Affine

export const encode = (phrase, key) => { let lower = phrase.toLowerCase().replaceAll(' ', ''); let alphabet = ['a','b','c','d','e','f','g','h','i','j','k','l','m', 'n','o','p','q','r','s','t','u','v','w','x','y','z']; let m = 26; let res = ""; let w = 0; if(!gdc(key['a'],m)) throw new Error("a and m must be coprime."); lower.split('').forEach((elm) =>{ if(/^[a-zA-Z]$/.test(elm)){ const index = alphabet.indexOf(elm); const num1 = key['a']; const num2 = key['b']; let ex = (num1*index + num2) % m; ex = (ex +m) % m; res += alphabet[ex]; } else if(!isNaN(Number(elm))){ res += elm; } else{return;} w++; if(w==5){ res += " "; w = 0; } }); return res.trim(); }; function gdc(a,b){ while(b!=0){ let temp = b; b = a % b; a = temp; } return a === 1; } function mmi(a) { let m=26; let res = 0; for(let i=0; i<m; i++){ if((a * i) % m === 1){ res = i; } } return res; } export const decode = (phrase, key) => { let m = 26; let alphabet = ['a','b','c','d','e','f','g','h','i','j','k','l','m', 'n','o','p','q','r','s','t','u','v','w','x','y','z']; let res = phrase.replaceAll(' ', ''); let resTot = ""; if(!gdc(key['a'],m)) throw new Error("a and m must be coprime."); res.split('').forEach((elm) =>{ if(/^[a-zA-Z]$/.test(elm)){ const index = alphabet.indexOf(elm); const num1 = key['a']; const num2 = key['b']; let mmiV = mmi(num1); let dx = (mmiV * (index - num2)) % m; dx = (dx +m) % m; resTot += alphabet[dx]; } else if(!isNaN(Number(elm))){ resTot += elm; } }); return resTot; }