Draw the fingers of the right hand on the upper surface of the khuffayn starting from the toes and ending (the masah) at the foreleg (just above the ankle). The masah should be done once only on each sock. The right hand should be used for the right khuff and the left hand for the left khuff.
If the back of the hand was used to make the masah, it will be valid. However, one should not unnecessarily depart from the correct Sunnah method.

It is not permissible to make masah on the side or at the under surface of the khuffayn. It is FARDH to make masah on each sock to the extent of three full fingers i.e. the full surface area of three fingers must be drawn from the toes to the foreleg.