Rename the coins folder to networks (#583)

* Rename the coins folder to networks

Ethereum isn't a coin. It's a network.

Resolves #357.

* More renames of coins -> networks in orchestration

* Correct paths in tests/

* cargo fmt

networks/bitcoin/Cargo.toml

@@ -0,0 +1,68 @@
+[package]
+name = "bitcoin-serai"
+version = "0.3.0"
+description = "A Bitcoin library for FROST-signing transactions"
+license = "MIT"
+repository = "https://github.com/serai-dex/serai/tree/develop/networks/bitcoin"
+authors = ["Luke Parker <lukeparker5132@gmail.com>", "Vrx <vrx00@proton.me>"]
+edition = "2021"
+rust-version = "1.79"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
+[lints]
+workspace = true
+
+[dependencies]
+std-shims = { version = "0.1.1", path = "../../common/std-shims", default-features = false }
+
+thiserror = { version = "1", default-features = false, optional = true }
+
+zeroize = { version = "^1.5", default-features = false }
+rand_core = { version = "0.6", default-features = false }
+
+bitcoin = { version = "0.32", default-features = false }
+
+k256 = { version = "^0.13.1", default-features = false, features = ["arithmetic", "bits"] }
+
+transcript = { package = "flexible-transcript", path = "../../crypto/transcript", version = "0.3", default-features = false, features = ["recommended"], optional = true }
+frost = { package = "modular-frost", path = "../../crypto/frost", version = "0.8", default-features = false, features = ["secp256k1"], optional = true }
+
+hex = { version = "0.4", default-features = false, optional = true }
+serde = { version = "1", default-features = false, features = ["derive"], optional = true }
+serde_json = { version = "1", default-features = false, optional = true }
+simple-request = { path = "../../common/request", version = "0.1", default-features = false, features = ["tls", "basic-auth"], optional = true }
+
+[dev-dependencies]
+secp256k1 = { version = "0.29", default-features = false, features = ["std"] }
+
+frost = { package = "modular-frost", path = "../../crypto/frost", features = ["tests"] }
+
+tokio = { version = "1", features = ["macros"] }
+
+[features]
+std = [
+  "std-shims/std",
+
+  "thiserror",
+
+  "zeroize/std",
+  "rand_core/std",
+
+  "bitcoin/std",
+  "bitcoin/serde",
+
+  "k256/std",
+
+  "transcript/std",
+  "frost",
+
+  "hex/std",
+  "serde/std",
+  "serde_json/std",
+  "simple-request",
+]
+hazmat = []
+default = ["std"]

networks/bitcoin/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2022-2023 Luke Parker
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

networks/bitcoin/README.md

@@ -0,0 +1,4 @@
+# bitcoin-serai
+
+An application of [modular-frost](https://docs.rs/modular-frost) to Bitcoin
+transactions, enabling extremely-efficient multisigs.

networks/bitcoin/src/crypto.rs

@@ -0,0 +1,166 @@
+use k256::{
+  elliptic_curve::sec1::{Tag, ToEncodedPoint},
+  ProjectivePoint,
+};
+
+use bitcoin::key::XOnlyPublicKey;
+
+/// Get the x coordinate of a non-infinity, even point. Panics on invalid input.
+pub fn x(key: &ProjectivePoint) -> [u8; 32] {
+  let encoded = key.to_encoded_point(true);
+  assert_eq!(encoded.tag(), Tag::CompressedEvenY, "x coordinate of odd key");
+  (*encoded.x().expect("point at infinity")).into()
+}
+
+/// Convert a non-infinity even point to a XOnlyPublicKey. Panics on invalid input.
+pub fn x_only(key: &ProjectivePoint) -> XOnlyPublicKey {
+  XOnlyPublicKey::from_slice(&x(key)).expect("x_only was passed a point which was infinity or odd")
+}
+
+/// Make a point even by adding the generator until it is even.
+///
+/// Returns the even point and the amount of additions required.
+#[cfg(any(feature = "std", feature = "hazmat"))]
+pub fn make_even(mut key: ProjectivePoint) -> (ProjectivePoint, u64) {
+  let mut c = 0;
+  while key.to_encoded_point(true).tag() == Tag::CompressedOddY {
+    key += ProjectivePoint::GENERATOR;
+    c += 1;
+  }
+  (key, c)
+}
+
+#[cfg(feature = "std")]
+mod frost_crypto {
+  use core::fmt::Debug;
+  use std_shims::{vec::Vec, io};
+
+  use zeroize::Zeroizing;
+  use rand_core::{RngCore, CryptoRng};
+
+  use bitcoin::hashes::{HashEngine, Hash, sha256::Hash as Sha256};
+
+  use transcript::Transcript;
+
+  use k256::{elliptic_curve::ops::Reduce, U256, Scalar};
+
+  use frost::{
+    curve::{Ciphersuite, Secp256k1},
+    Participant, ThresholdKeys, ThresholdView, FrostError,
+    algorithm::{Hram as HramTrait, Algorithm, Schnorr as FrostSchnorr},
+  };
+
+  use super::*;
+
+  /// A BIP-340 compatible HRAm for use with the modular-frost Schnorr Algorithm.
+  ///
+  /// If passed an odd nonce, it will have the generator added until it is even.
+  ///
+  /// If the key is odd, this will panic.
+  #[derive(Clone, Copy, Debug)]
+  pub struct Hram;
+  #[allow(non_snake_case)]
+  impl HramTrait<Secp256k1> for Hram {
+    fn hram(R: &ProjectivePoint, A: &ProjectivePoint, m: &[u8]) -> Scalar {
+      // Convert the nonce to be even
+      let (R, _) = make_even(*R);
+
+      const TAG_HASH: Sha256 = Sha256::const_hash(b"BIP0340/challenge");
+
+      let mut data = Sha256::engine();
+      data.input(TAG_HASH.as_ref());
+      data.input(TAG_HASH.as_ref());
+      data.input(&x(&R));
+      data.input(&x(A));
+      data.input(m);
+
+      Scalar::reduce(U256::from_be_slice(Sha256::from_engine(data).as_ref()))
+    }
+  }
+
+  /// BIP-340 Schnorr signature algorithm.
+  ///
+  /// This must be used with a ThresholdKeys whose group key is even. If it is odd, this will panic.
+  #[derive(Clone)]
+  pub struct Schnorr<T: Sync + Clone + Debug + Transcript>(FrostSchnorr<Secp256k1, T, Hram>);
+  impl<T: Sync + Clone + Debug + Transcript> Schnorr<T> {
+    /// Construct a Schnorr algorithm continuing the specified transcript.
+    pub fn new(transcript: T) -> Schnorr<T> {
+      Schnorr(FrostSchnorr::new(transcript))
+    }
+  }
+
+  impl<T: Sync + Clone + Debug + Transcript> Algorithm<Secp256k1> for Schnorr<T> {
+    type Transcript = T;
+    type Addendum = ();
+    type Signature = [u8; 64];
+
+    fn transcript(&mut self) -> &mut Self::Transcript {
+      self.0.transcript()
+    }
+
+    fn nonces(&self) -> Vec<Vec<ProjectivePoint>> {
+      self.0.nonces()
+    }
+
+    fn preprocess_addendum<R: RngCore + CryptoRng>(
+      &mut self,
+      rng: &mut R,
+      keys: &ThresholdKeys<Secp256k1>,
+    ) {
+      self.0.preprocess_addendum(rng, keys)
+    }
+
+    fn read_addendum<R: io::Read>(&self, reader: &mut R) -> io::Result<Self::Addendum> {
+      self.0.read_addendum(reader)
+    }
+
+    fn process_addendum(
+      &mut self,
+      view: &ThresholdView<Secp256k1>,
+      i: Participant,
+      addendum: (),
+    ) -> Result<(), FrostError> {
+      self.0.process_addendum(view, i, addendum)
+    }
+
+    fn sign_share(
+      &mut self,
+      params: &ThresholdView<Secp256k1>,
+      nonce_sums: &[Vec<<Secp256k1 as Ciphersuite>::G>],
+      nonces: Vec<Zeroizing<<Secp256k1 as Ciphersuite>::F>>,
+      msg: &[u8],
+    ) -> <Secp256k1 as Ciphersuite>::F {
+      self.0.sign_share(params, nonce_sums, nonces, msg)
+    }
+
+    #[must_use]
+    fn verify(
+      &self,
+      group_key: ProjectivePoint,
+      nonces: &[Vec<ProjectivePoint>],
+      sum: Scalar,
+    ) -> Option<Self::Signature> {
+      self.0.verify(group_key, nonces, sum).map(|mut sig| {
+        // Make the R of the final signature even
+        let offset;
+        (sig.R, offset) = make_even(sig.R);
+        // s = r + cx. Since we added to the r, add to s
+        sig.s += Scalar::from(offset);
+        // Convert to a Bitcoin signature by dropping the byte for the point's sign bit
+        sig.serialize()[1 ..].try_into().unwrap()
+      })
+    }
+
+    fn verify_share(
+      &self,
+      verification_share: ProjectivePoint,
+      nonces: &[Vec<ProjectivePoint>],
+      share: Scalar,
+    ) -> Result<Vec<(Scalar, ProjectivePoint)>, ()> {
+      self.0.verify_share(verification_share, nonces, share)
+    }
+  }
+}
+#[cfg(feature = "std")]
+pub use frost_crypto::*;

