Much cleaner Esab32 decoding

Tries all permutations of chunks in Esab32,
until it gets only printable characters.
This decodes all but one line of the data
I currently have:
that GUID is successfully decoded
later after another chunk is added.
So this is 100% successful.

sunburst.py

@@ -4,7 +4,7 @@
 # Unclassified/FOUO
 #
 # Created: 2020-12-14 16:49:51
-# Last-modified: 2020-12-22 17:57:54
+# Last-modified: 2020-12-22 21:42:40
 #
 # Based on work by @RedDrip7 (twitter),
 # who should be getting more credit in the English-speaking world.
@@ -26,10 +26,14 @@ knownDomains = [
     "avsvmcloud.com",
 ]
 
+
 def xor(key, buf):
     return bytes(b ^ k for b, k in zip(buf, itertools.cycle(key)))
 
-Bsae32Alphabet = "ph2eifo3n5utg1j8d94qrvbmk0sal76c"
+
+Esab32Alphabet = "ph2eifo3n5utg1j8d94qrvbmk0sal76c"
+SubstitutionAlphabet = 'rq3gsalt6u1iyfzop572d49bnx8cvmkewhj'
+SubstitutionAlphabet0 = '0_-.'
 
 
 def DecodeBase32(s: str):
@@ -39,63 +43,109 @@ def DecodeBase32(s: str):
     It doesn't work.
     """
 
-    t = s.translate(Bsae32Alphabet,
+    trans = str.maketrans(Esab32Alphabet,
                           "ABCDEFGHIJKLMNOPQRSTUVWXYZ2345678")
+    t = s.translate(trans)
     while len(t) % 8 > 0:
         t += '='
     return base64.b32decode(t)
 
 
-def DecodeBsae32(s: str):
-    """Decode using zany base32-like algorithm.
+def DecodeEsab32(s: str) -> (int, int):
+    """Decode using big-endian base32 algorithm.
 
-    The following opinion has been formed hastily and could be misinformed:
-
-    This is not proper Base32. It's more like somebody read about Base32,
-    implemented an encoder and decoder incorrectly, and went on to the next task.
+    Returns a bigint, and the number of bits contained therein
     """
 
-    bits = 0
-    acc = 0
+    acc = bits = 0
     for c in s:
-        acc |= Bsae32Alphabet.find(c) << bits
+        try:
+            p = Esab32Alphabet.index(c)
+        except ValueError:
+            raise RuntimeError(
+                "Not an Esab32 encoded character: %c in %s" % (c, s))
+        acc |= p << bits
         bits += 5
-
-    out8 = []
-    while bits > 0:
-        out8.append(acc & 255)
-        acc >>= 8
-        bits -= 8
-
-    if bits:
-        del out8[-1]
-    return bytes(out8)
+    return acc, bits
 
 
-SubstitutionAlphabet = 'rq3gsalt6u1iyfzop572d49bnx8cvmkewhj'
-SubstitutionXlat = str.maketrans(
-    SubstitutionAlphabet[4:] + SubstitutionAlphabet[:4], SubstitutionAlphabet)
-SubstitutionXlat0 = str.maketrans(
-    SubstitutionAlphabet, ('0_-.' * 9)[:len(SubstitutionAlphabet)])
-
-
-def DecodeSubst(s: str):
-    zeroBaby = False
+def DecodeSubst(s: str) -> str:
+    alphabet = SubstitutionAlphabet
     out = []
     for c in s:
         if c == '0':
-            zeroBaby = True
-            continue
-        if zeroBaby:
-            out.append(c.translate(SubstitutionXlat0))
+            alphabet = SubstitutionAlphabet0
         else:
-            out.append(c.translate(SubstitutionXlat))
-        zeroBaby = False
-    return ''.join(out)
+            try:
+                pos = (SubstitutionAlphabet.index(c) - 4) % len(alphabet)
+            except ValueError:
+                raise RuntimeError(
+                    "Not a subst encoded character: %c in %s" % (c, s))
+            out.append(alphabet[pos])
+            alphabet = SubstitutionAlphabet
+    return "".join(out)
 
