Monero: add more legacy verify functions (#383)

* Add v1 ring sig verifying

* allow calculating signature hash for v1 txs

* add unreduced scalar type with recovery

I have added this type for borromen sigs, the ee field can be a normal
scalar as in the verify function the ee
field is checked against a reduced scalar mean for it to verify as
correct ee must be reduced

* change block major/ minor versions to u8

this matches Monero

I have also changed a couple varint functions to accept the `VarInt`
trait

* expose `serialize_hashable` on `Block`

* add back MLSAG verifying functions

I still need to revert the commit removing support for >1 input MLSAG FULL

This adds a new rct type to separate Full and simple rct

* add back support for multiple inputs for RCT FULL

* comment `non_adjacent_form` function

also added `#[allow(clippy::needless_range_loop)]` around a loop as without a re-write satisfying clippy without it will make the function worse.

* Improve Mlsag verifying API

* fix rebase errors

* revert the changes on `reserialize_chain`
plus other misc changes

* fix no-std

* Reduce the amount of rpc calls needed for `get_block_by_number`.
This function was causing me problems, every now and then a node would return a block with a different number than requested.

* change `serialize_hashable` to give the POW hashing blob.

Monero calculates the POW hash and the block hash using *slightly* different blobs :/

* make ring_signatures public and add length check when verifying.

* Misc improvements and bug fixes

---------

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

coins/monero/src/ringct/mlsag.rs

@@ -3,17 +3,82 @@ use std_shims::{
   io::{self, Read, Write},
 };
 
-use curve25519_dalek::scalar::Scalar;
-#[cfg(feature = "experimental")]
-use curve25519_dalek::edwards::EdwardsPoint;
+use zeroize::Zeroize;
 
-use crate::serialize::*;
-#[cfg(feature = "experimental")]
-use crate::{hash_to_scalar, ringct::hash_to_point};
+use curve25519_dalek::{traits::IsIdentity, Scalar, EdwardsPoint};
 
-#[derive(Clone, PartialEq, Eq, Debug)]
+use monero_generators::H;
+
+use crate::{hash_to_scalar, ringct::hash_to_point, serialize::*};
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+#[cfg_attr(feature = "std", derive(thiserror::Error))]
+pub enum MlsagError {
+  #[cfg_attr(feature = "std", error("invalid ring"))]
+  InvalidRing,
+  #[cfg_attr(feature = "std", error("invalid amount of key images"))]
+  InvalidAmountOfKeyImages,
+  #[cfg_attr(feature = "std", error("invalid ss"))]
+  InvalidSs,
+  #[cfg_attr(feature = "std", error("key image was identity"))]
+  IdentityKeyImage,
+  #[cfg_attr(feature = "std", error("invalid ci"))]
+  InvalidCi,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize)]
+pub struct RingMatrix {
+  matrix: Vec<Vec<EdwardsPoint>>,
+}
+
+impl RingMatrix {
+  pub fn new(matrix: Vec<Vec<EdwardsPoint>>) -> Result<Self, MlsagError> {
+    if matrix.is_empty() {
+      Err(MlsagError::InvalidRing)?;
+    }
+    for member in &matrix {
+      if member.is_empty() || (member.len() != matrix[0].len()) {
+        Err(MlsagError::InvalidRing)?;
+      }
+    }
+
+    Ok(RingMatrix { matrix })
+  }
+
+  /// Construct a ring matrix for an individual output.
+  pub fn individual(
+    ring: &[[EdwardsPoint; 2]],
+    pseudo_out: EdwardsPoint,
+  ) -> Result<Self, MlsagError> {
+    let mut matrix = Vec::with_capacity(ring.len());
+    for ring_member in ring {
+      matrix.push(vec![ring_member[0], ring_member[1] - pseudo_out]);
+    }
+    RingMatrix::new(matrix)
+  }
+
+  pub fn iter(&self) -> impl Iterator<Item = &[EdwardsPoint]> {
+    self.matrix.iter().map(AsRef::as_ref)
+  }
+
+  /// Return the amount of members in the ring.
+  pub fn members(&self) -> usize {
+    self.matrix.len()
+  }
+
+  /// Returns the length of a ring member.
+  ///
+  /// A ring member is a vector of points for which the signer knows all of the discrete logarithms
+  /// of.
+  pub fn member_len(&self) -> usize {
+    // this is safe to do as the constructors don't allow empty rings
+    self.matrix[0].len()
+  }
+}
+
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize)]
 pub struct Mlsag {
-  pub ss: Vec<[Scalar; 2]>,
+  pub ss: Vec<Vec<Scalar>>,
   pub cc: Scalar,
 }
 
@@ -25,47 +90,124 @@ impl Mlsag {
     write_scalar(&self.cc, w)
   }
 
-  pub fn read<R: Read>(mixins: usize, r: &mut R) -> io::Result<Mlsag> {
+  pub fn read<R: Read>(mixins: usize, ss_2_elements: usize, r: &mut R) -> io::Result<Mlsag> {
     Ok(Mlsag {
-      ss: (0 .. mixins).map(|_| read_array(read_scalar, r)).collect::<Result<_, _>>()?,
+      ss: (0 .. mixins)
+        .map(|_| read_raw_vec(read_scalar, ss_2_elements, r))
+        .collect::<Result<_, _>>()?,
       cc: read_scalar(r)?,
     })
   }
 
