fix(python): replace base58 implementation with a more correct one

based on https://github.com/keis/base58/blob/master/base58/__init__.py

python/src/trezorlib/tools.py

@@ -126,59 +126,48 @@ __b58chars = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
 __b58base = len(__b58chars)
 
 
+def b58encode_int(i: int) -> str:
+    """Encode an integer using Base58"""
+    digits = []
+    while i:
+        i, idx = divmod(i, __b58base)
+        digits.append(__b58chars[idx])
+    return "".join(reversed(digits))
+
+
 def b58encode(v: bytes) -> str:
     """encode v, which is a string of bytes, to base58."""
+    origlen = len(v)
+    v = v.lstrip(b"\0")
+    newlen = len(v)
 
-    long_value = 0
-    for c in v:
-        long_value = long_value * 256 + c
+    acc = int.from_bytes(v, byteorder="big")  # first byte is most significant
 
-    result = ""
-    while long_value >= __b58base:
-        div, mod = divmod(long_value, __b58base)
-        result = __b58chars[mod] + result
-        long_value = div
-    result = __b58chars[long_value] + result
+    result = b58encode_int(acc)
+    return __b58chars[0] * (origlen - newlen) + result
 
-    # Bitcoin does a little leading-zero-compression:
-    # leading 0-bytes in the input become leading-1s
-    nPad = 0
-    for c in v:
-        if c == 0:
-            nPad += 1
-        else:
-            break
 
-    return (__b58chars[0] * nPad) + result
+def b58decode_int(v: str) -> int:
+    """Decode a Base58 encoded string as an integer"""
+    decimal = 0
+    try:
+        for char in v:
+            decimal = decimal * __b58base + __b58chars.index(char)
+    except KeyError:
+        raise ValueError(f"Invalid character {char!r}") from None  # type: ignore [possibly unbound]
+    return decimal
 
 
 def b58decode(v: AnyStr, length: Optional[int] = None) -> bytes:
     """decode v into a string of len bytes."""
-    str_v = v.decode() if isinstance(v, bytes) else v
+    v_str = v if isinstance(v, str) else v.decode()
+    origlen = len(v_str)
+    v_str = v_str.lstrip(__b58chars[0])
+    newlen = len(v_str)
 
-    for c in str_v:
-        if c not in __b58chars:
-            raise ValueError("invalid Base58 string")
+    acc = b58decode_int(v_str)
 
-    long_value = 0
-    for (i, c) in enumerate(str_v[::-1]):
-        long_value += __b58chars.find(c) * (__b58base**i)
-
-    result = b""
-    while long_value >= 256:
-        div, mod = divmod(long_value, 256)
-        result = struct.pack("B", mod) + result
-        long_value = div
-    result = struct.pack("B", long_value) + result
-
-    nPad = 0
-    for c in str_v:
-        if c == __b58chars[0]:
-            nPad += 1
-        else:
-            break
-
-    result = b"\x00" * nPad + result
+    result = acc.to_bytes(origlen - newlen + (acc.bit_length() + 7) // 8, "big")
     if length is not None and len(result) != length:
         raise ValueError("Result length does not match expected_length")
 

python/tests/test_tools.py

@@ -49,3 +49,41 @@ VECTORS = (  # descriptor, checksum
 @pytest.mark.parametrize("descriptor, checksum", VECTORS)
 def test_descriptor_checksum(descriptor, checksum):
     assert tools.descriptor_checksum(descriptor) == checksum
+
+
+BASE58_VECTORS = (  # data_hex, encoding_b58
+    ("", ""),
+    ("61", "2g"),
+    ("626262", "a3gV"),
+    ("636363", "aPEr"),
+    ("73696d706c792061206c6f6e6720737472696e67", "2cFupjhnEsSn59qHXstmK2ffpLv2"),
+    (
+        "00eb15231dfceb60925886b67d065299925915aeb172c06647",
+        "1NS17iag9jJgTHD1VXjvLCEnZuQ3rJDE9L",
+    ),
+    ("516b6fcd0f", "ABnLTmg"),
+    ("bf4f89001e670274dd", "3SEo3LWLoPntC"),
+    ("572e4794", "3EFU7m"),
+    ("ecac89cad93923c02321", "EJDM8drfXA6uyA"),
+    ("10c8511e", "Rt5zm"),
+    ("00000000000000000000", "1111111111"),
+    ("00" * 32, "11111111111111111111111111111111"),
+    (
+        "000111d38e5fc9071ffcd20b4a763cc9ae4f252bb4e48fd66a835e252ada93ff480d6dd43dc62a641155a5",
+        "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz",
+    ),
+    (
+        "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9fa0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebfc0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedfe0e1e2e3e4e5e6e7e8e9eaebecedeeeff0f1f2f3f4f5f6f7f8f9fafbfcfdfeff",
+        "1cWB5HCBdLjAuqGGReWE3R3CguuwSjw6RHn39s2yuDRTS5NsBgNiFpWgAnEx6VQi8csexkgYw3mdYrMHr8x9i7aEwP8kZ7vccXWqKDvGv3u1GxFKPuAkn8JCPPGDMf3vMMnbzm6Nh9zh1gcNsMvH3ZNLmP5fSG6DGbbi2tuwMWPthr4boWwCxf7ewSgNQeacyozhKDDQQ1qL5fQFUW52QKUZDZ5fw3KXNQJMcNTcaB723LchjeKun7MuGW5qyCBZYzA1KjofN1gYBV3NqyhQJ3Ns746GNuf9N2pQPmHz4xpnSrrfCvy6TVVz5d4PdrjeshsWQwpZsZGzvbdAdN8MKV5QsBDY",
+    ),
+)
+
+
+@pytest.mark.parametrize("data_hex,encoding_b58", BASE58_VECTORS)
+def test_b58encode(data_hex, encoding_b58):
+    assert tools.b58encode(bytes.fromhex(data_hex)) == encoding_b58
+
+
+@pytest.mark.parametrize("data_hex,encoding_b58", BASE58_VECTORS)
+def test_b58decode(data_hex, encoding_b58):
+    assert tools.b58decode(encoding_b58).hex() == data_hex