crypt(1) crypt(1)
NAME
crypt - encode/decode text
SYNOPSIS
crypt [-c] [key] Format 1
crypt [-k] Format 2
DESCRIPTION
crypt encodes and decodes the contents of files. crypt reads from
standard input and writes to standard output. Files encrypted without
the -c option are compatible with those created or edited by the edi-
tors ed, edit, ex and vi in encryption mode.
OPTIONS
Format 1:
-c (compatible) If the -c option is set, then
- files encrypted on systems in the MIPS range can be decrypted
on systems in the Intel range
- files encrypted on systems in the Intel range can be decrypted
on systems in the MIPS range
key You may enter any string (1 - 8 characters) of your choice as the
key with which you define the encryption or decryption mechanism.
key not specified:
You enter the required encryption key at the terminal. Your input
will not be echoed to the screen.
Format 2:
-k crypt uses the value of the CrYpTkEy variable as the encryption
or decryption key (see ENVIRONMENT VARIABLE). The case of the
letters in the variable name must be exactly as shown here.
Security criteria
The security of encrypted files essentially depends on the following
factors:
- The underlying encryption method must not be detectable.
- It must be impossible to directly search for the sequence of keys-
trokes entered for encryption.
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crypt(1) crypt(1)
Caution:
If you concatenate two or more files separately encrypted with the
same key into a single file and then try to decrypt the result,
only the contents of the first of the original files will be
decrypted correctly.
ENVIRONMENT VARIABLE
CrYpTkEy
The CrYpTkEy variable defines the encryption/decryption key for
crypt. The case of the letters in the variable name must be
exactly as shown here.
EXAMPLES
Example 1
The file Grandma.ltr contains the following message:
Dearest Granny,
I am sending you a secret message today so that the big bad wolf
won't be able to find out when I'll be visiting you again in the
forest with wine, cakes, and other goodies.
Love, Little Red Riding Hood.
It is now vital that this letter be encrypted! To do this, Little Red
Riding Hood uses the key abcd.
Encryption and redirection to topsecret-file:
$ crypt abcd < Grandma.ltr > topsecret-file
topsecret-file now contains unreadable garbage made up of special
characters and meaningless character sequences.
Grandmother can now decrypt the secret file, but only because Red Rid-
ing Hood first asked the good hunter to give her the keyword, and he
has told her that it is abcd:
Decryption and output on the screen:
$ crypt < topsecret-file
Enter key: abcd
Dearest Granny,
I am sending you a secret message today so that the big bad wolf
won't be able to find out when I'll be visiting you again in the
forest with wine, cakes, and other goodies.
Love, Little Red Riding Hood.
If Little Red Riding Hood encrypted her message on a system in the
MIPS range and Grandmother has an Intel-based machine (!), Grandmother
needs to enter:
$ crypt -c < topsecret-file
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crypt(1) crypt(1)
Example 2
The contents of letter are encrypted, and the encrypted output is
stored in letter.secr. crypt is called with the -k option. The keyword
defined with the CrYpTkEy variable is the string flatnix.
$ CrYpTkEy=flatnix; export CrYpTkEy
$ crypt -k < letter > letter.secr
SEE ALSO
ed(1), edit(1), ex(1), makekey(1), pg(1), ps(1), stty(1), vi(1).
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