rando: refactor random generation of keys and hashes (#117)

* Refactor random generation of keys and hashes.

* Add a unit test for rando.checkSeed.

decred/decred/crypto/crypto.py

@@ -1,6 +1,6 @@
 """
 Copyright (c) 2019, Brian Stafford
-Copyright (c) 2019, The Decred developers
+Copyright (c) 2019-2020, The Decred developers
 See LICENSE for details
 
 Cryptographic functions.
@@ -21,8 +21,6 @@
 from .secp256k1.curve import PrivateKey, PublicKey, curve as Curve
 
 
-KEY_SIZE = 32
-HASH_SIZE = 32
 BLAKE256_SIZE = 32
 RIPEMD160_SIZE = 20
 SERIALIZED_KEY_LENGTH = 4 + 1 + 4 + 4 + 32 + 33  # 78 bytes
@@ -628,9 +626,7 @@ def new(seed):
         Returns:
             crypto.ExtendedKey: A master hierarchical deterministic key.
         """
-        seedLen = len(seed)
-        if seedLen < rando.MinSeedBytes or seedLen > rando.MaxSeedBytes:
-            raise AssertionError("invalid seed length %d" % seedLen)
+        rando.checkSeedLength(len(seed))
 
         # First take the HMAC-SHA512 of the master key and the seed data:
         # SHA512 hash is 64 bytes.
@@ -1137,7 +1133,7 @@ def __init__(self, pw):
             pw (byte-like): A password that deterministically generates the key.
         """
         super().__init__()
-        salt = ByteArray(rando.generateSeed(KEY_SIZE))
+        salt = rando.newKey()
         b = lambda v: ByteArray(v).bytes()
         _, hashName, iterations = defaultKDFParams()
         self.key = ByteArray(

decred/decred/crypto/rando.py

@@ -1,17 +1,87 @@
 """
 Copyright (c) 2019, Brian Stafford
-Copyright (c) 2019, The Decred developers
+Copyright (c) 2019-20, The Decred developers
 See LICENSE for details
 """
 
 import os
 
+from decred import DecredError
+from decred.util.encode import ByteArray
+
+
+KEY_SIZE = 32
+HASH_SIZE = 32
 
 MinSeedBytes = 16  # 128 bits
 MaxSeedBytes = 64  # 512 bits
 
 
-def generateSeed(length=MaxSeedBytes):
+def checkSeedLength(length):
+    """
+    Check that seed length is correct.
+
+    Args:
+        length int: the seed length to be checked.
+
+    Raises:
+        DecredError if length is not between MinSeedBytes and MaxSeedBytes
+        included.
+    """
     if length < MinSeedBytes or length > MaxSeedBytes:
-        raise AssertionError("invalid seed length %d" % length)
+        raise DecredError(f"Invalid seed length {length}")
+
+
+def generateSeed(length=MaxSeedBytes):
+    """
+    Generate a cryptographically-strong random seed.
+
+    Returns:
+        bytes: a random bytes object of the given length.
+
+    Raises:
+        DecredError if length is not between MinSeedBytes and MaxSeedBytes
+        included.
+    """
+    checkSeedLength(length)
     return os.urandom(length)
+
+
+def newHashRaw():
+    """
+    Generate a random hash of HASH_SIZE length.
+
+    Returns:
+        bytes: a random object of HASH_SIZE length.
+    """
+    return generateSeed(HASH_SIZE)
+
+
+def newHash():
+    """
+    Generate a wrapped random hash of HASH_SIZE length.
+
+    Returns:
+        ByteArray: a random object of HASH_SIZE length.
+    """
+    return ByteArray(newHashRaw())
+
+
+def newKeyRaw():
+    """
+    Generate a random key of KEY_SIZE length.
+
+    Returns:
+        bytes: a random object of KEY_SIZE length.
+    """
+    return generateSeed(KEY_SIZE)
+
+
+def newKey():
+    """
+    Generate a wrapped random key of KEY_SIZE length.
+
+    Returns:
+        ByteArray: a random object of KEY_SIZE length.
+    """
+    return ByteArray(newKeyRaw())

decred/decred/wallet/simple.py

@@ -7,7 +7,7 @@
 from pathlib import Path
 
 from decred import DecredError
-from decred.crypto import crypto, mnemonic, rando
+from decred.crypto import mnemonic, rando
 from decred.dcr import nets
 from decred.dcr.dcrdata import DcrdataBlockchain
 from decred.util import chains, database
@@ -72,7 +72,7 @@ def __init__(self, walletDir, pw, network, signals=None, allowCreate=False):
         super().__init__(dbPath)
         # words is only set the first time a wallet is created.
         if not walletExists:
-            seed = rando.generateSeed(crypto.KEY_SIZE)
+            seed = rando.newKeyRaw()
             self.initialize(seed, pw.encode(), netParams)
             self.words = mnemonic.encode(seed)
 

decred/decred/wallet/wallet.py

@@ -1,6 +1,6 @@
 """
 Copyright (c) 2019, Brian Stafford
-Copyright (c) 2019, The Decred developers
+Copyright (c) 2019-2020, The Decred developers
 See LICENSE for details
 """
 
