Adjust computation of block number to sign

Substacting `1` to the result to account for the fact that a block range
end is exclusive.

Author: Alenar

mithril-aggregator/tests/create_certificate.rs

@@ -142,7 +142,7 @@ async fn create_certificate() {
 
     comment!(
         "Increase cardano chain block number to 185, 
-        the state machine should be signing CardanoTransactions for block 180"
+        the state machine should be signing CardanoTransactions for block 179"
     );
     tester.increase_block_number(85, 185).await.unwrap();
     cycle!(tester, "signing");
@@ -166,7 +166,7 @@ async fn create_certificate() {
                 .map(|s| s.signer_with_stake.clone().into())
                 .collect::<Vec<_>>(),
             fixture.compute_and_encode_avk(),
-            SignedEntityType::CardanoTransactions(Epoch(1), 180),
+            SignedEntityType::CardanoTransactions(Epoch(1), 179),
             ExpectedCertificate::genesis_identifier(&CardanoDbBeacon::new(
                 "devnet".to_string(),
                 1,
@@ -201,7 +201,7 @@ async fn create_certificate() {
                 .map(|s| s.signer_with_stake.clone().into())
                 .collect::<Vec<_>>(),
             fixture.compute_and_encode_avk(),
-            SignedEntityType::CardanoTransactions(Epoch(1), 120),
+            SignedEntityType::CardanoTransactions(Epoch(1), 119),
             ExpectedCertificate::genesis_identifier(&CardanoDbBeacon::new(
                 "devnet".to_string(),
                 1,

mithril-common/src/entities/signed_entity_config.rs

@@ -131,20 +131,25 @@ impl CardanoTransactionsSigningConfig {
     ///
     /// The formula is as follows:
     ///
-    /// `block_number = ⌊(tip.block_number - security_parameter) / step⌋ × step`
+    /// `block_number = ⌊(tip.block_number - security_parameter) / step⌋ × step - 1`
     ///
     /// where `⌊x⌋` is the floor function which rounds to the greatest integer less than or equal to `x`.
     ///
-    /// *Note: The step is adjusted to be a multiple of the block range length in order
+    /// *Notes:*
+    /// * *The step is adjusted to be a multiple of the block range length in order
     /// to guarantee that the block number signed in a certificate is effectively signed.*
+    /// * *1 is subtracted to the result because block range end is exclusive (ie: a BlockRange over
+    /// `30..45` finish at 44 included, 45 is included in the next block range).*
     pub fn compute_block_number_to_be_signed(&self, block_number: BlockNumber) -> BlockNumber {
         // TODO: See if we can remove this adjustment by including a "partial" block range in
         // the signed data.
         let adjusted_step = BlockRange::from_block_number(self.step).start;
         // We can't have a step lower than the block range length.
         let adjusted_step = std::cmp::max(adjusted_step, BlockRange::LENGTH);
 
-        (block_number.saturating_sub(self.security_parameter)) / adjusted_step * adjusted_step
+        let block_number_to_be_signed =
+            (block_number.saturating_sub(self.security_parameter)) / adjusted_step * adjusted_step;
+        block_number_to_be_signed.saturating_sub(1)
     }
 }
 
@@ -199,11 +204,11 @@ mod tests {
             )
         );
 
-        // The block number to be signed is 0 because the step is 15, the block number is 20, and
+        // The block number to be signed is 14 because the step is 15, the block number is 20, and
         // the security parameter is 0.
         // This is further tested in the "computing_block_number_to_be_signed" tests below.
         assert_eq!(
-            SignedEntityType::CardanoTransactions(Epoch(1), 15),
+            SignedEntityType::CardanoTransactions(Epoch(1), 14),
             config.time_point_to_signed_entity(
                 SignedEntityTypeDiscriminants::CardanoTransactions,
                 &time_point
@@ -220,7 +225,7 @@ mod tests {
                 step: 15,
             }
             .compute_block_number_to_be_signed(105),
-            105
+            104
         );
 
         assert_eq!(
@@ -229,7 +234,7 @@ mod tests {
                 step: 15,
             }
             .compute_block_number_to_be_signed(100),
-            90
+            89
         );
 
         assert_eq!(
@@ -238,7 +243,7 @@ mod tests {
                 step: 15,
             }
             .compute_block_number_to_be_signed(100),
-            15
+            14
         );
 
         assert_eq!(
@@ -271,7 +276,7 @@ mod tests {
                 step: BlockRange::LENGTH * 2 - 1,
             }
             .compute_block_number_to_be_signed(BlockRange::LENGTH * 5 + 1),
-            BlockRange::LENGTH * 5
+            BlockRange::LENGTH * 5 - 1
         );
 
         assert_eq!(
@@ -280,7 +285,7 @@ mod tests {
                 step: BlockRange::LENGTH * 2 + 1,
             }
             .compute_block_number_to_be_signed(BlockRange::LENGTH * 5 + 1),
-            BlockRange::LENGTH * 4
+            BlockRange::LENGTH * 4 - 1
         );
 
         // Adjusted step is always at least BLOCK_RANGE_LENGTH.
@@ -290,7 +295,7 @@ mod tests {
                 step: BlockRange::LENGTH - 1,
             }
             .compute_block_number_to_be_signed(BlockRange::LENGTH * 10 - 1),
-            BlockRange::LENGTH * 9
+            BlockRange::LENGTH * 9 - 1
         );
 
         assert_eq!(
@@ -424,7 +429,7 @@ mod tests {
                 SignedEntityType::MithrilStakeDistribution(beacon.epoch),
                 SignedEntityType::CardanoStakeDistribution(beacon.epoch),
                 SignedEntityType::CardanoImmutableFilesFull(beacon.clone()),
-                SignedEntityType::CardanoTransactions(beacon.epoch, chain_point.block_number),
+                SignedEntityType::CardanoTransactions(beacon.epoch, chain_point.block_number - 1),
             ],
             signed_entity_types
         );