**EXHIBIT 31.2****CERTIFICATIONS REQUIRED BY****RULE 13a-14(a) UNDER THE SECURITIES EXCHANGE ACT OF 1934**I, John A. Stone, certify that:1. I have reviewed this Form 10-Q of S1 Corporation; 2. Based on my knowledge, this report does not contain anyuntrue statement of a material fact or omit to state amaterial fact necessary to make the statements made, inlight of the circumstances under which such statementswere made, not misleading with respect to the periodcovered by this report; 3. Based on my knowledge, the financial statements, andother financial information included in this report,fairly present in all material respects the financialcondition, results of operations and cash flows of theregistrant as of, and for, the periods presented inthis report; 4. The registrant’s other certifying officers and I areresponsible for establishing and maintaining disclosurecontrols and procedures (as defined in Exchange ActRules 13a-15(e) and 15d-15(e)) and internal controlover financial reporting (as defined in Exchange ActRules 13a-15(f) and 15d-15(f)) for the registrant andhave: a) designed such disclosurecontrols and procedures,or caused suchdisclosure controls andprocedures to bedesigned under oursupervision, to ensurethat materialinformation relating tothe registrant,including itsconsolidatedsubsidiaries, is madeknown to us by otherswithin those entities,particularly during theperiod in which thisreport is beingprepared;  b) designed such internalcontrol over financialreporting, or causedsuch internal controlover financial reportingto be designed under oursupervision to providereasonable assuranceregarding thereliability of financialreporting and thepreparation of financialstatements for externalpurposes in accordancewith generally acceptedaccounting principles;  c) evaluated theeffectiveness of theregistrant’s disclosurecontrols and proceduresand presented in thisreport our conclusionsabout the effectivenessof the disclosurecontrols and procedures,as of the end of theperiod covered by thisreport based on suchevaluation; and  d) disclosed in this reportany change in theregistrant’s internalcontrol over financialreporting that occurredduring the registrant’smost recent fiscalquarter (theregistrant’s fourthfiscal quarter in thecase of an annualreport) that hasmaterially affected, oris reasonably likely tomaterially affect, theregistrant’s internalcontrol over financialreporting,5. The registrant’s other certifying officers and I havedisclosed, based on our most recent evaluation ofinternal control over financial reporting, to theregistrant’s auditors and the audit committee of theregistrant’s board of directors (or persons performingthe equivalent function): a) all significantdeficiencies andmaterial weaknesses inthe design or operationof internal control overfinancial reportingwhich are reasonablylikely to adverselyaffect the registrant’sability to record,process, summarize andreport financialinformation; and  b) any fraud, whether ornot material, thatinvolves management orother employees who havea significant role inthe registrant’sinternal control overfinancial reporting.Date May 6, 2008     /s/ John A. Stone  John A. Stone   Chief Financial Officer