How to construct the blind factors in practice?
Blinding technics are well know now to defeat most attacks against SCA.
You need a random number generator (True or Pseudo) to generate unpredictable random $r_i$.
Additionnal precautions against Zero Attacks values can alo be taken. 
Try this: $m_0=y_0 \times r_0 \; + \; r_1 \times p \; mod \;(r_2 \times p)$