...[How the cipher encodes?]
Input Data: helloaf
Key: love
l - 12th letter in Alphabet
o - 15th letter in Alphabet
v - 22nd letter in Alphabet
e - 5th letter in Alphabet
Now:
h(l) e(o) l(v) l(e) o(l) a(o) f(v)
Further:
h(+12) e(+15) l(+22) l(+5) o(+12) a(+15) f(+22)
where +(number) meaning shifting the character forward by the respective number of places.
So the result comes out to be:
tthqapb
and the data is encrypted.