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Clique signing

Last edited on December 20, 2022

Clique is a proof-of-authority system where new blocks can be created by authorized ‘signers’ only. The initial set of authorized signers is configured in the genesis block. Signers can be authorized and de-authorized using a voting mechanism, thus allowing the set of signers to change while the blockchain operates. Signing blocks in Clique networks classically uses the "unlock" feature of Geth so that each node is always ready to sign without requiring a user to manually provide authorization.

However, using the --unlock flag is generally a highly dangerous thing to do because it is indiscriminate, i.e. if an account is unlocked and an attacker obtains access to the RPC api, the attacker can sign anything without supplying a password.

Clef provides a way to safely circumvent --unlock while maintaining a enough automation for the network to be useable.

Prerequisites

It is useful to have basic knowledge of private networks and Clef. These topics are covered on our private networks and Introduction to Clef pages.

Prepping a Clique network

First of all, set up a rudimentary testnet to have something to sign. Create a new keystore (password testtesttest)

$ geth account new --datadir ./ddir INFO [06-16|11:10:39.600] Maximum peer count ETH=50 LES=0 total=50 Your new account is locked with a password. Please give a password. Do not forget this password. Password: Repeat password: Your new key was generated Public address of the key: 0x9CD932F670F7eDe5dE86F756A6D02548e5899f47 Path of the secret key file: ddir/keystore/UTC--2022-06-16T09-10-48.578523828Z--9cd932f670f7ede5de86f756a6d02548e5899f47 - You can share your public address with anyone. Others need it to interact with you. - You must NEVER share the secret key with anyone! The key controls access to your funds! - You must BACKUP your key file! Without the key, it's impossible to access account funds! - You must REMEMBER your password! Without the password, it's impossible to decrypt the key!

Create a genesis with that account as a sealer:

{
  "config": {
    "chainId": 15,
    "homesteadBlock": 0,
    "eip150Block": 0,
    "eip155Block": 0,
    "eip158Block": 0,
    "byzantiumBlock": 0,
    "constantinopleBlock": 0,
    "petersburgBlock": 0,
    "clique": {
      "period": 30,
      "epoch": 30000
    }
  },
  "difficulty": "1",
  "gasLimit": "8000000",
  "extradata": "0x00000000000000000000000000000000000000000000000000000000000000009CD932F670F7eDe5dE86F756A6D02548e5899f470000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  "alloc": {
    "0x9CD932F670F7eDe5dE86F756A6D02548e5899f47": {
      "balance": "300000000000000000000000000000000"
    }
  }
}

Initiate Geth:

$ geth  --datadir ./ddir init genesis.json
... INFO [06-16|11:14:54.123] Writing custom genesis block INFO [06-16|11:14:54.125] Persisted trie from memory database nodes=1 size=153.00B time="64.715µs" gcnodes=0 gcsize=0.00B gctime=0s livenodes=1 livesize=0.00B INFO [06-16|11:14:54.125] Successfully wrote genesis state database=lightchaindata hash=187412..4deb98

At this point a Geth has been initiated with a genesis configuration.

Prepping Clef

In order to make use of clef for signing:

  1. Ensure clef knows the password for the keystore.
  2. Ensure clef auto-approves clique signing requests.

These two things are independent of each other. First of all, however, clef must be initiated (for this example the password is clefclefclef)

$ clef --keystore ./ddir/keystore --configdir ./clef --chainid 15 --suppress-bootwarn init
The master seed of clef will be locked with a password. Please specify a password. Do not forget this password! Password: Repeat password: A master seed has been generated into clef/masterseed.json This is required to be able to store credentials, such as: * Passwords for keystores (used by rule engine) * Storage for JavaScript auto-signing rules * Hash of JavaScript rule-file You should treat 'masterseed.json' with utmost secrecy and make a backup of it! * The password is necessary but not enough, you need to back up the master seed too! * The master seed does not contain your accounts, those need to be backed up separately!

After this operation, clef has it's own vault where it can store secrets and attestations.

