August 8, 1996


Cylink Corporation
910 Hermosa Court
Sunnyvale, CA 94086

Gentlemen:

              At your request,  we have examined the  Registration  Statement on
Form S-8 executed by you on August 8, 1996,  and to be filed with the Securities
and Exchange  Commission (the "SEC") in connection with the  registration  under
the  Securities  Act of 1933,  as amended,  of an aggregate of 1,385,266 of your
Common  Stock,  $.01 par value (the "Common  Stock")  issuable  upon exercise of
options which have been and will be granted pursuant to the Amended and Restated
1994 Flexible Stock Incentive Plan (the "Plan").

              As your counsel in connection with the Registration  Statement, we
have examined the  proceedings  taken by you in connection  with the adoption of
the Plan and the  authorization  of the issuance of the Common Shares or options
or  warrants  to  purchase  shares of  Common  Stock  under the Plan (the  "Plan
Shares") and such documents as we have deemed necessary to render this opinion.

              Based upon the foregoing,  it is our opinion that the Plan Shares,
when issued and  outstanding  pursuant to the terms of the Plan, will be validly
issued, fully paid and nonassessable shares of Common Stock.

              We  consent  to the  use of  this  opinion  as an  exhibit  to the
Registration Statement.

                                         Very truly yours,

                                         /s/ Morrison & Foerster LLP



                                   Exhibit 5.1
                                Page 9 of 9 Pages