From a61db3060be3fb5f18992b1b0f527e219d85ab70 Mon Sep 17 00:00:00 2001 From: Erik Schierboom Date: Tue, 10 Dec 2024 17:19:48 +0100 Subject: [PATCH] Add `affine-cipher` exercise --- config.json | 8 ++ .../affine-cipher/.docs/instructions.md | 74 +++++++++++++++++++ .../practice/affine-cipher/.meta/config.json | 19 +++++ .../practice/affine-cipher/.meta/example.ua | 9 +++ .../practice/affine-cipher/.meta/tests.toml | 58 +++++++++++++++ .../practice/affine-cipher/affine-cipher.ua | 7 ++ exercises/practice/affine-cipher/tests.ua | 49 ++++++++++++ 7 files changed, 224 insertions(+) create mode 100644 exercises/practice/affine-cipher/.docs/instructions.md create mode 100644 exercises/practice/affine-cipher/.meta/config.json create mode 100644 exercises/practice/affine-cipher/.meta/example.ua create mode 100644 exercises/practice/affine-cipher/.meta/tests.toml create mode 100644 exercises/practice/affine-cipher/affine-cipher.ua create mode 100644 exercises/practice/affine-cipher/tests.ua diff --git a/config.json b/config.json index d762bfe..5733abb 100644 --- a/config.json +++ b/config.json @@ -522,6 +522,14 @@ "prerequisites": [], "difficulty": 6 }, + { + "slug": "affine-cipher", + "name": "Affine Cipher", + "uuid": "3ecb43fc-179d-4510-84a3-63859f72c9df", + "practices": [], + "prerequisites": [], + "difficulty": 6 + }, { "slug": "parallel-letter-frequency", "name": "Parallel Letter Frequency", diff --git a/exercises/practice/affine-cipher/.docs/instructions.md b/exercises/practice/affine-cipher/.docs/instructions.md new file mode 100644 index 0000000..f6329db --- /dev/null +++ b/exercises/practice/affine-cipher/.docs/instructions.md @@ -0,0 +1,74 @@ +# Instructions + +Create an implementation of the affine cipher, an ancient encryption system created in the Middle East. + +The affine cipher is a type of monoalphabetic substitution cipher. +Each character is mapped to its numeric equivalent, encrypted with a mathematical function and then converted to the letter relating to its new numeric value. +Although all monoalphabetic ciphers are weak, the affine cipher is much stronger than the Atbash cipher, because it has many more keys. + +[//]: # " monoalphabetic as spelled by Merriam-Webster, compare to polyalphabetic " + +## Encryption + +The encryption function is: + +```text +E(x) = (ai + b) mod m +``` + +Where: + +- `i` is the letter's index from `0` to the length of the alphabet - 1. +- `m` is the length of the alphabet. + For the Roman alphabet `m` is `26`. +- `a` and `b` are integers which make up the encryption key. + +Values `a` and `m` must be _coprime_ (or, _relatively prime_) for automatic decryption to succeed, i.e., they have number `1` as their only common factor (more information can be found in the [Wikipedia article about coprime integers][coprime-integers]). +In case `a` is not coprime to `m`, your program should indicate that this is an error. +Otherwise it should encrypt or decrypt with the provided key. + +For the purpose of this exercise, digits are valid input but they are not encrypted. +Spaces and punctuation characters are excluded. +Ciphertext is written out in groups of fixed length separated by space, the traditional group size being `5` letters. +This is to make it harder