Document:

<PAGE>
                                                                   EXHIBIT 10.21

                                  UNIT PURCHASE
                                    AGREEMENT

                           DATED AS OF _________, 2002

                                  BY AND AMONG

                           AUTHENTIDATE HOLDING CORP.

                                     AND THE

                       PURCHASERS SET FORTH ON SCHEDULE A
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                                TABLE OF CONTENTS

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                                                                                       Page
                                                                                       ----
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ARTICLE I
CERTAIN DEFINITIONS .................................................................  - 1 -

ARTICLE II
SALE OF UNITS .......................................................................  - 3 -
2.1     Sale of Units ...............................................................  - 3 -
2.2     Purchase Price ..............................................................  - 3 -
2.3     Issuance of Warrants ........................................................  - 3 -
2.4     Closing .....................................................................  - 3 -

ARTICLE III
REPRESENTATIONS AND WARRANTIES
OF THE COMPANY ......................................................................  - 4 -
3.1     Organization ................................................................  - 4 -
3.2     Capitalization ..............................................................  - 4 -
3.3     Use of Proceeds .............................................................  - 4 -
3.4     Authorization of Transaction ................................................  - 5 -
3.5     Valid Issuance ..............................................................  - 5 -
3.6     Noncontravention ............................................................  - 5 -
3.7     Offering ....................................................................  - 5 -

ARTICLE IV
REPRESENTATIONS AND WARRANTIES OF PURCHASERS ........................................  - 6 -
4.1     Organization. ...............................................................  - 6 -
4.2     Authorization of Transaction ................................................  - 6 -
4.3     Noncontravention ............................................................  - 6 -
4.4     Brokers and Finders. ........................................................  - 6 -
4.5     Investment Intent; Accredited Investor ......................................  - 6 -

ARTICLE V
CONDITIONS TO OBLIGATION TO CLOSE ...................................................  - 8 -
5.1     Conditions to Purchasers' Obligation ........................................  - 8 -
5.2     Conditions to the Company's Obligation ......................................  - 9 -

ARTICLE VI
COVENANTS OF THE COMPANY AFTER CLOSING ..............................................  - 9 -
6.1     Reservation of Shares .......................................................  - 9 -

ARTICLE VII
TERMINATION .........................................................................  - 9 -
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                                       i
<PAGE>
                                TABLE OF CONTENTS

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<S>                                                                                   <C>
7.1     Termination .................................................................  - 9 -
7.2     Effect of Termination ....................................................... - 10 -

ARTICLE VIII
REGISTRATION RIGHTS ................................................................. - 10 -
8.1     Registration Rights ......................................................... - 10 -

ARTICLE IX
MISCELLANEOUS ....................................................................... - 10 -
9.1     Survival .................................................................... - 10 -
9.2     Press Releases .............................................................. - 10 -
9.3     Expenses .................................................................... - 10 -
9.4     Entire Agreement ............................................................ - 10 -
9.5     Parties in Interest ......................................................... - 11 -
9.6     Amendment, Cancellation and Waiver .......................................... - 11 -
9.7     Severability ................................................................ - 11 -
9.8     Notices. .................................................................... - 11 -
9.9     Captions. ................................................................... - 12 -
9.10    Counterparts ................................................................ - 12 -
9.11    Assignment .................................................................. - 12 -
9.12    Governing Law ............................................................... - 12 -
9.13    Separate Counsel ............................................................ - 12 -
</TABLE>

Schedule A - List of Purchasers

List of Exhibits:

Exhibit "A"  -- Form of Warrant
Exhibit "B"  -- Form of Opinion
Exhibit "C"  -- Form of Registration Rights Agreement

                                       ii
<PAGE>
                             UNIT PURCHASE AGREEMENT

         THIS UNIT PURCHASE AGREEMENT (the "Agreement"), dated effective the _th
day of _____, 2002, is made by and among AUTHENTIDATE HOLDING CORP., a Delaware
corporation (the "Company") and the purchasers set forth on Schedule A annexed
hereto (the "Purchasers").

                                   WITNESSETH:

         WHEREAS, the Company is a Delaware corporation engaged in the
manufacture and distribution of document imaging systems, computer systems and
related peripheral equipment, components, and accessories, network and internet
services and Internet-based authentication services; and

         WHEREAS, subject to the terms and conditions of this Agreement, the
Purchasers have agreed to Purchase, and the Company has agreed to sell, a
minimum of $ 500,000 of Units (as defined below) on a "best efforts, all or none
basis" and a maximum of $4,800,000 of Units on a "best efforts" basis.

         NOW, THEREFORE, in consideration of the premises and of the mutual
covenants, agreements, representations and warranties herein contained, the
parties hereto do hereby agree as follows:

                                   ARTICLE I
                               CERTAIN DEFINITIONS

         For purposes of this Agreement, except as otherwise expressly provided,
the terms defined in this Article I have the meanings assigned to them in this
Article I and include the plural as well as the singular unless the context
otherwise requires.

         AFFILIATE -- With respect to any Person, any Person directly or
indirectly controlling, controlled by, or under common control with such other
Person. For purposes of this definition, "control" (including with correlative
meaning, the terms "controlled by" and "under common control with") as used with
respect to any Person, means the possession, directly or indirectly, of the
power to direct or cause the direction of the management and policies of such
Person, whether through ownership of voting securities, by contract or
otherwise.

         AGREEMENT -- This Stock Purchase Agreement and all exhibits and
schedules hereto as the same may from time to time be amended or supplemented by
one or more instruments executed by the parties hereto.

         CLOSING DATE -- The date and time of Closing(s) as defined in Section
2.4.
<PAGE>
         COMPANY-- Authentidate Holding Corp., a Delaware corporation, and,
where the context requires, its successors and assigns.

         FINAL CLOSING DATE -- The date and time of Closing of the Maximum
Offering (as defined herein), as set forth in Section 2.4.

         MAXIMUM OFFERING -- The offering by the Company of 1,584,158 Units (as
defined below) on a "best efforts" basis.

         MINIMUM OFFERING -- The offering by the Company of 165,017 Units on a
"best efforts, all or none" basis.

         PERSON -- Any individual, corporation, company, limited liability
company, partnership (limited or general), joint venture, association, trust or
other entity.

         PURCHASE PRICE -- means the purchase price of one Unit (defined below)
equal to $3.03.

         SHARES -- means one share of Common Stock of the Company, par value
$.001 per share.

         UNIT -- means the investment securities purchased hereunder, consisting
of one Share and 0.20 Warrants.

