P2P DNS and more - based on a Distributed Hash Table (DHT)
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Latest commit ae6de6d Feb 16, 2017 @mwarning openwrt => lede

README.md

kadnode(1) - P2P name resolution daemon

SYNOPSIS

kadnode [--value-id identifier] [--port port] [--daemon] [...]

kadnode-ctl [...]

DESCRIPTION

KadNode is a small P2P DNS resolution daemon based on a Distributed Hash Table (DHT). KadNode can intercept and resolve DNS request in the systems background. Every instance can also announce any domain like e.g. myname.p2p. People on others devices running KadNode can then enter myname.p2p into their browsers or console in order to reach the announcing host. To avoid name clashes, cryptographic public/private key pairs can be used. This makes it possible to have a personal and decentralized DynDNS service. The DHT is identical to the one used in the Transmission Bittorrent client and works on the Internet as well as on local networks.

Features:

  • IPv4/IPv6 support
  • UPnP/NAT-PMP support
  • local peer discovery
  • small size 75KB-125KB
  • public/secret key authentication (based on libsodium)
  • command line interface (kadnode-ctl)
  • NSS support through /etc/nsswitch.conf
  • integrated simplified DNS server (handles A, AAAA, and SRV requests)
  • packages for ArchLinux/Debian/FreeBSD/MacOSX/LEDE/Windows
  • peer file import/export on startup/shutdown and every 24h

Most features are optional and can be left out to reduce the binary size.

JOIN THE SWARM

KadNode needs to know at least one active peer to join a swarm. This can be achieved by inserting e.g. bttracker.debian.org, or any other address of an active peer, into a file and provide it to KadNode:

kadnode --peerfile peers.txt

This will cause KadNode to bootstrap into a network. On shutdown and also every 24h, KadNode writes at most 150 good peers back to the peer file. This ensures successful boostrapping on the next startup. The peer file is not written after at least 5 minutes of runtime.

Another source of peers is the local network. KadNode can find peers via local peer discovery and bootstrap that way. This is useful if the peers file only contains stale entries.

AUTHENTICATION

For most use cases you first need to create a secret/public key pair:

$kadnode --auth-gen-keys
public key: <public-key>
secret key: <secret-key>

(The keys are not displayed here for convenience.)

EXAMPLE 1

A typical use case would be to reach a computer (Node1) from another (Node2). On Node 1 we announce an identifier (sha1(myname)):

$kadnode --value-id myname.p2p

On other computers running KadNode, we can use myname.p2p to resolve the IP address of Node1 (e.g. in the web browser). It may take ~8 seconds on the first try. The problem with this approach is that others could also announce the same identifier. This would result in multiple IP addresses to be found and used. To avoid this you can use secret/public key pairs. See the next examples.

EXAMPLE 2

Now we want to reach a computer (Node1) from another (Node2) using cryptographic keys. We tell KadNode on Node1 to announce its secret key.

$kadnode --value-id <secret-key>.p2p

What is actually announced is the SHA1 hash of the derived public key (sha1(<public-key>)), not the secret key itself.

On Node2, we can now resolve <public-key>.p2p.

EXAMPLE 3

Instead of using keys directly as in example 1, we can also use domains.

On Node1, well tell Kadnode to announce that we have node1.p2p using the secret key.

$kadnode --auth-add-skey "node1.p2p:<secret-key>" --value-id node1.p2p

The announced identifier here is sha1(<public-key>+"node1").

On Node2, we tell the node to use the public key to verifiy requests for node1.p2p.

$kadnode --auth-add-pkey "node1.p2p:<public-key>"

The identifier that is searched for is sha1(<public-key>+"node1").

On Node2, we now can enter node1.p2p into the browser or try to ping node1.p2p to see if the address is resolved successfully. The authentication step uses the public key to filter out all nodes that do not know the secret key.

EXAMPLE 4

It is possible to associate a secret/public key to multiple domains using patterns:

Node1 will be reachable using node1.p2p and foobar.p2p.

$kadnode --auth-add-skey "*.p2p:<secret-key>" --value-id node1.p2p --value-id foobar.p2p

Node2 will be reachable using node2.p2p and foobar.p2p as well.

$kadnode --auth-add-skey "*.p2p:<secret-key>" --value-id node2.p2p --value-id foobar.p2p

On Node3, resolving "node1.p2p", "node2.p2p" and "foobar.p2p" to its IP address should now work.

$kadnode --auth-add-pkey "*.p2p:<public-key>"

Since foobar.p2p is used twice, KadNode will give both IP addresses. But almost all programs will just use the first address they get, which is the first that will be successfully verified.

Multiple --auth-add-key and multiple --value-id arguments are possible. Pattern conflicts will result in an error message on startup. Command line options can also be put inside a configuration file (see --config file).

IDENTIFIERS

Identifiers are what you use to lookup IP addresses (e.g. "foo.p2p"). They will be reduced to a 20 Byte representation based on the SHA-1 message digest algorithm. The digest is what will be then used in the actual lookup process. KadNode allows four types of identifiers:

  • Raw identifiers are 20 Byte identifiers written as hex strings. No digest will be applied.

    • E.g: <40_hex_characters>.p2p
  • Raw public key identifiers are 32 Byte hex strings. They will be interpreted as a public key.

