jeopardize law enforcement and national security objectives

[Anonymous <nobody@remailer.ch>]

                              SKIPJACK Review
                                      
                               Interim Report
                                      
                           The SKIPJACK Algorithm
                                      
              Ernest F. Brickell, Sandia National Laboratories
                 Dorothy E. Denning, Georgetown University
              Stephen T. Kent, BBN Communications Corporation
                            David P. Maher, AT&T
                    Walter Tuchman, Amperif Corporation
   
                               July 28, 1993
   
                             (Copyright � 1993)
     _________________________________________________________________
   
                             Executive Summary
                                      
   The objective of the SKIPJACK review was to provide a mechanism
   whereby persons outside the government could evaluate the strength of
   the classified encryption algorithm used in the escrowed encryption
   devices and publicly report their findings. Because SKIPJACK is but
   one component of a large, complex system, and because the security of
   communications encrypted with SKIPJACK depends on the security of the
   system as a whole, the review was extended to encompass other
   components of the system. The purpose of this Interim Report is to
   report on our evaluation of the SKIPJACK algorithm. A later Final
   Report will address the broader system issues.

[...]

       We examined the internal structure of SKIPJACK to determine its
       susceptibility to differential cryptanalysis. We concluded it was
       not possible to perform an attack based on differential
       cryptanalysis in less time than with exhaustive search.

[...]

       SKIPJACK algorithm is classified SECRET NOT RELEASABLE TO FOREIGN
       NATIONALS. This classification reflects the high quality of the
       algorithm, i.e., it incorporates design techniques that are
       representative of algorithms used to protect classified
       information. Disclosure of the algorithm would permit analysis
       that could result in discovery of these classified design
       techniques, and this would be detrimental to national security.
       However, while full exposure of the internal details of SKIPJACK
       would jeopardize law enforcement and national security objectives,
       it would not jeopardize the security of encrypted communications.
       This is because a shortcut attack is not feasible even with full
       knowledge of the algorithm. Indeed, our analysis of the
       susceptibility of SKIPJACK to a brute force or shortcut attack was
       based on the assumption that the algorithm was known.
       Conclusion 3: While the internal structure of SKIPJACK must be
       classified in order to protect law enforcement and national
       security objectives, the strength of SKIPJACK against a
       cryptanalytic attack does not depend on the secrecy of the
       algorithm.