Blind chain signature verification

- also adds serialisation, deserialisation and optional metadata

src/pyelliptic/blindchain.py

@@ -0,0 +1,77 @@
+"""
+Blind signature chain with a top level CA
+"""
+
+from eccblind import ECCBlind
+
+try:
+    import msgpack
+except ImportError:
+    try:
+        import umsgpack as msgpack
+    except ImportError:
+        import fallback.umsgpack.umsgpack as msgpack
+
+from eccblind import ECCBlind
+
+def encode_datetime(obj):
+    """
+    Method to format time
+    """
+    return {'Time': int(obj.strftime("%s"))}
+
+
+class ECCBlindChain(object):  # pylint: disable=too-many-instance-attributes
+    """
+    # Class for ECC Blind Chain signature functionality
+    """
+    chain = []
+    ca = []
+
+    def __init__(self, chain=None):
+        if chain is not None:
+            self.chain = chain
+
+    def serialize(self):
+        data = msgpack.packb(self.chain)
+        return data
+
+    @staticmethod
+    def deserialize(self, chain):
+        """
+        Deserialize the data using msgpack
+        """
+        data = msgpack.unpackb(chain)
+        return ECCBlindChain(data)
+
+    def add_level(self, pubkey, metadata, signature):
+        self.chain.append((pubkey, metadata, signature))
+
+    def add_ca(self, ca):
+        pubkey, metadata = ECCBlind.deserialize(ca)
+        self.ca.append(pubkey)
+
+    def verify(self, msg, value):
+        lastpubkey = None
+        retval = False
+        for level in reversed(self.chain):
+            pubkey, metadata, signature = level
+            verifier_obj = ECCBlind(pubkey=pubkey, metadata)
+            if not lastpubkey:
+                retval = verifier_obj.verify(msg, signature, value)
+            else:
+                retval = verifier_obj.verify(lastpubkey, signature, value)
+            if not reval:
+                break
+            lastpubkey = pubkey
+        if retval:
+            retval = False
+            for ca in self.ca:
+                match = True
+                for i in range(4):
+                    if lastpubkey[i] != ca[i]:
+                        match = False
+                        break
+                if match:
+                    return True
+        return retval

src/pyelliptic/eccblind.py

@@ -10,9 +10,52 @@ http://www.isecure-journal.com/article_39171_47f9ec605dd3918c2793565ec21fcd7a.pd
 # variable names are based on the math in the paper, so they don't conform
 # to PEP8
 
+from hashlib import sha256
+import time
+
+try:
+    import msgpack
+except ImportError:
+    try:
+        import umsgpack as msgpack
+    except ImportError:
+        import fallback.umsgpack.umsgpack as msgpack
+
 from .openssl import OpenSSL
 
 
+class Metadata(object):
+    """
+    Pubkey metadata
+    """
+    def __init__(self, exp=0, value=0):
+        self.exp = 0
+        self.value = 0
+        if exp:
+            self.exp = exp
+        if value:
+            self.value = value
+
+    def serialize(self):
+        if self.exp or self.value:
+            return [self.exp, self.value]
+        else:
+            return []
+
+    @staticmethod
+    def deserialize(self, data):
+        exp, value = data
+        return Medatadata(exp, value)
+
+    def verify(self, value):
+        if self.value and value > self.value:
+            return False
+        if self.exp:
+            if time.time() > self.exp:
+                return False
+        return True
+
+
 class ECCBlind(object):  # pylint: disable=too-many-instance-attributes
     """
     Class for ECC blind signature functionality
@@ -75,7 +118,21 @@ class ECCBlind(object):  # pylint: disable=too-many-instance-attributes
         OpenSSL.EC_POINT_get_affine_coordinates_GFp(group, F, x0, y0, ctx)
         return x0
 
-    def __init__(self, curve="secp256k1", pubkey=None):
+    @staticmethod
+    def deserialize(self, data):
+        pubkey_deserialized, meta = msgpack.unpackb(data)
+        if meta:
+            obj = ECCBlind(pubkey=pubkey_deserialized, metadata=meta)
+        else:
+            obj = ECCBlind(pubkey=pubkey_deserialized)
+        return obj
+
+    def serialize(self):
+        data = (self.pubkey, self.metadata.serialize)
+        retval = msgpack.packb(data)
+        return retval
+
+    def __init__(self, curve="secp256k1", pubkey=None, metadata=None):
         self.ctx = OpenSSL.BN_CTX_new()
 
         if pubkey:
@@ -101,6 +158,14 @@ class ECCBlind(object):  # pylint: disable=too-many-instance-attributes
         self.iO = OpenSSL.EC_POINT_new(self.group)
         OpenSSL.EC_POINT_set_to_infinity(self.group, self.iO)
 