-PayloadsByGuid = {}
 
-def DecodeDomain(domain: str):
+Guid = int
+
+
+def isprintable(c: int) -> bool:
+    return c >= 0x20 and c <= 0x7f
+
+
+def quopri(buf: bytes) -> str:
+    return codecs.encode(buf, "quopri").decode("utf-8")
+
+
+class DGADecoder:
+    def __init__(self, guid: Guid):
+        self.guid = guid
+        self.history = []
+        self._decoder = self.DecodeSubst
+
+    def decode(self, s: str):
+        if s.startswith("00"):
+            self._decoder = self.DecodeEsab32
+            # We'll throw away the information about which is first,
+            # since we do a computationally intensive trick later to determine ordering
+            s = s[2:]
+            self.history.insert(0, s)
+        else:
+            self.history.append(s)
+        return self._decoder()
+
+    def DecodeSubst(self) -> str:
+        decodes = {DecodeSubst(x) for x in self.history}
+        return ''.join(sorted(decodes, key=len, reverse=True))
+
+    def DecodeEsab32(self) -> str:
+        history = {x.rstrip("0") for x in self.history}
+
+        # "Why don't we just mix up absolutely everything and see what happens?"
+        # -- Ridcully, in Terry Pratchett's "The Hogfather"
+        possibilities = []
+        for attempt in itertools.permutations(history):
+            acc, abits = DecodeEsab32(''.join(attempt))
+            length = abits // 8
+            if abits % 8:
+                buf = acc.to_bytes(length+1, 'little')
+            else:
+                buf = acc.to_bytes(length, 'little')
+            buf = buf[:length]
+            if sum(isprintable(b) for b in buf) == length:
+                # Yay it's probably okay
+                possibilities.append(buf)
+        # Well, we tried.
+        if not possibilities:
+            return quopri(buf)
+        else:
+            return " | ".join(quopri(buf) for buf in possibilities)
+
+
+DecodersByGuid = {}
+
+
+def DecodeDomain(domain: str) -> (Guid, int, str):
     s = domain.strip()
     foundDomain = None
     for d in knownDomains:
@@ -110,35 +160,28 @@ def DecodeDomain(domain: str):
     assert(s[-1] == '.')
     s = s[:-1]
 
+    if foundDomain == "avsvmcloud.com":
+        return (None, None, "[Probably not a Sunburst domain]")
     if len(s) < 16:
-        return (None, None, "[unable to decode: too short for any known decoding rules]")
+        return (None, None, "[too short]")
+
+    dec, _ = DecodeEsab32(s[:15])
+    eguid = dec.to_bytes(10, 'little')[:9]
+    guid = int.from_bytes(xor(eguid[0:1], eguid[1:]), 'big')
 
-    eguid = DecodeBsae32(s[:15])
     unknown_a = s[15]
-    guid = xor(eguid[0:1], eguid[1:])
-    s = s[16:]
+    payload = s[16:]
 
-    payloads = PayloadsByGuid.setdefault(guid, [])
-    if s not in payloads:
-        if s.startswith("00"):
-            payloads.insert(0, s)
-        else:
-            payloads.append(s)
-            # People: friggin' preserve metadata, ugh. 
-            # If I gave you every line of The Empire Strikes Back, 
-            # sorted alphabetically, without timestamps,
-            # could you reconstruct the movie?
-            payloads.sort(key=len, reverse=True)
+    decoder = DecodersByGuid.get(guid)
+    if not decoder:
+        decoder = DGADecoder(guid)
+        DecodersByGuid[guid] = decoder
 
-    payload = ''.join(payloads)
+    decoded = decoder.decode(payload)
 
-    if payload.startswith("00"):
-        buf = DecodeBsae32(payload[2:])
-        decoded = codecs.encode(buf, "quopri").decode("utf-8")
-    else:
-        decoded = DecodeSubst(payload)
     return (guid, unknown_a, decoded)
 
+
 class TextReader:
     def __init__(self, infile):
         self.infile = infile
@@ -152,12 +195,14 @@ class TextReader:
 class CsvReader:
     def __init__(self, infile):
         self.reader = csv.DictReader(infile)
-        self.fieldnames = self.reader.fieldnames + ["guid", "unknown a", "decode"]
+        self.fieldnames = self.reader.fieldnames + \
+            ["guid", "unknown a", "decode"]
 
     def __iter__(self):
         for record in self.reader:
             yield record
 
+
 def main():
     parser = argparse.ArgumentParser(
         description="Decode sunburst Domain Generation Algorithm (DGA) names")
@@ -191,10 +236,11 @@ def main():
     for record in reader:
         name = record.get("name") or record.get("fqdn")
         guid, unknown_a, ptext = DecodeDomain(name)
-        record["guid"] = int.from_bytes(guid or b"", "big")
+        record["guid"] = guid
         record["unknown a"] = unknown_a
         record["decode"] = ptext
         writer.writerow(record)
 
+
 if __name__ == '__main__':
     main()