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Commitc4035de

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added Substitution Cipher and its test
1 parent5f1ed3e commitc4035de

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2 files changed

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2 files changed

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‎Ciphers/SubstitutionCipher.js

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/**
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* Substitution Cipher
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*
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* A monoalphabetic substitution cipher replaces each letter of the plaintext
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* with another letter based on a fixed permutation (key) of the alphabet.
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* https://en.wikipedia.org/wiki/Substitution_cipher
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*/
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constalphabet='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
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constdefaultKey='QWERTYUIOPASDFGHJKLZXCVBNM'
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/**
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* Encrypts a string using a monoalphabetic substitution cipher
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*@param {string} text - The text to encrypt
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*@param {string} key - The substitution key (must be 26 uppercase letters)
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*@returns {string}
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*/
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exportfunctionsubstitutionCipherEncryption(text,key=defaultKey){
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if(key.length!==26||!/^[A-Z]+$/.test(key)){
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thrownewRangeError('Key must be 26 uppercase English letters.')
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}
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letresult=''
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consttextUpper=text.toUpperCase()
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for(leti=0;i<textUpper.length;i++){
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constchar=textUpper[i]
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constindex=alphabet.indexOf(char)
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if(index!==-1){
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result+=key[index]
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}else{
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result+=char
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}
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}
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returnresult
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}
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/**
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* Decrypts a string encrypted with the substitution cipher
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*@param {string} text - The encrypted text
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*@param {string} key - The substitution key used during encryption
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*@returns {string}
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*/
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exportfunctionsubstitutionCipherDecryption(text,key=defaultKey){
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if(key.length!==26||!/^[A-Z]+$/.test(key)){
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thrownewRangeError('Key must be 26 uppercase English letters.')
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}
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letresult=''
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consttextUpper=text.toUpperCase()
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for(leti=0;i<textUpper.length;i++){
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constchar=textUpper[i]
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constindex=key.indexOf(char)
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if(index!==-1){
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result+=alphabet[index]
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}else{
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result+=char
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}
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}
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returnresult
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}
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import{describe,it,expect}from'vitest'
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import{
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substitutionCipherEncryption,
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substitutionCipherDecryption
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}from'../SubstitutionCipher.js'
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describe('Substitution Cipher',()=>{
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constkey='QWERTYUIOPASDFGHJKLZXCVBNM'
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it('correctly encrypts a message',()=>{
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constencrypted=substitutionCipherEncryption('HELLO WORLD',key)
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expect(encrypted).toBe('ITSSG VGKSR')
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})
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it('correctly decrypts a message',()=>{
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constdecrypted=substitutionCipherDecryption('ITSSG VGKSR',key)
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expect(decrypted).toBe('HELLO WORLD')
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})
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it('handles non-alphabetic characters',()=>{
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constencrypted=substitutionCipherEncryption('Test! 123',key)
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expect(encrypted).toBe('ZTLZ! 123')
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})
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it('throws error for invalid key',()=>{
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expect(()=>substitutionCipherEncryption('HELLO','BADKEY')).toThrow(
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RangeError
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)
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})
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})

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