Half of fees get rewarded, half burnt. Minor cleanups

Update coinbase building and block summation to account for half of
the fees going to the coinbase. Forcing fees to be even as a
consequence. Now that we can't build the coinbase independently
from the block (because fees), had to update the miner to keep the
key derivation so a new derivation isn't made any time a new block
gets worked on.

Minor doc and warning cleanups.

chain/src/types.rs

@@ -16,7 +16,6 @@
 
 use std::io;
 
-use secp;
 use secp::pedersen::Commitment;
 
 use grin_store as store;

core/src/consensus.rs

@@ -26,6 +26,11 @@ use core::target::Difficulty;
 /// The block subsidy amount
 pub const REWARD: u64 = 1_000_000_000;
 
+/// Actual block reward for a given total fee amount
+pub fn reward(fee: u64) -> u64 {
+	REWARD + fee / 2
+}
+
 /// Number of blocks before a coinbase matures and can be spent
 pub const COINBASE_MATURITY: u64 = 1_000;
 

core/src/core/block.rs

@@ -20,7 +20,7 @@ use std::collections::HashSet;
 
 use core::Committed;
 use core::{Input, Output, Proof, TxKernel, Transaction, COINBASE_KERNEL, COINBASE_OUTPUT};
-use consensus::REWARD;
+use consensus::{REWARD, reward};
 use consensus::MINIMUM_DIFFICULTY;
 use core::hash::{Hash, Hashed, ZERO_HASH};
 use core::target::Difficulty;
@@ -42,6 +42,10 @@ pub enum Error {
 	/// The sum of output minus input commitments does not match the sum of
 	/// kernel commitments
 	KernelSumMismatch,
+	/// Same as above but for the coinbase part of a block, including reward
+	CoinbaseSumMismatch,
+	/// Kernel fee can't be odd, due to half fee burning
+	OddKernelFee,
 	/// Underlying Secp256k1 error (signature validation or invalid public
 	/// key typically)
 	Secp(secp::Error),
@@ -237,7 +241,7 @@ impl Committed for Block {
 		&self.outputs
 	}
 	fn overage(&self) -> i64 {
-		(self.total_fees() as i64) - (REWARD as i64)
+		((self.total_fees() / 2) as i64) - (REWARD as i64)
 	}
 }
 
@@ -264,7 +268,8 @@ impl Block {
 		pubkey: keychain::Identifier,
 	) -> Result<Block, keychain::Error> {
 
-		let (reward_out, reward_proof) = Block::reward_output(keychain, pubkey)?;
+		let fees = txs.iter().map(|tx| tx.fee).sum();
+		let (reward_out, reward_proof) = Block::reward_output(keychain, pubkey, fees)?;
 		let block = Block::with_reward(prev, txs, reward_out, reward_proof)?;
 		Ok(block)
 	}
@@ -278,6 +283,7 @@ impl Block {
 		reward_out: Output,
 		reward_kern: TxKernel,
 	) -> Result<Block, secp::Error> {
+
 		// note: the following reads easily but may not be the most efficient due to
 		// repeated iterations, revisit if a problem
 		let secp = Secp256k1::with_caps(secp::ContextFlag::Commit);
@@ -420,13 +426,18 @@ impl Block {
 	/// trees, reward, etc.
 	pub fn validate(&self, secp: &Secp256k1) -> Result<(), Error> {
 		self.verify_coinbase(secp)?;
-		self.verify_kernels(secp)?;
+		self.verify_kernels(secp, false)?;
 		Ok(())
 	}
 
 	/// Validate the sum of input/output commitments match the sum in kernels
 	/// and that all kernel signatures are valid.
-	pub fn verify_kernels(&self, secp: &Secp256k1) -> Result<(), Error> {
+	fn verify_kernels(&self, secp: &Secp256k1, skip_sig: bool) -> Result<(), Error> {
+		for k in &self.kernels {
+			if k.fee & 1 != 0 {
+				return Err(Error::OddKernelFee);
+			}
+		}
 		// sum all inputs and outs commitments
 		let io_sum = self.sum_commitments(secp)?;
 