networks/bitcoin/src/lib.rs

@@ -0,0 +1,24 @@
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+
+/// The bitcoin Rust library.
+pub use bitcoin;
+
+/// Cryptographic helpers.
+#[cfg(feature = "hazmat")]
+pub mod crypto;
+#[cfg(not(feature = "hazmat"))]
+pub(crate) mod crypto;
+
+/// Wallet functionality to create transactions.
+pub mod wallet;
+/// A minimal asynchronous Bitcoin RPC client.
+#[cfg(feature = "std")]
+pub mod rpc;
+
+#[cfg(test)]
+mod tests;

networks/bitcoin/src/rpc.rs

@@ -0,0 +1,226 @@
+use core::fmt::Debug;
+use std::collections::HashSet;
+
+use thiserror::Error;
+
+use serde::{Deserialize, de::DeserializeOwned};
+use serde_json::json;
+
+use simple_request::{hyper, Request, Client};
+
+use bitcoin::{
+  hashes::{Hash, hex::FromHex},
+  consensus::encode,
+  Txid, Transaction, BlockHash, Block,
+};
+
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize)]
+pub struct Error {
+  code: isize,
+  message: String,
+}
+
+#[derive(Clone, Debug, Deserialize)]
+#[serde(untagged)]
+enum RpcResponse<T> {
+  Ok { result: T },
+  Err { error: Error },
+}
+
+/// A minimal asynchronous Bitcoin RPC client.
+#[derive(Clone, Debug)]
+pub struct Rpc {
+  client: Client,
+  url: String,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, Error)]
+pub enum RpcError {
+  #[error("couldn't connect to node")]
+  ConnectionError,
+  #[error("request had an error: {0:?}")]
+  RequestError(Error),
+  #[error("node replied with invalid JSON")]
+  InvalidJson(serde_json::error::Category),
+  #[error("node sent an invalid response ({0})")]
+  InvalidResponse(&'static str),
+  #[error("node was missing expected methods")]
+  MissingMethods(HashSet<&'static str>),
+}
+
+impl Rpc {
+  /// Create a new connection to a Bitcoin RPC.
+  ///
+  /// An RPC call is performed to ensure the node is reachable (and that an invalid URL wasn't
+  /// provided).
+  ///
+  /// Additionally, a set of expected methods is checked to be offered by the Bitcoin RPC. If these
+  /// methods aren't provided, an error with the missing methods is returned. This ensures all RPC
+  /// routes explicitly provided by this library are at least possible.
+  ///
+  /// Each individual RPC route may still fail at time-of-call, regardless of the arguments
+  /// provided to this library, if the RPC has an incompatible argument layout. That is not checked
+  /// at time of RPC creation.
+  pub async fn new(url: String) -> Result<Rpc, RpcError> {
+    let rpc = Rpc { client: Client::with_connection_pool(), url };
+
+    // Make an RPC request to verify the node is reachable and sane
+    let res: String = rpc.rpc_call("help", json!([])).await?;
+
+    // Verify all methods we expect are present
+    // If we had a more expanded RPC, due to differences in RPC versions, it wouldn't make sense to
+    // error if all methods weren't present
+    // We only provide a very minimal set of methods which have been largely consistent, hence why
+    // this is sane
+    let mut expected_methods = HashSet::from([
+      "help",
+      "getblockcount",
+      "getblockhash",
+      "getblockheader",
+      "getblock",
+      "sendrawtransaction",
+      "getrawtransaction",
+    ]);
+    for line in res.split('\n') {
+      // This doesn't check if the arguments are as expected
+      // This is due to Bitcoin supporting a large amount of optional arguments, which
+      // occasionally change, with their own mechanism of text documentation, making matching off
+      // it a quite involved task
+      // Instead, once we've confirmed the methods are present, we assume our arguments are aligned
+      // Else we'll error at time of call
+      if expected_methods.remove(line.split(' ').next().unwrap_or("")) &&
+        expected_methods.is_empty()
+      {
+        break;
+      }
+    }
+    if !expected_methods.is_empty() {
+      Err(RpcError::MissingMethods(expected_methods))?;
+    };
+
+    Ok(rpc)
+  }
+
+  /// Perform an arbitrary RPC call.
+  pub async fn rpc_call<Response: DeserializeOwned + Debug>(
+    &self,
+    method: &str,
+    params: serde_json::Value,
+  ) -> Result<Response, RpcError> {
+    let mut request = Request::from(
+      hyper::Request::post(&self.url)
+        .header("Content-Type", "application/json")
+        .body(
+          serde_json::to_vec(&json!({ "jsonrpc": "2.0", "method": method, "params": params }))
+            .unwrap()
+            .into(),
+        )
+        .unwrap(),
+    );
+    request.with_basic_auth();
+    let mut res = self
+      .client
+      .request(request)
+      .await
+      .map_err(|_| RpcError::ConnectionError)?
+      .body()
+      .await
+      .map_err(|_| RpcError::ConnectionError)?;
+
+    let res: RpcResponse<Response> =
+      serde_json::from_reader(&mut res).map_err(|e| RpcError::InvalidJson(e.classify()))?;
+    match res {
+      RpcResponse::Ok { result } => Ok(result),
+      RpcResponse::Err { error } => Err(RpcError::RequestError(error)),
+    }
+  }
+
+  /// Get the latest block's number.
+  ///
+  /// The genesis block's 'number' is zero. They increment from there.
+  pub async fn get_latest_block_number(&self) -> Result<usize, RpcError> {
+    // getblockcount doesn't return the amount of blocks on the current chain, yet the "height"
+    // of the current chain. The "height" of the current chain is defined as the "height" of the
+    // tip block of the current chain. The "height" of a block is defined as the amount of blocks
+    // present when the block was created. Accordingly, the genesis block has height 0, and
+    // getblockcount will return 0 when it's only the only block, despite their being one block.
+    self.rpc_call("getblockcount", json!([])).await
+  }
+
+  /// Get the hash of a block by the block's number.
+  pub async fn get_block_hash(&self, number: usize) -> Result<[u8; 32], RpcError> {
+    let mut hash = self
+      .rpc_call::<BlockHash>("getblockhash", json!([number]))
+      .await?
+      .as_raw_hash()
+      .to_byte_array();
+    // bitcoin stores the inner bytes in reverse order.
+    hash.reverse();
+    Ok(hash)
+  }
+
+  /// Get a block's number by its hash.
+  pub async fn get_block_number(&self, hash: &[u8; 32]) -> Result<usize, RpcError> {
+    #[derive(Deserialize, Debug)]
+    struct Number {
+      height: usize,
+    }
+    Ok(self.rpc_call::<Number>("getblockheader", json!([hex::encode(hash)])).await?.height)
+  }
+
+  /// Get a block by its hash.
+  pub async fn get_block(&self, hash: &[u8; 32]) -> Result<Block, RpcError> {
+    let hex = self.rpc_call::<String>("getblock", json!([hex::encode(hash), 0])).await?;
+    let bytes: Vec<u8> = FromHex::from_hex(&hex)
+      .map_err(|_| RpcError::InvalidResponse("node didn't use hex to encode the block"))?;
+    let block: Block = encode::deserialize(&bytes)
+      .map_err(|_| RpcError::InvalidResponse("node sent an improperly serialized block"))?;
+
+    let mut block_hash = *block.block_hash().as_raw_hash().as_byte_array();
+    block_hash.reverse();
+    if hash != &block_hash {
+      Err(RpcError::InvalidResponse("node replied with a different block"))?;
+    }
+
+    Ok(block)
+  }
+
+  /// Publish a transaction.
+  pub async fn send_raw_transaction(&self, tx: &Transaction) -> Result<Txid, RpcError> {
+    let txid = match self.rpc_call("sendrawtransaction", json!([encode::serialize_hex(tx)])).await {
+      Ok(txid) => txid,
+      Err(e) => {
+        // A const from Bitcoin's bitcoin/src/rpc/protocol.h
+        const RPC_VERIFY_ALREADY_IN_CHAIN: isize = -27;
+        // If this was already successfully published, consider this having succeeded
+        if let RpcError::RequestError(Error { code, .. }) = e {
+          if code == RPC_VERIFY_ALREADY_IN_CHAIN {
+            return Ok(tx.compute_txid());
+          }
+        }
+        Err(e)?
+      }
+    };
+    if txid != tx.compute_txid() {
+      Err(RpcError::InvalidResponse("returned TX ID inequals calculated TX ID"))?;
+    }
+    Ok(txid)
+  }
+
+  /// Get a transaction by its hash.
+  pub async fn get_transaction(&self, hash: &[u8; 32]) -> Result<Transaction, RpcError> {
+    let hex = self.rpc_call::<String>("getrawtransaction", json!([hex::encode(hash)])).await?;
+    let bytes: Vec<u8> = FromHex::from_hex(&hex)
+      .map_err(|_| RpcError::InvalidResponse("node didn't use hex to encode the transaction"))?;
+    let tx: Transaction = encode::deserialize(&bytes)
+      .map_err(|_| RpcError::InvalidResponse("node sent an improperly serialized transaction"))?;
+
+    let mut tx_hash = *tx.compute_txid().as_raw_hash().as_byte_array();
+    tx_hash.reverse();
+    if hash != &tx_hash {
+      Err(RpcError::InvalidResponse("node replied with a different transaction"))?;
+    }
+
+    Ok(tx)
+  }
+}

