diff --git a/fck/cktype/__init__.py b/fck/cktype/__init__.py
index 43058e5..ee85f18 100644
--- a/fck/cktype/__init__.py
+++ b/fck/cktype/__init__.py
@@ -1,19 +1,30 @@
-from re import search
-from typing import Optional
+from typing import Dict, Optional, Type
+
+from fck.cktype.cktypeinterface import CKTYPEINTERFACE as CKTYPEINTERFACE
+
 from .crc32 import CRC32
 
-CKTYPES = [
-    (CRC32)
-]
+CKTYPES: Dict[str, Type[MD5 | CRC32]] = {
+    "CRC32": (CRC32),
+}
 
 
 def resolve(fname: str, esum: Optional[str] = None, cstype: str = ""):
     """
-      Checks fname input for checksum pattern and returns first match.
-      Can be overridden with cstype.
-      If neither is applicable the first possible checksum type will be returned.
+    Checks fname input for checksum patterns and returns first match.
+    Can be overridden with cstype.
+    If neither is applicable it defaults to CRC32.
     """
-    if esum is None and (match := CKTYPES[0].REGEX.search(fname)):
-        esum = match.group(0)
+    cstype = cstype.upper()
+    if cstype in CKTYPES:
+        if esum is None and (match := CKTYPES[cstype].REGEX.search(fname)):
+            esum = match.group(0)
+        return CKTYPES[cstype](), esum
 
-    return CKTYPES[0](), esum
+    for cstname, csclass in CKTYPES.items():
+        if match := csclass.REGEX.search(fname):
+            if esum is None:
+                esum = match.group(0)
+            return csclass(), esum
+
+    return CRC32(), esum
diff --git a/fck/cktype/crc32.py b/fck/cktype/crc32.py
index e69bf36..98f52da 100644
--- a/fck/cktype/crc32.py
+++ b/fck/cktype/crc32.py
@@ -1,16 +1,20 @@
-from typing import Generator, List, Tuple, Optional
+from typing import List
 from re import compile, Pattern
 from zlib import crc32
+from .cktypeinterface import CKTYPEINTERFACE
 
 
-class CRC32(object):
+class CRC32(CKTYPEINTERFACE):
     NAME: str = "CRC32"
     EXT: List[str] = [".sfv"]
     SYNTAX: List[Pattern] = [
-        compile(r'^;*$'),
-        compile(r'^.* [0-9a-fA-F]{8}$')
+        # comment lines
+        compile(r"^;*$"),
+        # filepath checksum pair
+        compile(r"^.* [0-9a-fA-F]{8}$"),
     ]
-    REGEX: Pattern = compile(r'[0-9a-fA-F]{8}')
+    REGEX: Pattern = compile(r"[0-9a-fA-F]{8}")
+    NULL: str = "00000000"
 
     def __init__(self):
         self.cksum: int = 0
@@ -22,8 +26,5 @@ class CRC32(object):
         self.__init__()
 
     def __repr__(self) -> str:
-        cstring = str(hex(self.cksum))[2:].upper()
-        return ''.join([((8 - len(cstring)) * "0"), cstring])
-
-    def __eq__(self, other) -> bool:
-        return self.__repr__() == other.upper()
+        cstring = format(self.cksum, "x").upper()
+        return cstring.rjust(8, "0")