@@ -440,8 +451,10 @@ impl Block {
 		}
 
 		// verify all signatures with the commitment as pk
-		for proof in &self.kernels {
-			proof.verify(secp)?;
+		if !skip_sig {
+			for proof in &self.kernels {
+				proof.verify(secp)?;
+			}
 		}
 		Ok(())
 	}
@@ -452,25 +465,21 @@ impl Block {
 	// * That the sum of blinding factors for all coinbase-marked outputs match
 	//   the coinbase-marked kernels.
 	fn verify_coinbase(&self, secp: &Secp256k1) -> Result<(), Error> {
-		let cb_outs = self.outputs
-			.iter()
-			.filter(|out| out.features.contains(COINBASE_OUTPUT))
-			.map(|o| o.clone())
-			.collect::<Vec<_>>();
-		let cb_kerns = self.kernels
-			.iter()
-			.filter(|k| k.features.contains(COINBASE_KERNEL))
-			.map(|k| k.clone())
-			.collect::<Vec<_>>();
+		let cb_outs = filter_map_vec!(self.outputs, |out| {
+			if out.features.contains(COINBASE_OUTPUT) { Some(out.commitment()) } else { None }
+		});
+		let cb_kerns = filter_map_vec!(self.kernels, |k| {
+			if k.features.contains(COINBASE_KERNEL) { Some(k.excess) } else { None }
+		});
 
-		// verifying the kernels on a block composed of just the coinbase outputs
-		// and kernels checks all we need
-		Block {
-			header: BlockHeader::default(),
-			inputs: vec![],
-			outputs: cb_outs,
-			kernels: cb_kerns,
-		}.verify_kernels(secp)
+		let over_commit = secp.commit_value(reward(self.total_fees()))?;
+		let out_adjust_sum = secp.commit_sum(cb_outs, vec![over_commit])?;
+
+		let kerns_sum = secp.commit_sum(cb_kerns, vec![])?;
+		if kerns_sum != out_adjust_sum {
+			return Err(Error::CoinbaseSumMismatch);
+		}
+		Ok(())
 	}
 
 	/// Builds the blinded output and related signature proof for the block
@@ -478,16 +487,15 @@ impl Block {
 	pub fn reward_output(
 		keychain: &keychain::Keychain,
 		pubkey: keychain::Identifier,
+		fees: u64,
 	) -> Result<(Output, TxKernel), keychain::Error> {
+
 		let secp = keychain.secp();
 
-		let msg = secp::Message::from_slice(&[0; secp::constants::MESSAGE_SIZE])?;
-		let sig = keychain.sign(&msg, &pubkey)?;
-		let commit = keychain.commit(REWARD, &pubkey)?;
-		let msg = secp::pedersen::ProofMessage::empty();
+		let commit = keychain.commit(reward(fees), &pubkey)?;
 		// let switch_commit = keychain.switch_commit(pubkey)?;
-
-		let rproof = keychain.range_proof(REWARD, &pubkey, commit, msg)?;
+		let msg = secp::pedersen::ProofMessage::empty();
+		let rproof = keychain.range_proof(reward(fees), &pubkey, commit, msg)?;
 
 		let output = Output {
 			features: COINBASE_OUTPUT,
@@ -495,9 +503,12 @@ impl Block {
 			proof: rproof,
 		};
 
