##### 



EXHIBIT 31.2
 CERTIFICATIONS REQUIRED BY
RULE 13a-14(a) UNDER THE SECURITIES EXCHANGE ACT OF 1934
  1.
    
    I have reviewed this Form 10-Q 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 officers 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)) and internal control over
financial reporting (as defined in Exchange Act
Rules 13a-15(f) and 15d-15(f)) 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)
    
    designed such internal control
over financial reporting, or
caused such internal control
over financial reporting to be
designed under our supervision
to provide reasonable assurance
regarding the reliability of
financial reporting and the
preparation of financial
statements for external
purposes in accordance with
generally accepted accounting
principles;c)
    
    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; andd)
    
    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,
 5.
    
    The registrants other certifying officers 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 function):
 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; andb)
    
    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 9, 2007/s/ John A. Stone

John A. StoneChief Financial Officer