LOCK and UNLOCK                          Steven Holzner
File encryption and decryption	            Version 1.0
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Purpose
-------
LOCK encrypts a file, rendering it unreadable to anyone
who does not know the user-chosen passphrase.
Subsequently, using the same passphrase, UNLOCK will
decrypt the file.

Format
------

    LOCK plainFile codeFile      (to lock a file)

then

    UNLOCK codeFile plainFile    (to unlock a file)

Remarks
-------
The user-selected passphrase can be up to 64
characters in length; the programs prompt you
to supply it. Files to be LOCKed and
UNLOCKed must be less than 62K in length. If
you do not supply new filenames for the
locked and unlocked files, the programs use
the default filename FILE.LOC.

Example
-------
You have a file of student course evaluations
named CONFY on drive C: that you wish to mail
to a colleague in encrypted form. You put a
formatted floppy disk in drive A:, and at the
C> prompt you enter

    LOCK CONFY A:CRIMSON

When the program asks for a passphrase, you
enter VERITAS.

The CRIMSON file on the disk will be
unreadable. When your colleague--who must,
of course, have a copy of the program 
"UNLOCK" and be told the passphrase you have
used--puts the disk in his machine, he types

    UNLOCK A:CRIMSON GUIDE

When prompted, he supplies the passphrase
VERITAS, and his file GUIDE will be identical
to your original file CONFY.

Notes
-----
1. LOCK and UNLOCK do not delete any files,
   original or encoded.

2. You should always LOCK and UNLOCK from one
   filename to another. If you give the same
   filename for both the plain and encrypted
   files in a LOCK or UNLOCK command, you may
   not be able to recover your plain text.

3. Requires DOS version 2.0 or later.