to guess encrypted text based on word boundaries. + +## Decryption + +The decryption function is: + +```text +D(y) = (a^-1)(y - b) mod m +``` + +Where: + +- `y` is the numeric value of an encrypted letter, i.e., `y = E(x)` +- it is important to note that `a^-1` is the modular multiplicative inverse (MMI) of `a mod m` +- the modular multiplicative inverse only exists if `a` and `m` are coprime. + +The MMI of `a` is `x` such that the remainder after dividing `ax` by `m` is `1`: + +```text +ax mod m = 1 +``` + +More information regarding how to find a Modular Multiplicative Inverse and what it means can be found in the [related Wikipedia article][mmi]. + +## General Examples + +- Encrypting `"test"` gives `"ybty"` with the key `a = 5`, `b = 7` +- Decrypting `"ybty"` gives `"test"` with the key `a = 5`, `b = 7` +- Decrypting `"ybty"` gives `"lqul"` with the wrong key `a = 11`, `b = 7` +- Decrypting `"kqlfd jzvgy tpaet icdhm rtwly kqlon ubstx"` gives `"thequickbrownfoxjumpsoverthelazydog"` with the key `a = 19`, `b = 13` +- Encrypting `"test"` with the key `a = 18`, `b = 13` is an error because `18` and `26` are not coprime + +## Example of finding a Modular Multiplicative Inverse (MMI) + +Finding MMI for `a = 15`: + +- `(15 * x) mod 26 = 1` +- `(15 * 7) mod 26 = 1`, ie. `105 mod 26 = 1` +- `7` is the MMI of `15 mod 26` + +[mmi]: https://en.wikipedia.org/wiki/Modular_multiplicative_inverse +[coprime-integers]: https://en.wikipedia.org/wiki/Coprime_integers diff --git a/exercises/practice/affine-cipher/.meta/config.json b/exercises/practice/affine-cipher/.meta/config.json new file mode 100644 index 0000000..f7fa886 --- /dev/null +++ b/exercises/practice/affine-cipher/.meta/config.json @@ -0,0 +1,19 @@ +{ + "authors": [ + "erikschierboom" + ], + "files": { + "solution": [ + "affine-cipher.ua" + ], + "test": [ + "tests.ua" + ], + "example": [ + ".meta/example.ua" + ] + }, + "blurb": "Create an implementation of the Affine cipher, an ancient encryption algorithm from the Middle East.", + "source": "Wikipedia", + "source_url": "https://en.wikipedia.org/wiki/Affine_cipher" +} diff --git a/exercises/practice/affine-cipher/.meta/example.ua b/exercises/practice/affine-cipher/.meta/example.ua new file mode 100644 index 0000000..d2a62b7 --- /dev/null +++ b/exercises/practice/affine-cipher/.meta/example.ua @@ -0,0 +1,9 @@ +Coprime ← ¬/↥≡⌕ ∩(°/×) +MMI ← ⊗1◿:×⇡, +Validate ← ⍤"a and m must be coprime" (Coprime :26) +Groups ← ⊜(□∘)\+=0◿5°⊏ +Sanitize ← ▽+⊃(⌵±|×⊃(≥@0|≤@9)).¯⌵ +Encrypt ← ⍜(-@a▽)(◿26+×)⌵±. +Encode ← /$"_ _" Groups Encrypt Sanitize ⊃(⊙Validate|⋅∘) +Decrypt ← ◿26×⊃(⋅(MMI:26)|-:⊙⋅∘) +Decode ← ⍜(-@a▽|Decrypt)⌵±. ▽≠@\s. ⊃(⊙Validate|⋅∘) diff --git a/exercises/practice/affine-cipher/.meta/tests.toml b/exercises/practice/affine-cipher/.meta/tests.toml new file mode 100644 index 0000000..07cce7c --- /dev/null +++ b/exercises/practice/affine-cipher/.meta/tests.toml @@ -0,0 +1,58 @@ +# 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. + +[2ee1d9af-1c43-416c-b41b-cefd7d4d2b2a] +description = "encode -> encode yes" + +[785bade9-e98b-4d4f-a5b0-087ba3d7de4b] +description = "encode -> encode no" + +[2854851c-48fb-40d8-9bf6-8f192ed25054] +description = "encode -> encode OMG" + +[bc0c1244-b544-49dd-9777-13a770be1bad] +description = "encode -> encode O M G" + +[381a1a20-b74a-46ce-9277-3778625c9e27] +description = "encode -> encode mindblowingly" + +[6686f4e2-753b-47d4-9715-876fdc59029d] +description = "encode -> encode numbers" + +[ae23d5bd-30a8-44b6-afbe-23c8c0c7faa3] +description = "encode -> encode deep thought" + +[c93a8a4d-426c-42ef-9610-76ded6f7ef57] +description = "encode -> encode all the letters" + +[0673638a-4375-40bd-871c-fb6a2c28effb] +description = "encode -> encode with a not coprime to m" + +[3f0ac7e2-ec0e-4a79-949e-95e414953438] +description = "decode -> decode exercism" + +[241ee64d-5a47-4092-a5d7-7939d259e077] +description = "decode -> decode a sentence" + +[33fb16a1-765a-496f-907f-12e644837f5e] +description = "decode -> decode numbers" + +[20bc9dce-c5ec-4db6-a3f1-845c776bcbf7] +description = "decode -> decode all the letters" + +[623e78c0-922d-49c5-8702-227a3e8eaf81] +description = "decode -> decode with no spaces in input" + +[58fd5c2a-1fd9-4563-a80a-71cff200f26f] +description = "decode -> decode with too many spaces" + +[b004626f-c186-4af9-a3f4-58f74cdb86d5] +description = "decode -> decode with a not coprime to m" diff --git a/exercises/practice/affine-cipher/affine-cipher.ua b/exercises/practice/affine-cipher/affine-cipher.ua new file mode 100644 index 0000000..85ead0c --- /dev/null +++ b/exercises/practice/affine-cipher/affine-cipher.ua @@ -0,0 +1,7 @@ +# Encode plaintext using the Affine Cipher +# Ciphertext ? Key Plaintext +Encode ← |3 ⊙⋅⋅(⍤ "Please implement Encode" 0) + +# Decode plaintext using the Affine Cipher +# Plaintext ? Key Ciphertext +Decode ← |3 ⊙⋅⋅(⍤ "Please implement Decode" 0) diff --git a/exercises/practice/affine-cipher/tests.ua b/exercises/practice/affine-cipher/tests.ua new file mode 100644 index 0000000..0de38ac --- /dev/null +++ b/exercises/practice/affine-cipher/tests.ua @@ -0,0 +1,49 @@ +~ "affine-cipher.ua" ~ Decode Encode + +# encode yes +⍤⤙≍ "xbt" Encode "yes" 5 7 + +# encode no +⍤⤙≍ "fu" Encode "no" 15 18 + +# encode OMG +⍤⤙≍ "lvz" Encode "OMG" 21 3 + +# encode O M G +⍤⤙≍ "hjp" Encode "O M G" 25 47 + +# encode mindblowingly +⍤⤙≍ "rzcwa gnxzc dgt" Encode "mindblowingly" 11 15 + +# encode numbers +⍤⤙≍ "jqgjc rw123 jqgjc rw" Encode "Testing,1 2 3, testing." 3 4 + +# encode deep thought +⍤⤙≍ "iynia fdqfb ifje" Encode "Truth is fiction." 5 17 + +# encode all the letters +⍤⤙≍ "swxtj npvyk lruol iejdc blaxk swxmh qzglf" Encode "The quick brown fox jumps over the lazy dog." 17 33 + +# encode with a not coprime to m +⍤⤙≍ "a and m must be coprime" ⍣(Encode "This is a test." 6 17) + +# decode exercism +⍤⤙≍ "exercism" Decode "tytgn fjr" 3 7 + +# decode a sentence +⍤⤙≍ "anobstacleisoftenasteppingstone" Decode "qdwju nqcro muwhn odqun oppmd aunwd o" 19 16 + +# decode numbers +⍤⤙≍ "testing123testing" Decode "odpoz ub123 odpoz ub" 25 7 + +# decode all the letters +⍤⤙≍ "thequickbrownfoxjumpsoverthelazydog" Decode "swxtj npvyk lruol iejdc blaxk swxmh qzglf" 17 33 + +# decode with no spaces in input +⍤⤙≍ "thequickbrownfoxjumpsoverthelazydog" Decode "swxtjnpvyklruoliejdcblaxkswxmhqzglf" 17 33 + +# decode with too many spaces +⍤⤙≍ "jollygreengiant" Decode "vszzm cly yd cg qdp" 15 16 + +# decode with a not coprime to m +⍤⤙≍ "a and m must be coprime" ⍣(Decode "Test" 13 5)