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Annotation of coherent/a/usr/man/COHERENT/crypt.c, revision 1.1.1.1

1.1       root        1: 
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                      3: crypt                        Command                        crypt
                      4: 
                      5: 
                      6: 
                      7: 
                      8: Encrypt/decrypt text
                      9: 
                     10: ccrryypptt [_p_a_s_s_w_o_r_d]
                     11: 
                     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
                     29: 
                     30: 
                     31:         crypt COHERENT <file1 >file2
                     32:         crypt COHERENT <file2 >file3
                     33: 
                     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
                     70: 
                     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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