<PAGE>
EXHIBIT 31 (2)

                            CERTIFICATION PURSUANT TO
             RULE 13A-14(A) OF THE SECURITIES EXCHANGE ACT OF 1934,
                             AS ADOPTED PURSUANT TO
                  SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

I, John F. Corcoran, certify that:

1.   I have reviewed this quarterly report on Form 10-Q of CNA Surety
     Corporation;

2.   Based on my knowledge, this quarterly 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 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)) 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 quarterly report based on such
          evaluation; and

     d)   disclosed in this quarterly 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):

     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

     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: October 31, 2005                  /s/ John F. Corcoran
                                        ----------------------------------------
                                        John F. Corcoran
                                        Senior Vice President and Chief
                                        Financial Officer


                                       38