Monero: support for legacy transactions (#308)

* add mlsag

* fix last commit

* fix miner v1 txs

* fix non-miner v1 txs

* add borromean + fix mlsag

* add block hash calculations

* fix for the jokester that added unreduced scalars

to the borromean signature of
2368d846e671bf79a1f84c6d3af9f0bfe296f043f50cf17ae5e485384a53707b

* Add Borromean range proof verifying functionality

* Add MLSAG verifying functionality

* fmt & clippy :)

* update MLSAG, ss2_elements will always be 2

* Add MgSig proving

* Tidy block.rs

* Tidy Borromean, fix bugs in last commit, replace todo! with unreachable!

* Mark legacy EcdhInfo amount decryption as experimental

* Correct comments

* Write a new impl of the merkle algorithm

This one tries to be understandable.

* Only pull in things only needed for experimental when experimental

* Stop caching the Monero block hash now in processor that we have Block::hash

* Corrections for recent processor commit

* Use a clearer algorithm for the merkle

Should also be more efficient due to not shifting as often.

* Tidy Mlsag

* Remove verify_rct_* from Mlsag

Both methods were ports from Monero, overtly specific without clear
documentation. They need to be added back in, with documentation, or included
in a node which provides the necessary further context for them to be naturally
understandable.

* Move mlsag/mod.rs to mlsag.rs

This should only be a folder if it has multiple files.

* Replace EcdhInfo terminology

The ECDH encrypted the amount, yet this struct contained the encrypted amount,
not some ECDH.

Also corrects the types on the original EcdhInfo struct.

* Correct handling of commitment masks when scanning

* Route read_array through read_raw_vec

* Misc lint

* Make a proper RctType enum

No longer caches RctType in the RctSignatures as well.

* Replace Vec<Bulletproofs> with Bulletproofs

Monero uses aggregated range proofs, so there's only ever one Bulletproof. This
is enforced with a consensus rule as well, making this safe.

As for why Monero uses a vec, it's probably due to the lack of variadic typing
used. Its effectively an Option for them, yet we don't need an Option since we
do have variadic typing (enums).

* Add necessary checks to Eventuality re: supported protocols

* Fix for block 202612 and fix merkel root calculations

* MLSAG (de)serialisation fix

ss_2_elements will not always be 2 as rct type 1 transactions are not enforced to have one input

* Revert "MLSAG (de)serialisation fix"

This reverts commit 5e710e0c96.

here it checks number of MGs == number of inputs:
0a1eaf26f9/src/cryptonote_core/tx_verification_utils.cpp (L60-59)

and here it checks for RctTypeFull number of MGs == 1:
0a1eaf26f9/src/ringct/rctSigs.cpp (L1325)

so number of inputs == 1
so ss_2_elements == 2

* update `MlsagAggregate` comment

* cargo update

Resolves a yanked crate

* Move location of serai-client in Cargo.toml

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

coins/monero/src/block.rs

@@ -4,10 +4,17 @@ use std_shims::{
 };
 
 use crate::{
+  hash,
+  merkle::merkle_root,
   serialize::*,
   transaction::{Input, Transaction},
 };
 
+const CORRECT_BLOCK_HASH_202612: [u8; 32] =
+  hex_literal::hex!("426d16cff04c71f8b16340b722dc4010a2dd3831c22041431f772547ba6e331a");
+const EXISTING_BLOCK_HASH_202612: [u8; 32] =
+  hex_literal::hex!("bbd604d2ba11ba27935e006ed39c9bfdd99b76bf4a50654bc1e1e61217962698");
+
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct BlockHeader {
   pub major_version: u64,
@@ -68,6 +75,31 @@ impl Block {
     Ok(())
   }
 
+  fn tx_merkle_root(&self) -> [u8; 32] {
+    merkle_root(self.miner_tx.hash(), &self.txs)
+  }
+
+  fn serialize_hashable(&self) -> Vec<u8> {
+    let mut blob = self.header.serialize();
+    blob.extend_from_slice(&self.tx_merkle_root());
+    write_varint(&(1 + u64::try_from(self.txs.len()).unwrap()), &mut blob).unwrap();
+
+    let mut out = Vec::with_capacity(8 + blob.len());
+    write_varint(&u64::try_from(blob.len()).unwrap(), &mut out).unwrap();
+    out.append(&mut blob);
+
+    out
+  }
+
+  pub fn hash(&self) -> [u8; 32] {
+    let hash = hash(&self.serialize_hashable());
+    if hash == CORRECT_BLOCK_HASH_202612 {
+      return EXISTING_BLOCK_HASH_202612;
+    };
+
+    hash
+  }
+
   pub fn serialize(&self) -> Vec<u8> {
     let mut serialized = vec![];
     self.write(&mut serialized).unwrap();