Overview of Privacy Transactions

Privacy transactions on Wanchain are a way for a user to send WAN to another user without specifying who is the recipient. With a privacy transaction the world can see that a user made a transaction, and upon a deeper inspection of the transaction can see how much WAN was sent in the transaction, but the world cannot see who the recipient will be. The world, however, may be able to make an educated guess at who is the recipient, depending on some factors that we’ll discuss below.

Privacy transactions are carried out on Wanchain by way of a smart contract built into the protocol. The smart contract resides at the following hard-coded address, and has the following ABI.

Privacy Contract Address

0x0000000000000000000000000000000000000064

Privacy Contract ABI

[{"constant":false,"type":"function","stateMutability":"nonpayable","inputs":[{"name":"OtaAddr","type":"string"},{"name":"Value","type":"uint256"}],"name":"buyCoinNote","outputs":[{"name":"OtaAddr","type":"string"},{"name":"Value","type":"uint256"}]},{"constant":false,"type":"function","inputs":[{"name":"RingSignedData","type":"string"},{"name":"Value","type":"uint256"}],"name":"refundCoin","outputs":[{"name":"RingSignedData","type":"string"},{"name":"Value","type":"uint256"}]},{"constant":false,"inputs":[],"name":"getCoins","outputs":[{"name":"Value","type":"uint256"}]}]

Transaction Workflow

Unlike a regular transaction, which involves a single transaction on the blockchain that transfers the account balance, a privacy transaction consists of two underlying transactions: a lock (buyCoinNote) transaction made by the sender, which locks the WAN with the privacy smart contract, and a redeem (refundCoin) transaction made by the recipient, which transfers the WAN from the smart contract to the recipient.

When a user locks WAN in the privacy smart contract, it is not possible to see who the intended recipient is. This is because the lock transaction does not contain the recipient’s address within the transaction call data, but instead only contains ring signature data from the recipient’s one-time address. Thus, while we can see transactions that lock funds into the privacy contract, and other transactions that redeem funds from the privacy contract, we cannot link any lock and redeem transactions by anything other than value.

Allowed Transaction Amounts

Hypothetically, if a user were to lock 427 WAN into the privacy smart contract, and then soon after another user were to redeem 427 WAN from the contract, it would be fairly obvious that the two transactions were linked. Transaction values accordingly can reveal connections between senders and recipients. For this reason, the privacy contract was made to only allow certain values to be locked for a given privacy transaction.

Allowed amounts:

• 10 WAN
• 20
• 50
• 100
• 200
• 500
• 1000
• 5000
• 50000

When locking funds into the privacy contract, a user can thus only lock an amount in the list above. Likewise, a user cannot redeem partial amounts, but must redeem the full amount that was locked to the one-time address.