Exhibit 32.1

  CERTIFICATION OF CHIEF EXECUTIVE OFFICER PURSUANT TO 18 U.S.C. SECTION 1350,
      AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     In connection with the Quarterly Report of Transaction Systems Architects,
Inc. (the "Company") on Form 10-Q for the fiscal quarter ended June 30, 2004 as
filed with the Securities and Exchange Commission on the date hereof (the
"Report"), I, Gregory D. Derkacht, Chief Executive Officer of the Company,
certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906
of the Sarbanes-Oxley Act of 2002, that to my knowledge:

     1)  The Report fully complies with the requirements of Sections 13(a) or
         15(d) of the Securities Exchange Act of 1934; and

     2)  The information contained in the Report fairly presents, in all
         material respects, the financial condition and results of operations of
         the Company.


Date: August 10, 2004                      By:     /s/ GREGORY D. DERKACHT
                                              ----------------------------------
                                                     Gregory D. Derkacht
                                              President, Chief Executive Officer
                                                         and Director