PC Online 1996 November/PCO96_11.ISO/filesbbs/cryptext.arj/README.TXT

Text File | 1996-09-03 | 5.5 KB | 99 lines

Copyright (c) Nick Payne 1996

This readme is for Cryptext v1.2

Cryptext is a freeware Windows 95 / NT4 shell extension that performs strong file encryption.
It uses a combination of SHA and RC4 to encrypt files using a 160-bit key. The current version
of Cryptext can be found at www.pcug.org.au/~njpayne

Cryptext may be used in any way, for any purpose, at no cost. It may be distributed by any means,
provided that the original files as supplied by the author remain intact and that no charge is
made other than for reasonable distribution costs. Note that Cryptext contains strong
cryptographic routines upon which some countries place distribution and/or use restrictions.
Verify that you are allowed to use or distribute Cryptext before doing so.

DISCLAIMER OF WARRANTY
THIS SOFTWARE AND DOCUMENTATION ARE PROVIDED "AS IS" AND WITHOUT WARRANTIES AS TO PERFORMANCE
OF MERCHANTABILITY OR ANY OTHER WARRANTIES WHETHER EXPRESSED OR IMPLIED. BECAUSE OF THE VARIOUS
HARDWARE AND SOFTWARE ENVIRONMENTS INTO WHICH THIS PROGRAM MAY BE PUT, NO WARRANTY OF FITNESS
FOR PARTICULAR PURPOSE IS OFFERED. GOOD DATA PROCESSING PROCEDURE DICTATES THAT ANY PROGRAM BE
THOROUGHLY TESTED WITH NON-CRITICAL DATA BEFORE RELYING ON IT. THE USER MUST ASSUME THE ENTIRE
RISK OF USING THE PROGRAM.

Any product or brand names mentioned in this document are trademarks or registered trademarks
of their respective owners.

To install Cryptext
===================
1. Unzip the contents of CRYPTEXT.ZIP into a directory

2. In Explorer, right-click on CRYPTEXT.INF and select Install from the popup context menu
To install this shell extension on Windows NT you must be logged in as administrator or a
user who is a member of the Administrators group. This is because installing a shell extension
on NT requires update rights to a part of the registry to which a normal user cannot write.

To uninstall Cryptext
=====================
1. From the Start menu, select Settings, then Control Panel, then Add/Remove Programs.

2. If you are running on Windows 95, select the "Cryptext (Windows 95) (Remove only)" entry.
   If you are running on Windows NT, select the "Cryptext (Windows NT) (Remove only)" entry.

3. Click on the Add/Remove button.

How does it work?
=================
1. When you install Cryptext it adds "Encrypt" and "Decrypt" items to the context menu you
   get when right-clicking on a file or directory in Explorer.

2. When you encrypt or decrypt files, Cryptext takes your password and uses the SHA one-way
   hash function to generate a 160-bit key from the password. It uses this 160-bit key to
   encrypt or decrypt the files with the RC4 algorithm.

3. In order to verify your password on second and subsequent executions, Cryptext takes the
   160-bit key generated in step 2, adds it to the end of your password, and applies the SHA
   function to the concatenation of the password and key. The resultant hash is saved so that
   subsequent passwords can be checked for validity by being put through the same two-step
   hash and compared with the stored value.

Notes
=====
1. If you are running on Windows NT 4 then you have the option to retain the encryption password
   in memory for the duration of your NT session. If you are running on Windows 95 you must enter
   the password for each encryption or decryption.

2. After the initial execution of Cryptext, you cannot change your encryption password unless you
   know the existing password. If you forget the password, you have to uninstall and reinstall
   Cryptext. If you have files you have encrypted and you have forgotten the password then those
   files are not recoverable.
   To uninstall Cryptext:
   a) From the Start menu, select Settings / Control Panel
   b) In Control Panel, select Add/Remove Programs
   c) On the Install/Uninstall tab, select "Cryptext (Remove only)" in the list of installed
      programs and click on the Add/Remove button

3. Cryptext assumes that the file system on which it is running supports long filenames. When it
   encrypts a file it adds the extension ".$#!" to the filename. This name change will fail if the
   existing filename already exceeds 252 characters or if the file system does not support long
   filenames (such as a NetWare server volume which does not have long namespace support loaded).
   The resulting file is still encrypted but it does not have the extension which Cryptext
   recognises, and when you decrypt it you will be queried whether the file is actually encrypted.

4. Password selection. Cryptext allows a password to be up to 255 characters long. As a file
   encryption password is generally in use for much longer than a login password, you should use
   more care selecting it. For more information on good password selection, use one of the www
   search engines to search for web documents containing "password", "selection", and "good".

5. My thanks to Gary Mulhern for showing how to add the registry entries to get a meaningful
   icon and file type to display for encrypted files in Explorer.

If you are interested in finding out more about encryption and cryptography:
a) RSA's web site at www.rsa.com has a good cryptography FAQ available both
   online and as a downloadable PDF file
b) There is a lot of cryptographic source code at idea.sec.dsi.unimi.it/pub/security/crypt/code
c) Bruce Schneider's book "Applied Cryptography" has a comprehensive coverage of both protocols and
   algorithms

Nick Payne
[e-mail]