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Add Affine Cipher #1067
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Add Affine Cipher #1067
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,95 @@ | ||
| /** | ||
| * @description - The affine cipher is a type of monoalphabetic substitution cipher, where each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter | ||
| * @see - [wiki](https://en.wikipedia.org/wiki/Affine_cipher) | ||
| */ | ||
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| // Default key for Affine Cipher | ||
| const key = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' | ||
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| /** | ||
| * Fix result for negative value in modulas equation | ||
| * @param {Number} n - Constant number | ||
| * @param {Number} m - Modulos value | ||
| * @return {Number} Return n mod m | ||
| */ | ||
| function mod (n, m) { | ||
| return ((n % m) + m) % m | ||
| } | ||
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| /** | ||
| * Modular multiplicative inverse | ||
| * @param {Number} a - A coefficient | ||
| * @param {Number} m - Modulos value | ||
| * @return {Number} Return modular multiplicative inverse of coefficient a and modulos m | ||
| */ | ||
| function inverseMod (a, m) { | ||
| for (let x = 1; x < m; x++) { | ||
| if (mod(a * x, m) === 1) return x | ||
| } | ||
| } | ||
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| /** | ||
| * Argument validation | ||
| * @param {String} str - String to be checked | ||
| * @param {Number} a - A coefficient to be checked | ||
| * @param {Number} b - B coefficient to be checked | ||
| * @return {Boolean} Result of the checking | ||
| */ | ||
| function isCorrectFormat (str, a, b) { | ||
| if (typeof a !== 'number' || typeof b !== 'number') { | ||
| throw new TypeError('Coefficient a, b should be number') | ||
| } | ||
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| if (typeof str !== 'string') { | ||
| throw new TypeError('Argument str should be String') | ||
| } | ||
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| return true | ||
| } | ||
| /** | ||
| * Find character index based on ASCII order | ||
| * @param {String} char - Character index to be found | ||
| * @return {Boolean} Character index | ||
| */ | ||
| function findCharIndex (char) { | ||
| return char.toUpperCase().charCodeAt(0) - ('A').charCodeAt(0) | ||
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| } | ||
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| /** | ||
| * Encrypt a Affine Cipher | ||
| * @param {String} str - String to be encrypted | ||
| * @param {Number} a - A coefficient | ||
| * @param {Number} b - B coefficient | ||
| * @return {String} result - Encrypted string | ||
| */ | ||
| function encrypt (str, a, b) { | ||
| let result = '' | ||
| if (isCorrectFormat(str, a, b)) { | ||
| for (let x = 0; x < str.length; x++) { | ||
| const charIndex = findCharIndex(str[x]) | ||
| if (charIndex < 0) result += '-1' + ' ' | ||
| else result += mod(a * charIndex + b, 26) + ' ' | ||
| } | ||
| } | ||
| return result.trim() | ||
| } | ||
| /** | ||
| * Decrypt a Affine Cipher | ||
| * @param {String} str - String to be decrypted | ||
| * @param {Number} a - A coefficient | ||
| * @param {Number} b - B coefficient | ||
| * @return {String} result - Decrypted string | ||
| */ | ||
| function decrypt (str, a, b) { | ||
| let result = '' | ||
| if (isCorrectFormat(str, a, b)) { | ||
| str = str.split(' ') | ||
| for (let x = 0; x < str.length; x++) { | ||
| if (str[x] === '-1') result += ' ' | ||
| else result += key[mod(inverseMod(a, 26) * (parseInt(str[x]) - b), 26)] | ||
| } | ||
| } | ||
| return result | ||
| } | ||
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| export { encrypt, decrypt } | ||
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,27 @@ | ||
| import { encrypt, decrypt } from '../AffineCipher' | ||
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| describe('Test Affine Cipher', () => { | ||
| it('Test - 1, Pass invalid input to encrypt function', () => { | ||
| expect(() => encrypt(null, null, null)).toThrow() | ||
| expect(() => encrypt('null', null, null)).toThrow() | ||
| expect(() => encrypt('null', 1, null)).toThrow() | ||
| expect(() => encrypt('null', null, 1)).toThrow() | ||
| }) | ||
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| it('Test - 2, Pass invalid input to decrypt function', () => { | ||
| expect(() => decrypt(null, null, null)).toThrow() | ||
| expect(() => decrypt('null', null, null)).toThrow() | ||
| expect(() => decrypt('null', 1, null)).toThrow() | ||
| expect(() => decrypt('null', null, 1)).toThrow() | ||
| }) | ||
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| it('Test - 3 Pass string value to encrypt and ecrypt function', () => { | ||
| const a = 5 | ||
| const b = 8 | ||
| expect(decrypt(encrypt('HELLO WORLD', a, b), a, b)).toBe('HELLO WORLD') | ||
| expect(decrypt(encrypt('ABC DEF', a, b), a, b)).toBe('ABC DEF') | ||
| expect(decrypt(encrypt('Brown fox jump over the fence', a, b), a, b)).toBe( | ||
| 'BROWN FOX JUMP OVER THE FENCE' | ||
| ) | ||
| }) | ||
| }) |
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