bit flipping of bits at random positions

Dear members

I have stream of bits for ex. Ten bits generated in serial as follow 

1 0 1 0 0  1 1 1 0

and I want  make a flipping for these bits with specific ratio

for ex. If ratio=0.5 then 5 bits of the above bits stream will flipped (0 to 1 and 1 to 0) and the flipped bits selected at random positions (selected randomly for 10 positions)

for flip I can use xor gate

But for selecting which bits will flipped this is my problem??

any help , idea

best regards