Add features bitmask to Block, Output, Kernel; coinbase validation

Block, Output and Kernel now have bitmasks to hold supported
features and eventually versioning. Will make adding features and
updates easier and open the possibility of soft forks.

First added feature for Output and Kernel is the marking of coinbase
related ones. Allows the validation of the coinbase part of a block.

chain/src/pipe.rs

@@ -213,7 +213,7 @@ fn validate_header(header: &BlockHeader, ctx: &mut BlockContext) -> Result<(), E
 /// Fully validate the block content.
 fn validate_block(b: &Block, ctx: &mut BlockContext) -> Result<(), Error> {
 	let curve = secp::Secp256k1::with_caps(secp::ContextFlag::Commit);
-	try!(b.verify(&curve).map_err(&Error::InvalidBlockProof));
+	try!(b.validate(&curve).map_err(&Error::InvalidBlockProof));
 
 	if !ctx.opts.intersects(SYNC) {
 		// TODO check every input exists as a UTXO using the UXTO index

core/Cargo.toml

@@ -4,6 +4,7 @@ version = "0.1.0"
 authors = ["Ignotus Peverell <igno.peverell@protonmail.com>"]
 
 [dependencies]
+bitflags = "~0.7.0"
 byteorder = "^0.5"
 num-bigint = "^0.1.35"
 rust-crypto = "^0.2"

core/src/core/block.rs

@@ -21,13 +21,20 @@ use secp::key::SecretKey;
 use std::collections::HashSet;
 
 use core::Committed;
-use core::{Input, Output, Proof, TxKernel, Transaction};
+use core::{Input, Output, Proof, TxKernel, Transaction, COINBASE_KERNEL, COINBASE_OUTPUT};
 use core::transaction::merkle_inputs_outputs;
 use consensus::{REWARD, DEFAULT_SIZESHIFT};
 use core::hash::{Hash, Hashed, ZERO_HASH};
 use core::target::Difficulty;
 use ser::{self, Readable, Reader, Writeable, Writer};
 
+bitflags! {
+  /// Options for block validation
+  pub flags BlockFeatures: u8 {
+    const DEFAULT_BLOCK = 0b00000000,
+  }
+}
+
 /// Block header, fairly standard compared to other blockchains.
 pub struct BlockHeader {
 	/// Height of this block since the genesis block (height 0)
@@ -39,7 +46,10 @@ pub struct BlockHeader {
 	/// Length of the cuckoo cycle used to mine this block.
 	pub cuckoo_len: u8,
 	pub utxo_merkle: Hash,
+	/// Merkle tree of hashes for all inputs, outputs and kernels in the block
 	pub tx_merkle: Hash,
+	/// Features specific to this block, allowing possible future extensions
+	pub features: BlockFeatures,
 	/// Nonce increment used to mine this block.
 	pub nonce: u64,
 	/// Proof of work data.
@@ -61,6 +71,7 @@ impl Default for BlockHeader {
 			total_difficulty: Difficulty::one(),
 			utxo_merkle: ZERO_HASH,
 			tx_merkle: ZERO_HASH,
+			features: DEFAULT_BLOCK,
 			nonce: 0,
 			pow: Proof::zero(),
 		}
@@ -76,7 +87,8 @@ impl Writeable for BlockHeader {
 		                [write_i64, self.timestamp.to_timespec().sec],
 		                [write_u8, self.cuckoo_len],
 		                [write_fixed_bytes, &self.utxo_merkle],
-		                [write_fixed_bytes, &self.tx_merkle]);
+		                [write_fixed_bytes, &self.tx_merkle],
+                    [write_u8, self.features.bits()]);
 
