<PAGE>

                                                                   EXHIBIT 10.17

                            RSA DATA SECURITY, INC.
                         100 Marine Parkway, Suite 500
                          Redwood City, CA 94065 USA

                                March 31, 1998

Trintech Group                            * - Material has been omitted
Trintech House                            pursuant to a request for
South County Business Park,               confidential treatment.  This material
Leopardstown, Dublin 18, Ireland          has been filed separately.

Re:  Marketing Arrangements between RSA Data Security. Inc. ("RSA"), its parent,
     Security Dynamics Technologies, Inc. ("SDTI"), Trintech Manufacturing, Ltd.
     ("Trintech") and Trintech Inc. a U.S. subsidiary of Trintech ("Trintech
     Inc.").

Ladies and Gentlemen:

In connection with the Software Source Code License Agreement (the "License
Agreement") of even date herewith between RSA and Trintech, the parties will
engage in the following marketing, activities in order to publicize the
relationship between RSA and Trintech, and to encourage sales of Trintech
products which: (i) incorporate RSA's S/PAY(TM) technology, and/or (ii) which
are S/PAY enabled (such Trintech products collectively, the "S/PAY Products").

1)   Trade Show Participation Trintech Demo Space.
     ---------------------------------------------

     a)  Trade Show Participation. The parties shall share equally the cost of
         ------------------------
         participation in the Internet Electronic Commerce ("IEC") Show which
         will take place in April in New York City. These costs include costs
         associated with booth rental, mutually agreeable signage and shipping
         of necessary materials to the trade show. Such costs are estimated to
         be approximately $20,000 in the aggregate. Notwithstanding the
         foregoing, each party shall assume all travel, food and lodging costs
         incurred by its personnel in connection with such party's participation
         in the trade show.

     b)  Trintech Demo Space. RSA will reserve space in the IEC booth for
         -------------------
         demonstration by Trintech of its products (including the S/PAY
         Products), and in connection therewith, Trintech will keep one person
         in the IEC booth at all times during the hours of operation of the
         trade show.

     c)  Public Communications. The parties will work together to create
         ---------------------
         mutually acceptable marketing materials for purposes of communicating
         the substance of this joint marketing arrangement to the industry and
         press.

2)   Promotion of Trintech Products; Referral Fee.
     --------------------------------------------

     a)  Promotion or Trintech products. RSA and its parent, Security Dynamics
         -------------------------------
     Technologies, Inc. ("SDTI"), will use reasonable efforts to promote to
     their customers the S/PAY

                                      -1-
<PAGE>

          Products. In the event that RSA or SDTI identifies a prospective
          customer for the S/PAY Products, RSA or SDTI, as the case may be,
          shall refer that customer to Trintech so that Trintech may enter into
          a license agreement with such customer for the S/PAY Products.
          Trintech shall have sole and exclusive control over the terms and
          conditions of such license agreements.

     b)   Referral Fee. Upon execution of any license agreement for S/PAY
          -------------
          Products resulting from a Qualified Lead, Trintech shall pay RSA or
          SDTI, as appropriate, a referral fee ("Referral Fee") equal to * of
          the software license fees payable by the licensee to Trintech in the
          first year of that license agreement, net of any license fees paid by
          Trintech to third parties who have licensed to Trintech technology
          embedded in the S/PAY Products. Amounts due to RSA and SDTI hereunder
          shall be paid within forty-five (45) days following the end of any
          calendar quarter in which Trintech receives software license fees from
          customers for which a Referral Fee is due. For the purposes of this
          Section, a "Qualified Lead" is defined in Attachment "B", attached
          hereto

     c)   Amounts Due Upon Termination. Upon termination of this Agreement,
          ----------------------------
          Trintech shall pay RSA and SDTI all amounts due to such parties
          hereunder.

3)   Delivery of Product Documentation and Training. In order to facilitate the
     ----------------------------------------------
     promotional efforts referred to in the foregoing Paragraph, Trintech will
     furnish RSA and SDTI with copies of Trintech's product collateral,
     technical documentation, and other materials for the S/PAY Products. In
     addition, Trintech will train RSA and SDTI sales personnel regarding the
     features, selling points and distribution strategy of the S/PAY Products.
     Such training will take place at RSA and SDTI's facilities located in the
     United States.

