vigenere_cipher.js

var tabulaRecta = {
    a: "abcdefghijklmnopqrstuvwxyz",
    b: "bcdefghijklmnopqrstuvwxyza",
    c: "cdefghijklmnopqrstuvwxyzab",
    d: "defghijklmnopqrstuvwxyzabc",
    e: "efghijklmnopqrstuvwxyzabcd",
    f: "fghijklmnopqrstuvwxyzabcde",
    g: "ghijklmnopqrstuvwxyzabcdef",
    h: "hijklmnopqrstuvwxyzabcdefg",
    i: "ijklmnopqrstuvwxyzabcdefgh",
    j: "jklmnopqrstuvwxyzabcdefghi",
    k: "klmnopqrstuvwxyzabcdefghij",
    l: "lmnopqrstuvwxyzabcdefghijk",
    m: "mnopqrstuvwxyzabcdefghijkl",
    n: "nopqrstuvwxyzabcdefghijklm",
    o: "opqrstuvwxyzabcdefghijklmn",
    p: "pqrstuvwxyzabcdefghijklmno",
    q: "qrstuvwxyzabcdefghijklmnop",
    r: "rstuvwxyzabcdefghijklmnopq",
    s: "stuvwxyzabcdefghijklmnopqr",
    t: "tuvwxyzabcdefghijklmnopqrs",
    u: "uvwxyzabcdefghijklmnopqrst",
    v: "vwxyzabcdefghijklmnopqrstu",
    w: "wxyzabcdefghijklmnopqrstuv",
    x: "xyzabcdefghijklmnopqrstuvw",
    y: "yzabcdefghijklmnopqrstuvwx",
    z: "zabcdefghijklmnopqrstuvwxy"
};

function vigenereCipherCrypt(encryptWord, key) {
    var i, size = encryptWord.length,
        keySize = key.length,
        encryptedText = '',
        specialCharacterCount = 0;
    for(i = 0; i < size; i += 1) {
        var keyLetter = (i - specialCharacterCount) % keySize,
            keywordIndex = tabulaRecta.a.indexOf(key[keyLetter]);
        if(tabulaRecta[encryptWord[i]]){
            encryptedText += tabulaRecta[encryptWord[i]][keywordIndex];
        } else {
            encryptedText += encryptWord[i];
            specialCharacterCount++;
        }
    }
    return encryptedText;
}

vigenereCipherCrypt('steve', 'abc');