         UNIT OFFERING -- means the offering by the Company to the Purchasers of
the Units.

         WARRANTS -- The warrants to purchase shares of the Common Stock of the
Company issuable pursuant to Section 2.3 of this Agreement.

         WARRANT SHARES -- Shares of Common Stock of the Company issuable upon
the exercise of the Warrants in accordance with the terms thereof.

                                     - 2 -
<PAGE>
                                   ARTICLE II
                                  SALE OF UNITS

         2.1 SALE OF UNITS. The Company has authorized the issuance of a minimum
of $500,000 and a maximum of $4,800,000 of Units of investment securities, each
Unit consisting of one Share and 0.20 Warrants. The Units are being offered on a
"best efforts, all or none" basis as to the Minimum Offering of 165,017 Units
and on a "best efforts" basis as to an additional 1,419,142 Units.

         2.2 PURCHASE PRICE. Subject to the terms and conditions set forth
herein, upon the execution hereof, the Company agrees to sell, issue and deliver
to the Purchasers up to an aggregate amount of $4,800,000 of Units at the
Purchase Price of $3.03 per Unit, and the Purchasers, severally and not jointly,
agree to purchase the number of Units as set forth in Schedule A, opposite each
Purchaser's name.

         2.3 ISSUANCE OF WARRANTS. The Company has authorized the issuance of
such number of Warrants as shall equal 0.20 times the number of Units purchased
hereunder. The Warrants shall be exercisable for a period of five years,
commencing on the date of issuance. The Warrants shall be exercisable at an
exercise price of 107.5% of the Purchase Price. The Warrants shall be in the
form of Exhibit A.

         2.4 CLOSING. (a) An initial Closing shall be held at the offices of
Goldstein & DiGioia, LLP, 369 Lexington Ave., New York, NY 10017, or at such
other place as shall be agreeable to the parties. Such initial Closing shall be
held at 1:30 p.m., Eastern Time, on July 19, 2002 or such other time or date as
be agreeable to the parties (the "Closing Date"). Additional Closings may be
held as necessary at such times and dates and at such locations as may be
agreeable to the parties. Upon the sale of the Maximum Offering a Final Closing
shall be held at such time and date and at such location as may be agreeable to
the parties (the "Final Closing Date").

         (b) At the Closing the following actions shall be taken:

                  (i) The Purchasers, severally and not jointly, shall deliver
         the total Purchase Price set forth opposite such Purchaser's name on
         Schedule A to the Company in immediately available United States funds.
         The Purchase Price shall be delivered to an escrow account established
         for the benefit of the Company. Instructions for delivery of the
         Purchase Price to the escrow account may be obtained from the Company.

                  (ii) The Purchasers shall have received the opinion of
         Goldstein & DiGioia, LLP, counsel for the Company, in the form of
         Exhibit B attached hereto.

                  (iii) The Company shall deliver to the Purchasers the
         certificate or certificates representing the Shares.

                                     - 3 -
<PAGE>
                  (iv) The Company shall deliver to the Purchasers the
         certificate or certificates representing the Warrants.

                  (v) The Company shall deliver to the Purchasers a certificate
         from an executive officer of the Company stating that all
         representations and warranties in this Agreement are true and correct
         in all material respects.

                  (vi) The Company and the Purchasers shall have delivered, or
         make delivery, to one another of all documents referred to in Article
         VI of this Agreement.

                                   ARTICLE III
                         REPRESENTATIONS AND WARRANTIES
                                 OF THE COMPANY

         As a material inducement to the Purchasers' execution, delivery and
performance of this Agreement, the Company hereby represents and warrants to the
Purchasers that the statements contained in this Article III are correct and
complete as of the date of this Agreement and will be correct and complete as of
the Closing Date.

         3.1 ORGANIZATION. The Company is a corporation duly organized, validly
existing and in good standing under the laws of the state of Delaware with full
corporate power and authority to carry on its business as now conducted and as
currently proposed to be conducted and to own or lease all of its properties and
assets and is duly licensed or qualified to do business and is in good standing
in each state or jurisdiction where the ownership or leasing of its properties
or assets or the conduct of its business requires such licensing or
qualification, except where the failure to be so licensed or qualified would not
have a material adverse effect on the business, financial condition or results
of operations of the Company taken as a whole.

         3.2 CAPITALIZATION. The authorized capital stock of the Company
consists only of 40,000,000 shares of Common Stock, of which 5,000,000 shares of
Common Stock are reserved for issuance under the Company's employee stock option
plan, and 5,000,000 shares of Preferred Stock. On June 26, 2002, there were
issued and outstanding 19,314,685 shares of Common Stock and 32,100 shares of
Preferred Stock, as follows: 100 Shares of Series A Preferred Stock; 28,000
Shares of Series B Preferred Stock and 4,000 Shares of Series C Preferred Stock.
In addition, there are outstanding as of June 26, 2002, 4,823,599 shares
underlying options granted pursuant to the Company's Employee Stock Option
Plans; 160,000 shares underlying options granted pursuant to the Company's 1996
Non-Executive Directors Stock Option Plan; and 2,785,818 shares underlying
common stock purchase warrants previously granted by the Company.

         3.3 USE OF PROCEEDS. The Company shall use the Proceeds received from
the sale of the Shares and Warrants to the Purchasers for general corporate
purposes.

         3.4 AUTHORIZATION OF TRANSACTION. All corporate action on the part of
the Company, its officers, directors and stockholders necessary for the
authorization execution and delivery of this

                                     - 4 -
<PAGE>
Agreement, the performance of all obligations of the Company hereunder at the
Closing and the authorization, issuance, sale and delivery of the Shares and the
Warrants being sold hereunder and the common stock issuable upon conversion or
exercise thereof has been taken or will be taken prior to the Closing, and this
Agreement, when executed and delivered, will constitute valid and legally
binding obligations of the Company, enforceable in accordance with its terms
except (a) as limited by applicable bankruptcy, insolvency, reorganization,
moratorium, and other laws of general application affecting enforcement of
creditors' rights generally, and, (b) as limited by laws relating to the
availability of specific performance, injunctive relief, or other equitable
remedies.

         3.5 VALID ISSUANCE OF COMMON STOCK. The Shares, when issued, sold, and
delivered in accordance with the terms of this Agreement for the consideration
expressed herein, will be duly and validly issued, fully paid, and
nonassessable, and will be free of restrictions on transfer other than
restrictions on transfer under this Agreement and under applicable law. The
Warrant Shares have been duly and validly reserved for issuance and, upon
issuance in accordance with the terms hereof and the Warrants, will be duly and
validly issued, fully paid, and nonassessable and will be free of restrictions
on transfer other than restrictions on transfer under this Agreement and under
applicable law.