4)   Cross Linking of Internet Sites. During the term of this Agreement, each of
     --------------------------------
     RSA and Trintech shall maintain on their respective Internet sites a link
     to the other party's Internet site. Each link shall be located in a
     reasonably prominent position not more than one level away from the first
     page of each party's Internet site.

5)   Transfer of Sales Leads. During the ninety (90) day period following
     ------------------------
     execution of this Agreement, RSA will transfer to Trintech all sales leads
     for the S/PAY Products. To that end, as soon as practicable following
     execution of this Agreement, RSA shall deliver to Trintech a list of all
     current sales leads for such products, together with a description of the
     status of each such lead.

6)   SET Compliance Testing. RSA will use its reasonable engineering efforts to
     -----------------------
     assist Trintech Inc. in modifying the cardholder, merchant and acquirer
     entities of S/PAY: (i) to perform the minimum required functionality that
     conforms to the SET 1.0 Specification, as defined in the License Agreement
     and as further detailed in Attachment "A" hereto, and (ii) such that each
     of the cardholder, merchant and acquirer entities of S/PAY are capable of
     passing the compliance testing as defined by SETco, a company created to
     test compliance on behalf of MasterCard and Visa. For the purposes of this
     Section, "reasonable engineering efforts" means:

                                      -2-
<PAGE>

     (A)  RSA making available to Trintech Inc. (i) up to five (5) engineers
          beginning on the effective date hereof and continuing until April 30,
          1998; (ii) up to three (3) engineers and one (1) quality assurance
          testing person as needed from May 1, 1998 through August 31, 1998; and
          (iii) one (1) engineer from September 1, 1998, through November 1,
          1998. Such engineering resources shall only be available to Trintech
          Inc., either at Trintech Inc.'s or RSA's U.S. facilities, and Trintech
          Inc. agrees to reimburse RSA for reasonable travel and related
          expenses incurred by RSA in providing such engineering resources; and

     (B)  RSA hosting up to five (5) Trintech Inc. engineers at RSA's bay area
          facility beginning on the effective date hereof and continuing through
          July 1, 1998; provided RSA be given reasonable advance notice of the
          individuals' names, nationality, anticipated dates and duration of
          their respective visits to RSA.

    Any software created as a result of these efforts by RSA will be delivered
    to Trintech Inc. and considered a Derivative Work of the License Software
    created by of Trintech, Inc. under the License Agreement and so licensed
    thereunder according to the terms thereof.

7)  Best Customer Pricing. In the event that RSA offers an SSL-enabled product
    ----------------------
    generally available on a commercial basis, then RSA shall offer Trintech a
    license to such technology on substantially similar terms and conditions,
    which are no less favorable than offered to other licensees of such
    technology.

8)  Confidentiality.
    ----------------

    a)  "Confidential Information" means any information: (i) disclosed by one
         ------------------------
        Party (the "Disclosing Party") to the other (the "Receiving Party"),
                    ----------------                      ---------------
        which, if in written, graphic, machine-readable or other tangible form
        is marked as "Confidential" or "Proprietary", or which, if disclosed
        orally or by demonstration, is identified at the time of initial
        disclosure as confidential and reduced to writing and marked
        "Confidential" within thirty (30) days of such disclosure: or (ii) which
        is otherwise deemed to be confidential by the terms of this Agreement.

    b)  Exclusions. Notwithstanding the generality of the foregoing,
        ----------
        Confidential Information shall exclude information that the Receiving
        Party can demonstrate: (i) was independently developed by the Receiving
        Party without any use of the Disclosing Party's Confidential Information
        or by the Receiving Party's employees or other agents for independent
        contractors hired by the Receiving Party) who have not been exposed to
        the Disclosing Party's Confidential Information: (ii) becomes known to
        the Receiving Party, without restriction, from a source other than the
        Disclosing Party without breach of this Agreement and that had a right
        to disclose it; (iii) was in the public domain at the time it was
        disclosed or becomes in the public domain through no act or omission of
        the Receiving Party; or (iv) was rightfully known to the Receiving
        Party, without restriction, at the time of disclosure.

    c)  Compelled Disclosure, if the Confidential Information of a Disclosing
        --------------------
        Party must be disclosed by the Receiving Party pursuant to the order or
        requirement of a court.