 		try!(writer.write_u64(self.nonce));
 		try!(self.difficulty.write(writer));
@@ -97,7 +109,7 @@ impl Readable<BlockHeader> for BlockHeader {
 		let (timestamp, cuckoo_len) = ser_multiread!(reader, read_i64, read_u8);
 		let utxo_merkle = try!(Hash::read(reader));
 		let tx_merkle = try!(Hash::read(reader));
-		let nonce = try!(reader.read_u64());
+		let (features, nonce) = ser_multiread!(reader, read_u8, read_u64);
 		let difficulty = try!(Difficulty::read(reader));
 		let total_difficulty = try!(Difficulty::read(reader));
 		let pow = try!(Proof::read(reader));
@@ -112,6 +124,7 @@ impl Readable<BlockHeader> for BlockHeader {
 			cuckoo_len: cuckoo_len,
 			utxo_merkle: utxo_merkle,
 			tx_merkle: tx_merkle,
+			features: BlockFeatures::from_bits(features).ok_or(ser::Error::CorruptedData)?,
 			pow: pow,
 			nonce: nonce,
 			difficulty: difficulty,
@@ -344,15 +357,32 @@ impl Block {
 			.compact()
 	}
 
-	/// Checks the block is valid by verifying the overall commitments sums and
-	/// kernels.
-	pub fn verify(&self, secp: &Secp256k1) -> Result<(), secp::Error> {
+	/// Validates all the elements in a block that can be checked without
+	/// additional
+	/// data. Includes commitment sums and kernels, Merkle trees, reward, etc.
+	pub fn validate(&self, secp: &Secp256k1) -> Result<(), secp::Error> {
+		self.verify_coinbase(secp)?;
+		self.verify_kernels(secp)?;
+
+		// verify the transaction Merkle root
+		let tx_merkle = merkle_inputs_outputs(&self.inputs, &self.outputs);
+		if tx_merkle != self.header.tx_merkle {
+			// TODO more specific error
+			return Err(secp::Error::IncorrectCommitSum);
+		}
+		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<(), secp::Error> {
 		// sum all inputs and outs commitments
-		let io_sum = try!(self.sum_commitments(secp));
+		let io_sum = self.sum_commitments(secp)?;
 
 		// sum all kernels commitments
 		let proof_commits = map_vec!(self.kernels, |proof| proof.excess);
-		let proof_sum = try!(secp.commit_sum(proof_commits, vec![]));
+		let proof_sum = secp.commit_sum(proof_commits, vec![])?;
 
 		// both should be the same
 		if proof_sum != io_sum {
@@ -362,19 +392,39 @@ impl Block {
 
 		// verify all signatures with the commitment as pk
 		for proof in &self.kernels {
-			try!(proof.verify(secp));
+			proof.verify(secp)?;
 		}
-
-		// verify the transaction Merkle root
-		let tx_merkle = merkle_inputs_outputs(&self.inputs, &self.outputs);
-		if tx_merkle != self.header.tx_merkle {
-			// TODO more specific error
-			return Err(secp::Error::IncorrectCommitSum);
-		}
-
 		Ok(())
 	}
 
+	// Validate the coinbase outputs generated by miners. Entails 2 main checks:
+	//
+	// * That the sum of all coinbase-marked outputs equal the supply.
+	// * That the sum of blinding factors for all coinbase-marked outputs match
+	//   the coinbase-marked kernels.
+	fn verify_coinbase(&self, secp: &Secp256k1) -> Result<(), secp::Error> {
+		let cb_outs = self.outputs
+			.iter()
+			.filter(|out| out.features.intersects(COINBASE_OUTPUT))
+			.map(|o| o.clone())
+			.collect::<Vec<_>>();
+		let cb_kerns = self.kernels
+			.iter()
+			.filter(|k| k.features.intersects(COINBASE_KERNEL))
+			.map(|k| k.clone())
+			.collect::<Vec<_>>();
+
+		// 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)
+	}
+
 	// Builds the blinded output and related signature proof for the block reward.
 	fn reward_output(skey: secp::key::SecretKey,
 	                 secp: &Secp256k1)
@@ -385,6 +435,7 @@ impl Block {
 		let rproof = secp.range_proof(0, REWARD, skey, commit);
 
