diff --git a/simple_substitution_cipher.py b/simple_substitution_cipher.py
new file mode 100644
index 0000000..5a9d34e
--- /dev/null
+++ b/simple_substitution_cipher.py
@@ -0,0 +1,42 @@
+def input_key(key_dict):
+    # expecting string representation of dictionary
+    # ie {'a':'b', 'b':'c', . . .}
+    import ast
+
+    # for now, we expect everything fit in, lol
+    return ast.literal_eval(key_dict)
+
+
+def encrypt(plaintext, key):
+    # expecting plaintext of string
+    # expecting key from input_key
+    ciphertext = ""
+
+    for p in plaintext:
+        if p in key:
+            ciphertext += key[p]
+        else:
+            if p == ' ':
+                ciphertext += c
+            else:
+                ciphertext += '-'
+
+    # again, we expect no error
+    return ciphertext
+
+
+def decrypt(ciphertext, key):
+    # duplicated from encrypt :v
+    # please be aware that the key used in decrypt is way in encrypt
+    plaintext = ""
+
+    for c in ciphertext:
+        if c in key:
+            plaintext += key[c]
+        else:
+            if c == ' ':
+                plaintext += c
+            else:
+                plaintext += '-'
+
+    return plaintext