-		let over_commit = try!(secp.commit_value(REWARD as u64));
+		let over_commit = secp.commit_value(reward(fees))?;
 		let out_commit = output.commitment();
-		let excess = try!(secp.commit_sum(vec![out_commit], vec![over_commit]));
+		let excess = secp.commit_sum(vec![out_commit], vec![over_commit])?;
+
+		let msg = secp::Message::from_slice(&[0; secp::constants::MESSAGE_SIZE])?;
+		let sig = keychain.sign(&msg, &pubkey)?;
 
 		let proof = TxKernel {
 			features: COINBASE_KERNEL,
@@ -529,7 +540,7 @@ mod test {
 	// utility producing a transaction that spends an output with the provided
 	// value and blinding key
 	fn txspend1i1o(v: u64, keychain: &Keychain, pk1: Identifier, pk2: Identifier) -> Transaction {
-		build::transaction(vec![input(v, pk1), output(3, pk2), with_fee(1)], &keychain)
+		build::transaction(vec![input(v, pk1), output(3, pk2), with_fee(2)], &keychain)
 			.map(|(tx, _)| tx)
 			.unwrap()
 	}
@@ -544,13 +555,13 @@ mod test {
 
 		let mut btx1 = tx2i1o();
 		let (mut btx2, _) = build::transaction(
-			vec![input(5, pk1), output(4, pk2.clone()), with_fee(1)],
+			vec![input(7, pk1), output(5, pk2.clone()), with_fee(2)],
 			&keychain,
 		).unwrap();
 
 		// spending tx2 - reuse pk2
 
-		let mut btx3 = txspend1i1o(4, &keychain, pk2.clone(), pk3);
+		let mut btx3 = txspend1i1o(5, &keychain, pk2.clone(), pk3);
 		let b = new_block(vec![&mut btx1, &mut btx2, &mut btx3], &keychain);
 
 		// block should have been automatically compacted (including reward
@@ -572,12 +583,12 @@ mod test {
 		let mut btx1 = tx2i1o();
 
 		let (mut btx2, _) = build::transaction(
-			vec![input(5, pk1), output(4, pk2.clone()), with_fee(1)],
+			vec![input(7, pk1), output(5, pk2.clone()), with_fee(2)],
 			&keychain,
 		).unwrap();
 
 		// spending tx2 - reuse pk2
-		let mut btx3 = txspend1i1o(4, &keychain, pk2.clone(), pk3);
+		let mut btx3 = txspend1i1o(5, &keychain, pk2.clone(), pk3);
 
 		let b1 = new_block(vec![&mut btx1, &mut btx2], &keychain);
 		b1.validate(&keychain.secp()).unwrap();
@@ -632,13 +643,13 @@ mod test {
 
 		assert_eq!(
 			b.verify_coinbase(&keychain.secp()),
-			Err(Error::KernelSumMismatch)
+			Err(Error::CoinbaseSumMismatch)
 		);
-		assert_eq!(b.verify_kernels(&keychain.secp()), Ok(()));
+		assert_eq!(b.verify_kernels(&keychain.secp(), false), Ok(()));
 
 		assert_eq!(
 			b.validate(&keychain.secp()),
-			Err(Error::KernelSumMismatch)
+			Err(Error::CoinbaseSumMismatch)
 		);
 	}
 
@@ -656,7 +667,7 @@ mod test {
 			b.verify_coinbase(&keychain.secp()),
 			Err(Error::Secp(secp::Error::IncorrectCommitSum))
 		);
-		assert_eq!(b.verify_kernels(&keychain.secp()), Ok(()));
+		assert_eq!(b.verify_kernels(&keychain.secp(), true), Ok(()));
 
 		assert_eq!(
 			b.validate(&keychain.secp()),

core/src/core/mod.rs

@@ -219,7 +219,7 @@ mod test {
 		let mut vec = Vec::new();
 		ser::serialize(&mut vec, &tx).expect("serialization failed");
 		let dtx: Transaction = ser::deserialize(&mut &vec[..]).unwrap();
-		assert_eq!(dtx.fee, 1);
+		assert_eq!(dtx.fee, 2);
 		assert_eq!(dtx.inputs.len(), 2);
 		assert_eq!(dtx.outputs.len(), 1);
 		assert_eq!(tx.hash(), dtx.hash());
@@ -305,7 +305,7 @@ mod test {
 			// Alice builds her transaction, with change, which also produces the sum
 			// of blinding factors before they're obscured.
 			let (tx, sum) = build::transaction(
-				vec![in1, in2, output(1, pk3), with_fee(1)],
+				vec![in1, in2, output(1, pk3), with_fee(2)],
 				&keychain,
 			).unwrap();
 			tx_alice = tx;
@@ -317,7 +317,7 @@ mod test {
 		// ready for broadcast.
 		let (tx_final, _) =
 			build::transaction(
-				vec![initial_tx(tx_alice), with_excess(blind_sum), output(5, pk4)],
+				vec![initial_tx(tx_alice), with_excess(blind_sum), output(4, pk4)],
 				&keychain,
 			).unwrap();
 