                                      -3-
<PAGE>

        administrative agency, or other governmental body, the Receiving Party
        shall (i) provide prompt notice thereof to the Disclosing Party and (ii)
        use its best efforts to obtain a protective order or otherwise prevent
        public disclosure of such information.

     d) Confidentiality Obligation. The Receiving Party shall treat as
        --------------------------
        confidential all of the Disclosing Party's Confidential Information and
        shall not use such Confidential Information except as expressly
        permitted under this Agreement. Without limiting the foregoing, the
        Receiving Party shall use at least the same degree of care which it uses
        to prevent the disclosure of its own confidential information of like
        importance, but in no event with less than reasonable care, to prevent
        the disclosure of the Disclosing Party's Confidential Information.

     e) Confidentiality of Agreement. Each Party agrees that the terms and
        ----------------------------
        conditions, but not the existence, of this Agreement shall be treated as
        the other's Confidential Information and that no reference to the terms
        and conditions of this Agreement or to activities pertaining thereto can
        be made in any form of public or commercial advertising without the
        prior written consent of the other Party; provided, however, that each
                                                  --------  -------
        Party may disclose the terms and conditions of this Agreement: (i) as
        required by any court, or other governmental body; (ii) as otherwise
        required by law; (iii) to legal counsel of the Parties; (iv) in
        connection with the requirements of an initial public offering or
        securities filing (v) in confidence, to accountants, bunks, and
        financing sources and their advisors; (vi) in confidence, in connection
        with the enforcement of this Agreement or rights under this Agreement;
        or (vii) in confidence, in connection with a merger or acquisition or
        proposed merger or acquisition, or the like.

     f) Remedies. Unauthorized use by a Party of the other Party's Confidential
        --------
        Information will diminish the value of such information. Therefore, if a
        Party breaches any of its obligations with respect to confidentiality or
        use of Confidential Information hereunder, the other Party shall be
        entitled to seek equitable relief to protect its interest therein,
        including but not limited to injunctive relief, as well as money
        damages.

9)   LIMITATIONS OF LIABILITY. NEITHER PARTY HERETO SHALL BE LIABLE FOR ANY
     ------------------------
     CONSEQUENTIAL, INCIDENTAL, INDIRECT, SPECIAL OR PUNITIVE DAMAGES ARISING
     OUT OF OR IN CONNECTION WITH THIS AGREEMENT, EVEN IF ADVISED OF THE
     POSSIBILITY OF SUCH DAMAGES. SUCH LIMITATIONS OF LIABILITY SHALL APPLY
     REGARDLESS OF THE CAUSE OF ACTION UNDER WHICH SUCH DAMAGES ARE SOUGHT,
     INCLUDING, WITHOUT LIMITATION, BREACH OF CONTRACT, NEGLIGENCE, STRICT
     LIABILITY, OR OTHER TORT.

10)  Term and Termination.
     --------------------

     a)  Term. This Agreement shall remain in full force and effect for two (2)
         ----
         years from the date set forth above, unless terminated earlier pursuant
         to this Section 11. Thereafter, the term of this Agreement shall
         automatically extend for successive twelve (12) month renewal terms
         unless either party gives the other written notice, at least sixty (60)
         days

                                      -4-
<PAGE>

         prior to the expiration of the then-current term of its intention to
         terminate the Agreement effective 31 the end of the then-current term.

     b)  Termination Event. This Agreement will terminate on the occurrence of
         -----------------
         any or the following conditions:

         i)  at either party's option upon not less than thirty (30) days prior
             written notice to the other party if the other party has materially
             breached any of the terms and conditions of this Agreement and has
             failed to cure such breach within thirty (30) days of its receipt
             of written notice from the non-breaching party describing such
             breach; or

         ii) upon the mutual written consent of Trintech and RSA.

