From 3869c802cae2d330fb3f0605c555a3f5fb71ed1d Mon Sep 17 00:00:00 2001
From: Muneeb Sheikh <muneikh@gmail.com>
Date: Sun, 11 Oct 2026 13:18:52 -0400
Subject: [PATCH] Validate Base32 quantum lengths and padding

---
 src/validators/encoding.py | 10 +++++++++-
 tests/test_encoding.py     | 13 +++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/validators/encoding.py b/src/validators/encoding.py
index c4ec2cea..fb341b60 100644
--- a/src/validators/encoding.py
+++ b/src/validators/encoding.py
@@ -46,7 +46,15 @@ def base32(value: str, /):
         (Literal[True]): If `value` is a valid base32 encoding.
         (ValidationError): If `value` is an invalid base32 encoding.
     """
-    return re.fullmatch(r"^[A-Z2-7]+=*$", value) if value else False
+    return (
+        re.fullmatch(
+            r"(?:[A-Z2-7]{8})*(?:[A-Z2-7]{2}(?:={6})?|[A-Z2-7]{4}(?:={4})?|"
+            r"[A-Z2-7]{5}(?:={3})?|[A-Z2-7]{7}=?)?",
+            value,
+        )
+        if value
+        else False
+    )
 
 
 @validator
diff --git a/tests/test_encoding.py b/tests/test_encoding.py
index 9728a8fe..01a6a2fc 100644
--- a/tests/test_encoding.py
+++ b/tests/test_encoding.py
@@ -130,3 +130,16 @@ def test_encoding_rejects_trailing_characters(
 ):
     """Reject characters outside the encoded value."""
     assert isinstance(validate(value + suffix), ValidationError)
+
+
+@pytest.mark.parametrize("value", ["A", "AAA", "AAAAAA", "AB=", "AB===", "AB=======", "ABCDEFGH="])
+def test_base32_rejects_invalid_length_and_padding(value: str):
+    """Reject symbol counts and padding that cannot encode whole bytes."""
+    assert isinstance(base32(value), ValidationError)
+
+
+@pytest.mark.parametrize("value", ["MY======", "MZXQ====", "MZXW6===", "MZXW6YQ=", "MZXW6YTB"])
+def test_base32_accepts_valid_final_quanta(value: str):
+    """Accept each legal final quantum with or without padding."""
+    assert base32(value) is True
+    assert base32(value.rstrip("=")) is True