANA (at the time of writing this
document, less than 0.5% of v6 address space has been allocated to
the RIRs). The PoS algorithm should ignore this space (not count
it) to avoid IANA signing nearly all v6 blocks and thus,
preventing an IANA monopoly.
IPv4/v6 stake isolation: Since there are more IPv6 addresses than
IPv4, this creates an imbalance of power in a PoS blockchain:
randomly selecting from both pools of addresses naturally causes
v6 holders signing more blocks than v4 holders. Thus, some kind
of isolation between v4 and v6 stake is required. For example, we
could alternatively generate blocks with only v4 or v6
transactions, signed by a v4 or v6 holder, respectively.
7.5. Candidate PoS consensus algorithms
There are several existing PoS algorithms that could satisfy the
requirements of a blockchain for IP addresses. The following list
presents three of them that have been claimed by the authors to be
proven mathematically correct. A substantial difference among them
is the supported portion of offline participants. The list does not
pretend to be exhaustive.
Algorand: [Algorand] leverages a multi-step protocol to provide a
verifiable random selection of the block signer. The most
relevant features of Algorand are:
* A cryptographic sortition mechanism to randomly select the
participants in each step of the protocol, based on Verifiable
Random Functions [I-D.irtf-cfrg-vrf].
* The decoupling of block creation and block signing, to avoid
stake grinding attacks.
* A new Byzantine Agreement protocol (BA*) to achieve consensus.
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* Player replaceability: Algorand uses a different set of
participants for each of its steps. Thus, malicious
participants from one step cannot influence the following.
* Upper bound of 1/3 of dishonest players.
Ouroboros: [Ouroboros] presents a similar approach to Algorand:
first, it selects a subset of users. Then, these users perform
the random selection by means of a secure multiparty computation.
As opposed to Algorand, however, this subset lasts for several
blocks, called epochs. In addition, Ouroboros assumes that the
majority of participants are online when they have to participate
in the protocol, and that they remain offline only short periods
of time.
Snow White: The [SnowWhite] protocol improves on the previous two by
supporting also large amounts of offline participants, as long as
the majority of online members are honest. They call this
property 'Robustly Reconfigurable Consensus'. Snow White also
leverages a random function to decide if a participant has to sign
a block, and defines epochs similarly to Ouroboros: after each
epoch, participants for the new one are calculated.
7.6. Privacy concerns
In order to protect privacy, the blockchain should not contain
Personally Identifiable Information (PII). This is due to the fact
that data in the blockchain cannot be removed and that it is a public
ledger, accessible by anyone. Instead, PII like contact emails or
postal addresses should be stored in the Registry's database (e.g.
RIPE Database). Ideally, the blockchain should contain the minimum
amount of data for correct operation, that is: public keys, blocks of
IP addresses, AS numbers and their bindings (figure 11).
Public Private
+---------------------+ +-----------------------+
| Blockchain | +-----------+ | Registry Database |
| |<---|Update |<---| |
| Pairs of (Prefix, | |prefix, key| | *Registry Policies |
| Public key) | |pair | | *Contact data |
| | +-----------+ | |
+---------------------+ +-----------------------+
Figure 11.- Data flow between Registry and blockchain
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7.7. Governance
Blockchain does not mean anarchy. In fact, any blockchain requires a
governing entity that determines its rules and ensures that all of
its participants agree on its operation. The need of governance is
illustrated by the recent Bitcoin Cash fork [Bitcoincash]. Due to a
disagreement among Bitcoin users, they created a Bitcoin hard fork
called Bitcoin Cash. This split the Bitcoin blockchain in two,
causing some confusion. Proper governance should avoid such
situations.
This particular use case is not an exception: all concerned parties
(IANA, RIRs, ISPs, etc) should reach consensus regarding which rules
are enforced in the blockchain. For example, dispute resolution or
revocation procedures.
8. Implementations
There are several implementations to secure the allocation of IP
prefixes. They present different scopes and levels of maturity.
o IPchain uses a Proof of Stake algorithm and is specifically
tailored for the allocation of IP addresses. Its performance has
been evaluated [IPchain], and has been open-sourced
[IPchain-repo].
o [BGPCoin] runs on top of the Ethereum blockchain and provides
similar features to IPchain. It has not been possible to find
open-source code.
o Another project identically named BGPCoin is designed to allow
ISPs to exchange peering agreements and route advertisements by
means of a blockchain [BGPCoin-repo]. It uses a hybrid PoW/PoS
algorithm and has its own cryptocurrency.