 		let output = Output {
+			features: COINBASE_OUTPUT,
 			commit: commit,
 			proof: rproof,
 		};
@@ -394,6 +445,7 @@ impl Block {
 		let excess = try!(secp.commit_sum(vec![over_commit], vec![out_commit]));
 
 		let proof = TxKernel {
+			features: COINBASE_KERNEL,
 			excess: excess,
 			excess_sig: sig.serialize_der(&secp),
 			fee: 0,
@@ -430,7 +482,9 @@ impl Block {
 	// utility producing a transaction that spends an output with the provided
 	// value and blinding key
 	fn txspend1i1o(v: u64, b: SecretKey) -> Transaction {
-   build::transaction(vec![input(v, b), output_rand(3), with_fee(1)]).map(|(tx, _)| tx).unwrap()
+		build::transaction(vec![input(v, b), output_rand(3), with_fee(1)])
+			.map(|(tx, _)| tx)
+			.unwrap()
 	}
 
 	#[test]
@@ -441,7 +495,8 @@ impl Block {
 
 		let mut btx1 = tx2i1o();
 		let skey = SecretKey::new(secp, &mut rng);
-		let (mut btx2, _) = build::transaction(vec![input_rand(5), output(4, skey), with_fee(1)]).unwrap();
+		let (mut btx2, _) = build::transaction(vec![input_rand(5), output(4, skey), with_fee(1)])
+			.unwrap();
 
 		// spending tx2
 		let mut btx3 = txspend1i1o(4, skey);
@@ -449,7 +504,7 @@ impl Block {
 
 		// block should have been automatically compacted (including reward
 		// output) and should still be valid
- 		b.verify(&secp).unwrap();
+		b.validate(&secp).unwrap();
 		assert_eq!(b.inputs.len(), 3);
 		assert_eq!(b.outputs.len(), 3);
 	}
@@ -463,15 +518,16 @@ impl Block {
 
 		let mut btx1 = tx2i1o();
 		let skey = SecretKey::new(secp, &mut rng);
-		let (mut btx2, _) = build::transaction(vec![input_rand(5), output(4, skey), with_fee(1)]).unwrap();
+		let (mut btx2, _) = build::transaction(vec![input_rand(5), output(4, skey), with_fee(1)])
+			.unwrap();
 
 		// spending tx2
 		let mut btx3 = txspend1i1o(4, skey);
 
 		let b1 = new_block(vec![&mut btx1, &mut btx2], secp);
- 		b1.verify(&secp).unwrap();
+		b1.validate(&secp).unwrap();
 		let b2 = new_block(vec![&mut btx3], secp);
- 		b2.verify(&secp).unwrap();
+		b2.validate(&secp).unwrap();
 
 		// block should have been automatically compacted and should still be valid
 		let b3 = b1.merge(b2);

core/src/core/build.rs

@@ -31,7 +31,7 @@ use secp::key::SecretKey;
 use secp::pedersen::*;
 use rand::os::OsRng;
 
-use core::{Transaction, Input, Output};
+use core::{Transaction, Input, Output, DEFAULT_OUTPUT};
 
 /// Context information available to transaction combinators.
 pub struct Context {
@@ -113,6 +113,7 @@ pub fn output(value: u64, blinding: SecretKey) -> Box<Append> {
 		let commit = build.secp.commit(value, blinding).unwrap();
 		let rproof = build.secp.range_proof(0, value, blinding, commit);
 		(tx.with_output(Output {
+			features: DEFAULT_OUTPUT,
 			commit: commit,
 			proof: rproof,
 		}),
@@ -129,6 +130,7 @@ pub fn output_rand(value: u64) -> Box<Append> {
 		let commit = build.secp.commit(value, blinding).unwrap();
 		let rproof = build.secp.range_proof(0, value, blinding, commit);
 		(tx.with_output(Output {
+			features: DEFAULT_OUTPUT,
 			commit: commit,
 			proof: rproof,
 		}),

