Signet

Signet (BIP 0325) 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 V" 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 signet Bitcoin addresses will work on the production network. (0x6F rather than 0x00)
• The protocol message header bytes are *dynamically generated* based on the block challenge, i.e. every signet is different; the header for the current default signet is 0x0A03CF40 (that is reversed e.g. in Rust variables) (instead of 0xF9BEB4D9), but see #Genesis_Block_and_Message_Header
• Genesis block has timestamp 1534313275, nonce 100123, and difficulty 0x1e2adc28.
• 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 and Message Header

All signet networks share the same genesis block, but have a different message header. The message header is the 4 first bytes of the sha256d-hash of the block challenge, as a single script push operation. I.e. if the block challenge is 37 bytes, the message start would be sha256d(0x25 || challenge)[0..3].

Getting Started

Fetch and compile signet

$ git clone https://github.com/kallewoof/bitcoin.git signet
$ cd signet
$ git checkout signet
$ ./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

There is a command line tool you can use to get coins directly to your instance of Signet, assuming you are on the default network. You can also use the faucet online with an address of yours.

Using online faucet

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.

Using the command line tool

The tool is in contrib/signet and is called getcoins.sh. You can optionally provide a path to bitcoin-cli using --cmd=[path] and a compatible faucet using --faucet=[url] followed by any number of arguments to bitcoin-cli. The script attempts to autodetect these if left out.

$ cd ../contrib/signet
$ ./getcoins.sh -datadir=../../src/signet
Payment of 10.00000000 BTC sent with txid c0bfa...

Check that you received the coins

Check your faucet transaction confirming at e.g. https://explorer.bc-2.jp and then send coins around to people and/or use signet for testing your wallet/etc.

You can immediately see the amount using getunconfirmedbalance i.e.

$ cd ../../src # if you were in contrib/signet
$ ./bitcoin-cli -datadir=signet getunconfirmedbalance

You can also see info about the transaction that the faucet gave you.

$ ./bitcoin-cli -datadir=signet gettransaction THETXID

Once it has confirmed, you should see it in getbalance.

$ ./bitcoin-cli -datadir=signet getbalance

External links

• Pull request #16411 to Bitcoin Core
• Pull request #291 to Rust-Bitcoin
• Github gist explaining how to get started

Faucets

• https://signet.bc-2.jp/

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

Faucet source code, if you want your own:

• https://github.com/kallewoof/bitcoin-faucet.git (node.js and mongodb)
• https://github.com/stepansnigirev/tinyfaucet.git (python)

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 $ADDR | 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

Note: if you run into errors above, you may have a different signet running, which is blocking the ports. Either stop that, or set port and rpcport in the $datadir/bitcoin.conf file under the [signet] section and try again from the bitcoind part above.

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 and signet_genesisnonce to the same as above, and connecting to your node.