Storing passwords in clef

With that done, clef can be made aware of the password. To do this setpw <address> is invoked to store a password for a given address. clef asks for the password, and it also asks for the master-password, in order to update and store the new secrets inside the vault.

$ clef --keystore ./ddir/keystore --configdir ./clef --chainid 15 --suppress-bootwarn setpw 0x9CD932F670F7eDe5dE86F756A6D02548e5899f47
Please enter a password to store for this address: Password: Repeat password: Decrypt master seed of clef Password: INFO [06-16|11:27:09.153] Credential store updated set=0x9CD932F670F7eDe5dE86F756A6D02548e5899f47

At this point, if Clef is used as a sealer, each block would require manual approval, but without needing to provide the password.

Testing stored password

To test that the stored password is correct and being properly handled by Clef, first start clef:

$ clef --keystore ./ddir/keystore --configdir ./clef --chainid 15 --suppress-bootwarn

then start Geth:

$ geth  --datadir ./ddir --signer ./clef/clef.ipc --mine

Geth will ask what accounts are present - enter y to approve:

-------- List Account request-------------- A request has been made to list all accounts. You can select which accounts the caller can see [x] 0x9CD932F670F7eDe5dE86F756A6D02548e5899f47 URL: keystore:///home/user/tmp/clique_clef/ddir/keystore/UTC--2022-06-16T09-10-48.578523828Z--9cd932f670f7ede5de86f756a6d02548e5899f47 ------------------------------------------- Request context: NA - ipc - NA Additional HTTP header data, provided by the external caller: User-Agent: "" Origin: "" Approve? [y/N]: > y DEBUG[06-16|11:36:42.499] Served account_list reqid=2 duration=3.213768195s

After this, Geth will start asking clef to sign things:

-------- Sign data request-------------- Account: 0x9CD932F670F7eDe5dE86F756A6D02548e5899f47 [chksum ok] messages: Clique header [clique]: "clique header 1 [0x9b08fa3705e8b6e1b327d84f7936c21a3cb11810d9344dc4473f78f8da71e571]" raw data: "\xf9\x02\x14\xa0\x18t\x12:\x91f\xa2\x90U\b\xf9\xac\xc02i\xffs\x9f\xf4\xc9⮷!\x0f\x16\xaa?#M똠\x1d\xccM\xe8\xde\xc7]z\xab\x85\xb5g\xb6\xcc\xd4\x1a\xd3\x12E\x1b\x94\x8at\x13\xf0\xa1B\xfd@ԓG\x94\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xa0]1%\n\xfc\xee'\xd0e\xce\xc7t\xcc\\?\t4v\x8f\x06\xcb\xf8\xa0P5\xfeN\xea\x0ff\xfe\x9c\xa0V\xe8\x1f\x17\x1b\xccU\xa6\xff\x83E\xe6\x92\xc0\xf8n[H\xe0\x1b\x99l\xad\xc0\x01b/\xb5\xe3c\xb4!\xa0V\xe8\x1f\x17\x1b\xccU\xa6\xff\x83E\xe6\x92\xc0\xf8n[H\xe0\x1b\x99l\xad\xc0\x01b/\xb5\xe3c\xb4!\xb9\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x01\x83z0\x83\x80\x84b\xaa\xf9\xaa\xa0\u0603\x01\n\x14\x84geth\x88go1.18.1\x85linux\x00\x00\x00\x00\x00\x00\x00\xa0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x88\x00\x00\x00\x00\x00\x00\x00\x00" data hash: 0x9589ed81e959db6330b3d70e5f8e426fb683d03512f203009f7e41fc70662d03 ------------------------------------------- Request context: NA -> ipc -> NA Additional HTTP header data, provided by the external caller: User-Agent: "" Origin: "" Approve? [y/N]: > y

And indeed, after approving with y, the password is not required - the signed block is returned to Geth:

INFO [06-16|11:36:46.714] Successfully sealed new block number=1 sealhash=9589ed..662d03 hash=bd20b9..af8b87 elapsed=4.214s

This mode of operation offers quite a poor UX because each block to be sealed requires manual approval. That is fixed in the following section.