@@ -386,7 +386,7 @@ mod test {
 		let pk3 = keychain.derive_pubkey(3).unwrap();
 
 		build::transaction(
-			vec![input(10, pk1), input(11, pk2), output(20, pk3), with_fee(1)],
+			vec![input(10, pk1), input(11, pk2), output(19, pk3), with_fee(2)],
 			&keychain,
 		).map(|(tx, _)| tx).unwrap()
 	}
@@ -398,7 +398,7 @@ mod test {
 		let pk2 = keychain.derive_pubkey(2).unwrap();
 
 		build::transaction(
-			vec![input(5, pk1), output(4, pk2), with_fee(1)],
+			vec![input(5, pk1), output(3, pk2), with_fee(2)],
 			&keychain,
 		).map(|(tx, _)| tx).unwrap()
 	}

core/src/core/pmmr.rs

@@ -181,6 +181,10 @@ where
 	/// implementation.
 	fn append(&mut self, position: u64, data: Vec<HashSum<T>>) -> Result<(), String>;
 
+	/// Rewind the backend state to a previous position, as if all append
+	/// operations after that had been canceled. Expects a position in the PMMR
+	/// to rewind to as well as the consumer-provided index of when the change
+	/// occurred (see remove).
 	fn rewind(&mut self, position: u64, index: u32) -> Result<(), String>;
 
 	/// Get a HashSum by insertion position
@@ -382,6 +386,7 @@ pub struct VecBackend<T>
 where
 	T: Summable + Clone,
 {
+	/// Backend elements
 	pub elems: Vec<Option<HashSum<T>>>,
 }
 
@@ -397,6 +402,7 @@ where
 	fn get(&self, position: u64) -> Option<HashSum<T>> {
 		self.elems[(position - 1) as usize].clone()
 	}
+	#[allow(unused_variables)]
 	fn remove(&mut self, positions: Vec<u64>, index: u32) -> Result<(), String> {
 		for n in positions {
 			self.elems[(n - 1) as usize] = None
@@ -971,7 +977,7 @@ mod test {
 		{
 			let mut pmmr = PMMR::at(&mut ba, sz);
 			for n in 1..16 {
-				pmmr.prune(n, 0);
+				let _ = pmmr.prune(n, 0);
 			}
 			assert_eq!(orig_root, pmmr.root());
 		}

core/src/core/transaction.rs

@@ -34,6 +34,22 @@ bitflags! {
     }
 }
 
+/// Errors thrown by Block validation
+#[derive(Debug, PartialEq)]
+pub enum Error {
+	/// Transaction fee can't be odd, due to half fee burning
+	OddFee,
+	/// Underlying Secp256k1 error (signature validation or invalid public
+	/// key typically)
+	Secp(secp::Error),
+}
+
+impl From<secp::Error> for Error {
+	fn from(e: secp::Error) -> Error {
+		Error::Secp(e)
+	}
+}
+
 /// A proof that a transaction sums to zero. Includes both the transaction's
 /// Pedersen commitment and the signature, that guarantees that the commitments
 /// amount to zero. The signature signs the fee, which is retained for
@@ -245,11 +261,14 @@ impl Transaction {
 	/// Validates all relevant parts of a fully built transaction. Checks the
 	/// excess value against the signature as well as range proofs for each
 	/// output.
-	pub fn validate(&self, secp: &Secp256k1) -> Result<TxKernel, secp::Error> {
+	pub fn validate(&self, secp: &Secp256k1) -> Result<TxKernel, Error> {
+		if self.fee & 1 != 0 {
+			return Err(Error::OddFee);
+		}
 		for out in &self.outputs {
 			out.verify_proof(secp)?;
 		}
-		self.verify_sig(secp)
+		self.verify_sig(secp).map_err(&From::from)
 	}
 }
 

