Signet

Signet is a proposed new test network for the Bitcoin block chain which adds an additional signature requirement to block validation. Signet is similar in nature to testnet, but more reliable and centrally controlled. There is a default signet network ("Signet Global Test Net II" as of this writing), but anyone can run their own signet network at their whim.

Run bitcoind with the -signet flag to use the default global signet (or put signet=1 in the bitcoin.conf file). If you wish to use a custom signet, you need to provide the block challenge (aka the block script) using -signet_blockscript=<hex> and preferably also at least one seed node using -signet_seednode=<host>[:<port>].

Differences

• Default Bitcoin network protocol listen port is 38333 (instead of 8333)
• Default RPC connection port is 38332 (instead of 8332)
• A different value of ADDRESSVERSION field ensures no testnet Bitcoin addresses will work on the production network. (0x7D rather than 0x00)
• The protocol message header bytes are 0xF0C7706A (instead of 0xF9BEB4D9)
• Genesis block is generated based on the signet blockscript (and is thus not actually valid)
• Segwit is always enabled
• Additional consensus requirement that the coinbase witness commitment contains an extended signet commitment, which is a script satisfying the block script (usually a k-of-n multisig)

Why run Signet?

• You are an Instructor, and want to run a controlled Bitcoin network environment for teaching purposes.
• You are a Software Developer, and want to test your software.
• You want to try out experimental changes that you want to implement in Bitcoin.
• You want to test long-term running software and don't want to deal with tens of thousands of block reorgs, or days of no blocks being mined, as is the case with Testnet.
• You want an easy way to test double spends (signet plans to include support for automated double spends, where you provide two conflicting transactions and they are mined in order, with a reorg happening between them).

Genesis Block

Each signet network has its own genesis block. The coinbase signature of the genesis block for a signet network with the blockscript S is calculated as

    sha256(sha256(S))

and the output is simply

    OP_RETURN

The nTime is 1534313275, the nonce is 0, and the nBits (difficulty target) is 0x1e2adc28 (POW limit 00002adc28cf53b63c82faa55d83e40ac63b5f100aa5d8df62a429192f9e8ce5).

Getting Started

Fetch and compile signet

$ git clone https://github.com/kallewoof/bitcoin.git signet
$ cd signet
$ git checkout signet-0.18
$ ./autogen.sh
$ ./configure
$ make -j5

Create bitcoin.conf file and start up the daemon

$ cd src
$ mkdir signet
$ echo "signet=1
daemon=1" > signet/bitcoin.conf
$ ./bitcoind -datadir=signet

Verify that you're connected

$ ./bitcoin-cli -datadir=signet getconnectioncount
***SHOULD BE MORE THAN ZERO***
$ ./bitcoin-cli -datadir=signet getblockcount
***SHOULD BE MORE THAN ZERO***

Get some coins

You first need an address

$ ./bitcoin-cli -datadir=signet getnewaddress

Then go to a faucet, e.g. https://signet.bc-2.jp and enter your address.

Then see your transaction be confirmed at an explorer, e.g. https://explorer.bc-2.jp.

External links

• WIP pull request
• Github gist explaining how to get started

Faucets

• https://signet.bc-2.jp/

Can also ping @kallewoof on IRC (freenode)/Twitter.

Block explorers

• https://explorer.bc-2.jp/

Custom Signet

Creating your own signet involves a couple of steps: generate keys used for signing, define the block script, start up a node running on the new signet, and import the private key in order to sign blocks.

Generating keys used for signing a block

The most straightforward way is to simply start up a signet instance and then generating a new key from there.

$ cd PATHTOBITCOIN/bitcoin/src
$ ./bitcoind -signet -daemon
$ ADDR=$(./bitcoin-cli -signet getnewaddress)
$ PRIVKEY=$(./bitcoin-cli -signet dumpprivkey $ADDR)
$ ./bitcoin-cli -signet getaddressinfo $PRIVKEY | grep pubkey
  "pubkey": "02c60c3940e5REDACTEDbd0148cd",

We need to jot down the privkey (echo $PRIVKEY) and the pubkey (here 02c60...).

Defining the block script

The block script is just like any old Bitcoin script, but the most common type is a k-of-n multisig. Here we will do a 1-of-1 multisig with our single pubkey above. Our script becomes

• 51 "1" (signature count)
• 21 Push 0x21=33 bytes (the length of our pubkey above)
• 02c60c3940e5REDACTEDbd0148cd (our pubkey)
• 51 "1" (pubkey count)
• ae OP_CHECKMULTISIG opcode

Put together, our -signet_blockscript value becomes 512102c60c3940e5REDACTEDbd0148cd51ae.

Start up a node (issuer)

For the network to be useful, it needs to be generating blocks at decent intervals, so let's start up a node that does that (it may be useful to also use that node as a seed node for other peers).

Note that we are importing $PRIVKEY at the end; any node that needs to issue blocks must import the privkey we generated above, or it will fail to sign blocks.

$ ./bitcoin-cli -signet stop
$ datadir=$HOME/signet-custom
$ mkdir $datadir
$ echo "signet=1
[signet]
daemon=1
signet_blockscript=512102c60c3940e5REDACTEDbd0148cd51ae" > $datadir/bitcoin.conf
$ ./bitcoind -datadir=$datadir
$ ./bitcoin-cli -datadir=$datadir importprivkey $PRIVKEY

Run issuer

Lastly, we start the issuer script located in contrib/signet.

$ cd ../contrib/signet
$ ./issuer.sh 540 ../../src/bitcoin-cli -datadir=$datadir
- checking node status
- 23:51:01: node OK with 0 connection(s)
- 23:51:01: mining at maximum capacity with 540 second delay between each block
- 23:51:01: hit ^C to stop
- 23:51:01: generating next block
- 23:51:08: mined block 1 0000321422407052c06fef1eacbee402571787c9828051981adfbb5d50a2330a to 0 peer(s); idling for 540 seconds

This script will keep on mining blocks every 540 seconds (actually it will take about 60 seconds to generate a block after the difficulty has stabilized, so you should be seeing one block every 600 seconds) until you hit ctrl-C. It may be a good idea to run this in a screen, so you can check back on it occasionally.

You may also want to run the issuer with a lower idle time initially, so you get some mature coinbase outputs faster.

Next is to have your friends/colleagues/etc join the network by setting the signet_blockscript to the same as above, and connecting to your node.