Vigenere Cipher

The key K=(k1+k2+k3+..+kn) and the plaintext X=(x1+x2+x3+..+xM), encrypt as
follows: E(k)=(x1+k1)%26 + (x2+k2)%26+...+(xn+kn)%26
+ (x(n+1)+k1)%26 + (x(n+2)+k2)%26+..+(x(2n)+kn)%26
+ (x(2n+1)+k1)%26+....+(xM+kn)%26.
Decryption is the same general function, however, the key K is subtracted
from each encrypted letter.
TO DECRYPT: Please copy and paste the info from the output field into
the input field before clicking the decrypt button.

HERE is a copy of the java applet code