R4D mixer script example

ride4dapps/mixer/README.md

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+# R4D Mixer
+This is an example of the crypto coins mixer
+
+1. A user can send money with an arbitrary Blake2b256 hash
+2. After that, anyone with address matching that hash and knowing how much bytes of address used can take the money back
+
+Try now: https://mixer.waves.today (Requires Waves Keeper with InvokeScript support **in TESTNET mode**)
+
+# Example
+1. Taken destination address is `3Musn2zFuw3G71yg6G7PDRAq7CjWxK7Z4pk` and complexity is 3, caller takes first 3 and last 3 bytes of it: `3Mu + 4pk`, hashes it with Blake2b256 and invokes `deposit(hash)` with attached Waves payment
+2. Then owner of `3Musn2zFuw3G71yg6G7PDRAq7CjWxK7Z4pk` invokes `withdraw(3)`, script compares his address with stored hash and withdraws all money associated with it
+3. You can tune complexity from 1 to 9
+    1. With low complexity everyone can generate address that matches the resulting hash, but then no one can prove that you took the money
+    2. So with complexity = 9 address should match exactly, and it's safe but there is no [plausible deniability](https://en.wikipedia.org/wiki/Plausible_deniability)

ride4dapps/mixer/mixer.ride

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+{-# STDLIB_VERSION 3 #-}
+{-# CONTENT_TYPE DAPP #-}
+{-# SCRIPT_TYPE ACCOUNT #-}
+
+let FeePercent = 1
+
+@Callable(i)
+func deposit(hash: ByteVector) = {
+   let pmt = extract(i.payment)
+   if (isDefined(pmt.assetId) || pmt.amount < 100) then throw("can hold waves only at the moment")
+   else {
+        let currentKey = toBase58String(hash)
+        let currentAmount = match getInteger(this, currentKey) {
+            case a:Int => a
+            case _ => 0
+        }
+        let fee = pmt.amount * FeePercent / 100
+        let newAmount = currentAmount + pmt.amount - fee
+        WriteSet([DataEntry(currentKey, newAmount)])
+   }
+}
+
+@Callable(i)
+func withdraw(complexity: Int) = {
+    let currentKey = toBase58String(blake2b256(take(drop(i.caller.bytes, 2), complexity) + takeRight(i.caller.bytes, complexity)))
+    let amount = match getInteger(this, currentKey) {
+        case a:Int => a
+        case _ => 0
+    }
+    if (amount <= 0)
+        then throw("Can't withdraw negative amount")
+    else ScriptResult(
+        WriteSet([DataEntry(currentKey, 0)]),
+        TransferSet([ScriptTransfer(i.caller, amount, unit)])
+    )
+}

ride4dapps/mixer/mixer_test.js

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+describe('Mixer test', () => {
+     const dappAddress = "3MwmaLMtWTaTyjhzywLLRQa4BH1PYZdvpKy"
+
+      const hash = "8N5gCoRKcCD4BxJNGn2kKUzMBieetEh4r7DUMHa1m2gq"
+
+      it('Deposit funds', async function(){
+         const tx = invokeScript({ fee: 900000, dApp: dappAddress, call:{function:"deposit",args:[{"type": "binary", "value": hash}]},
+             payment: [{amount: 1000000, assetId: null}]})
+         await broadcast(tx)
+         await waitForTx(tx.id)
+     })
+ })