Using rules to approve blocks

Clef rules allow a piece of Javascript take over the Approve/Deny decision. The Javascript snippet has access to the same information as the manual operator.

The first approach, which approves listing, and returns the request data for ApproveListing, is demonstrated below:

function ApproveListing() {
  return 'Approve';
}

function ApproveSignData(r) {
  console.log('In Approve Sign data');
  console.log(JSON.stringify(r));
}

In order to use a certain ruleset, it must first be 'attested'. This is to prevent someone from modifying a ruleset-file on disk after creation.

$ clef --keystore ./ddir/keystore --configdir ./clef --chainid 15 --suppress-bootwarn  attest  `sha256sum rules.js | cut -f1`

which returns:

Decrypt master seed of clef Password: INFO [06-16|13:49:00.298] Ruleset attestation updated sha256=54aae496c3f0eda063a62c73ee284ca9fae3f43b401da847ef30ea30e85e35d1

And clef can be started, pointing out the rules.js file.

$ clef --keystore ./ddir/keystore --configdir ./clef --chainid 15  --suppress-bootwarn  --rules ./rules.js

Once Geth starts asking clef to seal blocks, the data will be displayed. From that data, rules can be defined that allow signing clique headers but nothing else.

The actual data that gets passed to the js environment (and which the ruleset display in the terminal) looks as follows:

{
  "content_type": "application/x-clique-header",
  "address": "0x9CD932F670F7eDe5dE86F756A6D02548e5899f47",
  "raw_data": "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",
  "messages": [
    {
      "name": "Clique header",
      "value": "clique header 2 [0xae525b65bc7f711bc136f502650039cd6959c3abc28fdf0ebfe2a5f85c92f3b6]",
      "type": "clique"
    }
  ],
  "call_info": null,
  "hash": "0x8ca6c78af7d5ae67ceb4a1e465a8b639b9fbdec4b78e4d19cd9b1232046fbbf4",
  "meta": {
    "remote": "NA",
    "local": "NA",
    "scheme": "ipc",
    "User-Agent": "",
    "Origin": ""
  }
}

To create an extremely trustless ruleset, the raw_data could be verified to ensure it has the right rlp structure for a Clique header:

 echo "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" | base64 -d | rlpdump
[
  bd20b98fbaea3669cd9875c035f84a2ff2717e330fc150a85ff5029cbfaf8b87,
  1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347,
  0000000000000000000000000000000000000000,
  5d31250afcee27d065cec774cc5c3f0934768f06cbf8a05035fe4eea0f66fe9c,
  56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421,
  56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421,
  00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000,
  02,
  02,
  7a4f0e,
  "",
  62ab18d6,
  d883010a14846765746888676f312e31382e31856c696e757800000000000000,
  0000000000000000000000000000000000000000000000000000000000000000,
  0000000000000000,
]

However, messages could also be used. They do not come from the external caller, but are generated inernally: clef parsed the incoming request and verified the Clique wellformedness of the content. The following simply checks for such a message:

function OnSignerStartup(info) {}

function ApproveListing() {
  return 'Approve';
}

function ApproveSignData(r) {
  if (r.content_type == 'application/x-clique-header') {
    for (var i = 0; i < r.messages.length; i++) {
      var msg = r.messages[i];
      if (msg.name == 'Clique header' && msg.type == 'clique') {
        return 'Approve';
      }
    }
  }
  return 'Reject';
}

Attest the ruleset:

$ clef --keystore ./ddir/keystore --configdir ./clef --chainid 15 --suppress-bootwarn  attest  `sha256sum rules.js | cut -f1`

returning

Decrypt master seed of clef Password: INFO [06-16|14:18:53.476] Ruleset attestation updated sha256=7d5036d22d1cc66599e7050fb1877f4e48b89453678c38eea06e3525996c2379

Run clef:

$ clef --keystore ./ddir/keystore --configdir ./clef --chainid 15  --suppress-bootwarn  --rules ./rules.js