networks/bitcoin/src/tests/crypto.rs

@@ -0,0 +1,46 @@
+use rand_core::OsRng;
+
+use secp256k1::{Secp256k1 as BContext, Message, schnorr::Signature};
+
+use k256::Scalar;
+use transcript::{Transcript, RecommendedTranscript};
+use frost::{
+  curve::Secp256k1,
+  Participant,
+  tests::{algorithm_machines, key_gen, sign},
+};
+
+use crate::{
+  bitcoin::hashes::{Hash as HashTrait, sha256::Hash},
+  crypto::{x_only, make_even, Schnorr},
+};
+
+#[test]
+fn test_algorithm() {
+  let mut keys = key_gen::<_, Secp256k1>(&mut OsRng);
+  const MESSAGE: &[u8] = b"Hello, World!";
+
+  for keys in keys.values_mut() {
+    let (_, offset) = make_even(keys.group_key());
+    *keys = keys.offset(Scalar::from(offset));
+  }
+
+  let algo =
+    Schnorr::<RecommendedTranscript>::new(RecommendedTranscript::new(b"bitcoin-serai sign test"));
+  let sig = sign(
+    &mut OsRng,
+    &algo,
+    keys.clone(),
+    algorithm_machines(&mut OsRng, &algo, &keys),
+    Hash::hash(MESSAGE).as_ref(),
+  );
+
+  BContext::new()
+    .verify_schnorr(
+      &Signature::from_slice(&sig)
+        .expect("couldn't convert produced signature to secp256k1::Signature"),
+      &Message::from_digest_slice(Hash::hash(MESSAGE).as_ref()).unwrap(),
+      &x_only(&keys[&Participant::new(1).unwrap()].group_key()),
+    )
+    .unwrap()
+}

networks/bitcoin/src/tests/mod.rs

@@ -0,0 +1 @@
+mod crypto;

