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Exhibit 31.1

CERTIFICATIONS

I, Jaime W. Ellertson, certify that:



| | 1. |  | I have reviewed this Quarterly Report on Form 10-Q of S1
Corporation;                                                                                                                                                                                                                                     
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| | 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;
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| | 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;                   
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| | 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:                                                                               

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|(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;         
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|(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                                                                                                    
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|(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):
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|(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
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|(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: November 14, 2003



| | /s/ Jaime W. Ellertson
Jaime W. Ellertson
Chief Executive Officer
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