@@ -64,7 +64,7 @@ def initialize(self, seed, pw, netParams):
             netParams (object): Network parameters.
         """
         pwKey = crypto.SecretKey(pw)
-        cryptoKey = encode.ByteArray(rando.generateSeed(crypto.KEY_SIZE))
+        cryptoKey = rando.newKey()
         root = crypto.ExtendedKey.new(seed)
         self.masterDB[DBKeys.cryptoKey] = pwKey.encrypt(cryptoKey)
         self.masterDB[DBKeys.root] = root.serialize()
@@ -95,7 +95,7 @@ def create(path, password, netParams):
         """
         if len(password) == 0:
             raise AssertionError("empty password not allowed")
-        seed = rando.generateSeed(crypto.KEY_SIZE)
+        seed = rando.newKeyRaw()
         wallet = Wallet(path)
         wallet.initialize(seed, password.encode(), netParams)
         words = mnemonic.encode(seed)

decred/tests/integration/dcr/test_dcrdata.py

@@ -13,10 +13,6 @@
 from decred.util.encode import ByteArray
 
 
-def newHash():
-    return ByteArray(rando.generateSeed(32))
-
-
 class TestDcrdata:
     def client(self, **k):
         return dcrdata.DcrdataClient("https://alpha.dcrdata.org", **k)
@@ -103,7 +99,7 @@ def utxosource(amt, filter):
                     addrString = addr.string()
                     keys[addrString] = privKey
                     pkScript = txscript.makePayToAddrScript(addrString, testnet)
-                    txHash = newHash()
+                    txHash = rando.newHash()
                     txid = reversed(txHash).hex()
                     utxos.append(
                         account.UTXO(

decred/tests/unit/crypto/test_crypto.py

@@ -121,7 +121,7 @@ def test_addr_script_hash(self):
             self.assertEqual(addr.string(), addrStr)
 
     def test_kdf_params(self):
-        salt = ByteArray(rando.generateSeed(32))
+        salt = rando.newHash()
         digest = ByteArray(32)
         kdf = crypto.KDFParams(salt, digest)
         b = kdf.serialize()

decred/tests/unit/crypto/test_rando.py

@@ -0,0 +1,20 @@
+"""
+Copyright (c) 2020, The Decred developers
+See LICENSE for details
+"""
+
+import pytest
+
+from decred import DecredError
+from decred.crypto import rando
+
+
+def test_checkSeedLength():
+    with pytest.raises(DecredError):
+        rando.checkSeedLength(rando.MinSeedBytes - 1)
+    assert rando.checkSeedLength(rando.MinSeedBytes) is None
+    assert rando.checkSeedLength(rando.HASH_SIZE) is None
+    assert rando.checkSeedLength(rando.KEY_SIZE) is None
+    assert rando.checkSeedLength(rando.MaxSeedBytes) is None
+    with pytest.raises(DecredError):
+        rando.checkSeedLength(rando.MaxSeedBytes + 1)

decred/tests/unit/dcr/test_account.py

@@ -9,7 +9,7 @@
 
 from decred import DecredError
 from decred.crypto import crypto, opcode, rando
-from decred.dcr import account, dcrdata, nets, txscript
+from decred.dcr import account, nets, txscript
 from decred.dcr.vsp import PurchaseInfo, VotingServiceProvider
 from decred.dcr.wire import msgblock, msgtx
 from decred.util.database import KeyValueDatabase
@@ -18,7 +18,7 @@
 
 LOGGER_ID = "test_account"
 
-cryptoKey = crypto.ByteArray(rando.generateSeed(32))
+cryptoKey = rando.newKey()
 
 ticketScript = ByteArray("baa914f5618dfc002becfe840da65f6a49457f41d4f21787")
 
@@ -177,7 +177,7 @@ def match(utxo):
 
 
 def test_tiny_block(prepareLogger):
-    blockHash = rando.generateSeed(32)
+    blockHash = rando.newHashRaw()
     height = 55
     TinyBlock = account.TinyBlock
     tb1 = TinyBlock(blockHash, height)
@@ -252,7 +252,7 @@ def test_account():
     for n in range(20):
         acct.nextExternalAddress()
     satoshis = int(round(5 * 1e8))
-    txHash = ByteArray(rando.generateSeed(32))
+    txHash = rando.newHash()
     txid = reversed(txHash).hex()
     vout = 2
     address = acct.nextExternalAddress()
@@ -314,11 +314,11 @@ def balance(cls, b):
     acct.signals = Signals
 
     # Add a txid for this first address
-    txid = ByteArray(rando.generateSeed(32)).hex()
+    txid = rando.newHash().hex()
     zerothAddr = acct.externalAddresses[0]
     acct.addTxid(zerothAddr, txid)
     # Add a voting service provider
-    vspKey = ByteArray(rando.generateSeed(32)).hex()
+    vspKey = rando.newKey().hex()
     ticketAddr = "ticketAddr"
     pi = PurchaseInfo("addr", 1.0, ByteArray(b"scripthashscript"), ticketAddr, 1, 0, 2)
     vsp = VotingServiceProvider("https://myvsp.com", vspKey, nets.mainnet.Name, pi)