EXHIBIT 23.1 CONSENT OF INDEPENDENT ACCOUNTANTS We hereby consent to the incorporation by reference in the Registration Statements on Form S-8 (No. 333-72250), Form S-8 (No. 333-37062), Form S-8 (No. 333-43370), Form S-8 (No. 333-43372), Form S-8 (No. 333-43376), Form S-8 (No. 333-45766), Form S-8 (No. 333-82369), Form S-8 (No. 333-82383), Form S-8 (No. 333-82381), Form S-8 (No. 333-82711), Form S-3, as amended (No. 333-75178), Form S-3 (No. 333-36470) and Form S-3, as amended (No. 333-85688) of S1 Corporation of our report dated March 12, 2004, relating to the financial statements and financial statement schedule, which appears in this Form 10-K. PricewaterhouseCoopers LLP Atlanta, Georgia March 15, 2004