11)  MISCELLANEOUS PROVISIONS

     a)  Governing Law and Jurisdiction. THIS AGREEMENT WILL BE GOVERNED BY AND
         ------------------------------
         CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF CALIFORNIA,
         IRRESPECTIVE OF ITS CHOICE OF LAW PRINCIPLES. All disputes arising out
         of this Agreement will be subject to the exclusive jurisdiction and
         venue of the California state courts and the United States District
         Court for the Northern District of California, and the parties consent
         to the personal and exclusive jurisdiction of these courts. The Parties
         agree that the United Nations Convention on Contracts for the
         International Sale of Goods shall not apply to this Agreement and
         hereby exclude such application.

     b)  Binding upon Success and Assigns. Neither Party shall assign or
         --------------------------------
         delegate this Agreement or any right or obligation hereunder, by
         operation of law or otherwise, and any purported assignment or
         delegation shall be void and without force or effect, except (i)
         Following the written consent of the other Party or (ii) in connection
         with a Change of Control of such Party: provided that (i) any permitted
         successor to a Party shall be bound by each and every obligation and
         restriction to which such Party is bound hereunder, (ii) no license
         granted hereunder shall apply to any conduct or product of any such
         successor prior to the relevant assignment of this Agreement and (iii)
         the assigning Party shall provide the other Party with prompt notice of
         the relevant assignment this Agreement. Notwithstanding any other
         provision hereof, neither (1) a sale of assets unrelated to this
         Agreement, (2) any merger or other transaction to which a Party is the
         surviving entity nor (3) any reincorporation shall be considered an
         assignment or delegation hereof. For purposes of this paragraph,
         "Change of Control" of a Party shall mean the direct or indirect
         acquisition of either (i) the majority of such Party's voting stock or
         (ii) all or substantially all of the assets of such Party to which this
         Agreement relates in a single transaction or a series of related
         transactions. Notwithstanding any other provision of this Agreement,
         Trintech may assign or sublicense this agreement or any right of
         Trintech hereunder to any Affiliate, as that term is defined in the
         License Agreement.

     c)  Severability. If any provision or this Agreement is found to be invalid
         ------------
         or unenforceable, such provision shall be severed from the Agreement
         and the remainder of this Agreement

                                      -5-
<PAGE>

         shall be interpreted so as best to reasonably effect the intent of the
         Parties. Entire Agreement.
                  ----------------

     d)  Entire Agreement. This Agreement, together with its exhibits,
         constitutes the entire understanding and agreement of the Parties with
         respect to the subject matter hereof and supersedes all prior and
         contemporaneous agreements, representations and understandings between
         the Parties.

     e)  Amendment and Waiver. Any term or provision of this Agreement may be
         amended, and the observance of any term of this Agreement may be
         waived, only by a writing signed by the Party to be bound. The failure
         of either Party to enforce at any time any of the previsions of this
         Agreement, or the failure to require at any time performance by the
         other Party of any of the provisions of this Agreement, shall in no way
         be construed to be a present or future waiver of such provisions, nor
         in any way affect the ability of either Party to enforce each and every
         such provision thereafter. The express waiver by either Party of any
         provision, condition or requirement of this Agreement shall not
         constitute a waiver of any future obligation to comply with such
         provision, condition or requirement.

     f)  Notices. Any notice, demand, or request with respect to this Agreement
         -------
         shall be in writing and shall be effective only if it is delivered by
         hand or mailed, certified or registered mail, postage prepaid, return
         receipt requested, addressed to the appropriate Party at its address
         first set forth above. Such communications shall be effective when they
         are received by the addressee; but if sent by certified or registered
         mail in the manner set forth above, they shall be effective not later
         than three (3) days after being deposited in the mail. Any Party may
         change its address for such communications by giving notice to the
         other Party in conformity with this paragraph.