grin/src/miner.rs

@@ -29,7 +29,7 @@ use core::core;
 use core::core::Proof;
 use pow::cuckoo;
 use core::core::target::Difficulty;
-use core::core::{Block, BlockHeader};
+use core::core::{Block, BlockHeader, Transaction};
 use core::core::hash::{Hash, Hashed};
 use pow::MiningWorker;
 use pow::types::MinerConfig;
@@ -43,7 +43,7 @@ use secp;
 use pool;
 use util;
 use keychain::Keychain;
-use wallet::{CbAmount, WalletReceiveRequest, CbData};
+use wallet::{BlockFees, WalletReceiveRequest, CbData};
 
 use pow::plugin::PluginMiner;
 
@@ -428,13 +428,16 @@ impl Miner {
 			));
 		}
 
-		let mut coinbase = self.get_coinbase();
+		// to prevent the wallet from generating a new HD key derivation for each
+		// iteration, we keep the returned derivation to provide it back when
+		// nothing has changed
+		let mut derivation = 0;
 
 		loop {
 			// get the latest chain state and build a block on top of it
 			let head = self.chain.head_header().unwrap();
 			let mut latest_hash = self.chain.head().unwrap().last_block_h;
-			let mut b = self.build_block(&head, coinbase.clone());
+			let (mut b, deriv) = self.build_block(&head, derivation);
 
 			let mut sol = None;
 			let mut use_async = false;
@@ -496,34 +499,37 @@ impl Miner {
 						self.debug_output_id,
 						e
 					);
-				} else {
-					coinbase = self.get_coinbase();
 				}
+				derivation = 0;
+			} else {
+				derivation = deriv;
 			}
 		}
 	}
 
 	/// Builds a new block with the chain head as previous and eligible
 	/// transactions from the pool.
-	fn build_block(
-		&self,
-		head: &core::BlockHeader,
-		coinbase: (core::Output, core::TxKernel),
-	) -> core::Block {
+	fn build_block(&self, head: &core::BlockHeader, deriv: u32) -> (core::Block, u32) {
+		// prepare the block header timestamp
 		let mut now_sec = time::get_time().sec;
 		let head_sec = head.timestamp.to_timespec().sec;
 		if now_sec == head_sec {
 			now_sec += 1;
 		}
 
+		// get the difficulty our block should be at
 		let diff_iter = self.chain.difficulty_iter();
 		let difficulty = consensus::next_difficulty(diff_iter).unwrap();
 
+		// extract current transaction from the pool
 		let txs_box = self.tx_pool.read().unwrap().prepare_mineable_transactions(
 			MAX_TX,
 		);
-		let txs = txs_box.iter().map(|tx| tx.as_ref()).collect();
-		let (output, kernel) = coinbase;
+		let txs: Vec<&Transaction> = txs_box.iter().map(|tx| tx.as_ref()).collect();
+
+		// build the coinbase and the block itself
+		let fees = txs.iter().map(|tx| tx.fee).sum();
+		let (output, kernel, deriv) = self.get_coinbase(fees, deriv);
 		let mut b = core::Block::with_reward(head, txs, output, kernel).unwrap();
 		debug!(
 			"(Server ID: {}) Built new block with {} inputs and {} outputs, difficulty: {}",
@@ -544,20 +550,21 @@ impl Miner {
 		self.chain.set_sumtree_roots(&mut b).expect(
 			"Error setting sum tree roots",
 		);
-		b
+		(b, deriv)
 	}
 
