def op=(op)
      fail "OP must be 128 bits" unless op.each_byte.to_a.length == 16
      @opc = xor(enc(op), op)
    end
def op=(op)
      fail "OP must be 128 bits" unless op.each_byte.to_a.length == 16
      @opc = xor(enc(op), op)
    end
Create a single user's kernel instance, remember to set OP or OPc before
 attempting to use the security functions.

 To change the algorithm variables as described in TS 35.206 subclass
 this Kernel class and modify `@c`, `@r` or `@kernel` after calling
 super. E.G.

   class MyKernel < Kernel
     def initialize(key)
       super
       @r = [10, 20, 30, 40, 50]
     end
   end

 When doing this, `@kernel` should be set to a 128-bit MAC function with
 the same API as `OpenSSL::Cipher`, if this is not the case, you may
 need to overload {#enc} as well to match the API.
 Set the Operator Variant Algorithm Configuration field.

 Either this or {#opc=} must be called before any of the security
 functions are evaluated.