In December, 2017 I spent time experimenting with a mesh overlay network called Cjdns that has some interesting qualities about it. I’m not a fan of the darkside-crypto-anarchy mentality that pervades some of the Hyperboria network participants as I believe it erodes the legitimacy of the technology in the same way as Torrent and Tor peer-to-peer systems have issues. With an information-security-hat on however it’s a technology to understand because among other things it can very easily bridge networks in ways you probably do not care for in your own environment.

There are several key concepts with Cjdns that when bought together that make it rather neat indeed, however the “thing” that I find most interesting is the approach to the address-allocation and key-verification.

Address allocation and keys

Cjdns is built on IPv6 networking which means you might need to (or rather I needed to) get over anxieties about growing up from an IPv4 world. The choice of IPv6 by Cjdns is important because the self-allocated IPv6 addresses are entangled with the node public key which tightly-couples addresses with public-keys and in-turn means network participants implicitly know that a public-key is the correct key for an IPv6 address. This very nicely deals with the key-distribution and verification hassles without needing any kind of central authority etc.

This is achieved by generating many private/public keypairs doing a double-sha512 on the first 16 bytes of the public-key until the result starts with FC which then forms the IPv6 address.

The following pseudo code describes the process

while ipv6_address is None:
    private_key, public_key = generate_private_public_keypair()
    ipv6_address_attempt = sha512(sha512(public_key[0:16]))
    if ipv6_address_attempt[0:2] == 'FC':
        ipv6_address = ipv6_address_attempt

Because the FC00::/8 address space is allocated as a IPv6 local-address space the network hence has an address space to operate within.

This leads to a natural question about brute-forcing the entire address-space. To put this into perspective this would mean computing key-pairs and hence IPv6 address of 16^(32-2) ~= 1.329E+36 addresses which if you are going to attempt you’ll want to store so you don’t have to re-compute. If we estimate 160 bytes per address (ipv6-address + public-key + private-key) as plain-text (non-optimal) then you’ll require something like 1.9E+26 petabytes of storage which means you’ll spend your entire time filling out AWS limit increase request forms - this is a very back of the envelope analysis and addresses the storage requirements without regard for any compute requirement, either way it would seem that brute forcing to obtain a given Cjdns node IPv6 address is probably difficult enough in 2018.

Network visualization

You can observe the scale of the Hyperboria network built using Cjdns at, there are a few interesting nodes to observe:-

  • the IPFS gateway nodes to 4 which is particularly interesting for sites hosted on IPFS in my view.
  • the mega peer at operated by magik6k
  • peer “5d11” that is stuck at cjdns version-16 with a deep family of children nodes all also on v16 - this node has been in place since at least 2016-03-21 if the Google search results for the full IPv6 address are correct.

Experimenting with it

Because Cjdns is just an overlay network it means you can simply fire up the daemon, attach to a public-peer and you are connected - that simplicity breeds hazard - consider what happens in an enterprise environment when your clever staff fire up a cjdns-node from an internal position, suddenly you are bridged and it can be rather difficult to manage even with restrictive firewalls and IDS/IPS systems in-place.

My initial concern in attaching anything to the Cjdns network was that it represents a whole new unregulated network where anything can happen with very limited recourse - this coupled with having to come up-to-speed with IPv6 at the same time made me uneasy so I settled on a plan to run the Cjdns node daemon on a temporary cloud-hosted compute provider where the bandwidth is plentiful and less bad things happen if the host somehow becomes compromised.

This in turn led me to check out several alternative cloud-hosting providers other than AWS, namely Softlayer, Azure, Alicloud and Digital Ocean where it became apparent the metric that mattes the most is the cost of traffic - the best options seem to be Digital Ocean and Alicloud when compared on this basis.

Provider $USD/TB Notes
AWS $90.00 US East 1 + extra for compute instance
Softlayer $45.00 Requires monthly contract, pain in the arse to deal with + extra for compute instance
Azure $88.65 US West + extra for compute instance
Alicloud $4.50 1TB transfer included on minimum instance size
Digital Ocean $5.00 1TB transfer included on minimum instance size

I ended up writing a Terraform module for Digital Ocean to quickly fire up instances running Cjdns which you can get for yourself here:-

Thoughts and outcomes

The Cjdns protocol itself is fine enough, but the flagship Hyperboria network that uses it lacks any DNS system which makes the network difficult to use because there is no (or limited) discoverability of network services. There seem to be proposals for a block-chain based DNS system which aligns with the decentralized aspirations of the Hyperboria community but host naming is just part of the problem-set. Content discoverability (aka a search engine) within the network would seem to be the greater challenge that requires real resources to address.

After running a cluster of 6x nodes (2x Singapore, 2x New York, 2x San Francisco) for a week where each peer was cross peered with each other and then publicly peered with ~8x lowest-latency peers relative to each region the total traffic levels were quite small with less than 10’s of GB of traffic over than time. I neglected to record the actual statistics at the time so I’ll need to redo and track this more carefully.

My sense is to write AWS and Alicloud Terraform modules and run a longer experiment across all three providers and examine more carefully the nature of the traffic - bearing in mind traffic content is entirely opaque unless such traffic is bound for your node.

If you have an interest in peering with me do get in contact.

Reminder to self, check out the nodes:-