         3.6 NONCONTRAVENTION. To the actual knowledge of the Company without
investigation, neither the execution and the delivery of this Agreement, nor the
consummation of the transactions contemplated hereby, will violate any
constitution, statute, regulation, rule, injunction, judgment, order, decree,
ruling, charge, or other restriction of any government, governmental agency, or
court to which the Company is subject under United States law or any provision
of the charter or bylaws of the Company, except where the violation would not
have a material adverse effect on the financial condition of the Company taken
as a whole or on the ability of the Parties to consummate the transactions
contemplated by this Agreement. To the actual knowledge of the Company without
investigation, the Company need not give any notice to, make any filing with, or
obtain any authorization, consent, or approval of any governmental agency of the
United States in order for the Parties to consummate the transactions
contemplated by this Agreement, except where the failure to give notice, to
file, or to obtain any authorization, consent, or approval would not have a
material adverse effect on the financial condition of the Company taken as a
whole or on the ability of the Parties to consummate the transactions
contemplated by this Agreement.

         3.7 OFFERING. Subject in part to the truth and accuracy of the
Purchasers' representations set forth in this Agreement, the offer, sale and
issuance of the Shares and the Warrants as contemplated by this Agreement are
exempt from the registration requirements of the Securities Act.

                                      - 5 -

<PAGE>

                                   ARTICLE IV
                REPRESENTATIONS AND WARRANTIES OF THE PURCHASERS

         As a material inducement to the Company's execution, delivery and
performance of this Agreement, each of the Purchasers, severally and not
jointly, hereby represents and warrants to the Company that the statements
contained in this Article IV are correct and complete as of the date of this
Agreement and will be correct and complete as of the Closing Date.

         4.1 ORGANIZATION. Each of the Purchasers is duly organized, validly
existing and in good standing under the laws of their respective states of
formation with requisite power and authority to carry on its business as now
conducted.

         4.2 AUTHORIZATION OF TRANSACTION. Each of the Purchasers has the
requisite power and authority to execute and deliver this Agreement and to
consummate the transactions contemplated hereby. The execution and delivery of
this Agreement and the consummation of the transactions contemplated hereby have
been duly authorized by all requisite action in respect thereof on the part of
the Purchasers and no other proceedings on the part of the Purchasers are
necessary to consummate the transactions contemplated hereby. This Agreement has
been duly and validly executed and delivered by the Purchasers and, assuming
this Agreement constitutes a valid and binding agreement of the Company,
constitutes a valid and binding obligation of the Purchasers, enforceable
against the Purchasers in accordance with its terms (subject to applicable
bankruptcy, insolvency and similar laws affecting creditors' rights generally
and subject, as to enforceability, to general principles of equity (whether
applied in a proceeding in equity or at law)).

         4.3 NONCONTRAVENTION. To the knowledge of each Purchaser, neither the
execution and the delivery of this Agreement, nor the consummation of the
transactions contemplated hereby, will violate any constitution, statute,
regulation, rule, injunction, judgment, order, decree, ruling, charge, or other
restriction of any government, governmental agency, or court to which each
Purchaser is subject or any provision of its charter or bylaws. To the knowledge
of each Purchaser, it need not give any notice to, make any filing with, or
obtain any authorization, consent, or approval of any government or governmental
agency in order to consummate the transactions contemplated by this Agreement.

         4.4 BROKERS AND FINDERS. Neither any Purchaser nor any of their
officers, directors, employees or agents has employed any broker, finder or
financial advisor or incurred any liability for any broker's or finder's fees or
commissions in connection with the transactions contemplated hereby.

         4.5 INVESTMENT INTENT; ACCREDITED INVESTOR.

         (a) The Shares, the Warrants and the Warrant Shares are being acquired
by the Purchaser for investment for Purchaser's own account, and not as a
nominee or agent or with a view to the resale or distribution of any part
thereof. Purchaser has no present intention of selling, granting any
participation in, or otherwise distributing, the Shares, Warrants and Warrant
Shares and Purchaser

                                      - 6 -
<PAGE>
does not have any contract, undertaking, agreement or arrangement with any
person to sell, transfer or grant participation to any person with respect to
the Shares, Warrants and Warrant Shares. The Purchaser has not construed the
contents of this Agreement or any additional agreement with respect to the
proposed investment in the Units or any prior or subsequent communications from
the Company, or any of its officers, employees or representatives, as
investment, tax or legal advice or as information necessarily applicable to such
Purchaser's particular financial situation. The Purchaser has consulted its own
financial advisor, tax advisor, legal counsel and accountant, as necessary or
desirable, as to matters concerning its investment in the Units.

         (b) Each of the Purchasers, severally and not jointly, represents and
warrants that it is an "accredited investor" as defined under Rule 501 of
Regulation D promulgated under the Securities Act of 1933, as amended.

         (c) Each Purchaser has received, read carefully and are familiar with
this Agreement. Respecting the Company, its business, plans and financial
condition, the terms of the Unit Offering and any other matters relating to the
Unit Offering; each Purchaser has received all materials which it requested; the
Company has answered all inquiries that each Purchaser or its representatives
have made; each Purchaser has had access to all additional information necessary
to verify the accuracy of the information set forth in this Agreement and any
other materials furnished herewith; and each Purchaser has taken all the steps
necessary to evaluate the merits and risks of an investment as proposed
hereunder.

         (d) Each Purchaser, or its representative, has such knowledge and
experience in finance, securities, investments and other business matters so as
to be able to protect its interests in connection with this transaction, and
each Purchaser's investment in the Company hereunder is not material when
compared to such Purchaser's total financial capacity.

         (e) Each Purchaser understands the various risks of an investment in
the Company as proposed herein and can afford to bear such risks, including, but
not limited to, the risks of losing such Purchaser's entire investment.

         (f) Each Purchaser acknowledges that no market for the Shares, Warrants
and Warrant Shares presently exists and none may develop in the future and that
it may find it impossible to liquidate its investment at a time when it may be
desirable to do so, or at any other time.

