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[CRYPT.HLP - %2(2)]
.sk;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:
.sk;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to be superceded by the encrypted file.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 key.
.sk;The user may include the key as a command line switch,
In this case the format would be
.sk;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.)
.sk;The encryption technique is cyclic;
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.
.sk;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.
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.