core/src/core/mod.rs

@@ -28,8 +28,9 @@ use secp::{self, Secp256k1};
 use secp::pedersen::*;
 
 use consensus::PROOFSIZE;
-pub use self::block::{Block, BlockHeader};
-pub use self::transaction::{Transaction, Input, Output, TxKernel};
+pub use self::block::{Block, BlockHeader, DEFAULT_BLOCK};
+pub use self::transaction::{Transaction, Input, Output, TxKernel, COINBASE_KERNEL,
+                            COINBASE_OUTPUT, DEFAULT_OUTPUT};
 use self::hash::{Hash, Hashed, HashWriter, ZERO_HASH};
 use ser::{Writeable, Writer, Reader, Readable, Error};
 
@@ -344,7 +345,7 @@ mod test {
 		let skey = SecretKey::new(secp, &mut rng);
 
 		let b = Block::new(&BlockHeader::default(), vec![], skey).unwrap();
-		b.compact().verify(&secp).unwrap();
+		b.compact().validate(&secp).unwrap();
 	}
 
 	#[test]
@@ -357,7 +358,7 @@ mod test {
 		tx1.verify_sig(&secp).unwrap();
 
 		let b = Block::new(&BlockHeader::default(), vec![&mut tx1], skey).unwrap();
-		b.compact().verify(&secp).unwrap();
+		b.compact().validate(&secp).unwrap();
 	}
 
 	#[test]
@@ -373,7 +374,7 @@ mod test {
 		tx2.verify_sig(&secp).unwrap();
 
 		let b = Block::new(&BlockHeader::default(), vec![&mut tx1, &mut tx2], skey).unwrap();
-		b.verify(&secp).unwrap();
+		b.validate(&secp).unwrap();
 	}
 
 	// utility producing a transaction with 2 inputs and a single outputs

core/src/core/transaction.rs

@@ -24,12 +24,22 @@ use core::MerkleRow;
 use core::hash::{Hash, Hashed};
 use ser::{self, Reader, Writer, Readable, Writeable};
 
+bitflags! {
+  /// Options for a kernel's structure or use
+  pub flags KernelFeatures: u8 {
+    const DEFAULT_KERNEL = 0b00000000,
+    const COINBASE_KERNEL = 0b00000001,
+  }
+}
+
 /// 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
 /// signature validation.
 #[derive(Debug, Clone)]
 pub struct TxKernel {
+	/// Options for a kernel's structure or use
+	pub features: KernelFeatures,
 	/// Remainder of the sum of all transaction commitments. If the transaction
 	/// is well formed, amounts components should sum to zero and the excess
 	/// is hence a valid public key.
@@ -43,20 +53,23 @@ pub struct TxKernel {
 
 impl Writeable for TxKernel {
 	fn write(&self, writer: &mut Writer) -> Result<(), ser::Error> {
-		try!(writer.write_fixed_bytes(&self.excess));
-		try!(writer.write_bytes(&self.excess_sig));
-		writer.write_u64(self.fee)
+		ser_multiwrite!(writer,
+                    [write_u8, self.features.bits()],
+                    [write_fixed_bytes, &self.excess],
+                    [write_bytes, &self.excess_sig],
+                    [write_u64, self.fee]);
+		Ok(())
 	}
 }
 
 impl Readable<TxKernel> for TxKernel {
 	fn read(reader: &mut Reader) -> Result<TxKernel, ser::Error> {
-		let excess = try!(Commitment::read(reader));
-		let (sig, fee) = ser_multiread!(reader, read_vec, read_u64);
 		Ok(TxKernel {
-			excess: excess,
-			excess_sig: sig,
-			fee: fee,
+			features:
+				KernelFeatures::from_bits(reader.read_u8()?).ok_or(ser::Error::CorruptedData)?,
+			excess: Commitment::read(reader)?,
+			excess_sig: reader.read_vec()?,
+			fee: reader.read_u64()?,
 		})
 	}
 }
@@ -212,6 +225,7 @@ impl Transaction {
 		try!(secp.verify(&msg, &sig, &pubk));
 
