From 4c19fe2d71dbd1b0e150bde1898368b77d3d9fa9 Mon Sep 17 00:00:00 2001
From: BNAndras <20251272+BNAndras@users.noreply.github.com>
Date: Sun, 15 Mar 2026 22:15:36 -0700
Subject: [PATCH 1/2] add `rotational-cipher`

---
 config.json                                   |  8 +++
 exercises/practice/rotational-cipher/.busted  |  5 ++
 .../rotational-cipher/.docs/instructions.md   | 29 +++++++++++
 .../rotational-cipher/.meta/config.json       | 19 +++++++
 .../rotational-cipher/.meta/example.moon      | 11 ++++
 .../.meta/spec_generator.moon                 | 11 ++++
 .../rotational-cipher/.meta/tests.toml        | 40 ++++++++++++++
 .../rotational-cipher/rotational_cipher.moon  |  4 ++
 .../rotational_cipher_spec.moon               | 52 +++++++++++++++++++
 9 files changed, 179 insertions(+)
 create mode 100644 exercises/practice/rotational-cipher/.busted
 create mode 100644 exercises/practice/rotational-cipher/.docs/instructions.md
 create mode 100644 exercises/practice/rotational-cipher/.meta/config.json
 create mode 100644 exercises/practice/rotational-cipher/.meta/example.moon
 create mode 100644 exercises/practice/rotational-cipher/.meta/spec_generator.moon
 create mode 100644 exercises/practice/rotational-cipher/.meta/tests.toml
 create mode 100644 exercises/practice/rotational-cipher/rotational_cipher.moon
 create mode 100644 exercises/practice/rotational-cipher/rotational_cipher_spec.moon

