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Fix Affine-Cipher encrypt and drypt func #1077

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Merged
merged 3 commits into from
Aug 3, 2022
Merged

Fix Affine-Cipher encrypt and drypt func #1077

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59caca1
fix decryt and encryt func
shidian00 Aug 2, 2022
b4065bb
Update AffineCipher.js
shidian00 Aug 2, 2022
904ef7c
Update AffineCipher.js
shidian00 Aug 3, 2022
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20 changes: 15 additions & 5 deletions Ciphers/AffineCipher.js
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Original file line number Diff line number Diff line change
@@ -1,8 +1,9 @@
/**
* @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
* @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)
*/

import { CoPrimeCheck } from '../Maths/CoPrimeCheck'
// Default key for Affine Cipher
const key = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

Expand Down Expand Up @@ -44,8 +45,13 @@ function isCorrectFormat (str, a, b) {
throw new TypeError('Argument str should be String')
}

if (!CoPrimeCheck(a, 26)) {
throw new Error(a + ' is not coprime of 26')
}

return true
}

/**
* Find character index based on ASCII order
* @param {String} char - Character index to be found
Expand All @@ -62,17 +68,19 @@ function findCharIndex (char) {
* @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) + ' '
else result += key.charAt(mod(a * charIndex + b, 26)) + ' '
}
}
return result.trim()
}

/**
* Decrypt a Affine Cipher
* @param {String} str - String to be decrypted
Expand All @@ -86,10 +94,12 @@ function decrypt (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)]
else {
const charIndex = findCharIndex(str[x])
result += key[mod(inverseMod(a, 26) * (charIndex - b), 26)]
}
}
return result
}
return result
}

export { encrypt, decrypt }
12 changes: 7 additions & 5 deletions Ciphers/test/AffineCipher.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,21 +6,23 @@ describe('Test Affine Cipher', () => {
expect(() => encrypt('null', null, null)).toThrow()
expect(() => encrypt('null', 1, null)).toThrow()
expect(() => encrypt('null', null, 1)).toThrow()
expect(() => encrypt('null', 2, 1)).toThrow()
expect(() => encrypt('null', 4, 1)).toThrow()
})

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()
expect(() => encrypt('null', 2, 1)).toThrow()
expect(() => encrypt('null', 4, 1)).toThrow()
})

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(
expect(decrypt(encrypt('HELLO WORLD', 5, 8), 5, 8)).toBe('HELLO WORLD')
expect(decrypt(encrypt('ABC DEF', 3, 5), 3, 5)).toBe('ABC DEF')
expect(decrypt(encrypt('Brown fox jump over the fence', 7, 3), 7, 3)).toBe(
'BROWN FOX JUMP OVER THE FENCE'
)
})
Expand Down