Kirk baird patch 01

py_ecc/bls/api.py

@@ -23,9 +23,8 @@
     multiply,
     neg,
     pairing,
-)
-from .typing import (
-    Domain,
+    is_inf,
+    curve_order,
 )
 from .utils import (
     G1_to_pubkey,
@@ -37,11 +36,10 @@
 
 
 def sign(message_hash: Hash32,
-         privkey: int,
-         domain: Domain) -> BLSSignature:
+         privkey: int) -> BLSSignature:
     return G2_to_signature(
         multiply(
-            hash_to_G2(message_hash, domain),
+            hash_to_G2(message_hash),
             privkey,
         ))
 
@@ -52,17 +50,18 @@ def privtopub(k: int) -> BLSPubkey:
 
 def verify(message_hash: Hash32,
            pubkey: BLSPubkey,
-           signature: BLSSignature,
-           domain: Domain) -> bool:
+           signature: BLSSignature) -> bool:
+    signature_point = signature_to_G2(signature)
+    if not is_inf(multiply(signature_point, curve_order)):
+        return False
     try:
         final_exponentiation = final_exponentiate(
             pairing(
-                signature_to_G2(signature),
+                signature_point,
                 G1,
                 final_exponentiate=False,
-            ) *
-            pairing(
-                hash_to_G2(message_hash, domain),
+            ) * pairing(
+                hash_to_G2(message_hash),
                 neg(pubkey_to_G1(pubkey)),
                 final_exponentiate=False,
             )
@@ -88,8 +87,7 @@ def aggregate_pubkeys(pubkeys: Sequence[BLSPubkey]) -> BLSPubkey:
 
 def verify_multiple(pubkeys: Sequence[BLSPubkey],
                     message_hashes: Sequence[Hash32],
-                    signature: BLSSignature,
-                    domain: Domain) -> bool:
+                    signature: BLSSignature) -> bool:
     len_msgs = len(message_hashes)
 
     if len(pubkeys) != len_msgs:
@@ -99,6 +97,10 @@ def verify_multiple(pubkeys: Sequence[BLSPubkey],
             )
         )
 
+    signature_point = signature_to_G2(signature)
+    if not is_inf(multiply(signature_point, curve_order)):
+        return False
+
     try:
         o = FQ12([1] + [0] * 11)
         for m_pubs in set(message_hashes):
@@ -108,8 +110,8 @@ def verify_multiple(pubkeys: Sequence[BLSPubkey],
                 if message_hashes[i] == m_pubs:
                     group_pub = add(group_pub, pubkey_to_G1(pubkeys[i]))
 
-            o *= pairing(hash_to_G2(m_pubs, domain), group_pub, final_exponentiate=False)
-        o *= pairing(signature_to_G2(signature), neg(G1), final_exponentiate=False)
+            o *= pairing(hash_to_G2(m_pubs), group_pub, final_exponentiate=False)
+        o *= pairing(signature_point, neg(G1), final_exponentiate=False)
 
         final_exponentiation = final_exponentiate(o)
         return final_exponentiation == FQ12.one()

py_ecc/bls/constants.py

@@ -5,13 +5,18 @@
     field_modulus as q,
 )
 
-G2_cofactor = 305502333931268344200999753193121504214466019254188142667664032982267604182971884026507427359259977847832272839041616661285803823378372096355777062779109  # noqa: E501
-FQ2_order = q ** 2 - 1
-eighth_roots_of_unity = tuple(
-    FQ2([1, 1]) ** ((FQ2_order * k) // 8)
+G2_COFACTOR = 305502333931268344200999753193121504214466019254188142667664032982267604182971884026507427359259977847832272839041616661285803823378372096355777062779109  # noqa: E501
+FQ2_ORDER = q ** 2 - 1
+EIGTH_ROOTS_OF_UNITY = tuple(
+    FQ2([1, 1]) ** ((FQ2_ORDER * k) // 8)
     for k in range(8)
 )
 
 POW_2_381 = 2**381
 POW_2_382 = 2**382
 POW_2_383 = 2**383
+
+# Ciphersuite BLS_SIG_BLS12381G2-SHA256-SSWU-RO_POP_ parameters
+DST = b'BLS_SIG_BLS12381G2-SHA256-SSWU-RO_POP_'
+HASH_LENGTH_BYTES = 32
+HASH_TO_G2_L = 64

py_ecc/bls/hash.py

@@ -1,17 +1,39 @@
+import math
 import hashlib
+import hmac
 from typing import Union
 
-from eth_typing import Hash32
+from .constants import HASH_LENGTH_BYTES
 
 
-def hash_eth2(data: Union[bytes, bytearray]) -> Hash32:
+def hkdf_extract(salt: Union[bytes, bytearray], ikm: Union[bytes, bytearray]) -> bytes:
     """
-    Return SHA-256 hashed result.
+    HKDF-Extract
 
-    Note: this API is currently under active research/development so is subject to change
-    without a major version bump.
+    https://tools.ietf.org/html/rfc5869
+    """
+    return hmac.new(salt, ikm, hashlib.sha256).digest()
+
+
+def hkdf_expand(prk: Union[bytes, bytearray], info: Union[bytes, bytearray], length: int) -> bytes:
+    """
+    HKDF-Expand
 
