Initially I tried doing this using caravan but had some issues:
Later, created a 2of3 multisig on electrum to do it. Assume there are 3 people and have access to 3 different wallets. Peer 1 and Peer 2 will do this transaction to pay Peer 3.
Peer 3 — Darknet Vendor
Peer 2 — Random Person Online
Peer 1 — Random Person Online or Someone you trust or A tumbler with multisig escrow
Lets say Peer 2 wants to buy something from Darknet and have to pay $100 for it
Peer 2 plans to send BTC to this guy (Peer 3) in installments on different addresses at different times or add to wallet of a DNM
Assumption: Peer 1 has one UTXO of 0.05 BTC after coinjoin and Peer 2 has one UTXO of 0.01 BTC after mix. These amounts are sent to multisig address: tb1qe58m5m3zwpufsq8fm5ajn4jnr7nmam9p22v7mxwdd670fgaewjuqfms834 in two different transactions involving 122 bytes of tx size and fee paid at 1 sat/byte. Next, transaction involves 11 outputs as shown below:
Since we are using CPFP in this setup, we can either do it for few transactions or all. Its not easy to achieve it with tBTC as 1 sat/byte transactions get confirmed soon on testnet however possible with BTC. We did 3 transactions and 2 of them confirmed in same block 1661561. Looking at the transactions, its difficult to predict how many people are involved and who paid for this transaction and what amount.
Imagine a chain of such mixing from one multisig to another and payment reaches ultimately to darknet vendor.
You can think of endless combinations of multisig and partial or full CPFP in the whole setup and different fees each time you do it.
Transaction: https://blockstream.info/testnet/tx/c59eda7dbb08ab799a97d11674f223e165d9566dfd6fe7e8f15b4f4cef089b83
This was just a POC transaction and will look to automate this process, build few setups, experiment more with caravan and PSBT transactions in next few months.
If you have any suggestions please let me know.
