diff --git a/ciphers/rot13.py b/ciphers/rot13.py
new file mode 100644
index 000000000..208de4890
--- /dev/null
+++ b/ciphers/rot13.py
@@ -0,0 +1,24 @@
+def dencrypt(s, n):
+    out = ''
+    for c in s:
+        if c >= 'A' and c <= 'Z':
+            out += chr(ord('A') + (ord(c) - ord('A') + n) % 26)
+        elif c >= 'a' and c <= 'z':
+            out += chr(ord('a') + (ord(c) - ord('a') + n) % 26)
+        else:
+            out += c
+    return out
+
+
+def main():
+    s0 = 'HELLO'
+
+    s1 = dencrypt(s0, 13)
+    print(s1)  # URYYB
+
+    s2 = dencrypt(s1, 13)
+    print(s2)  # HELLO
+
+
+if __name__ == '__main__':
+    main()