1CRYPT(1)                    General Commands Manual                   CRYPT(1)
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NAME

6       crypt - encode/decode
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SYNOPSIS

9       crypt [ password ]
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DESCRIPTION

12       Crypt  reads from the standard input and writes on the standard output.
13       The password is a key that selects a particular transformation.  If  no
14       password  is given, crypt demands a key from the terminal and turns off
15       printing while the key is being typed in.  Crypt encrypts and  decrypts
16       with the same key:
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18            crypt key <clear >cypher
19            crypt key <cypher | pr
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21       will print the clear.
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23       Files  encrypted by crypt are compatible with those treated by the edi‐
24       tor ed in encryption mode.
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26       The security of encrypted files depends on three factors: the fundamen‐
27       tal  method  must be hard to solve; direct search of the key space must
28       be infeasible; `sneak paths' by which keys or cleartext can become vis‐
29       ible must be minimized.
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31       Crypt  implements  a  one-rotor machine designed along the lines of the
32       German Enigma, but with a 256-element rotor.  Methods of attack on such
33       machines  are  known,  but  not  widely;  moreover  the  amount of work
34       required is likely to be large.
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36       The transformation of a key into the internal settings of  the  machine
37       is  deliberately  designed  to be expensive, i.e. to take a substantial
38       fraction of a second to compute.  However, if keys  are  restricted  to
39       (say)  three  lower-case  letters,  then encrypted files can be read by
40       expending only a substantial fraction of five minutes of machine time.
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42       Since the key is an argument to the crypt command,  it  is  potentially
43       visible  to  users  executing  ps(1) or a derivative.  To minimize this
44       possibility, crypt takes care to destroy any record of the key  immedi‐
45       ately upon entry.  No doubt the choice of keys and key security are the
46       most vulnerable aspect of crypt.
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FILES

49       /dev/tty for typed key
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SEE ALSO

52       ed(1), makekey(8)
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BUGS

55       There is no warranty of merchantability nor any warranty of fitness for
56       a particular purpose nor any other warranty, either express or implied,
57       as to the accuracy of the enclosed materials or as to their suitability
58       for  any  particular purpose.  Accordingly, Bell Telephone Laboratories
59       assumes no responsibility for their use by  the  recipient.    Further,
60       Bell  Laboratories  assumes  no obligation to furnish any assistance of
61       any kind whatsoever, or to furnish any additional information or  docu‐
62       mentation.
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