-    Note: it's a placeholder and we aim to migrate to a S[T/N]ARK-friendly hash function in
-    a future Ethereum 2.0 deployment phase.
+    https://tools.ietf.org/html/rfc5869
     """
-    return Hash32(hashlib.sha256(data).digest())
+    n = math.ceil(length / HASH_LENGTH_BYTES)
+
+    # okm = T(1) || T(2) || T(3) || ... || T(n)
+    okm = bytearray(0)
+    previous = bytearray(0)
+
+    for i in range(0, n):
+        # Concatenate (T(i) || info || i)
+        text = previous + info + bytes([i + 1])
+
+        # T(i + 1) = HMAC(T(i) || info || i)
+        previous = bytearray(hmac.new(prk, text, hashlib.sha256).digest())
+        okm.extend(previous)
+
+    # Return first `length` bytes.
+    return okm[:length]

py_ecc/bls/typing.py

@@ -17,5 +17,3 @@
 
 G2Uncompressed = Optimized_Point3D[optimized_bls12_381_FQ2]
 G2Compressed = NewType('G2Compressed', Tuple[int, int])
-
-Domain = NewType('Domain', bytes)  # bytes of length 8

py_ecc/bls/utils.py

@@ -19,23 +19,27 @@
     field_modulus as q,
     is_inf,
     is_on_curve,
-    multiply,
+    add,
     normalize,
+    optimized_swu_G2,
+    multiply_clear_cofactor_G2,
+    iso_map_G2,
 )
 
 from .constants import (
     POW_2_381,
     POW_2_382,
     POW_2_383,
-    FQ2_order,
-    G2_cofactor,
-    eighth_roots_of_unity,
+    FQ2_ORDER,
+    EIGTH_ROOTS_OF_UNITY,
+    HASH_TO_G2_L,
+    DST,
 )
 from .hash import (
-    hash_eth2,
+    hkdf_expand,
+    hkdf_extract,
 )
 from .typing import (
-    Domain,
     G1Compressed,
     G1Uncompressed,
     G2Compressed,
@@ -55,41 +59,75 @@ def modular_squareroot_in_FQ2(value: FQ2) -> FQ2:
     if both solutions have equal imaginary component the value with higher real
     component is favored.
     """
-    candidate_squareroot = value ** ((FQ2_order + 8) // 16)
+    candidate_squareroot = value ** ((FQ2_ORDER + 8) // 16)
     check = candidate_squareroot ** 2 / value
-    if check in eighth_roots_of_unity[::2]:
-        x1 = candidate_squareroot / eighth_roots_of_unity[eighth_roots_of_unity.index(check) // 2]
+    if check in EIGTH_ROOTS_OF_UNITY[::2]:
+        x1 = candidate_squareroot / EIGTH_ROOTS_OF_UNITY[EIGTH_ROOTS_OF_UNITY.index(check) // 2]
         x2 = -x1
         x1_re, x1_im = x1.coeffs
         x2_re, x2_im = x2.coeffs
         return x1 if (x1_im > x2_im or (x1_im == x2_im and x1_re > x2_re)) else x2
     return None
 
 
-def _get_x_coordinate(message_hash: Hash32, domain: Domain) -> FQ2:
-    # Initial candidate x coordinate
-    x_re = big_endian_to_int(hash_eth2(message_hash + domain + b'\x01'))
-    x_im = big_endian_to_int(hash_eth2(message_hash + domain + b'\x02'))
-    x_coordinate = FQ2([x_re, x_im])  # x_re + x_im * i
+def hash_to_G2(message_hash: Hash32) -> G2Uncompressed:
+    """
+    Convert a message to a point on G2 as defined here:
+    https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-05#section-3
 
-    return x_coordinate
+    Contants and inputs follow the ciphersuite ``BLS12381G2-SHA256-SSWU-RO-`` defined here:
+    https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-05#section-8.9.2
+    """
+    u0 = hash_to_base_FQ2(message_hash, 0)
+    u1 = hash_to_base_FQ2(message_hash, 1)
+    q0 = map_to_curve_G2(u0)
+    q1 = map_to_curve_G2(u1)
+    r = add(q0, q1)
+    p = clear_cofactor_G2(r)
+    return p
 
 
-def hash_to_G2(message_hash: Hash32, domain: Domain) -> G2Uncompressed:
-    x_coordinate = _get_x_coordinate(message_hash, domain)
+def hash_to_base_FQ2(message_hash: Hash32, ctr: int) -> FQ2:
+    """
+    Hash To Base for FQ2
 
-    # Test candidate y coordinates until a one is found
-    while 1:
-        y_coordinate_squared = x_coordinate ** 3 + FQ2([4, 4])  # The curve is y^2 = x^3 + 4(i + 1)
-        y_coordinate = modular_squareroot_in_FQ2(y_coordinate_squared)
-        if y_coordinate is not None:  # Check if quadratic residue found
-            break
-        x_coordinate += FQ2([1, 0])  # Add 1 and try again
+    Convert a message to a point in the finite field as defined here:
+    https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-05#section-5
+    """
+    m_prime = hkdf_extract(DST, message_hash + b'\x00')
+    info_pfx = b'H2C' + bytes([ctr])
+    e = []
 
