Add orchard_note.py

orchard_note.py

@@ -0,0 +1,61 @@
+import struct
+
+from orchard_commitments import value_commit, rcv_trapdoor, note_commit
+from orchard_key_components import diversify_hash, prf_expand, derive_nullifier, FullViewingKey, SpendingKey
+from orchard_pallas import Point, Scalar
+from orchard_utils import to_base, to_scalar
+
+from utils import leos2bsp
+
+class OrchardNote(object):
+    def __init__(self, d, pk_d, v, rho, rseed):
+        self.d = d
+        self.pk_d = pk_d
+        self.v = v
+        self.rho = rho
+        self.rseed = rseed
+        self.rcm = self.rcm(rho)
+        self.psi = self.psi(rho)
+
+    def rcm(self, rho):
+        return to_scalar(prf_expand(bytes(self.rseed), b'\x05' + bytes(rho)))
+
+    def psi(self, rho):
+        return to_base(prf_expand(bytes(self.rseed), b'\x09' + bytes(rho)))
+
+    def note_plaintext(self, memo):
+        return OrchardNotePlaintext(self.d, self.v, self.rseed, memo)
+
+# https://zips.z.cash/protocol/nu5.pdf#notept
+class OrchardNotePlaintext(object):
+    def __init__(self, d, v, rseed, memo):
+        self.leadbyte = b'0x02'
+        self.d = d
+        self.v = v
+        self.rseed = rseed
+        self.memo = memo
+
+    def __bytes__(self):
+        return (
+            self.leadbyte +
+            self.d +
+            struct.pack('<Q', self.v.s) +
+            bytes(self.rseed) +
+            self.memo
+        )
+
+    def dummy_nullifier(self, rand):
+        sk = SpendingKey(rand.b(32))
+        fvk = FullViewingKey(sk)
+        pk_d = fvk.default_pkd()
+        g_d = diversify_hash(fvk.default_d())
+
+        v = Scalar.ZERO
+
+        rho = Point.rand(rand)
+        rho_bytes = bytes(rho)
+        rho = rho.extract()
+
+        note = OrchardNote(fvk.default_d(), pk_d, v, rho, rho_bytes)
+        cm = note_commit(note.rcm, leos2bsp(bytes(g_d)), leos2bsp(bytes(pk_d)), v.s, rho, note.psi)
+        return derive_nullifier(fvk.nk, rho, note.psi, cm)