-  #[cfg(feature = "experimental")]
   pub fn verify(
     &self,
     msg: &[u8; 32],
-    ring: &[[EdwardsPoint; 2]],
-    key_image: &EdwardsPoint,
-  ) -> bool {
-    if ring.is_empty() {
-      return false;
+    ring: &RingMatrix,
+    key_images: &[EdwardsPoint],
+  ) -> Result<(), MlsagError> {
+    // Mlsag allows for layers to not need linkability, hence they don't need key images
+    // Monero requires that there is always only 1 non-linkable layer - the amount commitments.
+    if ring.member_len() != (key_images.len() + 1) {
+      Err(MlsagError::InvalidAmountOfKeyImages)?;
     }
 
     let mut buf = Vec::with_capacity(6 * 32);
+    buf.extend_from_slice(msg);
+
     let mut ci = self.cc;
-    for (i, ring_member) in ring.iter().enumerate() {
-      buf.extend_from_slice(msg);
 
-      #[allow(non_snake_case)]
-      let L =
-        |r| EdwardsPoint::vartime_double_scalar_mul_basepoint(&ci, &ring_member[r], &self.ss[i][r]);
+    // This is an iterator over the key images as options with an added entry of `None` at the
+    // end for the non-linkable layer
+    let key_images_iter = key_images.iter().map(|ki| Some(*ki)).chain(core::iter::once(None));
 
-      buf.extend_from_slice(ring_member[0].compress().as_bytes());
-      buf.extend_from_slice(L(0).compress().as_bytes());
-
-      #[allow(non_snake_case)]
-      let R = (self.ss[i][0] * hash_to_point(ring_member[0])) + (ci * key_image);
-      buf.extend_from_slice(R.compress().as_bytes());
-
-      buf.extend_from_slice(ring_member[1].compress().as_bytes());
-      buf.extend_from_slice(L(1).compress().as_bytes());
-
-      ci = hash_to_scalar(&buf);
-      buf.clear();
+    if ring.matrix.len() != self.ss.len() {
+      Err(MlsagError::InvalidSs)?;
     }
 
-    ci == self.cc
+    for (ring_member, ss) in ring.iter().zip(&self.ss) {
+      if ring_member.len() != ss.len() {
+        Err(MlsagError::InvalidSs)?;
+      }
+
+      for ((ring_member_entry, s), ki) in ring_member.iter().zip(ss).zip(key_images_iter.clone()) {
+        #[allow(non_snake_case)]
+        let L = EdwardsPoint::vartime_double_scalar_mul_basepoint(&ci, ring_member_entry, s);
+
+        buf.extend_from_slice(ring_member_entry.compress().as_bytes());
+        buf.extend_from_slice(L.compress().as_bytes());
+
+        // Not all dimensions need to be linkable, e.g. commitments, and only linkable layers need
+        // to have key images.
+        if let Some(ki) = ki {
+          if ki.is_identity() {
+            Err(MlsagError::IdentityKeyImage)?;
+          }
+
+          #[allow(non_snake_case)]
+          let R = (s * hash_to_point(ring_member_entry)) + (ci * ki);
+          buf.extend_from_slice(R.compress().as_bytes());
+        }
+      }
+
+      ci = hash_to_scalar(&buf);
+      // keep the msg in the buffer.
+      buf.drain(msg.len() ..);
+    }
+
+    if ci != self.cc {
+      Err(MlsagError::InvalidCi)?
+    }
+    Ok(())
+  }
+}
+
+/// An aggregate ring matrix builder, usable to set up the ring matrix to prove/verify an aggregate
+/// MLSAG signature.
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize)]
+pub struct AggregateRingMatrixBuilder {
+  key_ring: Vec<Vec<EdwardsPoint>>,
+  amounts_ring: Vec<EdwardsPoint>,
+  sum_out: EdwardsPoint,
+}
+
+impl AggregateRingMatrixBuilder {
+  /// Create a new AggregateRingMatrixBuilder.
+  ///
+  /// Takes in the transaction's outputs; commitments and fee.
+  pub fn new(commitments: &[EdwardsPoint], fee: u64) -> Self {
+    AggregateRingMatrixBuilder {
+      key_ring: vec![],
+      amounts_ring: vec![],
+      sum_out: commitments.iter().sum::<EdwardsPoint>() + (H() * Scalar::from(fee)),
+    }
+  }
+
+  /// Push a ring of [output key, commitment] to the matrix.
+  pub fn push_ring(&mut self, ring: &[[EdwardsPoint; 2]]) -> Result<(), MlsagError> {
+    if self.key_ring.is_empty() {
+      self.key_ring = vec![vec![]; ring.len()];
+      // Now that we know the length of the ring, fill the `amounts_ring`.
+      self.amounts_ring = vec![-self.sum_out; ring.len()];
+    }
+
+    if (self.amounts_ring.len() != ring.len()) || ring.is_empty() {
+      // All the rings in an aggregate matrix must be the same length.
+      return Err(MlsagError::InvalidRing);
+    }
+
+    for (i, ring_member) in ring.iter().enumerate() {
+      self.key_ring[i].push(ring_member[0]);
+      self.amounts_ring[i] += ring_member[1]
+    }
+
+    Ok(())
+  }
+
+  /// Build and return the [`RingMatrix`]
+  pub fn build(mut self) -> Result<RingMatrix, MlsagError> {
+    for (i, amount_commitment) in self.amounts_ring.drain(..).enumerate() {
+      self.key_ring[i].push(amount_commitment);
+    }
+    RingMatrix::new(self.key_ring)
   }
 }