-    return multiply(
-        (x_coordinate, y_coordinate, FQ2([1, 0])),
-        G2_cofactor,
-    )
+    #  for i in (1, ..., m), where m is the extension degree of FQ2
+    for i in range(1, 3):
+        info = info_pfx + bytes([i])
+        t = hkdf_expand(m_prime, info, HASH_TO_G2_L)
+        e.append(big_endian_to_int(t))
+
+    return FQ2(e)
+
+
+def map_to_curve_G2(u: FQ2) -> G2Uncompressed:
+    """
+    Map To Curve for G2
+
+    First, convert FQ2 point to a point on the 3-Isogeny curve.
+    SWU Map: https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-05#section-6.6.2
+
+    Second, map 3-Isogeny curve to BLS12-381-G2 curve.
+    3-Isogeny Map: https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-05#appendix-C.3
+    """
+    (x, y, z) = optimized_swu_G2(u)
+    return iso_map_G2(x, y, z)
+
+
+def clear_cofactor_G2(p: G2Uncompressed) -> G2Uncompressed:
+    """
+    Clear Cofactor via Multiplication
+
+    Ensure a point falls in the correct sub group of the curve.
+    """
+    return multiply_clear_cofactor_G2(p)
 
 
 #
@@ -221,8 +259,7 @@ def decompress_G2(p: G2Compressed) -> G2Uncompressed:
 def G2_to_signature(pt: G2Uncompressed) -> BLSSignature:
     z1, z2 = compress_G2(pt)
     return BLSSignature(
-        z1.to_bytes(48, "big") +
-        z2.to_bytes(48, "big")
+        z1.to_bytes(48, "big") + z2.to_bytes(48, "big")
     )
 
 

py_ecc/fields/field_elements.py

@@ -201,7 +201,7 @@ class FQP(object):
 
     def __init__(self,
                  coeffs: Sequence[IntOrFQ],
-                 modulus_coeffs: Sequence[IntOrFQ]=None) -> None:
+                 modulus_coeffs: Sequence[IntOrFQ] = None) -> None:
         if self.field_modulus is None:
             raise AttributeError("Field Modulus hasn't been specified")
 

py_ecc/fields/optimized_field_elements.py

@@ -182,6 +182,21 @@ def __repr__(self: T_FQ) -> str:
     def __int__(self: T_FQ) -> int:
         return self.n
 
+    def sgn0_be(self: T_FQ) -> int:
+        """
+        Calculates the sign of a value.
+        sgn0_be(x) = -1 when x > -x
+
+        Defined here:
+        https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-05#section-4.1.1
+        """
+        if self.n == 0:
+            return 1
+        neg = type(self)(-self)
+        if neg.n > self.n:
+            return 1
+        return -1
+
     @classmethod
     def one(cls: Type[T_FQ]) -> T_FQ:
         return cls(1)
@@ -201,7 +216,7 @@ class FQP(object):
 
     def __init__(self,
                  coeffs: Sequence[IntOrFQ],
-                 modulus_coeffs: Sequence[IntOrFQ]=None) -> None:
+                 modulus_coeffs: Sequence[IntOrFQ] = None) -> None:
         if self.field_modulus is None:
             raise AttributeError("Field Modulus hasn't been specified")
 
@@ -363,6 +378,33 @@ def __ne__(self: T_FQP, other: T_FQP) -> bool:     # type: ignore # https://gith
     def __neg__(self: T_FQP) -> T_FQP:
         return type(self)([-c for c in self.coeffs])
 
+    def sgn0_be(self: T_FQP) -> int:
+        """
+        Calculates the sign of a value.
+        sgn0_be(x) = -1 when x > -x
+
+        Defined here:
+        https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-05#section-4.1.1
+        """
+        sign = 0
+        for x_i in reversed(self.coeffs):
+            sign_i = 0
+            if isinstance(x_i, int):
+                if x_i == 0:
+                    sign_i = 0
+                elif (-x_i % self.field_modulus) > (x_i % self.field_modulus):
+                    sign_i = 1
+                else:
+                    sign_i = -1
+            elif isinstance(x_i, FQ):
+                sign_i = x_i.sgn0_be()
+            else:
+                raise TypeError("Only int and T_FQ types are accepted: got {type(x_i)}")
+
+            if sign == 0:
+                sign = sign_i
+        return sign
+
     @classmethod
     def one(cls: Type[T_FQP]) -> T_FQP:
         return cls([1] + [0] * (cls.degree - 1))

py_ecc/optimized_bls12_381/__init__.py

@@ -31,3 +31,10 @@
     pairing,
     final_exponentiate,
 )
+from .optimized_swu import (   # noqa: F401
+    optimized_swu_G2,
+    iso_map_G2,
+)
+from .optimized_clear_cofactor import (   # noqa: F401
+    multiply_clear_cofactor_G2,
+)