NFT sketching

implementation/contracts/deposit/DepositFunding.sol

@@ -23,6 +23,28 @@ library DepositFunding {
     using DepositLiquidation for DepositUtils.Deposit;
     using OutsourceDepositLogging for DepositUtils.Deposit;
 
+    function isLocked() returns (bool) {
+        return tbtcDrawn == 0;
+    }
+
+    function draw(uint amt) {
+        require(amt == 1 tbtc, "partial draw not permitted");
+        mintTbtc(msg.sender, amt);
+        drawn += amt;
+    }
+
+    function repay(uint amt) {
+        require(amt == 1 tbtc, "partial repay not permitted");
+        burnTbtc(msg.sender, amt);
+        drawn -= amt;
+    }
+
+    function setLocked(bool _locked) {
+        require(msg.sender == depositNft.ownerOf(this), "must be beneficiary");
+        require(drawn == 0, "deposit must be fully paid in tbtc");
+        locked = _locked;
+    }
+
     /// @notice     Deletes state after funding
     /// @dev        This is called when we go to ACTIVE or setup fails without fraud
     function fundingTeardown(DepositUtils.Deposit storage _d) public {

implementation/contracts/deposit/DepositRedemption.sol

@@ -71,6 +71,9 @@ library DepositRedemption {
         bytes8 _outputValueBytes,
         bytes20 _requesterPKH
     ) public {
+        if(_d.isLocked()) {
+            require(msg.sender == _d.beneficiary());
+        }
         require(_d.inRedeemableState(), "Redemption only available from Active or Courtesy state");
         require(_requesterPKH != bytes20(0), "cannot send value to zero pkh");
 

implementation/contracts/deposit/DepositUtils.sol

@@ -56,6 +56,9 @@ library DepositUtils {
         /// @dev Holds a timestamp from the moment when the transaction digest
         /// was approved for signing
         mapping (bytes32 => uint256) approvedDigests;
+
+        // Stateful locking mechanism
+        uint drawn; // amount of tbtc drawn from deposit
     }
 
     /// @notice         Gets the current block difficulty

implementation/contracts/system/VendingMachine.sol

@@ -0,0 +1,19 @@
+contract VendingMachine {
+	function isQualified(deposit, proof) {
+		// check deposit qualified	
+		totalValue = 0
+		unqualifiedDeposits = [...]
+		for deposit in unqualifiedDeposits:
+			totalValue += deposit.lotSize
+
+		blockReward = 12.5
+		minBlocksX = totalValue / blockReward
+
+		proof = verifyProof(proof)
+
+		// qualifier = 6 + n
+		// where 6 is the minimum number of confs to mint tbtc and
+		//       n is the security margin that fluctuates according to opened deposit volume
+		require(proof.blocks >= Math.min(6, minBlocksX));
+	}
+}