-	fn get_coinbase(&self) -> (core::Output, core::TxKernel) {
+	fn get_coinbase(&self, fees: u64, derivation: u32) -> (core::Output, core::TxKernel, u32) {
 		if self.config.burn_reward {
 			let keychain = Keychain::from_random_seed().unwrap();
 			let pubkey = keychain.derive_pubkey(1).unwrap();
-			core::Block::reward_output(&keychain, pubkey).unwrap()
+			let (out, kern) = core::Block::reward_output(&keychain, pubkey, fees).unwrap();
+			(out, kern, 0)
 		} else {
 			let url = format!(
 				"{}/v1/receive/coinbase",
 				self.config.wallet_receiver_url.as_str()
 			);
-			let request = WalletReceiveRequest::Coinbase(CbAmount { amount: consensus::REWARD });
+			let request = WalletReceiveRequest::Coinbase(BlockFees { fees: fees, derivation: derivation });
 			let res: CbData = api::client::post(url.as_str(), &request).expect(
 				format!(
 					"(Server ID: {}) Wallet receiver unreachable, could not claim reward. Is it running?",
@@ -570,7 +577,7 @@ impl Miner {
 			let output = ser::deserialize(&mut &out_bin[..]).unwrap();
 			let kernel = ser::deserialize(&mut &kern_bin[..]).unwrap();
 
-			(output, kernel)
+			(output, kernel, res.derivation)
 		}
 	}
 }

wallet/src/lib.rs

@@ -39,4 +39,4 @@ mod types;
 pub use info::show_info;
 pub use receiver::{WalletReceiver, receive_json_tx};
 pub use sender::issue_send_tx;
-pub use types::{WalletConfig, WalletReceiveRequest, CbAmount, CbData};
+pub use types::{WalletConfig, WalletReceiveRequest, BlockFees, CbData};

wallet/src/receiver.rs

@@ -49,7 +49,7 @@
 //! double-exchange will be required as soon as we support Schnorr signatures.
 //! So we may as well have it in place already.
 
-
+use core::consensus::reward;
 use core::core::{Block, Transaction, TxKernel, Output, build};
 use core::ser;
 use api::{self, ApiEndpoint, Operation, ApiResult};
@@ -106,16 +106,14 @@ impl ApiEndpoint for WalletReceiver {
 		match op.as_str() {
 			"coinbase" => {
 				match input {
-					WalletReceiveRequest::Coinbase(cb_amount) => {
-						debug!("Operation {} with amount {}", op, cb_amount.amount);
-						if cb_amount.amount == 0 {
-							return Err(api::Error::Argument(format!("Zero amount not allowed.")));
-						}
-						let (out, kern) =
+					WalletReceiveRequest::Coinbase(cb_fees) => {
+						debug!("Operation {} with amount {}", op, cb_fees.fees);
+						let (out, kern, derivation) =
 							receive_coinbase(
 								&self.config,
 								&self.keychain,
-								cb_amount.amount,
+								cb_fees.fees,
+								cb_fees.derivation,
 							).map_err(|e| {
 								api::Error::Internal(format!("Error building coinbase: {:?}", e))
 							})?;
@@ -130,6 +128,7 @@ impl ApiEndpoint for WalletReceiver {
 						Ok(CbData {
 							output: util::to_hex(out_bin),
 							kernel: util::to_hex(kern_bin),
+							derivation: derivation,
 						})
 					}
 					_ => Err(api::Error::Argument(
@@ -149,6 +148,7 @@ impl ApiEndpoint for WalletReceiver {
 						Ok(CbData {
 							output: String::from(""),
 							kernel: String::from(""),
+							derivation: 0,
 						})
 					}
 					_ => Err(api::Error::Argument(
@@ -165,20 +165,24 @@ impl ApiEndpoint for WalletReceiver {
 fn receive_coinbase(
 	config: &WalletConfig,
 	keychain: &Keychain,
-	amount: u64,
-) -> Result<(Output, TxKernel), Error> {
+	fees: u64,
+	mut derivation: u32,
+) -> Result<(Output, TxKernel, u32), Error> {
+
 	let fingerprint = keychain.clone().fingerprint();
 
