CLIPPER CHIP TECHNOLOGY


CLIPPER is an NSA developed, hardware oriented, cryptographic
device that implements a symmetric encryption/decryption
algorithm and a law enforcement satisfying key escrow system. 
While the escrow management system design is not completely
designed, the cryptographic algorithm (SKIPJACK) is completely
specified (and classified SECRET).

The cryptographic algorithm (called CA in this paper) has the
following characteristics:

     1.   Symmetric, 80-bit key encryption/decryption algorithm;
     2.   Similar in function to DES (i.e., basically a 64-bit
          code book transformation that can be used in the same
          four modes of operation as specified for DES in FIPS
          81);
     3.   32 rounds of processing per single encrypt/decrypt
          operation;
     4.   Design started by NSA in 1985; evaluation completed in
          1990.

The CLIPPER CHIP is just one implementation of the CA.  The
CLIPPER CHIP designed for the AT&T commercial secure voice
products has the following characteristics:

     1.   Functions specified by NSA; logic designed by
          MYKOTRONX; chip fabricated by VLSI, Inc.:  manufactured
          chip programmed (made unique) by MYKOTRONX to security
          equipment manufacturers willing to follow proper
          security procedures for handling and storage of the
          programmed chip; equipment sold to customers;

     2.   Resistant to reverse engineering against a very
          sophisticated, well funded adversary;

     3.   15-20 MB/S encryption/decryption constant throughout
          once cryptographic synchronization is established with
          distant CLIPPER Chip;

     4.   The chip programming equipment writes (one time) the
          following information into a special memory (called
          VROM or VIA-Link) on the chip:

          a.   (unique) serial number
          b.   (unique) unit key
          c.   family key
          d.   specialized control software

     5.   Upon generation (or entry) of a session key in the
          chip, the chip performs the following actions:


          a.   Encrypts the 80-bit session key under the unit key
               producing an 80-bit intermediate result;

          b.   Concatenates the 80-bit result with the 25-bit
               serial number and a 23-bit authentication pattern
               (total of 128 bits);

          c.   Enciphers this 128 bits with family key to produce
               a 128-bit cipher block chain called the Law
               Enforcement Field (LEF);

          d.   Transmits the LEF at least once to the intended
               receiving CLIPPER chip;

          e.   The two communicating CLIPPER chips use this field
               together with a random IV to establish
               Cryptographic Synchronization.

     6.   Once synchronized, the CLIPPER chips use the session
          key to encrypt/decrypt data in both directions;

     7.   The chips can be programmed to not enter secure mode if
          the LEF field has been tampered with (e.g., modified,
          superencrypted, replaced);

     8.   CLIPPER chips will be available from a second source in
          the future;

     9.   CLIPPER chips will be modified and upgraded in the
          future;

     10.  CLIPPER chips presently cost $16.00 (unprogrammed) and
          $26.00 (programmed).



4/30/93