EXHIBIT 23 CONSENT OF INDEPENDENT ACCOUNTANTS We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (No. 333-82369) of S1 Corporation of our report dated June 7, 2002 relating to the financial statements of the S1 Corporation 401(k) Savings Plan, which appears in this Form 11-K. PricewaterhouseCoopers LLP Atlanta, GA June 28, 2002