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                                                                   Exhibit 10.63

                               AMENDMENT NO. 4 TO

                  SECOND AMENDED AND RESTATED CREDIT AGREEMENT

     THIS AMENDMENT NO. 4 TO SECOND AMENDED AND RESTATED CREDIT AGREEMENT (this
"Amendment") is entered into as of May 10, 2002, by and between DATUM INC., a
Delaware corporation ("Borrower"), and WELLS FARGO BANK, NATIONAL ASSOCIATION
("Bank").

                                    RECITALS

     This Amendment is made with reference to the following facts:

     A.   Borrower is currently indebted to Bank pursuant to the terms and
conditions of that certain Second Amended and Restated Credit Agreement between
Borrower and Bank dated as of July 7, 2000, as amended from time to time
("Credit Agreement").

     B.   As evidenced by Borrower's financial statements for the fiscal quarter
ending March 31, 2002, Borrower has violated Section 5.9(c) and Section 5.9(d)
of the Credit Agreement (the "Existing Violations"). At Borrower's request, Bank
agreed to waive the Existing Violations, subject to the execution of this
Amendment.

     NOW, THEREFORE, for valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties hereto agree that the Credit
Agreement shall be amended as follows:

     1.   The definition of "Maximum Line Amount" in Section 1.1(a) of the
Credit Agreement is hereby amended and restated in its entirety to read as
follows:

          Maximum Line of Credit Amount" means, as of any date of
          determination, the sum of (a) $10,000,000.00 less (b) the
          amount outstanding under the Term Note.

     2.   Section 2.4(e) of the Credit Agreement is hereby amended by changing
the reference to "three-tenths of one percent (0.30%) per annum" therein to "one
half percent (0.50%) per annum."

     3.   Section 5.9(a) of the Credit Agreement is hereby amended and restated
in its entirety to read as follows:

          (a) Quick Ratio at all times greater than 1.5:1.0, with "Quick Ratio"
          defined as the aggregate of unrestricted domestic cash, unrestricted
          domestic marketable securities and receivables readily convertible
          into cash divided by total current liabilities. In calculating the
          foregoing, outstanding Advances on the Line of Credit and amortization
          payments on the Term Loan shall be deemed current liabilities.

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         4.   Section 5.9(c) of the Credit Agreement is hereby amended and
restated in its entirety to read as follows:

              (c) EBITDA not less than a negative $500,000.00 as of the end of
              the fiscal quarter ending June 30, 2002, not less than $850,000.00
              as of the end of the fiscal quarter ending September 30, 2002, not
              less than $2,000,000.00 as of the end of the fiscal quarter ending
              December 31, 2002, and not less than $2,000,000.00 as of the end
              of the fiscal quarter ending March 31, 2003, with "EBITDA" defined
              as net income plus income tax expense, (or less any income tax
              benefit), plus interest expense (net of capitalized interest
              expense), plus depreciation expense, plus amortization expense,
              plus losses on asset sales, minus gains on asset sales, plus
              extraordinary losses, minus extraordinary gains.

         5.   Section 5.9(d) of the Credit Agreement shall be deleted in its
entirety, without substitution therefor.

         6.   Section 6.2 of the Credit Agreement is hereby amended and restated
in its entirety to read as follows:

                   Section 6.2   CAPITAL EXPENDITURES. Make, or permit any
              Guarantor to make, any additional investment in fixed assets
              during the period from June 1, 2001 through and including May 29,
              2003 in excess of an aggregate of $6,000,000.00 for Borrower and
              all Guarantors combined, it being understood that the use of
              restricted cash associated with the expansion of Borrower's
              Lexington facility shall not be subject to this covenant.

         7.   Exhibit B attached to the Credit Agreement is replaced in its
entirety by Exhibit B attached hereto as Annex 2.

         8.   At Borrower's request, Bank shall, subject to documents in form
and substance satisfactory to Bank, increase the Maximum Line of Credit Amount
to $16,000,000.00 if and only if (a) Borrower's EBITDA is greater than or equal
to $8,000,000.00 during a period defined as the immediately preceding four or
fewer consecutive fiscal quarters prior to the measurement date, and (b) at such
time as the condition in (a) is satisfied, no Event of Default, and no event
which with the giving of notice or the passage of time or both would constitute
an Event of Default, shall have occurred and be continuing.

         9.   Conditions Precedent. The effectiveness of this Amendment and
Bank's agreements set forth herein are subject to the satisfaction of each of
the following conditions precedent:

              9.1  Documentation. Borrower shall have delivered or caused to
be delivered to Bank, at Borrower's sole cost and expense, the following, each
of which shall be in form and substance satisfactory to Bank:

              (a)  the executed original of this Amendment and the new Line of
                   Credit Note;

              (b)  written consent of Guarantors attached hereto as Annex 1; and

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              (c)    such authorization documents with respect to Guarantors as
                     Bank shall reasonably require.

              9.2    Representations and Warranties. All of the representations
and warranties of Borrower contained herein shall be true and correct on and as
of the date of execution hereof and no Event of Default shall have occurred and
be continuing under the Credit Agreement or any of the other Loan Documents, as
modified hereby.

