refactor(core): improve type signature of bech32.convertbits

core/src/apps/binance/helpers.py

@@ -91,7 +91,6 @@ def address_from_public_key(pubkey: bytes, hrp: str) -> str:
 
     h = sha256_ripemd160(pubkey).digest()
 
-    convertedbits = bech32.convertbits(h, 8, 5, False)
-    assert convertedbits is not None
-
+    assert (len(h) * 8) % 5 == 0  # no padding will be added by convertbits
+    convertedbits = bech32.convertbits(h, 8, 5)
     return bech32.bech32_encode(hrp, convertedbits, bech32.Encoding.BECH32)

core/src/apps/cardano/helpers/bech32.py

@@ -16,8 +16,6 @@ HRP_SHARED_KEY_HASH = "addr_shared_vkh"
 
 def encode(hrp: str, data: bytes) -> str:
     converted_bits = bech32.convertbits(data, 8, 5)
-    if converted_bits is None:
-        raise ValueError
     return bech32.bech32_encode(hrp, converted_bits, bech32.Encoding.BECH32)
 
 
@@ -40,7 +38,4 @@ def decode(hrp: str, bech: str) -> bytes:
         raise ValueError
 
     decoded = bech32.convertbits(data, 5, 8, False)
-    if decoded is None:
-        raise ValueError
-
     return bytes(decoded)

core/src/trezor/crypto/bech32.py

@@ -24,7 +24,7 @@ from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
     from enum import IntEnum
-    from typing import Iterable, Union, TypeVar
+    from typing import Sequence, Union, TypeVar
 
     A = TypeVar("A")
     B = TypeVar("B")
@@ -112,9 +112,22 @@ def bech32_decode(
 
 
 def convertbits(
-    data: Iterable[int], frombits: int, tobits: int, pad: bool = True
-) -> list[int] | None:
-    """General power-of-2 base conversion."""
+    data: Sequence[int], frombits: int, tobits: int, arbitrary_input: bool = True
+) -> list[int]:
+    """General power-of-2 base conversion.
+
+    The `arbitrary_input` parameter specifies what happens when the total length
+    of input bits is not a multiple of `tobits`.
+    If True (default), the overflowing bits are zero-padded to the right.
+    If False, the input must must be a valid output of `convertbits()` in the opposite
+    direction.
+    Namely:
+    (a) the overflow must only be the zero padding
+    (b) length of the overflow is less than `frombits`, meaning that there is no
+        additional all-zero `frombits`-sized group at the end.
+    If both conditions hold, the all-zero overflow is discarded.
+    Otherwise a ValueError is raised.
+    """
     acc = 0
     bits = 0
     ret = []
@@ -122,17 +135,22 @@ def convertbits(
     max_acc = (1 << (frombits + tobits - 1)) - 1
     for value in data:
         if value < 0 or (value >> frombits):
-            return None
+            raise ValueError  # input value does not match `frombits` size
         acc = ((acc << frombits) | value) & max_acc
         bits += frombits
         while bits >= tobits:
             bits -= tobits
             ret.append((acc >> bits) & maxv)
-    if pad:
+
+    if arbitrary_input:
         if bits:
+            # append remaining bits, zero-padded from right
             ret.append((acc << (tobits - bits)) & maxv)
     elif bits >= frombits or ((acc << (tobits - bits)) & maxv):
-        return None
+        # (1) either there is a superfluous group at end of input, and/or
+        # (2) the remainder is nonzero
+        raise ValueError
+
     return ret
 
 
@@ -145,12 +163,15 @@ def decode(hrp: str, addr: str) -> OptionalTuple2[int, list[int]]:
         return (None, None)
     if hrpgot != hrp:
         return (None, None)
-    decoded = convertbits(data[1:], 5, 8, False)
-    if decoded is None or len(decoded) < 2 or len(decoded) > 40:
+    try:
+        decoded = convertbits(data[1:], 5, 8, False)
+    except ValueError:
+        return (None, None)
+    if not 2 <= len(decoded) <= 40:
         return (None, None)
     if data[0] > 16:
         return (None, None)
-    if data[0] == 0 and len(decoded) != 20 and len(decoded) != 32:
+    if data[0] == 0 and len(decoded) not in (20, 32):
         return (None, None)
     if (
         data[0] == 0
@@ -162,11 +183,9 @@ def decode(hrp: str, addr: str) -> OptionalTuple2[int, list[int]]:
     return (data[0], decoded)
 
 
-def encode(hrp: str, witver: int, witprog: Iterable[int]) -> str | None:
+def encode(hrp: str, witver: int, witprog: bytes) -> str | None:
     """Encode a segwit address."""
     data = convertbits(witprog, 8, 5)
-    if data is None:
-        return None
     spec = Encoding.BECH32 if witver == 0 else Encoding.BECH32M
     ret = bech32_encode(hrp, [witver] + data, spec)
     if decode(hrp, ret) == (None, None):

core/src/trezor/crypto/cashaddr.py

@@ -20,8 +20,7 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
-if False:
-    from typing import Iterable
+from .bech32 import convertbits
 
 CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
 ADDRESS_TYPE_P2KH = 0
@@ -75,30 +74,6 @@ def b32encode(inputs: list[int]) -> str:
     return out
 
 
-def convertbits(
-    data: Iterable[int], frombits: int, tobits: int, pad: bool = True
-) -> list[int]:
-    acc = 0
-    bits = 0
-    ret = []
-    maxv = (1 << tobits) - 1
-    max_acc = (1 << (frombits + tobits - 1)) - 1
-    for value in data:
-        if value < 0 or (value >> frombits):
-            raise ValueError
-        acc = ((acc << frombits) | value) & max_acc
-        bits += frombits
-        while bits >= tobits:
-            bits -= tobits
-            ret.append((acc >> bits) & maxv)
-    if pad:
-        if bits:
-            ret.append((acc << (tobits - bits)) & maxv)
-    elif bits >= frombits or ((acc << (tobits - bits)) & maxv):
-        raise ValueError
-    return ret
-
-
 def encode(prefix: str, version: int, payload_bytes: bytes) -> str:
     payload_bytes = bytes([version]) + payload_bytes
     payload = convertbits(payload_bytes, 8, 5)