    • The SHA-1 digest of the key string respresentation is used to locate nodes.
    • The public key is used to verify that the found nodes have the corresponding secret key.
    • E.g.: <64_hex_characters>.p2p
  • Plain identifiers are just strings that have no key associated to them.

    • The SHA-1 digest of the string is used to find nodes.
    • E.g.: example.p2p
  • Plain identifiers that match a given pattern and have a public key assigned to them.

    • The SHA-1 digest of the string and public key is used to find nodes.
    • The public key is used to verify if the nodes found have the corresponding secret key.
    • E.g.: foo.p2p

All identifiers are converted to lowercase and are therefore case insensitive. A ".p2p" at the end of every identifier is ignored and not applied to the digest. It is used to direct requests to KadNode only.

OPTIONS

  • --value-id id[:port]
    Add a value identifier/domain and optional port to be announced every 30 minutes.
    The announcement will associate this nodes IP address with this identifier.
    This option may occur multiple times.

  • --peerfile file-path
    Import peers for bootstrapping and write good peers
    to this file every 24 hours and on shutdown.

  • --user name
    Change the UUID after start.

  • --port port
    Bind the DHT to this port (Default: 6881).

  • --config file
    Provide a configuration file with one command line
    option on each line. Comments start after '#'.

  • --ifname interface
    Bind to this specific interface.

  • --fwd-disable
    Disable UPnP/NAT-PMP to forward router ports.

  • --daemon
    Run in background.

  • --query-tld domain
    Top level domain used to filter queries to be resolved by KadNode. (Default: ".p2p")

  • --verbosity level
    Verbosity level: quiet, verbose or debug (Default: verbose).

  • --pidfile file-path
    Write process pid to a file.

  • --lpd-addr address
    Send LPD packets to this multicast address as long no peers were found.
    Default: 239.192.152.143:6771 / [ff15::efc0:988f]:6771

  • --lpd-disable
    Disable Local Peer Discovery (LPD).

  • --cmd-disable-stdin
    Disable the local control interface.

  • --cmd-port port
    Bind the remote control interface to this local port (Default: 1700).

  • --dns-port port
    Bind the DNS server interface to this local port (Default: 3535).

  • --dns-server address
    IP address of an external DNS server. Enables DNS proxy mode (Default: none).

  • --nss-port port
    Bind the "Name Service Switch" to this local port (Default: 4053).

  • --web-port port
    Bind the web server to this local port (Default: 8053).

  • --auth-gen-keys
    Generate a secret/public key pair.

  • --auth-add-pkey [pattern:]public-key
    Associate a public key with any value id that matches the pattern.
    Used to verify that the other side has the secret key.
    This option can occur multiple times.

  • --auth-add-skey [pattern:]secret-key
    Associate a secret key with any value id that matches the pattern.
    Used to prove the ownership of the domain.
    This option can occur multiple times.

  • --mode protocol
    Enable IPv4 or IPv6 mode for the DHT (Default: ipv4).

  • -h, --help
    Print the list of accepted options.

  • -v, --version
    Print program version and included features.

KadNode Console Commands

When not started in background, KadNode accepts a variety of commands from standard input.

  • status
    Print the node id, the number of known nodes / searches / stored hashes and more.

  • lookup query
    Lookup the IP addresses of all nodes that claim to satisfy the query.
    The first call will start the search.

  • announce [query[:port] [minutes]]
    Announce that this instance is associated with a query
    and an optional port. The default port is random (but not equal 0).
    No minutes trigger a single announcement. Negative minutes
    last for the entire runtime. Otherwise the lifetime is set minutes into the future.
    No arguments will announce all identifiers at once.

  • import addr
    Send a ping to another KadNode instance to establish a connection.

  • export
    Print a few good nodes.

  • list [blacklist|buckets|constants|forwardings|results|searches|storage|values]
    List various internal data structures.

  • blacklist addr
    Blacklist a specifc IP address.

KadNode External Console

KadNode allows a limited set of commands to be send from any user from other consoles.

kadnode-ctl [-p port] [status|lookup|announce|import|export|blacklist]

  • -p port
    The port used to connect to the command shell of a local KadNode instance (Default: 1700).

  • -h
    Print this help.

Web Interface

The optional web interface allows queries of these forms:

  • http://localhost:8053/lookup?foo.p2p
  • http://localhost:8053/announce?foobar
  • http://localhost:8053/blacklist?1.2.3.4

If the interface cannot be reached then the interface might be disabled (port set to 0) or not compiled in (check kadnode --version). In case the IPv6 entry for localhost is not used or missing, try [::1] instead of localhost.

PORT FORWARDINGS

If KadNode runs on a computer in a private network, it will try to establish a port forwarding for the DHT port. Port forwarding only works if UPnP/NAT-PMP is compiled into KadNode and is supported by the gateway/router. Also, ports attached to announcement values (e.g. --value-id foo.p2p:80) will result in additional port forwardings. This is useful to make a local service (e.g. a web server) reachable from the Internet without the need to configure port forwardings manually.

NOTES

  • .p2p at the end of an identifier (or set by --query-tld) is ignored by KadNode. It is used to filter requests and divert them to KadNode.
  • The interfaces (NSS, DNS, command line) may return the localhost address if the node itself announced a value.

LICENSE

MIT/X11

AUTHORS