Mask generation function in ABAP

mgf1.abap

  METHOD mgf1.

* https://en.wikipedia.org/wiki/Mask_generation_function

    DATA lv_counter TYPE i.
    DATA lv_sha1    TYPE xstring.
    DATA lv_xstr    TYPE xstring.
    DATA lv_c       TYPE x LENGTH 4.

    WHILE xstrlen( rv_mask ) < iv_length.

* Convert counter to an octet string C of length 4
      lv_c = lv_counter.

      CONCATENATE iv_seed lv_c INTO lv_xstr IN BYTE MODE.
      cl_abap_message_digest=>calculate_hash_for_raw(
        EXPORTING
          if_data        = lv_xstr
        IMPORTING
          ef_hashxstring = lv_sha1 ).

* Concatenate the hash of the seed Z and C to the octet string
      CONCATENATE rv_mask lv_sha1 INTO rv_mask IN BYTE MODE.

      lv_counter = lv_counter + 1.
    ENDWHILE.

    rv_mask = rv_mask(iv_length).

  ENDMETHOD.