code: def eval(w,t,x,msk,s):
      
      # Construct the key
      kw = genKw(w,msk,s)
  
      # Multiply x by kw (it's fastest this way), hash the tweak, and compute
      # the pairing.
      tTilde = hashG2(t)
      y = pair(x*kw, tTilde)
      return y,kw,tTilde
docs: Pythia server-side computation of intermediate PRF output.
      @w: ensemble key selector (e.g. webserver ID)
      @t: tweak (e.g. user ID)
      @x: blinded message (element of G1)
      @msk: Pythia server's master secret key
      @s: state value from Pythia server's key table
      @returns: (y, kw, tTile)
       where: y: intermediate result
              kw: secret key bound to w (needed for proof)
              tTilde: hashed tweak (needed for proof)