Difference between revisions of "Signet"
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Revision as of 13:38, 30 November 2021
Signet (BIP 0325) is a new test network for Bitcoin 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 VI" 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
-signetchallenge=<hex>, and preferably also at least one seed node using
- 1 Differences
- 2 Why run Signet?
- 3 Genesis Block and Message Header
- 4 Getting Started
- 5 External links
- 6 Custom Signet
- 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 1598918400, nonce 52613770, and difficulty 0x1e0377ae.
- 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].
NOTE: signet (IV) was merged into the master branch of Bitcoin Core as of https://github.com/bitcoin/bitcoin/pull/18267
Fetch and compile signet
$ git clone https://github.com/bitcoin/bitcoin $ cd bitcoin $ ./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
--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
$ 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
$ ./bitcoin-cli -datadir=signet getbalance
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)
NOTE: Until it is merged into master branch, you may first need to check-out (or merge) the code referred in https://github.com/bitcoin/bitcoin/pull/19937 in order to get the script
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 regtest node and then generating a new key from there.
$ cd PATHTOBITCOIN/bitcoin/src $ ./bitcoind -regtest -daemon -wallet="test" $ ADDR=$(./bitcoin-cli -regtest getnewaddress) $ PRIVKEY=$(./bitcoin-cli -regtest dumpprivkey $ADDR) $ ./bitcoin-cli -regtest getaddressinfo $ADDR | grep pubkey "pubkey": "THE_REAL_PUBKEY",
We need to jot down the privkey (
echo $PRIVKEY) and the pubkey (here
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)
21Push 0x21=33 bytes (the length of our pubkey above)
51"1" (pubkey count)
Put together, our
-signetchallenge value becomes
... stands for
THE_REAL_PUBKEY (see above).
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 -regtest stop $ datadir=$HOME/signet-custom $ mkdir $datadir $ echo "signet=1 [signet] daemon=1 signetchallenge=5121...51ae # fill in THE_REAL_PUBKEY" > $datadir/bitcoin.conf $ ./bitcoind -datadir=$datadir -wallet="test" $ ./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.
Lastly, we're going to get an issuer up and running to mine blocks.
We'll need to provide a value for
nbits which is the mining target and is inversely proportional to the difficulty. This will allow us to set the average time between mined blocks.
We can use the
calibrate command to give us the
nbits for an average mining time of 10 min (600 s):
$ ../contrib/signet/miner --cli="./bitcoin-cli" calibrate --grind-cmd="./bitcoin-util grind" --seconds=600
Referring to our
nbits value with the variable
$NBITS, we need to specify
--set-block-time when mining the first block in a new signet:
$ ADDR=$(./bitcoin-cli -datadir=$datadir getnewaddress); ../contrib/signet/miner --cli="./bitcoin-cli -datadir=$datadir" generate --address $ADDR --grind-cmd="./bitcoin-util grind" --nbits=$NBITS --set-block-time=$(date +%s)
This will create an address, and then mine the first block to that address. (Note that you may need to create a wallet first.)
To keep the mining ongoing from there, aiming for blocks arriving every 10 minutes on average, we can run:
$ ../contrib/signet/miner --cli="./bitcoin-cli -datadir=$datadir" generate --address $ADDR --grind-cmd="./bitcoin-util grind" --nbits=$NBITS --ongoing
Next is to have your friends/colleagues/etc join the network by setting the
signetchallenge to the same as above, and connecting to your node.
A full example script can be found at https://en.bitcoin.it/wiki/Signet:Custom:Script