Merge pull request #14 from ignopeverell/topic/fees-in-sig

Slight changes to transaction signature. The transaction fee gets signed (instead of the empty string) and the fee amount is attached to the transaction proof in blocks.

core/src/core/block.rs

@@ -35,7 +35,6 @@ pub struct BlockHeader {
 	pub td: u64, // total difficulty up to this block
 	pub utxo_merkle: Hash,
 	pub tx_merkle: Hash,
-	pub total_fees: u64,
 	pub nonce: u64,
 	pub pow: Proof,
 }
@@ -49,7 +48,6 @@ impl Default for BlockHeader {
 			td: 0,
 			utxo_merkle: ZERO_HASH,
 			tx_merkle: ZERO_HASH,
-			total_fees: 0,
 			nonce: 0,
 			pow: Proof::zero(),
 		}
@@ -65,8 +63,7 @@ impl Writeable for BlockHeader {
 		                [write_fixed_bytes, &self.previous],
 		                [write_i64, self.timestamp.to_timespec().sec],
 		                [write_fixed_bytes, &self.utxo_merkle],
-		                [write_fixed_bytes, &self.tx_merkle],
+		                [write_fixed_bytes, &self.tx_merkle]);
-		                [write_u64, self.total_fees]);
 		// make sure to not introduce any variable length data before the nonce to
 		// avoid complicating PoW
 		try!(writer.write_u64(self.nonce));
@@ -117,14 +114,12 @@ impl Writeable for Block {
 /// from a binary stream.
 impl Readable<Block> for Block {
 	fn read(reader: &mut Reader) -> Result<Block, ser::Error> {
-		let (height, previous, timestamp, utxo_merkle, tx_merkle, total_fees, nonce) =
+		let (height, previous, timestamp, utxo_merkle, tx_merkle, nonce) = ser_multiread!(reader,
-			ser_multiread!(reader,
 			               read_u64,
 			               read_32_bytes,
 			               read_i64,
 			               read_32_bytes,
 			               read_32_bytes,
-			               read_u64,
 			               read_u64);
 
 		// cuckoo cycle of 42 nodes
@@ -156,7 +151,6 @@ impl Readable<Block> for Block {
 				td: td,
 				utxo_merkle: Hash::from_vec(utxo_merkle),
 				tx_merkle: Hash::from_vec(tx_merkle),
-				total_fees: total_fees,
 				pow: Proof(pow),
 				nonce: nonce,
 			},
@@ -178,7 +172,7 @@ impl Committed for Block {
 		&self.outputs
 	}
 	fn overage(&self) -> i64 {
-		(REWARD as i64) - (self.header.total_fees as i64)
+		(REWARD as i64) - (self.total_fees() as i64)
 	}
 }
 
@@ -234,12 +228,10 @@ impl Block {
 		outputs.sort_by_key(|out| out.hash());
 
 		// calculate the overall Merkle tree and fees
-		let fees = txs.iter().map(|tx| tx.fee).sum();
 
 		Ok(Block {
 				header: BlockHeader {
 					height: prev.height + 1,
-					total_fees: fees,
 					timestamp: time::now(),
 					..Default::default()
 				},
@@ -254,6 +246,10 @@ impl Block {
 		self.header.hash()
 	}
 
+	pub fn total_fees(&self) -> u64 {
+		self.proofs.iter().map(|p| p.fee).sum()
+	}
+
 	/// Matches any output with a potential spending input, eliminating them
 	/// from the block. Provides a simple way to compact the block. The
 	/// elimination is stable with respect to inputs and outputs order.
@@ -311,11 +307,7 @@ impl Block {
 
 		Block {
 				// compact will fix the merkle tree
-				header: BlockHeader {
+				header: BlockHeader { pow: self.header.pow.clone(), ..self.header },
-					total_fees: self.header.total_fees + other.header.total_fees,
-					pow: self.header.pow.clone(),
-					..self.header
-				},
 				inputs: all_inputs,
 				outputs: all_outputs,
 				proofs: all_proofs,
@@ -339,11 +331,8 @@ impl Block {
 		}
 
 		// verify all signatures with the commitment as pk
-		let msg = try!(Message::from_slice(&[0; 32]));
 		for proof in &self.proofs {
-			let pubk = try!(proof.remainder.to_pubkey(secp));
+			try!(proof.verify(secp));
-			let sig = try!(Signature::from_der(secp, &proof.sig));
-			try!(secp.verify(&msg, &sig, &pubk));
 		}
 		Ok(())
 	}
@@ -367,6 +356,7 @@ impl Block {
 		let proof = TxProof {
 			remainder: remainder,
 			sig: sig.serialize_der(&secp),
+			fee: 0,
 		};
 		Ok((output, proof))
 	}

core/src/core/transaction.rs

@@ -14,6 +14,7 @@
 
 //! Transactions
 
+use byteorder::{ByteOrder, BigEndian};
 use secp::{self, Secp256k1, Message, Signature};
 use secp::key::SecretKey;
 use secp::pedersen::{RangeProof, Commitment};
@@ -24,34 +25,54 @@ use core::MerkleRow;
 use core::hash::{Hash, Hashed};
 use ser::{self, Reader, Writer, Readable, Writeable};
 
