feat(leader_coin): add nonce and coin.evolve() api

cryptarchia/cryptarchia.py

@@ -79,8 +79,24 @@ class Slot:
 
 @dataclass
 class Coin:
-    pk: int
+    sk: int
     value: int
+    nonce: bytes = bytes(32)
+
+    @property
+    def pk(self):
+        return self.sk
+
+    def evolve(self) -> "Coin":
+        sk_bytes = int.to_bytes(self.sk, length=32, byteorder="little")
+
+        h = blake2b(digest_size=32)
+        h.update(b"coin-evolve")
+        h.update(sk_bytes)
+        h.update(self.nonce)
+        evolved_nonce = h.digest()
+
+        return Coin(nonce=evolved_nonce, sk=self.sk, value=self.value)
 
     def commitment(self) -> Id:
         # TODO: mocked until CL is understood
@@ -88,6 +104,8 @@ class Coin:
         value_bytes = int.to_bytes(self.value, length=32, byteorder="little")
 
         h = sha256()
+        h.update(b"coin-commitment")
+        h.update(self.nonce)
         h.update(pk_bytes)
         h.update(value_bytes)
         return h.digest()
@@ -98,9 +116,10 @@ class Coin:
         value_bytes = int.to_bytes(self.value, length=32, byteorder="little")
 
         h = sha256()
+        h.update(b"coin-nullifier")
+        h.update(self.nonce)
         h.update(pk_bytes)
         h.update(value_bytes)
-        h.update(b"\x00")  # extra 0 byte to differentiate from commitment
         return h.digest()
 
 
@@ -108,10 +127,17 @@ class Coin:
 class MockLeaderProof:
     commitment: Id
     nullifier: Id
+    evolved_commitment: Id
 
     @staticmethod
     def from_coin(coin: Coin):
-        return MockLeaderProof(commitment=coin.commitment(), nullifier=coin.nullifier())
+        evolved_coin = coin.evolve()
+
+        return MockLeaderProof(
+            commitment=coin.commitment(),
+            nullifier=coin.nullifier(),
+            evolved_commitment=evolved_coin.commitment(),
+        )
 
     def verify(self, slot):
         # TODO: verification not implemented

cryptarchia/test_fork_choice.py

@@ -23,7 +23,7 @@ def make_block(parent_id: Id, slot: Slot, content: bytes) -> BlockHeader:
         content_size=1,
         slot=slot,
         content_id=content_id,
-        leader_proof=MockLeaderProof.from_coin(Coin(pk=0, value=10)),
+        leader_proof=MockLeaderProof.from_coin(Coin(sk=0, value=10)),
     )
 
 

cryptarchia/test_leader.py

@@ -23,7 +23,7 @@ class TestLeader(TestCase):
             epoch_period_nonce_stabilization=3,
             time=TimeConfig(slot_duration=1, chain_start_time=0),
         )
-        l = Leader(config=config, coin=Coin(pk=0, value=10))
+        l = Leader(config=config, coin=Coin(sk=0, value=10))
 
         # We'll use the Margin of Error equation to decide how many samples we need.
         # https://en.wikipedia.org/wiki/Margin_of_error

cryptarchia/test_ledger_state_update.py

@@ -50,7 +50,7 @@ def config() -> Config:
 
 class TestLedgerStateUpdate(TestCase):
     def test_ledger_state_prevents_coin_reuse(self):
-        leader_coin = Coin(pk=0, value=100)
+        leader_coin = Coin(sk=0, value=100)
         genesis = mk_genesis_state([leader_coin])
 
         follower = Follower(genesis, config())
@@ -76,9 +76,9 @@ class TestLedgerStateUpdate(TestCase):
         assert follower.local_chain.tip() == block
 
     def test_ledger_state_is_properly_updated_on_reorg(self):
-        coin_1 = Coin(pk=0, value=100)
-        coin_2 = Coin(pk=1, value=100)
-        coin_3 = Coin(pk=2, value=100)
+        coin_1 = Coin(sk=0, value=100)
+        coin_2 = Coin(sk=1, value=100)
+        coin_3 = Coin(sk=2, value=100)
 
         genesis = mk_genesis_state([coin_1, coin_2, coin_3])
 
@@ -114,7 +114,7 @@ class TestLedgerStateUpdate(TestCase):
         assert follower.ledger_state[block_3.id()].verify_unspent(coin_1.nullifier())
 
     def test_epoch_transition(self):
-        leader_coins = [Coin(pk=i, value=100) for i in range(4)]
+        leader_coins = [Coin(sk=i, value=100) for i in range(4)]
         genesis = mk_genesis_state(leader_coins)
 
         # An epoch will be 10 slots long, with stake distribution snapshot taken at the start of the epoch
@@ -145,12 +145,12 @@ class TestLedgerStateUpdate(TestCase):
         # To ensure this is the case, we add a new coin just to the state associated with that slot,
         # so that the new block can be accepted only if that is the snapshot used
         # first, verify that if we don't change the state, the block is not accepted
-        block_4 = mk_block(slot=20, parent=block_3.id(), coin=Coin(pk=4, value=100))
+        block_4 = mk_block(slot=20, parent=block_3.id(), coin=Coin(sk=4, value=100))
         follower.on_block(block_4)
         assert follower.tip() == block_3
         # then we add the coin to the state associated with slot 9
         follower.ledger_state[block_2.id()].commitments.add(
-            Coin(pk=4, value=100).commitment()
+            Coin(sk=4, value=100).commitment()
         )
         follower.on_block(block_4)
         assert follower.tip() == block_4