 	// operate within a lock on wallet data
 	WalletData::with_wallet(&config.data_file_dir, |wallet_data| {
-		let derivation = wallet_data.next_child(fingerprint.clone());
+		if derivation == 0 {
+			derivation = wallet_data.next_child(fingerprint.clone());
+		}
 		let pubkey = keychain.derive_pubkey(derivation)?;
 
 		// track the new output and return the stuff needed for reward
 		wallet_data.append_output(OutputData {
 			fingerprint: fingerprint.clone(),
 			n_child: derivation,
-			value: amount,
+			value: reward(fees),
 			status: OutputStatus::Unconfirmed,
 			height: 0,
 			lock_height: 0,
@@ -186,8 +190,8 @@ fn receive_coinbase(
 		debug!("Received coinbase and built output - {}, {}, {}",
 			fingerprint.clone(), pubkey.fingerprint(), derivation);
 
-		let result = Block::reward_output(&keychain, pubkey)?;
-		Ok(result)
+		let (out, kern) = Block::reward_output(&keychain, pubkey, fees)?;
+		Ok((out, kern, derivation))
 	})?
 }
 
@@ -199,6 +203,7 @@ fn receive_transaction(
 	blinding: BlindingFactor,
 	partial: Transaction,
 ) -> Result<Transaction, Error> {
+
 	let fingerprint = keychain.clone().fingerprint();
 
 	// operate within a lock on wallet data

wallet/src/types.rs

@@ -23,7 +23,7 @@ use serde_json;
 use secp;
 
 use api;
-use core::core::Transaction;
+use core::core::{Transaction, transaction};
 use core::ser;
 use keychain;
 use util;
@@ -36,6 +36,7 @@ const LOCK_FILE: &'static str = "wallet.lock";
 pub enum Error {
 	NotEnoughFunds(u64),
 	Keychain(keychain::Error),
+	Transaction(transaction::Error),
 	Secp(secp::Error),
 	WalletData(String),
 	/// An error in the format of the JSON structures exchanged by the wallet
@@ -52,6 +53,10 @@ impl From<secp::Error> for Error {
 	fn from(e: secp::Error) -> Error { Error::Secp(e) }
 }
 
+impl From<transaction::Error> for Error {
+	fn from(e: transaction::Error) -> Error { Error::Transaction(e) }
+}
+
 impl From<serde_json::Error> for Error {
 	fn from(e: serde_json::Error) -> Error { Error::Format(e.to_string()) }
 }
@@ -268,8 +273,7 @@ impl WalletData {
 	}
 
 	/// Select a subset of unspent outputs to spend in a transaction
-	/// transferring
-	/// the provided amount.
+	/// transferring the provided amount.
 	pub fn select(
 		&self,
 		fingerprint: keychain::Fingerprint,
@@ -356,15 +360,16 @@ pub fn partial_tx_from_json(
 /// Amount in request to build a coinbase output.
 #[derive(Serialize, Deserialize, Debug, Clone)]
 pub enum WalletReceiveRequest {
-	Coinbase(CbAmount),
+	Coinbase(BlockFees),
 	PartialTransaction(String),
 	Finalize(String),
 }
 
-/// Amount in request to build a coinbase output.
+/// Fees in block to use for coinbase amount calculation
 #[derive(Serialize, Deserialize, Debug, Clone)]
-pub struct CbAmount {
-	pub amount: u64,
+pub struct BlockFees {
+	pub fees: u64,
+	pub derivation: u32,
 }
 
 /// Response to build a coinbase output.
@@ -372,4 +377,5 @@ pub struct CbAmount {
 pub struct CbData {
 	pub output: String,
 	pub kernel: String,
+	pub derivation: u32,
 }