-/// A proof that a transaction did not create (or remove) funds. Includes both
+/// A proof that a transaction sums to zero. Includes both the transaction's
-/// the transaction's Pedersen commitment and the signature that guarantees
+/// Pedersen commitment and the signature, that guarantees that the commitments
-/// that the commitment amounts to zero.
+/// amount to zero. The signature signs the fee, which is retained for
+/// signature validation.
 #[derive(Debug, Clone)]
 pub struct TxProof {
-	/// temporarily public
+	/// Remainder of the sum of all transaction commitments. If the transaction
+	/// is well formed, amounts components should sum to zero and the remainder
+	/// is hence a valid public key.
 	pub remainder: Commitment,
-	/// temporarily public
+	/// The signature proving the remainder is a valid public key, which signs
+	/// the transaction fee.
 	pub sig: Vec<u8>,
+	/// Fee originally included in the transaction this proof is for.
+	pub fee: u64,
 }
 
 impl Writeable for TxProof {
 	fn write(&self, writer: &mut Writer) -> Result<(), ser::Error> {
 		try!(writer.write_fixed_bytes(&self.remainder));
-		writer.write_bytes(&self.sig)
+		try!(writer.write_bytes(&self.sig));
+		writer.write_u64(self.fee)
 	}
 }
 
 impl Readable<TxProof> for TxProof {
 	fn read(reader: &mut Reader) -> Result<TxProof, ser::Error> {
-		let (remainder, sig) = ser_multiread!(reader, read_33_bytes, read_vec);
+		let (remainder, sig, fee) = ser_multiread!(reader, read_33_bytes, read_vec, read_u64);
 		Ok(TxProof {
 			remainder: Commitment::from_vec(remainder),
 			sig: sig,
+			fee: fee,
 		})
 	}
 }
 
+impl TxProof {
+	/// Verify the transaction proof validity. Entails handling the commitment
+	/// as a public key and checking the signature verifies with the fee as
+	/// message.
+	pub fn verify(&self, secp: &Secp256k1) -> Result<(), secp::Error> {
+		let msg = try!(Message::from_slice(&u64_to_32bytes(self.fee)));
+		let pubk = try!(self.remainder.to_pubkey(secp));
+		let sig = try!(Signature::from_der(secp, &self.sig));
+		secp.verify(&msg, &sig, &pubk)
+	}
+}
+
 /// A transaction
 #[derive(Debug)]
 pub struct Transaction {
@@ -172,7 +193,7 @@ impl Transaction {
 
 		// and sign with the remainder so the signature can be checked to match with
 		// the k.G commitment leftover, that should also be the pubkey
-		let msg = try!(Message::from_slice(&[0; 32]));
+		let msg = try!(Message::from_slice(&u64_to_32bytes(self.fee)));
 		let sig = try!(secp.sign(&msg, &remainder));
 
 		Ok(Transaction {
@@ -205,13 +226,14 @@ impl Transaction {
 		// pretend the sum is a public key (which it is, being of the form r.G) and
 		// verify the transaction sig with it
 		let pubk = try!(rsum.to_pubkey(secp));
-		let msg = try!(Message::from_slice(&[0; 32]));
+		let msg = try!(Message::from_slice(&u64_to_32bytes(self.fee)));
 		let sig = try!(Signature::from_der(secp, &self.zerosig));
 		try!(secp.verify(&msg, &sig, &pubk));
 
 		Ok(TxProof {
 			remainder: rsum,
 			sig: self.zerosig.clone(),
+			fee: self.fee,
 		})
 	}
 }
@@ -365,6 +387,12 @@ pub fn merkle_inputs_outputs(inputs: &Vec<Input>, outputs: &Vec<Output>) -> Hash
 	MerkleRow::new(all_hs).root()
 }
 
+fn u64_to_32bytes(n: u64) -> [u8; 32] {
+	let mut bytes = [0; 32];
+	BigEndian::write_u64(&mut bytes[24..32], n);
+	bytes
+}
+
 #[cfg(test)]
 mod test {
 	use super::*;

core/src/genesis.rs

@@ -31,7 +31,7 @@ pub fn genesis() -> core::Block {
 	core::Block {
 		header: core::BlockHeader {
 			height: 0,
-			previous: core::hash::ZERO_HASH,
+			previous: core::hash::Hash([0xff; 32]),
 			timestamp: time::Tm {
 				tm_year: 1997,
 				tm_mon: 7,
@@ -41,7 +41,6 @@ pub fn genesis() -> core::Block {
 			td: 0,
 			utxo_merkle: core::hash::Hash::from_vec(empty_h.to_vec()),
 			tx_merkle: core::hash::Hash::from_vec(empty_h.to_vec()),
-			total_fees: 0,
 			nonce: 0,
 			pow: core::Proof::zero(), // TODO get actual PoW solution
 		},

core/src/pow/mod.rs

@@ -47,7 +47,6 @@ struct PowHeader {
 	pub timestamp: time::Tm,
 	pub utxo_merkle: Hash,
 	pub tx_merkle: Hash,
-	pub total_fees: u64,
 	pub n_in: u64,
 	pub n_out: u64,
 	pub n_proofs: u64,
@@ -64,7 +63,6 @@ impl Writeable for PowHeader {
 		try!(writer.write_i64(self.timestamp.to_timespec().sec));
 		try!(writer.write_fixed_bytes(&self.utxo_merkle));
 		try!(writer.write_fixed_bytes(&self.tx_merkle));
-		try!(writer.write_u64(self.total_fees));
 		try!(writer.write_u64(self.n_in));
 		try!(writer.write_u64(self.n_out));
 		writer.write_u64(self.n_proofs)
@@ -81,7 +79,6 @@ impl PowHeader {
 			timestamp: h.timestamp,
 			utxo_merkle: h.utxo_merkle,
 			tx_merkle: h.tx_merkle,
-			total_fees: h.total_fees,
 			n_in: b.inputs.len() as u64,
 			n_out: b.outputs.len() as u64,
 			n_proofs: b.proofs.len() as u64,