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[CRYPT.HLP - %2(2)]
CRYPT is a program to encrypt files of arbitrary format. The procedure
requires that the user specify an input file, an output file and an
encryption key. The output file is the encrypted form of the input file.
The dialogue format is the following:
The program prompts for the input and output file specifications which
it expects to receive in the traditional format as shown above. The
equal sign and the input file are mandatory. If the output file is
missing, it is assumed to be the same as the input file. This will cause
the original file to be superceded by the encrypted file. The program
then asks the user to supply the encryption key (shown above as "xxx").
To help keep the key secure keyboard echoing is suppressed at this time
(on full duplex terminals). In addition the user will be asked to verify
The user may include the key as a command line switch, if desired. In
this case the format would be
A disadvantage of this format is that each character is echoed as typed
which compromises the security of the key. If this format is chosen and
the key contains any non-alphanumeric characters, double quotes must be
used to delimit the key. (A double quote character may be used in the
key by typing succesive double quotes.)
The encryption technique is cyclic; thus, decryption requires only that
the encrypted file be the input file and the same key be used. A
multiply encrypted file (i.e., one resulting from successive encryption
with different keys) may be decrypted by applying the keys successively
in reverse order. The final output file will be identical to the
original unencrypted file.
The key may contain up to 25 characters. Most printable characters may
be used. Control characters and "space" are illegal. (The legal ASCII
characters are those with octal values between 41 and 172.) Upper and
lower case alphabetic characters are not differentiated.
WARNING: Although the encryption technique used by CRYPT is the same as
that used in BACKUP, no attempt has been made to maintain compatibility
with any other encryption program. Also, note that the key is NOT
written to the file and it is the user's responsibility to remember the
key for a particular file. If the key is lost, there is no way to
decrypt the file. It is recommended that potential users experiment with
CRYPT before putting it into production.