       10.    Representations and Warranties. Borrower makes the following
representations and warranties to Bank as of the date hereof which
representations and warranties shall survive the execution, termination or
expiration of this Amendment and shall continue in full force and effect until
the full and final satisfaction and discharge of all obligations of Borrower to
Bank under the Credit Agreement and the other Loan Documents:

              10.1   Reaffirmation of Prior Representations and Warranties.
Borrower hereby reaffirms and restates as of the date hereof, all of the
representations and warranties made by Borrower in the Credit Agreement and the
other Loan Documents, except to the extent such representations and warranties
specifically relate to an earlier date.

              10.2   No Default. No Event of Default or other default has
occurred and remains continuing under any of the Loan Documents.

              10.3   Due Execution. The execution, delivery and performance of
this Amendment and any instruments, documents or agreements executed in
connection herewith are within the powers of Borrower and the other Loan Parties
party thereto, have been duly authorized by all necessary action, and do not
contravene any law, the articles of incorporation, bylaws, articles of
organization, operating agreement, partnership agreement or other organizational
documents of such parties, result in a breach of, or constitute a default under,
any contractual restriction, indenture, trust agreement or other instrument or
agreement binding upon any of such parties.

              10.4   No Further Consent. The execution, delivery and performance
of this Amendment and any documents or agreements executed in connection
herewith do not require any consent or approval not previously obtained of any
governmental agency, equity holder, beneficiary or creditor of Borrower.

              10.5   Binding Agreement. This Amendment, and each of the other
instruments, documents and agreements executed in connection herewith constitute
the legal, valid and binding obligation of Borrower or other Loan Parties party
thereto and are enforceable against such parties in accordance with their terms,
except as such enforceability may be limited by bankruptcy, insolvency,
moratorium, reorganization or similar laws or equitable principles relating to
or limiting creditors' rights generally.

       11.    Miscellaneous

              11.1   Recitals Incorporated. The Recitals set forth above are
incorporated into and are made a part of this Amendment.

              11.2   Further Assurances. Borrower, at its sole cost and expense,
agrees to execute and deliver all documents and instruments and to take all
other actions as may be specifically provided for herein and as may be required
in order to consummate the purposes of

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this Amendment. Borrower shall diligently and in good faith pursue the
satisfaction of any conditions or contingencies in this Amendment.

          11.3  No Third Parties. Except as specifically provided herein, no
third party shall be benefitted by any of the provisions of this Amendment; nor
shall any such third party have the right to rely in any manner upon any of the
terms hereof, and none of the covenants, representations, warranties or
agreements herein contained shall run in favor of any third party.

          11.4  Time is of the Essence. Time is of the essence for the
performance of all obligations and the satisfaction of all conditions of this
Amendment. The parties intend that all time periods specified in this Amendment
shall be strictly applied, without any extension (whether or not material)
unless specifically agreed to in writing by all parties hereto.

          11.5  Costs and Expenses. In addition to the obligations of Borrower
under the Credit Agreement, Borrower agrees to pay all costs and expenses
(including without limitation reasonable attorneys' fees) expended or incurred
by Bank in connection with the negotiation documentation and preparation of this
Amendment and any other documents executed in connection herewith, and in
carrying out the terms of this Amendment, whether incurred before or after the
effective date hereof.

          11.6  Integration; Interpretation. The Loan Documents, including this
Amendment and the documents, instruments and agreements executed in connection
herewith, contain or expressly incorporate by reference the entire agreement of
the parties with respect to the matters contemplated herein and supersede all
prior negotiations, discussions and correspondence. The Loan Documents shall not
be modified except by written instrument executed by all parties thereto.

          11.7  Counterparts and Execution. This Amendment may be executed in
counterparts, each of which shall be deemed an original, and all of which
together shall constitute one and the same instrument. However, this Amendment
shall not be binding on Bank until all parties have executed it.

          11.8  Governing Law. This Amendment shall be governed by and construed
in accordance with the laws of the State of California.

          11.9  Non-Impairment of Loan Documents. On the date all conditions
precedent set forth herein are satisfied in full, this Amendment shall be a part
of the Credit Agreement. Except as expressly provided in this Amendment or in
any other document, instrument or agreement executed by Bank, all provisions of
the Loan Documents shall remain in full force and effect, and Bank shall
continue to have all its rights and remedies under the Loan Documents.

          11.10 No Waiver. Nothing herein shall be deemed a waiver by Bank of
any Event of Default, and nothing herein shall be deemed a waiver by Bank of any
other default under the Loan Agreement or any document executed in connection
with the Loan Agreement. No delay or omission of Bank to exercise any right,
remedy or power under any of the Loan Documents shall impair such right, remedy
or power or be construed to be a waiver of any default or an acquiescence
therein, and single or partial exercise of any such right, remedy or power shall
not preclude other or further exercise thereof or the exercise of any other
right, remedy or power. No waiver of any term, covenant, or condition shall be
deemed to waive Bank's right to enforce such term, covenant or condition at any
other time.

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                  11.11 Successors and Assigns. The terms of this Amendment
shall be binding upon and inure to the benefit of the successors and assigns of
the parties to this Amendment.

         IN WITNESS WHEREOF, this Amendment has been duly executed as of the
date first set forth above.


   DATUM INC.,                                    WELLS FARGO BANK,
   a Delaware corporation                          NATIONAL ASSOCIATION


   By: /s/ Bob Krist                              By: /s/ Stephen M. Amendt
       --------------------------------               --------------------------
                                                      Stephen M. Amendt
   Title: VP CFO Treasurer & Secretary                Vice President
          ----------------------------

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