code: def eval(w,t,x,msk,s):
      
      # Verify types
      assertType(w, (str, int, long))
      assertType(t, (str, int, long))
      assertType(x, (str, int, long))
  
      # Construct the key
      kw = genKw(w,msk,s)
  
      # Compute y
      beta = hashG1(t, x)
      y = beta*kw
      return y,kw,beta
docs: Pythia server-side computation of intermediate PRF output.
      @w: ensemble key selector (any string, e.g. webserver ID)
      @t: tweak (any string, e.g. user ID)
      @x: message (any string)
      @msk: Pythia server's master secret key
      @s: state value from Pythia server's key table
      @returns: (y, kw, dummy=None)
       where: y: intermediate result
              kw: secret key bound to w (needed for proof)
              beta: H(kw,t,x) (needed for proof)