Vigenère Cipher

Blaise de Vigenère, a 16th-century French diplomat and cryptographer, described a cipher that uses a combination of several Caesar ciphers.

• Instead of shifting each letter of your data by a fixed number, each letter will be shifted by a different number, using a fixed keyword.
• For example, if your data is hello world, and the keyword is cisc, you'll add c = 2 to h to get j, add i = 8 to e to get m, add s = 18 to l to get d, add c = 2 to l to get n, and repeat this for as many copies of the cisc keyword as needed. The end result is the cipher text: jmdnq egtnl.

Data	h	e	l	l	o		w	o	r	l	d
Keyword	c	i	s	c	c		i	s	c	c	i
Result	j	m	d	n	q		e	g	t	n	l