         (g) Each Purchaser has been advised by the Company that the Shares,
Warrants and Warrant Shares have not been registered under the Securities Act,
that such securities will be issued on the basis of the statutory exemption
provided by Section 4(2) of the Securities Act and/or Regulation D promulgated
thereunder relating to transactions by an issuer not involving any public
offering and under similar exemptions under certain state securities laws; that
this transaction has not been reviewed by, passed on or submitted to any Federal
or state agency or self-regulatory organization where an exemption is being
relied upon, and that the Company's reliance thereon is based in part upon the
representations made by each Purchaser in this Agreement. Each Purchaser
acknowledges that it have been informed by the Company of, or are otherwise
familiar with, the

                                      - 7 -
<PAGE>
nature of the limitations imposed by the Securities Act and the rules and
regulations thereunder on the transfer of securities. In particular, each
Purchaser agrees that no sale, assignment or transfer of the Shares, Warrants or
Warrant Shares shall be valid or effective, and the Company shall not be
required to give any effect to any such sale, assignment or transfer, unless (i)
the sale, assignment or transfer of the such securities is registered under the
Securities Act, or (ii) the securities are sold, assigned or transferred in
accordance with all the requirements and limitations of Rule 144 under the
Securities Act, it being understood that Rule 144 is not available at the
present time for the sale of the securities, or (iii) such sale, assignment, or
transfer is otherwise exempt from registration under the Securities Act. Each
Purchaser acknowledges that the Shares, Warrants and Warrant Shares shall be
subject to a stop transfer order and the certificate or certificates evidencing
any Shares, Warrants and Warrant Shares shall bear the following or a
substantially similar legend and such other legends as may be required by state
blue sky laws:

                  THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
                  ACT OF 1933. SUCH SECURITIES MAY NOT BE SOLD OR OFFERED FOR
                  SALE, TRANSFERRED, HYPOTHECATED OR OTHERWISE ASSIGNED IN THE
                  ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT WITH RESPECT
                  THERETO UNDER SUCH ACT OR AN OPINION REASONABLY ACCEPTABLE TO
                  THE COMPANY OF COUNSEL REASONABLY ACCEPTABLE TO THE COMPANY
                  THAT AN EXEMPTION FROM REGISTRATION FOR SUCH SALE, OFFER,
                  TRANSFER, HYPOTHECATION OR OTHER ASSIGNMENT IS AVAILABLE UNDER
                  SUCH ACT."

                                    ARTICLE V
                        CONDITIONS TO OBLIGATION TO CLOSE

         5.1 CONDITIONS TO OBLIGATION OF THE PURCHASERS. The obligation of each
Purchaser to consummate the transactions to be performed by it in connection
with the Closing is subject to satisfaction of the following conditions:

                  (a) the representations and warranties set forth in Article
III above shall be true and correct in all material respects;

                  (b) all actions to be taken by the Company in connection with
consummation of the transactions contemplated hereby and the following
certificates, opinions, instruments, and other documents required to effect the
transactions contemplated hereby will be reasonably satisfactory in form and
substance to the Purchasers:

                           (i) the Shares;

                           (ii) the Warrant  (in the form of Exhibit A); and

                                      - 8 -
<PAGE>
                           (i) a legal opinion of Goldstein & DiGioia, LLP,
                           counsel to the Company, on the laws of the United
                           States of America, dated as of the Closing Date; and

                  (c) the Company shall have performed all obligations under
this Agreement which are to be performed prior to or on the Closing Date.

         The Purchasers may waive any condition specified in this Section 5.1 if
it executes a writing so stating at or prior to the Closing and shall be deemed
to have so waived all conditions if it elects to proceed with the Closing.

         5.2 CONDITIONS TO OBLIGATION OF THE COMPANY. The obligation of the
Company to consummate the transactions to be performed by them in connection
with the Closing is subject to satisfaction of the following conditions:

                  (a) the representations and warranties set forth in Article IV
above shall be true and correct in all material respects;

                  (b) all actions to be taken by the Purchasers in connection
with consummation of the transactions contemplated hereby and all certificates,
opinions, instruments, and other documents required to effect the transactions
contemplated hereby will be reasonably satisfactory in form and substance to the
Company; and

                  (c) The Purchasers shall have performed all obligations under
this Agreement which are to be performed prior to the Closing Date.

         The Company may waive any condition specified in this Section 5.2 if
they execute a writing so stating at or prior to the Closing and shall be deemed
to have so waived all conditions if it elects to proceed with the Closing.

                                   ARTICLE VI
                     COVENANTS OF THE COMPANY AFTER CLOSING

         6.1 RESERVATION OF SHARES. The Company shall at all times have
authorized and reserved, for the purpose of issuance, a sufficient number of
shares of Common Stock to provide for the issuance of the Warrant Shares
underlying the then outstanding Warrants.

                                   ARTICLE VII
                                   TERMINATION

         7.1 TERMINATION. The Parties may terminate this Agreement:

                  (a) by mutual written consent at any time;

                                      - 9 -
<PAGE>
                  (b) unilaterally, upon the material breach of this Agreement
by the other party; and

                  (c) automatically, if the transaction contemplated herein are
not consummated by August 31, 2002.

         7.2 EFFECT OF TERMINATION. Upon any such termination of this Agreement
pursuant to Section 7.1, the parties hereto shall (except for any liability
arising before or in relation to such termination) be released and discharged
from their respective obligations under this Agreement.

                                  ARTICLE VIII
                               REGISTRATION RIGHTS

         8.1 On or before October 15, 2002, the Company shall register for
resale under the Securities Act of 1933 all of the shares of the Company's
Common Stock issuable hereunder and all of the shares of Common Stock issuable
as Warrant Shares. The Company will use its best efforts to cause the
registration statement to be declared effective on or before November 1, 2002
and to cause such registration statement to remain effective until the first
anniversary of its effective date. Subject to the provisions of the Registration
Rights Agreement, in the event the Company does not file the registration
statement contemplated herein (the "Registration Statement") on or prior to
October 15, 2002, is unable to cause the Registration Statement to be declared
effective on or prior to November 1, 2002, or if the effectiveness of the
Registration Statement is subsequently suspended within a period of one year
from the effective date, than the Company shall pay to the Purchasers, as
liquidated damages, an aggregate amount equal to 2% of the Purchase Price per
month that such event is in occurrence. The rights and obligations of the
Company and Purchasers with respect to such registration shall be governed by
the Registration Rights Agreement entered into between the Company and
Purchasers, the form of which is attached as Exhibit C to this Agreement.

                                   ARTICLE IX
                                  MISCELLANEOUS

         9.1 SURVIVAL. The representations and warranties set forth in Articles
III and IV hereof shall survive the Closing. No investigation made by or on
behalf of either party shall affect the representations and warranties made
pursuant to this Agreement.