diff --git a/config.json b/config.json
index 6050599..b9b385f 100644
--- a/config.json
+++ b/config.json
@@ -170,6 +170,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "rotational-cipher",
+        "name": "Rotational Cipher",
+        "uuid": "365fb81f-c059-4231-954b-bac1878e2a0c",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "rna-transcription",
         "name": "RNA Transcription",
diff --git a/exercises/practice/rotational-cipher/.busted b/exercises/practice/rotational-cipher/.busted
new file mode 100644
index 0000000..86b84e7
--- /dev/null
+++ b/exercises/practice/rotational-cipher/.busted
@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}
diff --git a/exercises/practice/rotational-cipher/.docs/instructions.md b/exercises/practice/rotational-cipher/.docs/instructions.md
new file mode 100644
index 0000000..4bf64ca
--- /dev/null
+++ b/exercises/practice/rotational-cipher/.docs/instructions.md
@@ -0,0 +1,29 @@
+# Instructions
+
+Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
+
+The Caesar cipher is a simple shift cipher that relies on transposing all the letters in the alphabet using an integer key between `0` and `26`.
+Using a key of `0` or `26` will always yield the same output due to modular arithmetic.
+The letter is shifted for as many values as the value of the key.
+
+The general notation for rotational ciphers is `ROT + <key>`.
+The most commonly used rotational cipher is `ROT13`.
+
+A `ROT13` on the Latin alphabet would be as follows:
+
+```text
+Plain:  abcdefghijklmnopqrstuvwxyz
+Cipher: nopqrstuvwxyzabcdefghijklm
+```
+
+It is stronger than the Atbash cipher because it has 27 possible keys, and 25 usable keys.
+
+Ciphertext is written out in the same formatting as the input including spaces and punctuation.
+
+## Examples
+
+- ROT5 `omg` gives `trl`
+- ROT0 `c` gives `c`
+- ROT26 `Cool` gives `Cool`
+- ROT13 `The quick brown fox jumps over the lazy dog.` gives `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.`
+- ROT13 `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.` gives `The quick brown fox jumps over the lazy dog.`
diff --git a/exercises/practice/rotational-cipher/.meta/config.json b/exercises/practice/rotational-cipher/.meta/config.json
new file mode 100644
index 0000000..d920778
--- /dev/null
+++ b/exercises/practice/rotational-cipher/.meta/config.json
@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "rotational_cipher.moon"
+    ],
+    "test": [
+      "rotational_cipher_spec.moon"
+    ],
+    "example": [
+      ".meta/example.moon"
+    ]
+  },
+  "blurb": "Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Caesar_cipher"
+}
diff --git a/exercises/practice/rotational-cipher/.meta/example.moon b/exercises/practice/rotational-cipher/.meta/example.moon
new file mode 100644
index 0000000..4889100
--- /dev/null
+++ b/exercises/practice/rotational-cipher/.meta/example.moon
@@ -0,0 +1,11 @@
+{
+  rotate: (text, shift_key) ->
+    text\gsub '.', (char) ->
+      byte = string.byte char
+      if byte >= 97 and byte <= 122
+        string.char (byte - 97 + shift_key) % 26 + 97
+      elseif byte >= 65 and byte <= 90
+        string.char (byte - 65 + shift_key) % 26 + 65
+      else
+        char
+}
diff --git a/exercises/practice/rotational-cipher/.meta/spec_generator.moon b/exercises/practice/rotational-cipher/.meta/spec_generator.moon
new file mode 100644
index 0000000..5c53ae0
--- /dev/null
+++ b/exercises/practice/rotational-cipher/.meta/spec_generator.moon
@@ -0,0 +1,11 @@
+{
+  module_name: 'RotationalCipher',
+
+  generate_test: (case, level) ->
+    lines = {
+      "result = RotationalCipher.rotate #{quote case.input.text}, #{case.input.shiftKey}",
+      "expected = #{quote case.expected}",
+      "assert.are.equal expected, result"
+    }
+    table.concat [indent line, level for line in *lines], '\n'
+}
diff --git a/exercises/practice/rotational-cipher/.meta/tests.toml b/exercises/practice/rotational-cipher/.meta/tests.toml
new file mode 100644
index 0000000..53441ed
--- /dev/null
+++ b/exercises/practice/rotational-cipher/.meta/tests.toml
@@ -0,0 +1,40 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[74e58a38-e484-43f1-9466-877a7515e10f]
+description = "rotate a by 0, same output as input"
+
+[7ee352c6-e6b0-4930-b903-d09943ecb8f5]
+description = "rotate a by 1"
+
+[edf0a733-4231-4594-a5ee-46a4009ad764]
+description = "rotate a by 26, same output as input"
+
+[e3e82cb9-2a5b-403f-9931-e43213879300]
+description = "rotate m by 13"
+
+[19f9eb78-e2ad-4da4-8fe3-9291d47c1709]
+description = "rotate n by 13 with wrap around alphabet"
+
+[a116aef4-225b-4da9-884f-e8023ca6408a]
+description = "rotate capital letters"
+
+[71b541bb-819c-4dc6-a9c3-132ef9bb737b]
+description = "rotate spaces"
+
+[ef32601d-e9ef-4b29-b2b5-8971392282e6]
+description = "rotate numbers"
+
+[32dd74f6-db2b-41a6-b02c-82eb4f93e549]
+description = "rotate punctuation"
+
+[9fb93fe6-42b0-46e6-9ec1-0bf0a062d8c9]
+description = "rotate all letters"
diff --git a/exercises/practice/rotational-cipher/rotational_cipher.moon b/exercises/practice/rotational-cipher/rotational_cipher.moon
new file mode 100644
index 0000000..8fc1d85
--- /dev/null
+++ b/exercises/practice/rotational-cipher/rotational_cipher.moon
@@ -0,0 +1,4 @@
+{
+  rotate: (text, shift_key) ->
+    error 'Implement me'
+}
diff --git a/exercises/practice/rotational-cipher/rotational_cipher_spec.moon b/exercises/practice/rotational-cipher/rotational_cipher_spec.moon
new file mode 100644
index 0000000..f673f9d
--- /dev/null
+++ b/exercises/practice/rotational-cipher/rotational_cipher_spec.moon
@@ -0,0 +1,52 @@
+RotationalCipher = require 'rotational_cipher'
+
+describe 'rotational-cipher', ->
+  it 'rotate a by 0, same output as input', ->
+    result = RotationalCipher.rotate 'a', 0
+    expected = 'a'
+    assert.are.equal expected, result
+
+  pending 'rotate a by 1', ->
+    result = RotationalCipher.rotate 'a', 1
+    expected = 'b'
+    assert.are.equal expected, result
+
+  pending 'rotate a by 26, same output as input', ->
+    result = RotationalCipher.rotate 'a', 26
+    expected = 'a'
+    assert.are.equal expected, result
+
+  pending 'rotate m by 13', ->
+    result = RotationalCipher.rotate 'm', 13
+    expected = 'z'
+    assert.are.equal expected, result
+
+  pending 'rotate n by 13 with wrap around alphabet', ->
+    result = RotationalCipher.rotate 'n', 13
+    expected = 'a'
+    assert.are.equal expected, result
+
+  pending 'rotate capital letters', ->
+    result = RotationalCipher.rotate 'OMG', 5
+    expected = 'TRL'
+    assert.are.equal expected, result
+
+  pending 'rotate spaces', ->
+    result = RotationalCipher.rotate 'O M G', 5
+    expected = 'T R L'
+    assert.are.equal expected, result
+
+  pending 'rotate numbers', ->
+    result = RotationalCipher.rotate 'Testing 1 2 3 testing', 4
+    expected = 'Xiwxmrk 1 2 3 xiwxmrk'
+    assert.are.equal expected, result
+
+  pending 'rotate punctuation', ->
+    result = RotationalCipher.rotate "Let's eat, Grandma!", 21
+    expected = "Gzo'n zvo, Bmviyhv!"
+    assert.are.equal expected, result
+
+  pending 'rotate all letters', ->
+    result = RotationalCipher.rotate 'The quick brown fox jumps over the lazy dog.', 13
+    expected = 'Gur dhvpx oebja sbk whzcf bire gur ynml qbt.'
+    assert.are.equal expected, result

From e4b685baee1a56acf3f7934390040824d9238afd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A1s=20B=20Nagy?=
 <20251272+BNAndras@users.noreply.github.com>
Date: Tue, 17 Mar 2026 17:26:54 -0700
Subject: [PATCH 2/2] Bump difficulty

Co-authored-by: Glenn Jackman <glenn.jackman@gmail.com>
---
 config.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/config.json b/config.json
index b9b385f..8a8f418 100644
--- a/config.json
+++ b/config.json
@@ -176,7 +176,7 @@
         "uuid": "365fb81f-c059-4231-954b-bac1878e2a0c",
         "practices": [],
         "prerequisites": [],
-        "difficulty": 2
+        "difficulty": 3
       },
       {
         "slug": "rna-transcription",