Exhibit No. 5



                                               December 6, 2002


Authentidate Holding Corp.
2165 Technology Drive
Schenectady, New York 12308


                  Re:      Authentidate Holding Corp.
                           Registration Statement on Form S-3
                           SEC File No. 333-101354

Ladies/Gentlemen:

            We have reviewed the pre-effective Amendment No. 1 to the
Registration Statement on Form S-3/A, filed on December 6, 2002 (File No.
333-101354) (the "Registration Statement"), under the Securities Act of l933, as
amended (the "Act"), by Authentidate Holding Corp., a Delaware corporation (the
"Company"). The Registration Statement has been filed for the purpose of
registering the securities described therein for offer and sale under the Act.
All capitalized terms not defined herein have the meanings ascribed to them in
the Registration Statement.

      This opinion has been rendered with respect to 1,480,000 shares of common
stock issuable upon conversion of convertible debentures (the "Debentures"), an
aggregate of 540,863 shares issuable upon the exercise of common stock purchase
warrants (the "Warrants") and an aggregate of 310,800 shares of common stock
which we may issue as interest payments on the debentures. The shares of common
stock issuable as described in the foregoing sentence may be referred to herein
as the "Shares".

      In connection with the opinions rendered herein, we have examined the
Certificate of Incorporation of the Company, its By-Laws, the Debentures, the
Warrants and such other documents, corporate records and questions of law as we
have deemed necessary solely for the purpose of enabling us to render this
opinion. On the basis of such examination, we are of the opinion that:

      1. The Company is a corporation duly organized and validly existing and in
good standing under the laws of Delaware, with corporate power to conduct the
business which it conducts as described in the Registration Statement.

      2. The Company has an authorized capitalization of 40,000,000 shares of
Common


Stock, par value $.001 per share and 5,000,000 shares of Preferred Stock, par
value $.01 per share.

      3. The Shares issuable upon conversion of the Debentures have been duly
authorized and when issued, sold and paid for, as described in the Registration
Statement, will be validly issued, fully paid and non-assessable.

      4. The Shares issuable upon exercise of the Warrants have been duly
authorized and when issued, sold and paid for, as described in the Registration
Statement, will be validly issued, fully paid and non-assessable.

      5. The Shares issuable as interest payments on the Debentures have been
duly authorized and when issued, sold and paid for, as described in the
Registration Statement, will be validly issued, fully paid and non-assessable.

            We hereby consent to the use of this opinion as an exhibit to the
Registration Statement and to the reference to our firm under the caption "Legal
Opinions" in the Prospectus forming a part of the Registration Statement. As set
forth in the Registration Statement, certain members of our firm own securities
of Authentidate Holding Corp.

                                               Very truly yours,

                                               /s/ Goldstein & DiGioia, LLP

                                               GOLDSTEIN & DIGIOIA, LLP