         9.2 PRESS RELEASES AND PUBLIC ANNOUNCEMENTS. Purchaser shall not issue
any press release or make any public announcement relating to the subject matter
of this Agreement without the prior written approval of the Company; provided,
however, that Purchaser may make any public disclosure it believes in good faith
is required by applicable law or any listing or trading agreement concerning its
publicly-traded securities (in which case Purchaser will use its best efforts to
advise the Company prior to making the disclosure).

         9.3 EXPENSES. Except as otherwise specified in this Agreement, each
party hereto shall bear and pay all costs and expenses incurred by it in
connection with the transactions contemplated

                                     - 10 -
<PAGE>
hereby, including fees and expenses of its own brokers, finders, financial
consultants, accountants and counsel.

         9.4 ENTIRE AGREEMENT. This Agreement, including the Exhibits, contains
the entire agreement and understanding of the parties with respect to its
subject matter. This Agreement supersedes all prior arrangements and
understandings between the parties, both written or oral, with respect to its
subject matter.

         9.5 PARTIES IN INTEREST. The Agreement shall be binding upon and shall
inure to the benefit of and be binding upon the parties hereto and their
respective successors and assigns; provided, however, that nothing in this
Agreement, expressed or implied, is intended to confer upon any other Person any
rights, remedies, obligations or liabilities of any nature whatsoever under or
by reason of this Agreement.

         9.6 AMENDMENT, CANCELLATION AND WAIVER. This Agreement and the Exhibits
hereto may be amended modified, superseded or cancelled, and any of the terms
hereof or thereof may be waived, only by a written instrument executed by the
Company and Purchaser hereto or thereto, as the case may be, or, in the case of
a waiver, by the party or parties waiving compliance. The failure of any party
at any time or times to require performance of any provision hereof or of any
Exhibit thereto shall in no manner affect the rights at a later time to enforce
the same. No waiver by any party of any condition or of the breach of any term
contained in this Agreement or in any Exhibit hereto, whether by conduct or
otherwise, in any one or more instances, shall be deemed to be construed as a
further or continuing waiver of any such breach or the breach of any other term
of this Agreement or of the Exhibits hereto.

         9.7 SEVERABILITY. Any term or provision of this Agreement that is
invalid or unenforceable in any situation in any jurisdiction shall not affect
the validity or enforceability of the remaining terms and provisions hereof or
the validity or enforceability of the offending term or provision in any other
situation or in any other jurisdiction.

         9.8 NOTICES. All notices or other communications hereunder shall be in
writing and shall be in the English language and shall be deemed given if
delivered personally or by overnight courier, or telecopy or on the third (3rd)
business day after mailing if mailed by prepaid registered or certified mail
(return receipt requested), addressed as follows:

         (a) If to Company, to:       Authentidate Holding Corp.
                                      2165 Technology Drive
                                      Schenectady, New York  12308
                                      Attention: President
                                      Facsimile: (518) 346-3644

                 Copies to:           Goldstein & DiGioia, LLP
                                      369 Lexington Avenue

                                       - 11 -
<PAGE>
                                      New York, New York 10017
                                      Attention: Victor J. DiGioia
                                      Facsimile: (212) 557-0295

         (b) If to the Purchasers:    to the address appearing next to its name
                                      on Schedule A.

         9.9 CAPTIONS. The table of contents and captions contained in this
Agreement are for reference purposes only and are not part of this Agreement.

         9.10 COUNTERPARTS. This Agreement may be executed in any number of
counterparts, and each such counterpart shall be deemed to be an original
instrument, but all such counterparts together shall constitute but one
Agreement.

         9.11 ASSIGNMENT. No party hereto may assign any of its rights or
obligations hereunder to any other Person, without prior written consent of the
other parties.

         9.12 GOVERNING LAW. This Agreement shall be governed by and construed
in accordance with the domestic laws of the State of New York without giving
effect to any choice or conflict of law provision or rule that would cause the
application of the laws of any jurisdiction other than the State of New York.
The parties submit to the jurisdiction of the State of New York and its courts
and waives any affirmative defenses based on lack of jurisdiction.

         9.13 SEPARATE COUNSEL. The Purchasers acknowledge that the Company has
been represented in this transaction by Goldstein & DiGioia, LLP, and that none
of the purchasers has been represented in this transaction by the attorneys for
the Company, and each Purchaser has been advised that it is important for him to
seek separate legal advice and representation in this matter.

      Remainder of page intentionally left blank. Signature page follows.

                                     - 12 -
<PAGE>
         IN WITNESS WHEREOF, the parties hereto have executed or caused this
Agreement to be executed by their signature as natural persons or by individuals
by their duly authorized officers as of the date first written above.

                                   AUTHENTIDATE HOLDING CORP.

                                   By:
                                      ------------------------------------------
                                          Name: John T. Botti
                                          Title:   President

                                   PURCHASERS:

                                   By:
                                      ------------------------------------------
                                          Name:
                                          Title:

                                   By:
                                      ------------------------------------------
                                          Name:
                                          Title:

                                   By:
                                      ------------------------------------------
                                          Name:
                                          Title:

                 [SIGNATURE PAGE TO SERIES A PURCHASE AGREEMENT]<PAGE>

                                                                   EXHIBIT 10.22

                          REGISTRATION RIGHTS AGREEMENT

         This Registration Rights Agreement (the "Agreement") is made and
entered into as of this __ day of ______, 2002 by and among AUTHENTIDATE HOLDING
CORP., a Delaware corporation (the "Company") and the purchasers signing this
Agreement (the "Shareholders").

         WHEREAS, the Company desires to grant registration rights to the
Shareholders in connection with its purchase of Units of the Company's
securities, each Unit consisting of one share of Common Stock (the "Shares") and
0.20 Common Stock Purchase Warrants (the "Warrants") under that certain Unit
Purchase Agreement, dated as of the __th day of _______, 2002, by and among the
Company and the Shareholders (the "Unit Purchase Agreement"); and

         WHEREAS, the execution and delivery of this Agreement by the Company
and the Shareholders is a condition to the closing under the Unit Purchase
Agreement;

         NOW THEREFORE, in consideration of the mutual promises and covenants
contained in this Agreement, the parties hereto agree as follows:

         1. Registration Rights.

         1.1 Certain Definitions. As used in this Agreement, the terms set forth
below shall have the following respective meanings:

         "Commission" means the Securities and Exchange Commission, or any other
Federal agency at the time administering the Securities Act.

