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                                                                    EXHIBIT 31.1


                                 CERTIFICATIONS


I, Jaime W. Ellertson, certify that:

1.      I have reviewed this Annual Report on Form 10-K of S1 Corporation;

2.       Based on my knowledge, this report does not contain any untrue
         statement of a material fact or omit to state a material fact necessary
         to make the statements made, in light of the circumstances under which
         such statements were made, not misleading with respect to the period
         covered by this report;

3.       Based on my knowledge, the financial statements, and other financial
         information included in this report, fairly present in all material
         respects the financial condition, results of operations and cash flows
         of the registrant as of, and for, the periods presented in this report;

4.       The registrant's other certifying officer and I are responsible for
         establishing and maintaining disclosure controls and procedures (as
         defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the
         registrant and have:


                  (a)      Designed such disclosure controls and procedures, or
                           caused such disclosure controls and procedures to be
                           designed under our supervision, to ensure that
                           material information relating to the registrant,
                           including its consolidated subsidiaries, is made
                           known to us by others within those entities,
                           particularly during the period in which this report
                           is being prepared;


                  (b)      Evaluated the effectiveness of the registrant's
                           disclosure controls and procedures and presented in
                           this report our conclusions about the effectiveness
                           of the disclosure controls and procedures, as of the
                           end of the period covered by this report based on
                           such evaluation; and


                  (c)      Disclosed in this report any change in the
                           registrant's internal control over financial
                           reporting that occurred during the registrant's most
                           recent fiscal quarter (the registrant's fourth fiscal
                           quarter in the case of an annual report) that has
                           materially affected, or is reasonably likely to
                           materially affect, the registrant's internal control
                           over financial reporting; and

5.       The registrant's other certifying officer and I have disclosed, based
         on our most recent evaluation of internal control over financial
         reporting, to the registrant's auditors and the audit committee of the
         registrant's board of directors (or persons performing the equivalent
         functions):


                  (a)      All significant deficiencies and material weaknesses
                           in the design or operation of internal control over
                           financial reporting which are reasonably likely to
                           adversely affect the registrant's ability to record,
                           process, summarize and report financial information;
                           and


                  (b)      Any fraud, whether or not material, that involves
                           management or other employees who have a significant
                           role in the registrant's internal control over
                           financial reporting.

Date: March 15, 2004
                             /S/ JAIME W. ELLERTSON
                             -----------------------------
                             Jaime W. Ellertson
                             Chief Executive Officer