networks/bitcoin/src/wallet/mod.rs

@@ -0,0 +1,193 @@
+use std_shims::{
+  vec::Vec,
+  collections::HashMap,
+  io::{self, Write},
+};
+#[cfg(feature = "std")]
+use std::io::{Read, BufReader};
+
+use k256::{
+  elliptic_curve::sec1::{Tag, ToEncodedPoint},
+  Scalar, ProjectivePoint,
+};
+
+#[cfg(feature = "std")]
+use frost::{
+  curve::{Ciphersuite, Secp256k1},
+  ThresholdKeys,
+};
+
+use bitcoin::{
+  consensus::encode::serialize, key::TweakedPublicKey, OutPoint, ScriptBuf, TxOut, Transaction,
+  Block,
+};
+#[cfg(feature = "std")]
+use bitcoin::consensus::encode::Decodable;
+
+use crate::crypto::x_only;
+#[cfg(feature = "std")]
+use crate::crypto::make_even;
+
+#[cfg(feature = "std")]
+mod send;
+#[cfg(feature = "std")]
+pub use send::*;
+
+/// Tweak keys to ensure they're usable with Bitcoin.
+///
+/// Taproot keys, which these keys are used as, must be even. This offsets the keys until they're
+/// even.
+#[cfg(feature = "std")]
+pub fn tweak_keys(keys: &ThresholdKeys<Secp256k1>) -> ThresholdKeys<Secp256k1> {
+  let (_, offset) = make_even(keys.group_key());
+  keys.offset(Scalar::from(offset))
+}
+
+/// Return the Taproot address payload for a public key.
+///
+/// If the key is odd, this will return None.
+pub fn p2tr_script_buf(key: ProjectivePoint) -> Option<ScriptBuf> {
+  if key.to_encoded_point(true).tag() != Tag::CompressedEvenY {
+    return None;
+  }
+
+  Some(ScriptBuf::new_p2tr_tweaked(TweakedPublicKey::dangerous_assume_tweaked(x_only(&key))))
+}
+
+/// A spendable output.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct ReceivedOutput {
+  // The scalar offset to obtain the key usable to spend this output.
+  offset: Scalar,
+  // The output to spend.
+  output: TxOut,
+  // The TX ID and vout of the output to spend.
+  outpoint: OutPoint,
+}
+
+impl ReceivedOutput {
+  /// The offset for this output.
+  pub fn offset(&self) -> Scalar {
+    self.offset
+  }
+
+  /// The Bitcoin output for this output.
+  pub fn output(&self) -> &TxOut {
+    &self.output
+  }
+
+  /// The outpoint for this output.
+  pub fn outpoint(&self) -> &OutPoint {
+    &self.outpoint
+  }
+
+  /// The value of this output.
+  pub fn value(&self) -> u64 {
+    self.output.value.to_sat()
+  }
+
+  /// Read a ReceivedOutput from a generic satisfying Read.
+  #[cfg(feature = "std")]
+  pub fn read<R: Read>(r: &mut R) -> io::Result<ReceivedOutput> {
+    let offset = Secp256k1::read_F(r)?;
+    let output;
+    let outpoint;
+    {
+      let mut buf_r = BufReader::with_capacity(0, r);
+      output =
+        TxOut::consensus_decode(&mut buf_r).map_err(|_| io::Error::other("invalid TxOut"))?;
+      outpoint =
+        OutPoint::consensus_decode(&mut buf_r).map_err(|_| io::Error::other("invalid OutPoint"))?;
+    }
+    Ok(ReceivedOutput { offset, output, outpoint })
+  }
+
+  /// Write a ReceivedOutput to a generic satisfying Write.
+  pub fn write<W: Write>(&self, w: &mut W) -> io::Result<()> {
+    w.write_all(&self.offset.to_bytes())?;
+    w.write_all(&serialize(&self.output))?;
+    w.write_all(&serialize(&self.outpoint))
+  }
+
+  /// Serialize a ReceivedOutput to a `Vec<u8>`.
+  pub fn serialize(&self) -> Vec<u8> {
+    let mut res = Vec::new();
+    self.write(&mut res).unwrap();
+    res
+  }
+}
+
+/// A transaction scanner capable of being used with HDKD schemes.
+#[derive(Clone, Debug)]
+pub struct Scanner {
+  key: ProjectivePoint,
+  scripts: HashMap<ScriptBuf, Scalar>,
+}
+
+impl Scanner {
+  /// Construct a Scanner for a key.
+  ///
+  /// Returns None if this key can't be scanned for.
+  pub fn new(key: ProjectivePoint) -> Option<Scanner> {
+    let mut scripts = HashMap::new();
+    scripts.insert(p2tr_script_buf(key)?, Scalar::ZERO);
+    Some(Scanner { key, scripts })
+  }
+
+  /// Register an offset to scan for.
+  ///
+  /// Due to Bitcoin's requirement that points are even, not every offset may be used.
+  /// If an offset isn't usable, it will be incremented until it is. If this offset is already
+  /// present, None is returned. Else, Some(offset) will be, with the used offset.
+  ///
+  /// This means offsets are surjective, not bijective, and the order offsets are registered in
+  /// may determine the validity of future offsets.
+  pub fn register_offset(&mut self, mut offset: Scalar) -> Option<Scalar> {
+    // This loop will terminate as soon as an even point is found, with any point having a ~50%
+    // chance of being even
+    // That means this should terminate within a very small amount of iterations
+    loop {
+      match p2tr_script_buf(self.key + (ProjectivePoint::GENERATOR * offset)) {
+        Some(script) => {
+          if self.scripts.contains_key(&script) {
+            None?;
+          }
+          self.scripts.insert(script, offset);
+          return Some(offset);
+        }
+        None => offset += Scalar::ONE,
+      }
+    }
+  }
+
+  /// Scan a transaction.
+  pub fn scan_transaction(&self, tx: &Transaction) -> Vec<ReceivedOutput> {
+    let mut res = Vec::new();
+    for (vout, output) in tx.output.iter().enumerate() {
+      // If the vout index exceeds 2**32, stop scanning outputs
+      let Ok(vout) = u32::try_from(vout) else { break };
+
+      if let Some(offset) = self.scripts.get(&output.script_pubkey) {
+        res.push(ReceivedOutput {
+          offset: *offset,
+          output: output.clone(),
+          outpoint: OutPoint::new(tx.compute_txid(), vout),
+        });
+      }
+    }
+    res
+  }
+
+  /// Scan a block.
+  ///
+  /// This will also scan the coinbase transaction which is bound by maturity. If received outputs
+  /// must be immediately spendable, a post-processing pass is needed to remove those outputs.
+  /// Alternatively, scan_transaction can be called on `block.txdata[1 ..]`.
+  pub fn scan_block(&self, block: &Block) -> Vec<ReceivedOutput> {
+    let mut res = Vec::new();
+    for tx in &block.txdata {
+      res.extend(self.scan_transaction(tx));
+    }
+    res
+  }
+}