         "Common Stock" means the shares of Common Stock, par value $.001 per
share, of the Company.

         "Exchange Act" means the Securities Exchange Act of 1934, as amended,
or any similar Federal statute, and the rules and regulations of the Commission
issued under such Act, as they each may, from time to time, be in effect.

         "Registration Statement" means a registration statement filed by the
Company with the Commission for a public offering and sale of securities of the
Company (other than a registration statement on Form S-8 for the registration of
any option plan or Form S-4 in connection with a merger or acquisition, or their
successors, or any other form for a limited purpose (not including any issuance
of securities of the Company for cash consideration), or any registration
statement covering only securities proposed to be issued in exchange for
securities or assets of another corporation).

                                        1
<PAGE>
         "Registrable Shares" means (i) the Shares issued pursuant to the terms
of the Unit Purchase Agreement; (ii) any shares of Common Stock issuable upon
exercise of the Warrants; (iii) any other shares of Common Stock of the Company
issued to the Shareholders from time to time hereafter as contemplated under the
Unit Purchase Agreement, if any; (iv) shares of any class of capital stock or
other securities into which or for which any such shares of Common Stock held by
the Shareholders shall have been converted or exchanged pursuant to any
recapitalization, reorganization, merger or consolidation of the Company or sale
of all or substantially all of the assets of the Company; (v) any other shares
of Common Stock of the Company issued in respect of such shares described in
clauses (i) through (iv) of this definition (because of stock splits, stock
dividends, reclassification, recapitalization, or similar events); and (vi) any
shares of Common Stock issuable upon exercise of the common stock purchase
warrants issued to a Shareholder dated February 19, 2002; provided, however,
that shares of Common Stock that are Registrable Shares shall cease to be
Registrable Shares upon any sale pursuant to a Registration Statement or Rule
144 under the Securities Act or at such time that the Registrable Share ceases
to be outstanding.

         "Securities Act" means the Securities Act of 1933, as amended, or any
similar Federal statute, and the rules and regulations of the Commission issued
under such Act, as they each may, from time to time, be in effect.

         1.2 Sale or Transfer of Registrable Shares; Legend.

         (a) The Registrable Shares and shares issued in respect of the
Registrable Shares shall not be sold or transferred, except as may be permitted
under the Unit Purchase Agreement or upon the receipt by the Company of an
opinion of legal counsel, reasonably satisfactory to the Company, to the effect
that such sale or transfer is exempt from the registration requirements of the
Securities Act.

         (b) Each certificate representing the Registrable Shares and shares
issued in respect of the Registrable Shares shall have such legends as required
by the Unit Purchase Agreement. Such legends may be removed from the
certificates representing any Registrable Shares, at the request of the holder
thereof, at such time as such securities are registered under the Securities Act
or as otherwise permitted by the Securities Act or regulations promulgated
thereunder.

         1.3 Required Registration.

         (a) On or before October 15, 2002, the Company shall file a
Registration Statement with the Commission covering all of the Registrable
Shares issued to the Shareholders pursuant to the Unit Purchase Agreement. The
Company shall use its best efforts to effect the registration, qualification or
compliance (including, without limitation, appropriate qualification under
applicable blue sky or other state securities laws and appropriate compliance
with applicable regulations issued under the Securities Act and any other
governmental requirements or regulations) of all Registrable Shares, and have
the Commission declare the Registration Statement effective on or before
November 1, 2002. Notwithstanding the foregoing, the Company may delay the
filing, amendment

                                        2
<PAGE>
and/or the effectiveness of such Registration Statement, for a period not to
exceed 90 days in the aggregate during any 12 month period, if at the time the
Company is engaged in a material transaction and the filing, amendment and/ or
effectiveness of such Registration Statement would have a material adverse
effect on such transaction. Subject to the foregoing sentence, in the event (i)
the Company does not timely file the Registration Statement or is unable to have
the Registration Statement declared effective on or before the date set forth
above or (ii) the effectiveness of the Registration Statement is subsequently
suspended prior to the first anniversary of the effective date of the
Registration Statement, than the Company shall pay to the Shareholders an
aggregate amount of liquidated damages equal 2% of the Purchase Price paid by
such Shareholders (as defined in the Unit Purchase Agreement) per month for each
month that any of the above-defined events occur.

         1.4 Registration Procedures. If and whenever the Company is required by
the provisions of this Agreement to use its best efforts to effect the
registration of any of the Registrable Shares under the Securities Act, the
Company shall:

         (a) in connection with any registration of Registrable Securities
pursuant to Section 1.3 above, the Company shall furnish the Shareholders
included in a Registration Statement with such reasonable number of copies of
such Registration Statement, related preliminary prospectus and prospectus
meeting the requirements of the Act, and other documents necessary or incidental
to the registration and public offering of such Registrable Shares, as shall be
reasonably requested by the Shareholders to permit the Shareholders to make a
public distribution of such Registrable Securities;

         (b) as expeditiously as reasonable, prepare and file with the
Commission any amendments and supplements to the Registration Statement and the
prospectus included in the Registration Statement as may be necessary to keep
the Registration Statement effective until the earlier of the sale of all
Registrable Shares covered thereby or the date that the Shareholders of the
Registrable Shares receive an opinion of counsel to the Company that all of the
Registrable Shares may be freely traded (without limitation or restriction as to
quantity or timing and without registration under the Act) pursuant to Rule 144
or otherwise;

         (c) as expeditiously as reasonable, furnish to each selling
Shareholders such reasonable numbers of copies of the Registration Statement,
each amendment and supplement thereto, the prospectus, including a preliminary
prospectus, in conformity with the requirements of the Securities Act and each
prospectus filed under Rule 424 of the Securities Act, and such other documents
as the selling Shareholders may reasonably request in order to facilitate the
public sale or other disposition of the Registrable Shares owned by the selling
Shareholders;

         (d) as expeditiously as reasonable, use its best efforts to register or
qualify the Registrable Shares covered by the Registration Statement under the
securities or Blue Sky laws of such states as the selling Shareholders shall
reasonably request, and do any and all other acts and things that may be
necessary or desirable to enable the selling Shareholders to consummate the
public sale or other disposition in such states of the Registrable Shares owned
by the selling Shareholders; provided,

                                        3
<PAGE>
however, that the Company shall not be required in connection with this Section
1.4(d) to qualify as a foreign corporation or execute a general consent to
service of process in any jurisdiction; and

         (e) in the event of the issuance of any stop order suspending the
effectiveness of a Registration Statement, or of any order suspending or
preventing the use of any related prospectus or suspending the qualification of
any Registrable Shares included in such Registration Statement for sale in any
jurisdiction, the Company will use its best efforts promptly to obtain the
withdrawal of such order.

