Fill BlindingFactor with zeros on Drop (#2847)

* Implement simple zeroing of BlindingFactor in Drop

* rustfmt

* Make Debug implementation for BlindingFactor empty

* Implement BlindingFactor zeroing unit test

* mnemonic.rs: fix deprecated warning in test_bip39_random test

* Use zeroize crate to clear BlindingFactor

* Fix comment and implement dummy Debug trait for BlindingFactor

* Fix formatter

core/src/core/block.rs

@@ -384,7 +384,7 @@ impl BlockHeader {
 
 	/// Total kernel offset for the chain state up to and including this block.
 	pub fn total_kernel_offset(&self) -> BlindingFactor {
-		self.total_kernel_offset
+		self.total_kernel_offset.clone()
 	}
 }
 
@@ -560,8 +560,10 @@ impl Block {
 			.with_kernel(reward_kern);
 
 		// Now add the kernel offset of the previous block for a total
-		let total_kernel_offset =
-			committed::sum_kernel_offsets(vec![agg_tx.offset, prev.total_kernel_offset], vec![])?;
+		let total_kernel_offset = committed::sum_kernel_offsets(
+			vec![agg_tx.offset.clone(), prev.total_kernel_offset.clone()],
+			vec![],
+		)?;
 
 		let now = Utc::now().timestamp();
 		let timestamp = DateTime::<Utc>::from_utc(NaiveDateTime::from_timestamp(now, 0), Utc);
@@ -698,7 +700,7 @@ impl Block {
 		// verify.body.outputs and kernel sums
 		let (_utxo_sum, kernel_sum) = self.verify_kernel_sums(
 			self.header.overage(),
-			self.block_kernel_offset(*prev_kernel_offset)?,
+			self.block_kernel_offset(prev_kernel_offset.clone())?,
 		)?;
 
 		Ok(kernel_sum)

core/src/core/transaction.rs

@@ -957,7 +957,7 @@ impl Transaction {
 	) -> Result<(), Error> {
 		self.body.validate(weighting, verifier)?;
 		self.body.verify_features()?;
-		self.verify_kernel_sums(self.overage(), self.offset)?;
+		self.verify_kernel_sums(self.overage(), self.offset.clone())?;
 		Ok(())
 	}
 

core/src/libtx/build.rs

@@ -158,7 +158,7 @@ where
 {
 	Box::new(
 		move |_build, (tx, kern, sum)| -> (Transaction, TxKernel, BlindSum) {
-			(tx.with_offset(offset), kern, sum)
+			(tx.with_offset(offset.clone()), kern, sum)
 		},
 	)
 }