diff --git a/src/codext/crypto/__init__.py b/src/codext/crypto/__init__.py
index 21da6d9..43aa888 100644
--- a/src/codext/crypto/__init__.py
+++ b/src/codext/crypto/__init__.py
@@ -9,6 +9,7 @@
 from .rot import *
 from .scytale import *
 from .shift import *
+from .trithemius import *
 from .vigenere import *
 from .xor import *
 
diff --git a/src/codext/crypto/trithemius.py b/src/codext/crypto/trithemius.py
new file mode 100644
index 0000000..c72e744
--- /dev/null
+++ b/src/codext/crypto/trithemius.py
@@ -0,0 +1,45 @@
+# -*- coding: UTF-8 -*-
+"""Trithemius Cipher Codec - trithemius content encoding.
+
+This codec:
+- en/decodes strings from str to str
+- en/decodes strings from bytes to bytes
+- decodes file content to str (read)
+- encodes file content from str to bytes (write)
+"""
+from string import ascii_lowercase as LC, ascii_uppercase as UC
+
+from ..__common__ import *
+
+
+__examples__ = {
+    'enc(trithemius|trithemius-cipher)': {'this is a test': "tikv mx g ambd"},
+    'enc(trithemius)':                   {'': "", 'HELLO': "HFNOS", '12345!@#$': "12345!@#$"},
+    'enc-dec(trithemius)':               ["Hello, World!", "@random"],
+}
+__guess__ = ["trithemius"]
+
+
+def _trithemius(text, decode=False):
+    r, pos = "", 0
+    for c in ensure_str(text):
+        if c in LC or c in UC:
+            r += (a := LC if c in LC else UC)[(a.index(c) + [1, -1][decode] * pos) % 26]
+            pos += 1
+        else:
+            r += c
+    return r
+
+
+def trithemius_encode(text, errors="strict"):
+    r = _trithemius(ensure_str(text))
+    return r, len(r)
+
+
+def trithemius_decode(text, errors="strict"):
+    r = _trithemius(ensure_str(text), True)
+    return r, len(r)
+
+
+add("trithemius", trithemius_encode, trithemius_decode, r"trithemius(?:[-_]cipher)?$", printables_rate=lambda pr: pr,
+    entropy=lambda e: e)