Atomic Swaps

In order to do an atomic swap with someone, you will first have to agree on what tokens you wish to swap. For example, let’s say you want to swap 40 ANON for your counterparty’s 20 DAWN. You can do this tutorial with a real counterparty or with yourself. This tutorial assumes the counterparty is yourself, but we will indicate which steps differ so you should be able to do the tutorial with a real counterparty as well.

The swap uses one coin per party so the counterparty only sees the single coin you’re using, not your other coins.

Note: A “coin” is a single cryptographic record. Your wallet balance is the sum of all coins you own, and each coin must be spent entirely.

You must use a coin worth the exact amount you want to swap. To create a smaller coin denomination, send yourself the amount you want to swap. Then check you have a spendable coin to swap with. Note that the coin overview might look very different depending on your activity:

drk> wallet coins

 Coin            | Spent | Token ID        | Aliases | Value                    | Spend Hook | User Data | Spent TX
-----------------+-------+-----------------+---------+--------------------------+------------+-----------+-----------------
 EGV6rS...pmmm6H | true  | 241vAN...KcLssb | DRK     | 2000000000 (20)          | -          | -         | fbbd7a...5f2b19
...
 H6Bc49...Zb6k8h | false | {TOKEN2}        | DAWN    | 2000000000 (20)          | -          | -         | -
 47QnyR...1T7igm | true  | {TOKEN1}        | ANON    | 4269000000 (42.69)       | -          | -         | 47b481...b07395
 5UUJbH...trdQHY | false | {TOKEN1}        | ANON    | 4000000000 (40)          | -          | -         | -
 EEneNB...m6mxTC | false | 241vAN...KcLssb | DRK     | 1999442971 (19.97253683) | -          | -         | -

You’ll have to initiate the swap and build your half of the swap tx:

drk> otc init 40.0:20.0 ANON:DAWN > half_swap

Then you can send this half_swap file to the counterparty and they can create the other half and sign it by running:

drk> otc join < half_swap > full_swap

The counterparty can now send it back to you. Finally, to make the swap transaction valid, you need to sign it as well.

Note: If you are doing this tutorial by yourself, you don’t need to send the half_swap or full_swap file anywhere, and can just create the full_swap followed by the signed_swap directly.

drk> otc sign < full_swap > signed_swap

Now that the swap is signed, one of the parties (or a third one) must attach the corresponding fee:

drk> attach-fee < signed_swap > full_swap_with_fee

Since a new call has been added to the transaction, both parties must re-sign the full_swap_with_fee file, one by one.

Party A:

drk> otc sign < full_swap_with_fee > signed_full_swap_with_fee

Party B:

drk> otc sign < signed_full_swap_with_fee > swap.tx

Now the complete swap transaction can be broadcast:

drk> broadcast < swap.tx

[mark_tx_spend] Processing transaction: d2a5e288e6ba44583ee12db9c7a0ed154c736d1aa841d70c7d3fa121c92dfc69
[mark_tx_spend] Found Money contract in call 0
[mark_tx_spend] Found Money contract in call 1
Broadcasting transaction...
Transaction ID: d2a5e288e6ba44583ee12db9c7a0ed154c736d1aa841d70c7d3fa121c92dfc69

On success, you should see a transaction ID. This transaction will now be in the mempool, and you should wait until it’s confirmed.

After a while you should see the change in balances in your wallet:

drk> wallet balance

 Token ID                                     | Aliases | Balance
----------------------------------------------+---------+-------------
 241vANigf1Cy3ytjM1KHXiVECxgxdK4yApddL8KcLssb | DRK     | 19.96835727
 {TOKEN1}                                     | ANON    | 40
 {TOKEN2}                                     | DAWN    | 20

Since in this example we did an atomic swap with ourself, the balances are unchanged. We can confirm it actually happened successfully by checking our coins:

drk> wallet coins

 Coin            | Spent | Token ID        | Aliases | Value                    | Spend Hook | User Data | Spent TX
-----------------+-------+-----------------+---------+--------------------------+------------+-----------+-----------------
 EGV6rS...pmmm6H | true  | 241vAN...KcLssb | DRK     | 2000000000 (20)          | -          | -         | fbbd7a...5f2b19
...
 EEneNB...m6mxTC | true  | 241vAN...KcLssb | DRK     | 1999442971 (19.97253683) | -          | -         | d2a5e2...2dfc69
 H6Bc49...Zb6k8h | true  | {TOKEN2}        | DAWN    | 2000000000 (20)          | -          | -         | d2a5e2...2dfc69
 5UUJbH...trdQHY | true  | {TOKEN1}        | ANON    | 4000000000 (40)          | -          | -         | d2a5e2...2dfc69
 4zwzZf...uMbVir | false | {TOKEN2}        | DAWN    | 2000000000 (20)          | -          | -         | -
 BrqQuk...FcwW6d | false | {TOKEN1}        | ANON    | 4000000000 (40)          | -          | -         | -
 EEneNB...m6mxTC | false | 241vAN...KcLssb | DRK     | 1999442971 (19.96834924) | -          | -         | -

Here you can see there are two entries for the tokens we used in the swap: 40.00 ANON and 20.00 DAWN . The first entry shows the Spent flag as true and the second entry shows the Spent flag as false. This means the transaction was successful. Since we are swapping with ourself, we successfully spent the coins in the first half of the transaction, and re-minted them to ourselves in the second half of the transaction.

If you’re testing atomic swaps with a counterparty and you can see their tokens, that means the swap was successful. In case you still see your old tokens, that could mean that the swap transaction has not yet been confirmed.