9. Security Considerations
This document aims to understand the security implications of using
the blockchain technology to secure IP addresses allocation.
10. IANA Considerations
This memo includes no request to IANA.
11. Acknowledgements
The authors wish to thank Jordi Herrera-Joancomarti, Andreu
Rodriguez-Donaire and Jordi Baylina for their helpful discussions
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about Bitcoin and blockchain technology, as well as Marco Chiesa for
the heartbeat transaction idea.
12. Informative References
[Algorand]
Gilad, Y., Hemo, R., Micali, S., Vlachos, G., and N.
Zeldovich, "Algorand: Scaling byzantine agreements for
cryptocurrencies. Proceedings of the 26th Symposium on
Operating Systems Principles (pp. 51-68). ACM.", 2017.
[Antonopoulos2015]
Antonopoulos, A. M., "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.
[BGPCoin-repo]
BGPCoin GitHub repository, , "https://github.com/bgpcoin",
2018.
[BGPCoin] Xing, Q., Wang, B., and X. Wang, "POSTER: BGPCoin: A
Trustworthy Blockchain-based Resource Management Solution
for BGP Security. ACM Conference on Computer and
Communications Security (CCS) 2017", 2017.
[Bitcoin] Nakamoto, S., "Bitcoin: A Peer-to-Peer Electronic Cash
System. https://bitcoin.org/bitcoin.pdf", 2008.
[Bitcoincash]
Bitcoin split in two, here's what that means, , "http://
money.cnn.com/2017/08/01/technology/business/bitcoin-cash-
new-currency/index.html", 2017.
[Blockstack]
Ali, et al., M., "Blockstack : A Global Naming and Storage
System Secured by Blockchains, USENIX Annual Technical
Conference", 2016.
[Byzantine]
Lamport, L., Shostak, R., and M. Pease, "The Byzantine
Generals Problem. ACM Transactions on Programming
Languages and Systems", 1982.
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[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.
[I-D.irtf-cfrg-vrf]
Goldberg, S., Reyzin, L., Papadopoulos, D., and J. Vcelak,
"Verifiable Random Functions (VRFs)", draft-irtf-cfrg-
vrf-01 (work in progress), March 2018.
[IPchain-repo]
IPchain GitHub repository, , "https://github.com/
OpenOverlayRouter/blockchain-mapping-system", 2018.
[IPchain] Paillisse, J., Ferriol, M., Garcia, E., Latif, H., Piris,
C., Lopez, A., Kuerbis, B., Rodriguez-Natal, A., Ermagan,
V., Maino, Fabio., and A. Cabellos, "IPchain: Securing IP
Prefix Allocation and Delegation with Blockchain, arXiv
preprint: https://arxiv.org/abs/1805.04439", 2018.
[Namecoin]
Namecoin, , "https://namecoin.org/", 2011.
[Ouroboros]
Kiayias, A., Russell, A., David, B., and R. Oliynykov,
"Ouroboros: A provably secure proof-of-stake blockchain
protocol. Annual International Cryptology Conference (pp.
357-388). Springer, Cham.", 2017.
[Peercoin]
The Peercoin cryptocurrency, , "https://peercoin.net/",
2016.
[SnowWhite]
Bentov, I., Pass, R., and E. Shi, "Snow White: Provably
Secure Proofs of Stake. IACR Cryptology ePrint Archive,
2016, 919.", 2016.
[miningfarm]
Inside a mining farm, , "http://www.bbc.com/future/story/
20160504-we-looked-inside-a-secret-chinese-bitcoin-mine",
2016.
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[monero] Monero PoW algorithm update, , "https://www.ethnews.com/
monero-team-mulls-changing-pow-algorithm-to-preempt-asic-
miners", 2018.
[realrouteattack]
Hacker Redirects Traffic From 19 Internet Providers to
Steal Bitcoins, , "https://www.wired.com/2014/08/isp-
bitcoin-theft/", 2014.
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
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Leo Vegoda
Individual
4712 Admiralty Way, #152
Marina del Rey, CA 90292
USA
Email: leo@vegoda.org
Albert Cabellos
UPC-BarcelonaTech
c/ Jordi Girona 1-3
Barcelona, Catalonia 08034
Spain
Email: acabello@ac.upc.edu
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