networks/bitcoin/src/wallet/send.rs

@@ -0,0 +1,453 @@
+use std_shims::{
+  io::{self, Read},
+  collections::HashMap,
+};
+
+use thiserror::Error;
+
+use rand_core::{RngCore, CryptoRng};
+
+use transcript::{Transcript, RecommendedTranscript};
+
+use k256::{elliptic_curve::sec1::ToEncodedPoint, Scalar};
+use frost::{curve::Secp256k1, Participant, ThresholdKeys, FrostError, sign::*};
+
+use bitcoin::{
+  hashes::Hash,
+  sighash::{TapSighashType, SighashCache, Prevouts},
+  absolute::LockTime,
+  script::{PushBytesBuf, ScriptBuf},
+  transaction::{Version, Transaction},
+  OutPoint, Sequence, Witness, TxIn, Amount, TxOut,
+};
+
+use crate::{
+  crypto::Schnorr,
+  wallet::{ReceivedOutput, p2tr_script_buf},
+};
+
+#[rustfmt::skip]
+// https://github.com/bitcoin/bitcoin/blob/306ccd4927a2efe325c8d84be1bdb79edeb29b04/src/policy/policy.cpp#L26-L63
+// As the above notes, a lower amount may not be considered dust if contained in a SegWit output
+// This doesn't bother with delineation due to how marginal these values are, and because it isn't
+// worth the complexity to implement differentation
+pub const DUST: u64 = 546;
+
+#[derive(Clone, PartialEq, Eq, Debug, Error)]
+pub enum TransactionError {
+  #[error("no inputs were specified")]
+  NoInputs,
+  #[error("no outputs were created")]
+  NoOutputs,
+  #[error("a specified payment's amount was less than bitcoin's required minimum")]
+  DustPayment,
+  #[error("too much data was specified")]
+  TooMuchData,
+  #[error("fee was too low to pass the default minimum fee rate")]
+  TooLowFee,
+  #[error("not enough funds for these payments")]
+  NotEnoughFunds,
+  #[error("transaction was too large")]
+  TooLargeTransaction,
+}
+
+/// A signable transaction, clone-able across attempts.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct SignableTransaction {
+  tx: Transaction,
+  offsets: Vec<Scalar>,
+  prevouts: Vec<TxOut>,
+  needed_fee: u64,
+}
+
+impl SignableTransaction {
+  fn calculate_weight_vbytes(
+    inputs: usize,
+    payments: &[(ScriptBuf, u64)],
+    change: Option<&ScriptBuf>,
+  ) -> (u64, u64) {
+    // Expand this a full transaction in order to use the bitcoin library's weight function
+    let mut tx = Transaction {
+      version: Version(2),
+      lock_time: LockTime::ZERO,
+      input: vec![
+        TxIn {
+          // This is a fixed size
+          // See https://developer.bitcoin.org/reference/transactions.html#raw-transaction-format
+          previous_output: OutPoint::default(),
+          // This is empty for a Taproot spend
+          script_sig: ScriptBuf::new(),
+          // This is fixed size, yet we do use Sequence::MAX
+          sequence: Sequence::MAX,
+          // Our witnesses contains a single 64-byte signature
+          witness: Witness::from_slice(&[vec![0; 64]])
+        };
+        inputs
+      ],
+      output: payments
+        .iter()
+        // The payment is a fixed size so we don't have to use it here
+        // The script pub key is not of a fixed size and does have to be used here
+        .map(|payment| TxOut {
+          value: Amount::from_sat(payment.1),
+          script_pubkey: payment.0.clone(),
+        })
+        .collect(),
+    };
+    if let Some(change) = change {
+      // Use a 0 value since we're currently unsure what the change amount will be, and since
+      // the value is fixed size (so any value could be used here)
+      tx.output.push(TxOut { value: Amount::ZERO, script_pubkey: change.clone() });
+    }
+
+    let weight = tx.weight();
+
+    // Now calculate the size in vbytes
+
+    /*
+      "Virtual transaction size" is weight ceildiv 4 per
+      https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki
+
+      https://github.com/bitcoin/bitcoin/blob/306ccd4927a2efe325c8d84be1bdb79edeb29b04
+        /src/policy/policy.cpp#L295-L298
+      implements this almost as expected, with an additional consideration to signature operations
+
+      Signature operations (the second argument of the following call) do not count Taproot
+      signatures per https://github.com/bitcoin/bips/blob/master/bip-0342.mediawiki#cite_ref-11-0
+
+      We don't risk running afoul of the Taproot signature limit as it allows at least one per
+      input, which is all we use
+    */
+    (
+      weight.to_wu(),
+      u64::try_from(bitcoin::policy::get_virtual_tx_size(
+        i64::try_from(weight.to_wu()).unwrap(),
+        0i64,
+      ))
+      .unwrap(),
+    )
+  }
+
+  /// Returns the fee necessary for this transaction to achieve the fee rate specified at
+  /// construction.
+  ///
+  /// The actual fee this transaction will use is `sum(inputs) - sum(outputs)`.
+  pub fn needed_fee(&self) -> u64 {
+    self.needed_fee
+  }
+
+  /// Returns the fee this transaction will use.
+  pub fn fee(&self) -> u64 {
+    self.prevouts.iter().map(|prevout| prevout.value.to_sat()).sum::<u64>() -
+      self.tx.output.iter().map(|prevout| prevout.value.to_sat()).sum::<u64>()
+  }
+
+  /// Create a new SignableTransaction.
+  ///
+  /// If a change address is specified, any leftover funds will be sent to it if the leftover funds
+  /// exceed the minimum output amount. If a change address isn't specified, all leftover funds
+  /// will become part of the paid fee.
+  ///
+  /// If data is specified, an OP_RETURN output will be added with it.
+  pub fn new(
+    mut inputs: Vec<ReceivedOutput>,
+    payments: &[(ScriptBuf, u64)],
+    change: Option<ScriptBuf>,
+    data: Option<Vec<u8>>,
+    fee_per_vbyte: u64,
+  ) -> Result<SignableTransaction, TransactionError> {
+    if inputs.is_empty() {
+      Err(TransactionError::NoInputs)?;
+    }
+
+    if payments.is_empty() && change.is_none() && data.is_none() {
+      Err(TransactionError::NoOutputs)?;
+    }
+
+    for (_, amount) in payments {
+      if *amount < DUST {
+        Err(TransactionError::DustPayment)?;
+      }
+    }
+
+    if data.as_ref().map_or(0, Vec::len) > 80 {
+      Err(TransactionError::TooMuchData)?;
+    }
+
+    let input_sat = inputs.iter().map(|input| input.output.value.to_sat()).sum::<u64>();
+    let offsets = inputs.iter().map(|input| input.offset).collect();
+    let tx_ins = inputs
+      .iter()
+      .map(|input| TxIn {
+        previous_output: input.outpoint,
+        script_sig: ScriptBuf::new(),
+        sequence: Sequence::MAX,
+        witness: Witness::new(),
+      })
+      .collect::<Vec<_>>();
+
+    let payment_sat = payments.iter().map(|payment| payment.1).sum::<u64>();
+    let mut tx_outs = payments
+      .iter()
+      .map(|payment| TxOut { value: Amount::from_sat(payment.1), script_pubkey: payment.0.clone() })
+      .collect::<Vec<_>>();
+
+    // Add the OP_RETURN output
+    if let Some(data) = data {
+      tx_outs.push(TxOut {
+        value: Amount::ZERO,
+        script_pubkey: ScriptBuf::new_op_return(
+          PushBytesBuf::try_from(data)
+            .expect("data didn't fit into PushBytes depsite being checked"),
+        ),
+      })
+    }
+
+    let (mut weight, vbytes) = Self::calculate_weight_vbytes(tx_ins.len(), payments, None);
+
+    let mut needed_fee = fee_per_vbyte * vbytes;
+    // Technically, if there isn't change, this TX may still pay enough of a fee to pass the
+    // minimum fee. Such edge cases aren't worth programming when they go against intent, as the
+    // specified fee rate is too low to be valid
+    // bitcoin::policy::DEFAULT_MIN_RELAY_TX_FEE is in sats/kilo-vbyte
+    if needed_fee < ((u64::from(bitcoin::policy::DEFAULT_MIN_RELAY_TX_FEE) * vbytes) / 1000) {
+      Err(TransactionError::TooLowFee)?;
+    }
+
+    if input_sat < (payment_sat + needed_fee) {
+      Err(TransactionError::NotEnoughFunds)?;
+    }
