Fixes, tests passing.

tests/test_chacha.py

@@ -1,44 +1,12 @@
 from secrets import randbelow, token_bytes
 
-import numpy as np
+import pytest
 from cryptography.hazmat.primitives.ciphers import Cipher
 from cryptography.hazmat.primitives.ciphers.algorithms import ChaCha20
-from scipy.stats import chisquare
 
 from randquik import cha
 
 
-def test_cha_generate_statistical():
-    """Requests in multiple of ChaCha20 block size 64 bytes"""
-    ROUNDS = 100
-    min_p = 1 - 0.99 ** (1 / ROUNDS)  # 99 % confidence over the entire test
-    print(min_p)
-
-    for round in range(ROUNDS):
-        # First round both zero, use 8-byte nonce as round counter
-        key = bytes(32)
-        nonce = round.to_bytes(8, "little")
-        iv = bytes(8) + nonce  # Cryptography module requires IV (counter, nonce)
-        # Varying sizes to test internal processing that occurs in 64 bit blocks
-        # and with SIMD implementations also 256 or 512 bytes at a time.
-        N = 10000 + randbelow(10000)
-        ct0, ct1 = bytearray(N), bytearray(N)
-        Cipher(ChaCha20(key, iv), None, None).encryptor().update_into(bytes(N), ct0)
-        cha.generate(ct1, key, nonce)
-        assert len(ct0) == len(ct1)
-        assert ct0.hex() == ct1.hex()
-        assert ct1.count(0)
-
-        # Zeroing out 50 bytes fail the test in ~30 rounds
-        # ct1[:50] = bytes(50)
-
-        # Test that all byte values are equivalently common (despite zero inputs)
-        observed = np.bincount(ct1, minlength=256)
-        expected = np.full(256, N / 256)
-        chi2, p_value = chisquare(observed, expected)
-        assert p_value >= min_p, f"{round=} {N=}"
-
-
 def test_cipherstreams_fullblocks():
     """Requests in multiple of ChaCha20 block size 64 bytes"""
     key = token_bytes(32)
@@ -51,7 +19,30 @@ def test_cipherstreams_fullblocks():
         ct0 = c0.update(bytes(N))
         ct1 = c1(bytearray(N))
         assert len(ct0) == len(ct1)
-        assert ct0.hex() == ct1.hex()
+        assert ct0.hex() == ct1.hex(), f"{i=} {N=}"
+
+
+@pytest.mark.parametrize(
+    "counter",
+    [
+        b"\x00\x00\x00\x00\x00\x00\x00\x00",
+        b"\xFF\xFF\xFF\xFF\x00\x00\x00\x00",
+        b"\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF",
+        b"\xFF\xFF\xFF\x7F\xFF\xFF\xFF\xFF",
+        b"\x00\x00\x00\x80\xFF\xFF\xFF\xFF",
+    ],
+)
+def test_counter_wrap(counter):
+    """Tests carry handling of counter increments"""
+    key = bytes(32)
+    iv = counter + b"--------"
+    c0 = Cipher(ChaCha20(key, iv), None, None).encryptor()
+    c1 = cha.Cha(key, iv)
+    N = 128
+    ct0 = c0.update(bytes(N))
+    ct1 = c1(bytearray(N))
+    assert len(ct0) == len(ct1)
+    assert ct0.hex() == ct1.hex()
 
 
 def test_cipherstreams_partial_updates():
@@ -66,7 +57,7 @@ def test_cipherstreams_partial_updates():
         ct0 = c0.update(bytes(N))
         ct1 = c1(bytearray(N))
         assert len(ct0) == len(ct1)
-        assert ct0.hex() == ct1.hex()
+        assert ct0.hex() == ct1.hex(), f"{i=} {N=}"
 
 
 def test_cipherstreams_32leftover():