crypto: add chacha20_decrypt; unused for now

electrum/crypto.py

@@ -338,6 +338,8 @@ def chacha20_poly1305_encrypt(
     assert isinstance(nonce, (bytes, bytearray))
     assert isinstance(associated_data, (bytes, bytearray, type(None)))
     assert isinstance(data, (bytes, bytearray))
+    assert len(key) == 32, f"unexpected key size: {len(nonce)} (expected: 32)"
+    assert len(nonce) == 12, f"unexpected nonce size: {len(nonce)} (expected: 12)"
     if HAS_CRYPTODOME:
         cipher = CD_ChaCha20_Poly1305.new(key=key, nonce=nonce)
         if associated_data is not None:
@@ -361,6 +363,8 @@ def chacha20_poly1305_decrypt(
     assert isinstance(nonce, (bytes, bytearray))
     assert isinstance(associated_data, (bytes, bytearray, type(None)))
     assert isinstance(data, (bytes, bytearray))
+    assert len(key) == 32, f"unexpected key size: {len(nonce)} (expected: 32)"
+    assert len(nonce) == 12, f"unexpected nonce size: {len(nonce)} (expected: 12)"
     if HAS_CRYPTODOME:
         cipher = CD_ChaCha20_Poly1305.new(key=key, nonce=nonce)
         if associated_data is not None:
@@ -380,14 +384,33 @@ def chacha20_encrypt(*, key: bytes, nonce: bytes, data: bytes) -> bytes:
     assert isinstance(key, (bytes, bytearray))
     assert isinstance(nonce, (bytes, bytearray))
     assert isinstance(data, (bytes, bytearray))
-    assert len(nonce) == 8, f"unexpected nonce size: {len(nonce)} (expected: 8)"
+    assert len(key) == 32, f"unexpected key size: {len(nonce)} (expected: 32)"
+    assert len(nonce) in (8, 12), f"unexpected nonce size: {len(nonce)} (expected: 8 or 12)"
     if HAS_CRYPTODOME:
         cipher = CD_ChaCha20.new(key=key, nonce=nonce)
         return cipher.encrypt(data)
     if HAS_CRYPTOGRAPHY:
-        nonce = bytes(8) + nonce  # cryptography wants 16 byte nonces
+        nonce = bytes(16 - len(nonce)) + nonce  # cryptography wants 16 byte nonces
         algo = CG_algorithms.ChaCha20(key=key, nonce=nonce)
         cipher = CG_Cipher(algo, mode=None, backend=CG_default_backend())
         encryptor = cipher.encryptor()
         return encryptor.update(data)
     raise Exception("no chacha20 backend found")
+
+
+def chacha20_decrypt(*, key: bytes, nonce: bytes, data: bytes) -> bytes:
+    assert isinstance(key, (bytes, bytearray))
+    assert isinstance(nonce, (bytes, bytearray))
+    assert isinstance(data, (bytes, bytearray))
+    assert len(key) == 32, f"unexpected key size: {len(nonce)} (expected: 32)"
+    assert len(nonce) in (8, 12), f"unexpected nonce size: {len(nonce)} (expected: 8 or 12)"
+    if HAS_CRYPTODOME:
+        cipher = CD_ChaCha20.new(key=key, nonce=nonce)
+        return cipher.decrypt(data)
+    if HAS_CRYPTOGRAPHY:
+        nonce = bytes(16 - len(nonce)) + nonce  # cryptography wants 16 byte nonces
+        algo = CG_algorithms.ChaCha20(key=key, nonce=nonce)
+        cipher = CG_Cipher(algo, mode=None, backend=CG_default_backend())
+        decryptor = cipher.decryptor()
+        return decryptor.update(data)
+    raise Exception("no chacha20 backend found")

electrum/tests/test_bitcoin.py

@@ -302,12 +302,22 @@ class Test_bitcoin(ElectrumTestCase):
                          crypto.chacha20_poly1305_decrypt(key=key, nonce=nonce, data=data, associated_data=b''))
 
     @needs_test_with_all_chacha20_implementations
-    def test_chacha20_encrypt(self):
+    def test_chacha20_encrypt__8_byte_nonce(self):
         key = bytes.fromhex('37326d9d69a83b815ddfd947d21b0dd39111e5b6a5a44042c44d570ea03e3179')
         nonce = bytes.fromhex('0102030405060708')
         data = bytes.fromhex('38a0e0a7c865fe9ca31f0730cfcab610f18e6da88dc3790f1d243f711a257c78')
-        self.assertEqual(bytes.fromhex('f62fbd74d197323c7c3d5658476a884d38ee6f4b5500add1e8dc80dcd9c15dff'),
-                         crypto.chacha20_encrypt(key=key, nonce=nonce, data=data))
+        ciphertext = crypto.chacha20_encrypt(key=key, nonce=nonce, data=data)
+        self.assertEqual(bytes.fromhex('f62fbd74d197323c7c3d5658476a884d38ee6f4b5500add1e8dc80dcd9c15dff'), ciphertext)
+        self.assertEqual(data, crypto.chacha20_decrypt(key=key, nonce=nonce, data=ciphertext))
+
+    @needs_test_with_all_chacha20_implementations
+    def test_chacha20_encrypt__12_byte_nonce(self):
+        key = bytes.fromhex('37326d9d69a83b815ddfd947d21b0dd39111e5b6a5a44042c44d570ea03e3179')
+        nonce = bytes.fromhex('010203040506070809101112')
+        data = bytes.fromhex('38a0e0a7c865fe9ca31f0730cfcab610f18e6da88dc3790f1d243f711a257c78')
+        ciphertext = crypto.chacha20_encrypt(key=key, nonce=nonce, data=data)
+        self.assertEqual(bytes.fromhex('c0b1cb75c3c23c13f47dab393add738c92c62c4e2546cb3bf2b48269a4184028'), ciphertext)
+        self.assertEqual(data, crypto.chacha20_decrypt(key=key, nonce=nonce, data=ciphertext))
 
     def test_sha256d(self):
         self.assertEqual(b'\x95MZI\xfdp\xd9\xb8\xbc\xdb5\xd2R&x)\x95\x7f~\xf7\xfalt\xf8\x84\x19\xbd\xc5\xe8"\t\xf4',