+
+    // If there's a change address, check if there's change to give it
+    if let Some(change) = change {
+      let (weight_with_change, vbytes_with_change) =
+        Self::calculate_weight_vbytes(tx_ins.len(), payments, Some(&change));
+      let fee_with_change = fee_per_vbyte * vbytes_with_change;
+      if let Some(value) = input_sat.checked_sub(payment_sat + fee_with_change) {
+        if value >= DUST {
+          tx_outs.push(TxOut { value: Amount::from_sat(value), script_pubkey: change });
+          weight = weight_with_change;
+          needed_fee = fee_with_change;
+        }
+      }
+    }
+
+    if tx_outs.is_empty() {
+      Err(TransactionError::NoOutputs)?;
+    }
+
+    if weight > u64::from(bitcoin::policy::MAX_STANDARD_TX_WEIGHT) {
+      Err(TransactionError::TooLargeTransaction)?;
+    }
+
+    Ok(SignableTransaction {
+      tx: Transaction {
+        version: Version(2),
+        lock_time: LockTime::ZERO,
+        input: tx_ins,
+        output: tx_outs,
+      },
+      offsets,
+      prevouts: inputs.drain(..).map(|input| input.output).collect(),
+      needed_fee,
+    })
+  }
+
+  /// Returns the TX ID of the transaction this will create.
+  pub fn txid(&self) -> [u8; 32] {
+    let mut res = self.tx.compute_txid().to_byte_array();
+    res.reverse();
+    res
+  }
+
+  /// Returns the outputs this transaction will create.
+  pub fn outputs(&self) -> &[TxOut] {
+    &self.tx.output
+  }
+
+  /// Create a multisig machine for this transaction.
+  ///
+  /// Returns None if the wrong keys are used.
+  pub fn multisig(
+    self,
+    keys: &ThresholdKeys<Secp256k1>,
+    mut transcript: RecommendedTranscript,
+  ) -> Option<TransactionMachine> {
+    transcript.domain_separate(b"bitcoin_transaction");
+    transcript.append_message(b"root_key", keys.group_key().to_encoded_point(true).as_bytes());
+
+    // Transcript the inputs and outputs
+    let tx = &self.tx;
+    for input in &tx.input {
+      transcript.append_message(b"input_hash", input.previous_output.txid);
+      transcript.append_message(b"input_output_index", input.previous_output.vout.to_le_bytes());
+    }
+    for payment in &tx.output {
+      transcript.append_message(b"output_script", payment.script_pubkey.as_bytes());
+      transcript.append_message(b"output_amount", payment.value.to_sat().to_le_bytes());
+    }
+
+    let mut sigs = vec![];
+    for i in 0 .. tx.input.len() {
+      let mut transcript = transcript.clone();
+      // This unwrap is safe since any transaction with this many inputs violates the maximum
+      // size allowed under standards, which this lib will error on creation of
+      transcript.append_message(b"signing_input", u32::try_from(i).unwrap().to_le_bytes());
+
+      let offset = keys.clone().offset(self.offsets[i]);
+      if p2tr_script_buf(offset.group_key())? != self.prevouts[i].script_pubkey {
+        None?;
+      }
+
+      sigs.push(AlgorithmMachine::new(
+        Schnorr::new(transcript),
+        keys.clone().offset(self.offsets[i]),
+      ));
+    }
+
+    Some(TransactionMachine { tx: self, sigs })
+  }
+}
+
+/// A FROST signing machine to produce a Bitcoin transaction.
+///
+/// This does not support caching its preprocess. When sign is called, the message must be empty.
+/// This will panic if either `cache` is called or the message isn't empty.
+pub struct TransactionMachine {
+  tx: SignableTransaction,
+  sigs: Vec<AlgorithmMachine<Secp256k1, Schnorr<RecommendedTranscript>>>,
+}
+
+impl PreprocessMachine for TransactionMachine {
+  type Preprocess = Vec<Preprocess<Secp256k1, ()>>;
+  type Signature = Transaction;
+  type SignMachine = TransactionSignMachine;
+
+  fn preprocess<R: RngCore + CryptoRng>(
+    mut self,
+    rng: &mut R,
+  ) -> (Self::SignMachine, Self::Preprocess) {
+    let mut preprocesses = Vec::with_capacity(self.sigs.len());
+    let sigs = self
+      .sigs
+      .drain(..)
+      .map(|sig| {
+        let (sig, preprocess) = sig.preprocess(rng);
+        preprocesses.push(preprocess);
+        sig
+      })
+      .collect();
+
+    (TransactionSignMachine { tx: self.tx, sigs }, preprocesses)
+  }
+}
+
+pub struct TransactionSignMachine {
+  tx: SignableTransaction,
+  sigs: Vec<AlgorithmSignMachine<Secp256k1, Schnorr<RecommendedTranscript>>>,
+}
+
+impl SignMachine<Transaction> for TransactionSignMachine {
+  type Params = ();
+  type Keys = ThresholdKeys<Secp256k1>;
+  type Preprocess = Vec<Preprocess<Secp256k1, ()>>;
+  type SignatureShare = Vec<SignatureShare<Secp256k1>>;
+  type SignatureMachine = TransactionSignatureMachine;
+
+  fn cache(self) -> CachedPreprocess {
+    unimplemented!(
+      "Bitcoin transactions don't support caching their preprocesses due to {}",
+      "being already bound to a specific transaction"
+    );
+  }
+
+  fn from_cache(
+    (): (),
+    _: ThresholdKeys<Secp256k1>,
+    _: CachedPreprocess,
+  ) -> (Self, Self::Preprocess) {
+    unimplemented!(
+      "Bitcoin transactions don't support caching their preprocesses due to {}",
+      "being already bound to a specific transaction"
+    );
+  }
+
+  fn read_preprocess<R: Read>(&self, reader: &mut R) -> io::Result<Self::Preprocess> {
+    self.sigs.iter().map(|sig| sig.read_preprocess(reader)).collect()
+  }
+
+  fn sign(
+    mut self,
+    commitments: HashMap<Participant, Self::Preprocess>,
+    msg: &[u8],
+  ) -> Result<(TransactionSignatureMachine, Self::SignatureShare), FrostError> {
+    if !msg.is_empty() {
+      panic!("message was passed to the TransactionSignMachine when it generates its own");
+    }
+
+    let commitments = (0 .. self.sigs.len())
+      .map(|c| {
+        commitments
+          .iter()
+          .map(|(l, commitments)| (*l, commitments[c].clone()))
+          .collect::<HashMap<_, _>>()
+      })
+      .collect::<Vec<_>>();
+
+    let mut cache = SighashCache::new(&self.tx.tx);
+    // Sign committing to all inputs
+    let prevouts = Prevouts::All(&self.tx.prevouts);
+
+    let mut shares = Vec::with_capacity(self.sigs.len());
+    let sigs = self
+      .sigs
+      .drain(..)
+      .enumerate()
+      .map(|(i, sig)| {
+        let (sig, share) = sig.sign(
+          commitments[i].clone(),
+          cache
+            .taproot_key_spend_signature_hash(i, &prevouts, TapSighashType::Default)
+            // This should never happen since the inputs align with the TX the cache was
+            // constructed with, and because i is always < prevouts.len()
+            .expect("taproot_key_spend_signature_hash failed to return a hash")
+            .as_ref(),
+        )?;
+        shares.push(share);
+        Ok(sig)
+      })
+      .collect::<Result<_, _>>()?;
+
+    Ok((TransactionSignatureMachine { tx: self.tx.tx, sigs }, shares))
+  }
+}
+
+pub struct TransactionSignatureMachine {
+  tx: Transaction,
+  sigs: Vec<AlgorithmSignatureMachine<Secp256k1, Schnorr<RecommendedTranscript>>>,
+}
+
+impl SignatureMachine<Transaction> for TransactionSignatureMachine {
+  type SignatureShare = Vec<SignatureShare<Secp256k1>>;
+
+  fn read_share<R: Read>(&self, reader: &mut R) -> io::Result<Self::SignatureShare> {
+    self.sigs.iter().map(|sig| sig.read_share(reader)).collect()
+  }
+
+  fn complete(
+    mut self,
+    mut shares: HashMap<Participant, Self::SignatureShare>,
+  ) -> Result<Transaction, FrostError> {
+    for (input, schnorr) in self.tx.input.iter_mut().zip(self.sigs.drain(..)) {
+      let sig = schnorr.complete(
+        shares.iter_mut().map(|(l, shares)| (*l, shares.remove(0))).collect::<HashMap<_, _>>(),
+      )?;
+
+      let mut witness = Witness::new();
+      witness.push(sig);
+      input.witness = witness;
+    }
+
+    Ok(self.tx)
+  }
+}