 		Ok(TxKernel {
+			features: DEFAULT_KERNEL,
 			excess: rsum,
 			excess_sig: self.excess_sig.clone(),
 			fee: self.fee,
@@ -258,6 +272,14 @@ impl Input {
 	}
 }
 
+bitflags! {
+  /// Options for block validation
+  pub flags OutputFeatures: u8 {
+    const DEFAULT_OUTPUT = 0b00000000,
+    const COINBASE_OUTPUT = 0b00000001,
+  }
+}
+
 /// Output for a transaction, defining the new ownership of coins that are being
 /// transferred. The commitment is a blinded value for the output while the
 /// range
@@ -265,6 +287,7 @@ impl Input {
 /// and the ownership of the private key.
 #[derive(Debug, Copy, Clone)]
 pub struct Output {
+	pub features: OutputFeatures,
 	pub commit: Commitment,
 	pub proof: RangeProof,
 }
@@ -273,10 +296,10 @@ pub struct Output {
 /// an Output as binary.
 impl Writeable for Output {
 	fn write(&self, writer: &mut Writer) -> Result<(), ser::Error> {
-		// The hash of an output is only the hash of its commitment.
-		try!(writer.write_fixed_bytes(&self.commit));
+		ser_multiwrite!(writer, [write_u8, self.features.bits()], [write_fixed_bytes, &self.commit]);
+		// The hash of an output doesn't include the range proof
 		if writer.serialization_mode() == ser::SerializationMode::Full {
-			try!(writer.write_bytes(&self.proof.bytes()))
+			writer.write_bytes(&self.proof.bytes())?
 		}
 		Ok(())
 	}
@@ -286,11 +309,11 @@ impl Writeable for Output {
 /// an Output from a binary stream.
 impl Readable<Output> for Output {
 	fn read(reader: &mut Reader) -> Result<Output, ser::Error> {
-		let commit = try!(Commitment::read(reader));
-		let proof = try!(RangeProof::read(reader));
 		Ok(Output {
-			commit: commit,
-			proof: proof,
+			features:
+				OutputFeatures::from_bits(reader.read_u8()?).ok_or(ser::Error::CorruptedData)?,
+			commit: Commitment::read(reader)?,
+			proof: RangeProof::read(reader)?,
 		})
 	}
 }

core/src/genesis.rs

@@ -39,6 +39,7 @@ pub fn genesis() -> core::Block {
 			total_difficulty: Difficulty::one(),
 			utxo_merkle: [].hash(),
 			tx_merkle: [].hash(),
+			features: core::DEFAULT_BLOCK,
 			nonce: 0,
 			pow: core::Proof::zero(), // TODO get actual PoW solution
 		},

core/src/lib.rs

@@ -21,6 +21,8 @@
 #![deny(unused_mut)]
 #![warn(missing_docs)]
 
+#[macro_use]
+extern crate bitflags;
 extern crate byteorder;
 extern crate crypto;
 extern crate num_bigint as bigint;

doc/intro.md

@@ -13,7 +13,7 @@ cryptocurrency deployment.
 The main goal and characteristics of the Grin project are:
 
 * Privacy by default. This enables complete fungibility without precluding
-	the possibility to ability to selectively disclose information as needed.
+	the ability to selectively disclose information as needed.
 * Scales with the number of users and not the number of transactions, with very
   large space savings compared to other blockchains.
 * Strong and proven cryptography. MimbleWimble only relies on Elliptic Curve

p2p/src/types.rs

@@ -81,7 +81,7 @@ impl Default for P2PConfig {
 }
 
 bitflags! {
-  /// Options for block validation
+  /// Options for what type of interaction a peer supports
   pub flags Capabilities: u32 {
     /// We don't know (yet) what the peer can do.
     const UNKNOWN = 0b00000000,