+        if metadata:
+            self._set_metadata(self, metadata)
+        else: 
+            self.metadata = Metadata()
+
+    def _set_metadata(self, metadata):
+        self.metadata = Metadata.deserialise(metadata)
+
     def signer_init(self):
         """
         Init signer
@@ -119,6 +184,7 @@ class ECCBlind(object):  # pylint: disable=too-many-instance-attributes
         Requester creates a new signing request
         """
         self.R = R
+        msghash = sha256(msg)
 
         # Requester: 3 random blinding factors
         self.F = OpenSSL.EC_POINT_new(self.group)
@@ -151,7 +217,7 @@ class ECCBlind(object):  # pylint: disable=too-many-instance-attributes
 
         # Requester: Blinding (m' = br(m) + a)
         self.m = OpenSSL.BN_new()
-        OpenSSL.BN_bin2bn(msg, len(msg), self.m)
+        OpenSSL.BN_bin2bn(msghash, len(msghash), self.m)
 
         self.m_ = OpenSSL.BN_new()
         OpenSSL.BN_mod_mul(self.m_, self.b, self.r, self.n, self.ctx)
@@ -180,14 +246,15 @@ class ECCBlind(object):  # pylint: disable=too-many-instance-attributes
         self.signature = (s, self.F)
         return self.signature
 
-    def verify(self, msg, signature):
+    def verify(self, msg, signature, value=0):
         """
         Verify signature with certifier's pubkey
         """
 
         # convert msg to BIGNUM
         self.m = OpenSSL.BN_new()
-        OpenSSL.BN_bin2bn(msg, len(msg), self.m)
+        msghash = sha256(msg)
+        OpenSSL.BN_bin2bn(msghash, len(msghash), self.m)
 
         # init
         s, self.F = signature
@@ -206,5 +273,8 @@ class ECCBlind(object):  # pylint: disable=too-many-instance-attributes
         retval = OpenSSL.EC_POINT_cmp(self.group, lhs, rhs, self.ctx)
         if retval == -1:
             raise RuntimeError("EC_POINT_cmp returned an error")
-        else:
+        elif retval != 0:
-            return retval == 0
+            return False
+        elif self.metadata:
+            return self.metadata.verify(value)
+        return True

src/tests/test_blindsig.py

@@ -2,10 +2,12 @@
 Test for ECC blind signatures
 """
 import os
+import time
 import unittest
 from ctypes import cast, c_char_p
 
-from pybitmessage.pyelliptic.eccblind import ECCBlind
+from pybitmessage.pyelliptic.eccblind import ECCBlind, Metadata
+from pybitmessage.pyelliptic.eccblindchain import ECCBlindChain
 from pybitmessage.pyelliptic.openssl import OpenSSL
 
 
@@ -50,3 +52,47 @@ class TestBlindSig(unittest.TestCase):
         # (5) Verification
         verifier_obj = ECCBlind(pubkey=signer_obj.pubkey)
         self.assertTrue(verifier_obj.verify(msg, signature))
+
+        # Serialization and deserialisation
+        pk = signer_obj.serialize()
+        pko = ECCBlind.deserialize(pk)
+        self.assertTrue(pko.verify(msg, signature))
+
+    def test_blind_sig_chain(self):
+        """Test blind signature chain using a random certifier key and a random message"""
+
+        test_levels = 5
+        value = 1
+        msg = os.urandom(1024)
+
+        chain = ECCBlindChain()
+        ca = ECCBlind()
+        signer_obj = ca
+        signer_pubkey = signer_obj.serialize()
+
+        for level in range(test_levels):
+            if level == 0:
+                metadata = Metadata(exp=int(time.time()) + 100,
+                                    value=value).serialize()
+                requester_obj = ECCBlind(pubkey=signer_obj.pubkey,
+                                         metadata=metadata)
+            else:
+                requester_obj = ECCBlind(pubkey=signer_obj.pubkey)
+            point_r = signer_obj.signer_init()
+
+            if level == test_levels - 1:
+                msg_blinded = requester_obj.create_signing_request(point_r,
+                                                                   msg)
+            else:
+                msg_blinded = requester.obj.create_signing_request(point_r,
+                                                                   signer_pubkey)
+            signature_blinded = signer_obj.blind_sign(msg_blinded)
+            signature = requester_obj.unblind(signature_blinded)
+            chain.add_level(signer_obj.pubkey,
+                            signer_obj.metadata.serialize,
+                            signature)
+            signer_obj = requester_obj
+            signer_pubkey = requester_obj.serialize()
+        sigchain = chain.serialize()
+        verifychain = ECCBlindChain.deserialize(sigchain)
+        self.assertTrue(verifychain.verify(msg, value))