Run Geth:

$ geth  --datadir ./ddir --signer ./clef/clef.ipc --mine

And clef should now happily sign blocks:

DEBUG[06-16|14:20:02.136] Served account_version reqid=1 duration="131.38µs" INFO [06-16|14:20:02.289] Op approved DEBUG[06-16|14:20:02.289] Served account_list reqid=2 duration=4.672441ms INFO [06-16|14:20:02.303] Op approved DEBUG[06-16|14:20:03.450] Served account_signData reqid=3 duration=1.152074109s INFO [06-16|14:20:03.456] Op approved DEBUG[06-16|14:20:04.267] Served account_signData reqid=4 duration=815.874746ms INFO [06-16|14:20:32.823] Op approved DEBUG[06-16|14:20:33.584] Served account_signData reqid=5 duration=766.840681ms

Refinements

If an attacker find the Clef "external" interface (which would only happen if you start it with http enabled), they

  • cannot make it sign arbitrary transactions,
  • cannot sign arbitrary data message,

However, they could still make it sign e.g. 1000 versions of a certain block height, making the chain very unstable.

It is possible for rule execution to be stateful (i.e. storing data). In this case, one could, for example, store what block heights have been sealed and reject sealing a particular block height twice. In other words, these rules could be used to build a miniature version of an execution layer slashing-db.

The clique header 2 [0xae525b65bc7f711bc136f502650039cd6959c3abc28fdf0ebfe2a5f85c92f3b6] line is split, and the number stored using storage.get and storage.put:

function OnSignerStartup(info) {}

function ApproveListing() {
  return 'Approve';
}

function ApproveSignData(r) {
  if (r.content_type != 'application/x-clique-header') {
    return 'Reject';
  }
  for (var i = 0; i < r.messages.length; i++) {
    var msg = r.messages[i];
    if (msg.name == 'Clique header' && msg.type == 'clique') {
      var number = parseInt(msg.value.split(' ')[2]);
      var latest = storage.get('lastblock') || 0;
      console.log('number', number, 'latest', latest);
      if (number > latest) {
        storage.put('lastblock', number);
        return 'Approve';
      }
    }
  }
  return 'Reject';
}

Running with this ruleset:

JS:> number 45 latest 44 INFO [06-16|22:26:43.023] Op approved DEBUG[06-16|22:26:44.305] Served account_signData reqid=3 duration=1.287465394s JS:> number 46 latest 45 INFO [06-16|22:26:44.313] Op approved DEBUG[06-16|22:26:45.317] Served account_signData reqid=4 duration=1.010612774s

This might be a bit over-the-top, security-wise, and may cause problems if, for some reason, a clique-deadlock needs to be resolved by rolling back and continuing on a side-chain. It is mainly meant as a demonstration that rules can use Javascript and statefulness to construct very intricate signing logic.

TLDR quick-version

Creation and attestation is a one-off event:

## Create the rules-file
cat << END > rules.js
function OnSignerStartup(info){}

function ApproveListing(){
  return "Approve"
}

function ApproveSignData(r){
  if (r.content_type == "application/x-clique-header"){
    for(var i = 0; i < r.messages.length; i++){
      var msg = r.messages[i]
      if (msg.name=="Clique header" && msg.type == "clique"){
        return "Approve"
      }
    }
  }
  return "Reject"
}
END
## Attest it, assumes clef master password is in `./clefpw`
clef --keystore ./ddir/keystore \
  --configdir ./clef --chainid 15 \
  --suppress-bootwarn --signersecret ./clefpw \
    attest  `sha256sum rules.js | cut -f1`

The normal startup command for clef:

clef --keystore ./ddir/keystore \
    --configdir ./clef --chainid 15  \
    --suppress-bootwarn --signersecret ./clefpw --rules ./rules.js

For Geth, the only change is to provide --signer <path to clef ipc>.

Summary

Clef can be used as a signer that automatically seals Clique blocks. This is a much more secure option than unlocking accounts using Geth's built-in account manager.

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