networks/bitcoin/tests/rpc.rs

@@ -0,0 +1,25 @@
+use bitcoin_serai::{bitcoin::hashes::Hash as HashTrait, rpc::RpcError};
+
+mod runner;
+use runner::rpc;
+
+async_sequential! {
+  async fn test_rpc() {
+    let rpc = rpc().await;
+
+    // Test get_latest_block_number and get_block_hash by round tripping them
+    let latest = rpc.get_latest_block_number().await.unwrap();
+    let hash = rpc.get_block_hash(latest).await.unwrap();
+    assert_eq!(rpc.get_block_number(&hash).await.unwrap(), latest);
+
+    // Test this actually is the latest block number by checking asking for the next block's errors
+    assert!(matches!(rpc.get_block_hash(latest + 1).await, Err(RpcError::RequestError(_))));
+
+    // Test get_block by checking the received block's hash matches the request
+    let block = rpc.get_block(&hash).await.unwrap();
+    // Hashes are stored in reverse. It's bs from Satoshi
+    let mut block_hash = *block.block_hash().as_raw_hash().as_byte_array();
+    block_hash.reverse();
+    assert_eq!(hash, block_hash);
+  }
+}

networks/bitcoin/tests/runner.rs

@@ -0,0 +1,48 @@
+use std::sync::OnceLock;
+
+use bitcoin_serai::rpc::Rpc;
+
+use tokio::sync::Mutex;
+
+static SEQUENTIAL_CELL: OnceLock<Mutex<()>> = OnceLock::new();
+#[allow(non_snake_case)]
+pub fn SEQUENTIAL() -> &'static Mutex<()> {
+  SEQUENTIAL_CELL.get_or_init(|| Mutex::new(()))
+}
+
+#[allow(dead_code)]
+pub(crate) async fn rpc() -> Rpc {
+  let rpc = Rpc::new("http://serai:seraidex@127.0.0.1:8332".to_string()).await.unwrap();
+
+  // If this node has already been interacted with, clear its chain
+  if rpc.get_latest_block_number().await.unwrap() > 0 {
+    rpc
+      .rpc_call(
+        "invalidateblock",
+        serde_json::json!([hex::encode(rpc.get_block_hash(1).await.unwrap())]),
+      )
+      .await
+      .unwrap()
+  }
+
+  rpc
+}
+
+#[macro_export]
+macro_rules! async_sequential {
+  ($(async fn $name: ident() $body: block)*) => {
+    $(
+      #[tokio::test]
+      async fn $name() {
+        let guard = runner::SEQUENTIAL().lock().await;
+        let local = tokio::task::LocalSet::new();
+        local.run_until(async move {
+          if let Err(err) = tokio::task::spawn_local(async move { $body }).await {
+            drop(guard);
+            Err(err).unwrap()
+          }
+        }).await;
+      }
+    )*
+  }
+}

