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Annotation of coherent/a/usr/man/COHERENT/crypt.c, revision 1.1

1.1     ! root        1: 
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        !             3: crypt                        Command                        crypt
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        !             7: 
        !             8: Encrypt/decrypt text
        !             9: 
        !            10: ccrryypptt [_p_a_s_s_w_o_r_d]
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        !            12: The command crypt  encrypts data.  It emulates a rotor-encryption
        !            13: machine,  such as  the Enigma  or  Hagelin C-48  cipher machines.
        !            14: Unlike these  machines, crypt  uses only  one rotor, with  a 256-
        !            15: character alphabet and a keying sequence of period 2^32.
        !            16: 
        !            17: crypt  reads text  from standard input  and writes  the encrypted
        !            18: text to standard output.  password is used to construct the model
        !            19: of the machine and to  start the keying sequence.  If no password
        !            20: is given,  crypt prompts for a password on  the terminal and dis-
        !            21: ables echo while it is being typed in.  The password may be up to
        !            22: ten characters  long, but must not be  empty; all characters past
        !            23: the first ten are ignored.  All characters are legal, although it
        !            24: may not  be possible  to input  certain characters from  the ter-
        !            25: minal.
        !            26: 
        !            27: crypt uses the  same password for both encryption and decryption.
        !            28: For example, the commands
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        !            31:         crypt COHERENT <file1 >file2
        !            32:         crypt COHERENT <file2 >file3
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        !            34: 
        !            35: leave file3 identical to file1.
        !            36: 
        !            37: Encrypted files produced by ed with  its -x option may be read by
        !            38: crypt, and  vice versa, as  ed uses crypt to  perform its encryp-
        !            39: tion.
        !            40: 
        !            41: Security of a cryptosystem depends on several factors:
        !            42: 
        !            43: 11. Brute-force attempts to break the system should be infeasible.
        !            44:    Passwords should  be at  least five characters  long; although
        !            45:    the construction of  the machine model from the password takes
        !            46:    a substantial fraction of a second, it is still plausible that
        !            47:    encrypted files  could be  read by  a brute-force search  of a
        !            48:    portion of  the password space  (say, all passwords  less than
        !            49:    four characters long).
        !            50: 
        !            51: 22. Cryptanalysis  of the basic  encryption scheme should  be very
        !            52:    hard.   Analysis of  rotor machines is  understood, but  it is
        !            53:    difficult and in most cases probably not worth the trouble.
        !            54: 
        !            55: 33. Passwords must be  kept secret.  crypt erases password as soon
        !            56:    as it  can, to avoid  the possibility that it  could appear in
        !            57:    the output of ps.
        !            58: 
        !            59: 44.  Privileged  access  to the  system  must  be guarded.   Under
        !            60:    COHERENT,  the security  of crypt  can be  no better  than the
        !            61:    security governing access to superuser status, because the su-
        !            62: 
        !            63: 
        !            64: COHERENT Lexicon                                           Page 1
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        !            68: 
        !            69: crypt                        Command                        crypt
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        !            71: 
        !            72: 
        !            73:    peruser can do practically anything.  This is probably crypt's
        !            74:    most vulnerable point.
        !            75: 
        !            76: ***** Files *****
        !            77: 
        !            78: /ddeevv/ttttyy -- Typed passwords
        !            79: 
        !            80: ***** See Also *****
        !            81: 
        !            82: commands
        !            83: Kahn D: _T_h_e _C_o_d_e _B_r_e_a_k_e_r_s.  New York, Macmillan, 1967.
        !            84: Morris R: The  Hagelin cipher machine (M-209).  _C_r_y_p_t_o_l_o_g_i_a, July
        !            85: 1978.
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        !           130: COHERENT Lexicon                                           Page 2
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