     g)  Export Compliance and Foreign Reshipment Liability. THIS AGREEMENT IS
         --------------------------------------------------
         EXPRESSLY MADE SUBJECT TO ANY LAWS, REGULATIONS, ORDERS OR OTHER
         RESTRICTIONS ON THE EXPORT FROM THE UNITED STATES OF AMERICA OF THE
         LICENSED SOFTWARE OR LICENSED PRODUCTS OR OF INFORMATION ABOUT THE
         LICENSED SOFTWARE OR LICENSED PRODUCTS WHICH MAY BE IMPOSED FROM TIME
         TO TIME BY THE GOVERNMENT OF THE UNITED STATES OF AMERICA.
         NOTWITHSTANDING ANYTHING CONTAINED IN THIS AGREEMENT TO THE CONTRARY,
         NEITHER TRINTECH NOR TRINTECH INC SHALL EXPORT OR REEXPORT, DIRECTLY OR
         INDIRECTLY, ANY LICENSED SOFTWARE OR LICENSED PRODUCTS OR INFORMATION
         PERTAINING THERETO TO ANY COUNTRY TO WHICH SUCH EXPORT OR REEXPORT IS
         RESTRICTED OR PROHIBITED, OR AS TO WHICH SUCH GOVERNMENT OR ANY AGENCY
         THEREOF REQUIRES AN EXPORT LICENSE OR OTHER GOVERNMENTAL APPROVAL AT
         THE TIME OF EXPORT OR REEXPORT WITHOUT FIRST OBTAINING SUCH LICENSE OR
         APPROVAL

     h)  Remedies Non-Exclusive. Except as otherwise expressly provided, any
         ----------------------
         remedy provided for in this Agreement is deemed cumulative with, and
         not exclusive of, any other remedy provided for in this Agreement or
         otherwise available at law or in equity. The exercise

                                      -6-
<PAGE>

     k)  Counterparts. This Agreement may he executed in counterparts or
         ------------
         duplicate originals, both of which shall be regarded as one and the
         same instrument, and which shall be the official and governing version
         in the interpretation of this Agreement.

          IN WITNESS WHEREOF, each of RSA, SDTI and Trintech have executed this
Agreement by their duly authorized officers.

RSA Data Security, Inc.                 Trintech Manufacturing, Ltd.

By:   /s/ [ILLEGIBLE]^^                 By:        /s/ [ILLEGIBLE]^^
    ------------------------------              -------------------------
Title:  Chief Operating Officer         Title:    DIRECTOR
       ---------------------------              -------------------------
Phone:  (650) 595-8782                  Phone:    353-1-2956766
       ---------------------------              -------------------------
Fax:    (650) 595-5198                  Fax:      353-1-2954735
      ----------------------------              -------------------------

Security Dynamics Technologies, Inc.    Trintech, Inc.

By:  /s/ [ILLEGIBLE]^^                  By:     /s/ [ILLEGIBLE]^^
   -------------------------------              -------------------------
Title: Senior Vice President            Title:   DIRECTOR
      ----------------------------              -------------------------
Phone:  (650) 595-8782                  Phone:    408 879 1901
       ---------------------------              -------------------------
Fax:    (650) 595-5198                  Fax:      408 559 9537
      ----------------------------              -------------------------

                                      -7-
<PAGE>

                                 Attachment A

------------------------------------------------------
                           Work in Process
------------------------------------------------------
    S/PAY                      BCI/CRL
                         Certificate Renewal
                            Root History
                              Bug Fixes
                            Release Notes
------------------------------------------------------

                                      -8-
<PAGE>

                                 Attachment B

                          "Qualified Lead" Definition

Qualification of interest in Trintech Products including S/PAY requires the
following:


1.  Provide potential customer with Product information from Trintech

2.  Provide formal introduction for Trintech sales personnel

3.  Deliver joint sales presentation and Product demonstration

4.  Deliver a follow-up presentation to customer/prospect

5.  Assist Trintech personnel in contract negotiation and closing

                                      -9-