         1.5 Allocation of Expenses. The Company will pay all Registration
Expenses (as defined herein) of all registrations under this Agreement. For
purposes of this Agreement, the term "Registration Expenses" shall mean all
expenses incurred by the Company in complying with this Section 1.5, including,
without limitation, all registration and filing fees, exchange listing fees,
printing expenses, messenger, telephone and delivery expenses, fees, and
expenses of counsel for the Company, state Blue Sky fees and expenses, and the
expense of any special audits incident to or required by any such registration
(including the expenses related to the preparation and delivery of any "cold
comfort" letters required by or incident to such registration). Provided,
however, that the Shareholders shall be solely responsible for the fees of any
counsel retained by the Shareholders in connection with such registration and
any transfer taxes or underwriting discounts, commissions or fees applicable to
the Registrable Securities sold by the Shareholders pursuant thereto.

         1.6 Information by Holder. The Shareholders of Registrable Shares
included in any Registration Statement shall furnish to the Company such
information regarding such holder and the distribution proposed by such holder
as the Company may reasonably request in writing and as shall be required in
connection with any registration, qualification, or compliance referred to in
Sections 1.3.

         1.7 Lawful Compliance. Notwithstanding anything to the contrary in this
Agreement, the Company shall not be required to violate or breach any applicable
federal or state security law, rule, or regulation.

         2. Indemnification and Contribution. (a) In the event of any
registration of any the Registrable Securities under the Securities Act, the
Company shall indemnify and hold harmless the Shareholders, the affiliates of
the Shareholders, the directors, partners, officers, employees and agents of the
Shareholders and any person who controls the Shareholders within the meaning of
the Securities Act or the Exchange Act, against any and all losses, claims,
damages or liabilities, joint or several, to which they or any of them may
become subject under the Securities Act, the Exchange Act or other Federal or
State statutory law or regulation, at common law or otherwise, insofar as such
losses, claims, damages or liabilities (or actions in respect thereof) caused
by, arising out of or based on any untrue statement or alleged untrue statement
of a material fact contained in any registration statement under which such
securities were registered under the Securities Act, any preliminary prospectus,
final prospectus or summary prospectus contained therein, or any amendment or
supplement thereto, or arise out of or are based upon any omission or alleged
omission to state

                                        4
<PAGE>
therein a material fact required to be stated therein or necessary to make the
statements therein not misleading, and agrees to reimburse each such indemnified
party, as incurred, for any legal or other expenses reasonably incurred by them
in connection with investigating or defending any such loss, claim, damage,
liability or action; provided, however, that (i) the Company will not be liable
in any case to the extent that any such loss, claim, damage or liability arises
out of or is based upon any such untrue statement or alleged untrue statement or
omission or alleged omission made therein in reliance upon and in conformity
with written information furnished to the Company by or on behalf of any such
Shareholders specifically for inclusion therein, (ii) the Company will not be
liable to any indemnified party under this indemnity agreement with respect to
any Registration Statement or Prospectus to the extent that any such loss,
claim, damage or liability of such indemnified party results from the use of the
Prospectus during a period when the use of the Prospectus has been suspended,
provided that the Shareholders received prior notice of such suspension, which
notice shall be deemed to have been received by the Shareholders within 48 hours
after the giving thereof; and (iii) the Company shall not be liable to any
indemnified party with respect to any preliminary Prospectus to the extent that
any such loss, claim, damage or liability of such indemnified party results from
the fact that such indemnified party sold Registrable Securities to a person as
to whom there was not sent or given, at or prior to the written confirmation of
such sale, a copy of the Prospectus or of the Prospectus as then amended or
supplemented in any case where such delivery is required by the Act, if the
loss, claim, damage or liability of such indemnified party results from an
untrue statement or omission of a material fact contained in the preliminary
Prospectus which was corrected in the Prospectus or in the Prospectus as then
amended or supplemented. This indemnity agreement will be in addition to any
liability which the Company may otherwise have. The Company also agrees to
indemnify and provide contribution to each person who may be deemed to be an
underwriter (for purposes of the Act) with respect to the Registrable Securities
("Underwriter" or "Underwriters"), their officers and directors, and each person
who controls each such Underwriter, on substantially the same basis as that of
the indemnification of and contribution to the Shareholders provided in this
Section 2.

         (b) As a condition to including any of the Registrable Securities in
any registration statement filed pursuant to this Agreement, the Shareholders of
the Registrable Securities, as a prospective seller of the Registrable
Securities hereby agrees to indemnify and hold harmless (in the same manner and
to the same extent as set forth in subdivision (a) of this Section 2) the
Company, each director of the Company, each officer, employee or agent of the
Company and each Underwriter of the Registrable Securities and each other person
or entity, if any, which controls the Company or such Underwriter within the
meaning of the Securities Act, with respect to any statement or alleged
statement in, or omission or alleged omission from, such registration statement,
any preliminary Prospectus, Prospectus or summary Prospectus contained therein,
or any amendment or supplement thereto, if such statement or alleged statement
or omission or alleged omission was made in reliance upon and in conformity with
written information furnished to the Company by the Shareholders for use in the
preparation of such registration statement, preliminary Prospectus, Prospectus,
summary Prospectus, amendment or supplement. Any such indemnity shall remain in
full force and effect, regardless of any investigation made by or on behalf of
the Company or any such director, officer or controlling person and shall
survive the transfer of such securities by the

                                        5
<PAGE>
Shareholders. Anything in this Agreement contained to the contrary
notwithstanding, the liability of the Shareholders for indemnification or
contribution hereunder shall be limited to the amount of proceeds received by
such Shareholders in the Offering giving rise to such liability.

