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BallotVerification.md

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Ballot Verification

This process will allow you to verify your ballot was constructed and cast as intended.

From the voting site, you should have details like these:

var ballotEncPk = "14108a8f844f506d91daedfd3542425bd5b4e2b1b3e7d959a2344907689dea7e";
var myPubkey = "3687cd75e4415e4b126583751b66c8a3b17eaf8eaaa0754a4638452d5602ce4c";
var mySeckey = "e314013176e70a9cc4b46c96b93115ade6ec66843cdba1fb23544345683c9b9b";
var myDelegate = "0x9999999999999999999999999999999999999999";
var myVotesRaw = [1,3,-3,0];
var myVotesOffset = [4,6,0,3];
var encBallot = "0325252d3e6bd1b7e5bf085096bb07e3132d114623e123d9ebd48d411fb65ad2";
var submitBallotPrefix = "13c04769";
var txData = "0x13c047690325252d3e6bd1b7e5bf085096bb07e3132d114623e123d9ebd48d411fb65ad23687cd75e4415e4b126583751b66c8a3b17eaf8eaaa0754a4638452d5602ce4c";
var votingContract = "0x2Bb10945E9f0C9483022dc473aB4951BC2a77d0f";

Deterministically validating your ballot

The above information has everything you need to verify your ballot was constructed honestly.

We're going to go through a number of steps that transform your ballot from what you intend it to be, into the data structure recorded in the blockchain.

To follow along, you'll need to have node js installed, and install a few libraries:

  • mkdir -p ballotVerification && cd ballotVerification
  • npm install js-nacl ramda

Next, open a node REPL by running node and import js-nacl. Copy in and run these commands:

var jsNacl = require('js-nacl')
var R = require('ramda')
var nacl; jsNacl.instantiate(_nacl => { nacl = _nacl; })

Finally, paste in the variables you received from the SWM Release Schedule voting site.

Now you're ready to go.

1. Offset your raw votes

Each vote you cast is in the range [-3, 3], but that's a bit annoying to store (worrying about signs and all that) so instead we translate each vote to the range [0, 6] by adding 3 to each vote.

This is done for you in the above list of variables: myVotesRaw are the original votes, and myVotesOffset are the translated votes.

2. Convert the offset votes to binary

Next, we need to convert your offset votes to binary. We can use the following table for this:

  • 0 -> "000"
  • 1 -> "001"
  • 2 -> "010"
  • 3 -> "011"
  • 4 -> "100"
  • 5 -> "101"
  • 6 -> "110"

Run in node:

binaryVotes = R.map(v => {
    var b = v.toString(2);
    return R.join('', R.repeat('0', 3 - b.length)) + b;
}, myVotesOffset)

3. Concatenate your votes

We need to move all your votes into one string. The way we do this is by concatenating them in order.

If your votes were [1, 3, -3, 0] (and therefore [4,6,0,3] when offset) then your binary representation would be ['100', '110', '000', '011'].

We then concatenate these into one string: '100110000011'

Run in node:

binVotesUnpadded = R.join('', binaryVotes)

4. Pad right with 0s

We're going to take this string of 12 bits and transform it into 2 bytes, for that we need 16 bits total.

Add 4 0s to the right of your string: '1001100000110000'

binVotes = binVotesUnpadded + R.join('', R.repeat('0', 16 - binVotesUnpadded.length))

5. Convert to bytes

We need to convert this bit-string to bytes.

Following our example:

  • '1001100000110000' becomes ['10011000', '00110000']
  • ['10011000', '00110000'] becomes [0x98, 0x30] (which is [152, 48] in decimal)
voteBytes = R.map(bStr => parseInt(bStr, 2), R.splitAt(8, binVotes))

6. Take the left-most 14 bytes of your delegate address

If you haven't selected a delegate then your delegate address is set to 0x9999999999999999999999999999999999999999. This is okay, since nobody can ever own the account 0x9999999999999999999999999999999999999999 (or, if they did then Ethereum's entire security model would be broken). This works the same for any arbitrarily (or randomly) chosen address, like 0x0000000000000000000000000000000000000000, or 0x1111111111111111111111111111111111111111.

In our example, '0x9999999999999999999999999999999999999999' becomes '9999999999999999999999999999'

delegatePrefix = R.take(14*2, R.drop(2, myDelegate))

7. Calculate the ballot plaintext

We have everything we need to create your unencrypted ballot now.

In our example we woudl end up with '98309999999999999999999999999999'

ballotPlaintext = nacl.to_hex(voteBytes) + delegatePrefix

8. Calculate your encryption nonce

Using Curve25519 through the NaCl library requires using a nonce during encryption. To avoid including an extra 24 bytes with your ballot unnecessarily, we use something we can generate from data we already have: your public key. Since we're only going to use the curve25519 key pair we generated just for one ballot, this is okay, since we're going to throw away the key pair after we're done voting.

nonce = nacl.to_hex(nacl.crypto_hash_sha256(nacl.from_hex(myPubkey)).slice(0, 24))

This will generate a Uint8Array so won't look like hex anymore.

9. Encrypt your ballot

Now we need to encrypt your ballot:

generatedEncBallot = nacl.to_hex(nacl.crypto_box.apply(null, R.map(nacl.from_hex, [ballotPlaintext, nonce, ballotEncPk, mySeckey])))

This will give you a 32 byte encrypted ballot.

You can verify this matches what the voting UI generated with:

encBallot == generatedEncBallot

(this should equal true)

10. Generate transaction data

Next, we'll confirm the transaction data we broadcast to Ethereum was accurate:

generatedTxData = "0x" + submitBallotPrefix + generatedEncBallot + myPubkey

Again, we can verify this matches our transaction with:

txData == generatedTxData

Which should once again equal true

11. Double check this matches what you broadcast to the ethereum network

At this point you should look up your transaction via etherscan.io or your preferred Ethereum block explorer.

Copy your input data into node to confirm:

var dataInEthereum = "YOUR TX DATA HERE"
dataInEthereum == generatedTxData

If this returns true then you can be 100% sure your ballot was generated and recorded honestly and accurately.