networks/bitcoin/tests/wallet.rs

@@ -0,0 +1,363 @@
+use std::collections::HashMap;
+
+use rand_core::{RngCore, OsRng};
+
+use transcript::{Transcript, RecommendedTranscript};
+
+use k256::{
+  elliptic_curve::{
+    group::{ff::Field, Group},
+    sec1::{Tag, ToEncodedPoint},
+  },
+  Scalar, ProjectivePoint,
+};
+use frost::{
+  curve::Secp256k1,
+  Participant, ThresholdKeys,
+  tests::{THRESHOLD, key_gen, sign_without_caching},
+};
+
+use bitcoin_serai::{
+  bitcoin::{
+    hashes::Hash as HashTrait,
+    blockdata::opcodes::all::OP_RETURN,
+    script::{PushBytesBuf, Instruction, Instructions, Script},
+    OutPoint, Amount, TxOut, Transaction, Network, Address,
+  },
+  wallet::{
+    tweak_keys, p2tr_script_buf, ReceivedOutput, Scanner, TransactionError, SignableTransaction,
+  },
+  rpc::Rpc,
+};
+
+mod runner;
+use runner::rpc;
+
+const FEE: u64 = 20;
+
+fn is_even(key: ProjectivePoint) -> bool {
+  key.to_encoded_point(true).tag() == Tag::CompressedEvenY
+}
+
+async fn send_and_get_output(rpc: &Rpc, scanner: &Scanner, key: ProjectivePoint) -> ReceivedOutput {
+  let block_number = rpc.get_latest_block_number().await.unwrap() + 1;
+
+  rpc
+    .rpc_call::<Vec<String>>(
+      "generatetoaddress",
+      serde_json::json!([
+        1,
+        Address::from_script(&p2tr_script_buf(key).unwrap(), Network::Regtest).unwrap()
+      ]),
+    )
+    .await
+    .unwrap();
+
+  // Mine until maturity
+  rpc
+    .rpc_call::<Vec<String>>(
+      "generatetoaddress",
+      serde_json::json!([100, Address::p2sh(Script::new(), Network::Regtest).unwrap()]),
+    )
+    .await
+    .unwrap();
+
+  let block = rpc.get_block(&rpc.get_block_hash(block_number).await.unwrap()).await.unwrap();
+
+  let mut outputs = scanner.scan_block(&block);
+  assert_eq!(outputs, scanner.scan_transaction(&block.txdata[0]));
+
+  assert_eq!(outputs.len(), 1);
+  assert_eq!(outputs[0].outpoint(), &OutPoint::new(block.txdata[0].compute_txid(), 0));
+  assert_eq!(outputs[0].value(), block.txdata[0].output[0].value.to_sat());
+
+  assert_eq!(
+    ReceivedOutput::read::<&[u8]>(&mut outputs[0].serialize().as_ref()).unwrap(),
+    outputs[0]
+  );
+
+  outputs.swap_remove(0)
+}
+
+fn keys() -> (HashMap<Participant, ThresholdKeys<Secp256k1>>, ProjectivePoint) {
+  let mut keys = key_gen(&mut OsRng);
+  for keys in keys.values_mut() {
+    *keys = tweak_keys(keys);
+  }
+  let key = keys.values().next().unwrap().group_key();
+  (keys, key)
+}
+
+fn sign(
+  keys: &HashMap<Participant, ThresholdKeys<Secp256k1>>,
+  tx: &SignableTransaction,
+) -> Transaction {
+  let mut machines = HashMap::new();
+  for i in (1 ..= THRESHOLD).map(|i| Participant::new(i).unwrap()) {
+    machines.insert(
+      i,
+      tx.clone()
+        .multisig(&keys[&i].clone(), RecommendedTranscript::new(b"bitcoin-serai Test Transaction"))
+        .unwrap(),
+    );
+  }
+  sign_without_caching(&mut OsRng, machines, &[])
+}
+
+#[test]
+fn test_tweak_keys() {
+  let mut even = false;
+  let mut odd = false;
+
+  // Generate keys until we get an even set and an odd set
+  while !(even && odd) {
+    let mut keys = key_gen(&mut OsRng).drain().next().unwrap().1;
+    if is_even(keys.group_key()) {
+      // Tweaking should do nothing
+      assert_eq!(tweak_keys(&keys).group_key(), keys.group_key());
+
+      even = true;
+    } else {
+      let tweaked = tweak_keys(&keys).group_key();
+      assert_ne!(tweaked, keys.group_key());
+      // Tweaking should produce an even key
+      assert!(is_even(tweaked));
+
+      // Verify it uses the smallest possible offset
+      while keys.group_key().to_encoded_point(true).tag() == Tag::CompressedOddY {
+        keys = keys.offset(Scalar::ONE);
+      }
+      assert_eq!(tweaked, keys.group_key());
+
+      odd = true;
+    }
+  }
+}
+
+async_sequential! {
+  async fn test_scanner() {
+    // Test Scanners are creatable for even keys.
+    for _ in 0 .. 128 {
+      let key = ProjectivePoint::random(&mut OsRng);
+      assert_eq!(Scanner::new(key).is_some(), is_even(key));
+    }
+
+    let mut key = ProjectivePoint::random(&mut OsRng);
+    while !is_even(key) {
+      key += ProjectivePoint::GENERATOR;
+    }
+
+    {
+      let mut scanner = Scanner::new(key).unwrap();
+      for _ in 0 .. 128 {
+        let mut offset = Scalar::random(&mut OsRng);
+        let registered = scanner.register_offset(offset).unwrap();
+        // Registering this again should return None
+        assert!(scanner.register_offset(offset).is_none());
+
+        // We can only register offsets resulting in even keys
+        // Make this even
+        while !is_even(key + (ProjectivePoint::GENERATOR * offset)) {
+          offset += Scalar::ONE;
+        }
+        // Ensure it matches the registered offset
+        assert_eq!(registered, offset);
+        // Assert registering this again fails
+        assert!(scanner.register_offset(offset).is_none());
+      }
+    }
+
+    let rpc = rpc().await;
+    let mut scanner = Scanner::new(key).unwrap();
+
+    assert_eq!(send_and_get_output(&rpc, &scanner, key).await.offset(), Scalar::ZERO);
+
+    // Register an offset and test receiving to it
+    let offset = scanner.register_offset(Scalar::random(&mut OsRng)).unwrap();
+    assert_eq!(
+      send_and_get_output(&rpc, &scanner, key + (ProjectivePoint::GENERATOR * offset))
+        .await
+        .offset(),
+      offset
+    );
+  }
+
+  async fn test_transaction_errors() {
+    let (_, key) = keys();
+
+    let rpc = rpc().await;
+    let scanner = Scanner::new(key).unwrap();
+
+    let output = send_and_get_output(&rpc, &scanner, key).await;
+    assert_eq!(output.offset(), Scalar::ZERO);
+
+    let inputs = vec![output];
+    let addr = || p2tr_script_buf(key).unwrap();
+    let payments = vec![(addr(), 1000)];
+
+    assert!(SignableTransaction::new(inputs.clone(), &payments, None, None, FEE).is_ok());
+
+    assert_eq!(
+      SignableTransaction::new(vec![], &payments, None, None, FEE),
+      Err(TransactionError::NoInputs)
+    );
+
+    // No change
+    assert!(SignableTransaction::new(inputs.clone(), &[(addr(), 1000)], None, None, FEE).is_ok());
+    // Consolidation TX
+    assert!(SignableTransaction::new(inputs.clone(), &[], Some(addr()), None, FEE).is_ok());
+    // Data
+    assert!(SignableTransaction::new(inputs.clone(), &[], None, Some(vec![]), FEE).is_ok());
+    // No outputs
+    assert_eq!(
+      SignableTransaction::new(inputs.clone(), &[], None, None, FEE),
+      Err(TransactionError::NoOutputs),
+    );
+
+    assert_eq!(
+      SignableTransaction::new(inputs.clone(), &[(addr(), 1)], None, None, FEE),
+      Err(TransactionError::DustPayment),
+    );
+
+    assert!(
+      SignableTransaction::new(inputs.clone(), &payments, None, Some(vec![0; 80]), FEE).is_ok()
+    );
+    assert_eq!(
+      SignableTransaction::new(inputs.clone(), &payments, None, Some(vec![0; 81]), FEE),
+      Err(TransactionError::TooMuchData),
+    );
+
+    assert_eq!(
+      SignableTransaction::new(inputs.clone(), &[], Some(addr()), None, 0),
+      Err(TransactionError::TooLowFee),
+    );
+
+    assert_eq!(
+      SignableTransaction::new(inputs.clone(), &[(addr(), inputs[0].value() * 2)], None, None, FEE),
+      Err(TransactionError::NotEnoughFunds),
+    );
+
+    assert_eq!(
+      SignableTransaction::new(inputs, &vec![(addr(), 1000); 10000], None, None, FEE),
+      Err(TransactionError::TooLargeTransaction),
+    );
+  }
+
+  async fn test_send() {
+    let (keys, key) = keys();
+
+    let rpc = rpc().await;
+    let mut scanner = Scanner::new(key).unwrap();
+
+    // Get inputs, one not offset and one offset
+    let output = send_and_get_output(&rpc, &scanner, key).await;
+    assert_eq!(output.offset(), Scalar::ZERO);
+
+    let offset = scanner.register_offset(Scalar::random(&mut OsRng)).unwrap();
+    let offset_key = key + (ProjectivePoint::GENERATOR * offset);
+    let offset_output = send_and_get_output(&rpc, &scanner, offset_key).await;
+    assert_eq!(offset_output.offset(), offset);
+
+    // Declare payments, change, fee
+    let payments = [
+      (p2tr_script_buf(key).unwrap(), 1005),
+      (p2tr_script_buf(offset_key).unwrap(), 1007)
+    ];
+
+    let change_offset = scanner.register_offset(Scalar::random(&mut OsRng)).unwrap();
+    let change_key = key + (ProjectivePoint::GENERATOR * change_offset);
+    let change_addr = p2tr_script_buf(change_key).unwrap();
+
+    // Create and sign the TX
+    let tx = SignableTransaction::new(
+      vec![output.clone(), offset_output.clone()],
+      &payments,
+      Some(change_addr.clone()),
+      None,
+      FEE
+    ).unwrap();
+    let needed_fee = tx.needed_fee();
+    let expected_id = tx.txid();
+    let tx = sign(&keys, &tx);
+
+    assert_eq!(tx.output.len(), 3);
+
+    // Ensure we can scan it
+    let outputs = scanner.scan_transaction(&tx);
+    for (o, output) in outputs.iter().enumerate() {
+      assert_eq!(output.outpoint(), &OutPoint::new(tx.compute_txid(), u32::try_from(o).unwrap()));
+      assert_eq!(&ReceivedOutput::read::<&[u8]>(&mut output.serialize().as_ref()).unwrap(), output);
+    }
+
+    assert_eq!(outputs[0].offset(), Scalar::ZERO);
+    assert_eq!(outputs[1].offset(), offset);
+    assert_eq!(outputs[2].offset(), change_offset);
+
+    // Make sure the payments were properly created
+    for ((output, scanned), payment) in tx.output.iter().zip(outputs.iter()).zip(payments.iter()) {
+      assert_eq!(
+        output,
+        &TxOut { script_pubkey: payment.0.clone(), value: Amount::from_sat(payment.1) },
+      );
+      assert_eq!(scanned.value(), payment.1 );
+    }
+
+    // Make sure the change is correct
+    assert_eq!(needed_fee, u64::try_from(tx.vsize()).unwrap() * FEE);
+    let input_value = output.value() + offset_output.value();
+    let output_value = tx.output.iter().map(|output| output.value.to_sat()).sum::<u64>();
+    assert_eq!(input_value - output_value, needed_fee);
+
+    let change_amount =
+      input_value - payments.iter().map(|payment| payment.1).sum::<u64>() - needed_fee;
+    assert_eq!(
+      tx.output[2],
+      TxOut { script_pubkey: change_addr, value: Amount::from_sat(change_amount) },
+    );
+
+    // This also tests send_raw_transaction and get_transaction, which the RPC test can't
+    // effectively test
+    rpc.send_raw_transaction(&tx).await.unwrap();
+    let mut hash = *tx.compute_txid().as_raw_hash().as_byte_array();
+    hash.reverse();
+    assert_eq!(tx, rpc.get_transaction(&hash).await.unwrap());
+    assert_eq!(expected_id, hash);
+  }
+
+  async fn test_data() {
+    let (keys, key) = keys();
+
+    let rpc = rpc().await;
+    let scanner = Scanner::new(key).unwrap();
+
+    let output = send_and_get_output(&rpc, &scanner, key).await;
+    assert_eq!(output.offset(), Scalar::ZERO);
+
+    let data_len = 60 + usize::try_from(OsRng.next_u64() % 21).unwrap();
+    let mut data = vec![0; data_len];
+    OsRng.fill_bytes(&mut data);
+
+    let tx = sign(
+      &keys,
+      &SignableTransaction::new(
+        vec![output],
+        &[],
+        Some(p2tr_script_buf(key).unwrap()),
+        Some(data.clone()),
+        FEE
+      ).unwrap()
+    );
+
+    assert!(tx.output[0].script_pubkey.is_op_return());
+    let check = |mut instructions: Instructions| {
+      assert_eq!(instructions.next().unwrap().unwrap(), Instruction::Op(OP_RETURN));
+      assert_eq!(
+        instructions.next().unwrap().unwrap(),
+        Instruction::PushBytes(&PushBytesBuf::try_from(data.clone()).unwrap()),
+      );
+      assert!(instructions.next().is_none());
+    };
+    check(tx.output[0].script_pubkey.instructions());
+    check(tx.output[0].script_pubkey.instructions_minimal());
+  }
+}