         (c) Promptly after receipt by an indemnified party of notice of the
commencement of any action or proceeding involving a claim referred to in the
preceding subdivisions of this Section 2, such indemnified party will, if a
claim in respect thereof is to be made against an indemnifying party, give
written notice to the latter of the commencement of such action, provided that
the failure of any indemnified party to give notice as provided herein shall not
relieve the indemnifying party of its obligations under the preceding
subdivisions of this Section 2, except to the extent that the indemnifying party
is materially prejudiced by such failure to give notice. In case any such action
is brought against an indemnified party, unless in such indemnified party's
reasonable judgment a conflict of interest between such indemnified and
indemnifying parties may exist in respect of such claim, the indemnifying party
shall be entitled to participate in and to assume the defense thereof, jointly
with any other indemnifying party similarly notified, to the extent that the
indemnifying party may wish, with counsel reasonably satisfactory to such
indemnified party, and after notice from the indemnifying party to such
indemnified party of its election so to assume the defense thereof, the
indemnifying party shall not be liable to such indemnified party for any legal
or other expenses subsequently incurred by the latter in connection with the
defense thereof other than reasonable costs of investigation. Notwithstanding
the indemnifying party's election to appoint counsel to represent the
indemnified party in an action, the indemnified party shall have the right to
employ separate counsel (including local counsel), and the indemnifying party
shall bear the reasonable fees, costs and expenses of such separate counsel (and
local counsel) if (i) the use of counsel chosen by the indemnifying party to
represent the indemnified party would present such counsel with a conflict of
interest, (ii) the actual or potential defendants in, or targets of, any such
action include both the indemnified party and the indemnifying party and the
indemnified party shall have reasonably concluded that there may be legal
defenses available to it and/or other indemnified parties which are different
from or additional to those available to the indemnifying party, (iii) the
indemnifying party shall not have employed counsel satisfactory to the
indemnified party to represent the indemnified party within a reasonable time
after notice of the institution of such action or (iv) the indemnifying party
shall authorize the indemnified party to employ separate counsel at the expense
of the indemnifying party. An indemnified party shall not settle or compromise
any action for which it seeks indemnification or contribution hereunder without
the prior written consent of the indemnifying party, which consent shall not be
unreasonably withheld. An indemnifying party will not, without the prior written
consent of the indemnified parties, settle or compromise or consent to the entry
of any judgment with respect to any pending or threatened claim, action, suit or
proceeding in respect of which indemnification or contribution may be sought
hereunder (whether or not the indemnified parties are actual or potential
parties to such claim or action) unless such settlement, compromise or consent
includes an unconditional release of each indemnified party from all liability
arising out of such claim, action, suit or proceeding.

         (d) In the event that the indemnity provided in Section 2(a) or 2(b) is
unavailable to or insufficient to hold harmless an indemnified party for any
reason, then each applicable indemnifying

                                        6
<PAGE>
party, in lieu of indemnifying such indemnified party, shall contribute to the
aggregate losses, claims, damages and liabilities (including legal or other
expenses reasonably incurred in connection with investigating or defending same)
(collectively "losses") to which such indemnified party may be subject in such
proportion as is appropriate to reflect the relative benefits received by such
indemnifying party, on the one hand, and such indemnified party, on the other
hand, from the Registration Statement which resulted in such losses.

         (e) The provisions of this Section 2 shall remain in full force and
effect regardless of any investigation made by or on behalf of any Shareholder
or the Company or any other persons who are entitled to indemnification pursuant
to the provisions of this Section 2, and shall survive the sale by a Shareholder
of Registrable Securities pursuant to the Registration Statement.

         3 Miscellaneous.

         3.1 Survival of Agreements. All agreements contained herein shall
survive the execution and delivery of this Agreement and the closing of the
transactions contemplated hereby.

         3.2 Notices. All notices or other communications hereunder shall be in
writing and shall be deemed given if delivered personally or by overnight
courier, or telecopy or on the third (3rd) business day after mailing if mailed
by prepaid registered or certified mail (return receipt requested), addressed as
follows:

         (a)      If to Company, to:        Authentidate Holding Corp.
                                            2165 Technology Drive
                                            Schenectady, NY 12308
                                            Attention: President
                                            Facsimile: (518) 346-7799

                           Copies to:       Goldstein & DiGioia, LLP
                                            369 Lexington Avenue
                                            New York, New York 10017
                                            Attention: Victor J. DiGioia, Esq.
                                            Facsimile: (212) 557-0295

         (b)      If to the Shareholders, at the address set forth on the
                  register of the Company.

         3.3 Successors and Assigns. The provisions of this Agreement shall be
binding upon, and inure to the benefit of, the respective successors, assigns,
heirs, executors, and administrators of the parties hereto.

         3.4 Amendments and Waivers. Except as otherwise expressly set forth in
this Agreement, any term of this Agreement may be amended and the observance of
any term of this Agreement may be waived (either generally or in a particular
instance and either retroactively or

                                        7
<PAGE>
prospectively), with the written consent of the Company and the holders of at
least fifty-one percent (51%) of the outstanding Registrable Shares only in a
manner that affects all Registrable Shares in the same fashion. Any amendment or
waiver effected in accordance with this Section 3.4 shall be binding upon each
holder of any Registrable Shares (including shares of Common Stock into which
such Registrable Shares have been converted), each future holder of all such
securities, and the Company. No waivers of or exceptions to any term, condition,
or provision of this Agreement, in any one or more instances, shall be deemed to
be, or construed as, a further or continuing waiver of any such term, condition,
or provision.

         3.5 Counterparts. This Agreement may be executed in several
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         3.6 Sections and Exhibits. The headings of sections in this Agreement
are provided for convenience only and will not affect the Agreement's
construction or interpretation. Unless otherwise indicated, all references to
"Section," "Sections," or "Exhibit" refer to the corresponding section,
sections, or exhibit, respectively, of this Agreement.

         3.7 Severability. The invalidity or unenforceability of any provision
of this Agreement shall not affect the validity or enforceability of any other
provision.

         3.8 Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of New York applicable to contracts made
and to be performed wholly within such state without regard to its conflict of
laws rules.

         3.9 Entire Agreement. This Agreement embodies the entire agreement and
understanding between the parties hereto with respect to the subject matter
hereof and supersedes all prior agreements and understandings relating to such
subject matter.

      Remainder of page intentionally left blank. Signature page follows.

                                        8
<PAGE>
         IN WITNESS WHEREOF, the parties hereto have executed or caused this
Agreement to be executed by their signature as natural persons or by individuals
by their duly authorized officers as of the date first written above.

                                    AUTHENTIDATE HOLDING CORP.

                                    By:
                                       -----------------------------------------
                                           Name: John T. Botti
                                           Title:   President

                                    THE PURCHASERS

                                    By:
                                       -----------------------------------------
                                           Name:
                                           Title:

                                    By:
                                       -----------------------------------------
                                           Name:
                                           Title:

                                    By:
                                       -----------------------------------------
                                           Name:
                                           Title:

                                        9

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