1blowfish(n)                  Blowfish Block Cipher                 blowfish(n)
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5______________________________________________________________________________
6

NAME

8       blowfish - Implementation of the Blowfish block cipher
9

SYNOPSIS

11       package require Tcl  8.4
12
13       package require blowfish  ?1.0.4?
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15       ::blowfish::blowfish  ?-mode  [ecb|cbc]?  ?-dir [encrypt|decrypt]? -key
16       keydata ?-iv vector? ?-out channel? ?-chunksize size? ?-pad padchar?  [
17       -in channel | ?--? data ]
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19       ::blowfish::Init mode keydata iv
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21       ::blowfish::Encrypt Key data
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23       ::blowfish::Decrypt Key data
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25       ::blowfish::Reset Key iv
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27       ::blowfish::Final Key
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29_________________________________________________________________
30

DESCRIPTION

32       This  package  is  an  implementation  in Tcl of the Blowfish algorithm
33       developed by Bruce Schneier [1]. Blowfish  is  a  64-bit  block  cipher
34       designed  to  operate  quickly  on 32 bit architectures and accepting a
35       variable key length. This implementation  supports  ECB  and  CBC  mode
36       blowfish encryption.
37

COMMANDS

39       ::blowfish::blowfish  ?-mode  [ecb|cbc]?  ?-dir [encrypt|decrypt]? -key
40       keydata ?-iv vector? ?-out channel? ?-chunksize size? ?-pad padchar?  [
41       -in channel | ?--? data ]
42              Perform  the  blowfish  algorithm on either the data provided by
43              the argument or on the data read from the  -in  channel.  If  an
44              -out  channel  is  given then the result will be written to this
45              channel.
46
47              The -key option must be given. This  parameter  takes  a  binary
48              string  of  variable length and is used to generate the blowfish
49              key schedule. You should be aware that creating a  key  schedule
50              is  quite  an  expensive  operation  in  blowfish so it is worth
51              reusing the key where possible. See Reset.
52
53              The -mode and -dir options are optional and default to cbc  mode
54              and encrypt respectively. The initialization vector -iv takes an
55              8 byte binary argument which defaults to 8 zeros.  See MODES  OF
56              OPERATION for more about available modes and their uses.
57
58              Blowfish is a 64-bit block cipher. This means that the data must
59              be provided in units that are a multiple of 8 bytes.  The  blow‐
60              fish command will by default add nul characters to pad the input
61              data to a multiple of 8 bytes if necessary. The programming  api
62              commands  will never add padding and instead will raise an error
63              if the input is not a multiple  of  the  block  size.  The  -pad
64              option can be used to change the padding character or to disable
65              padding if the empty string is provided as the argument.
66

PROGRAMMING INTERFACE

68       ::blowfish::Init mode keydata iv
69              Construct a new blowfish key schedule using  the  specified  key
70              data  and  the  given  initialization vector. The initialization
71              vector is not used with ECB mode but is important for CBC  mode.
72              See MODES OF OPERATION for details about cipher modes.
73
74       ::blowfish::Encrypt Key data
75              Use  a prepared key acquired by calling Init to encrypt the pro‐
76              vided data. The data argument should be a binary array that is a
77              multiple  of  the  block size of 8 bytes. The result is a binary
78              array the same size as the input of encrypted data.
79
80       ::blowfish::Decrypt Key data
81              Decipher data using the key. Note that the same key may be  used
82              to  encrypt  and  decrypt  data provided that the initialization
83              vector is reset appropriately for CBC mode.
84
85       ::blowfish::Reset Key iv
86              Reset the initialization vector. This permits the programmer  to
87              re-use  a key and avoid the cost of re-generating the key sched‐
88              ule where the same key data is being used multiple times.
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90       ::blowfish::Final Key
91              This should be called to clean up resources associated with Key.
92              Once  this  function  has  been  called  the key may not be used
93              again.
94

MODES OF OPERATION

96       Electronic Code Book (ECB)
97              ECB is the basic mode  of  all  block  ciphers.  Each  block  is
98              encrypted independently and so identical plain text will produce
99              identical output when encrypted with the same key.  Any  encryp‐
100              tion errors will only affect a single block however this is vul‐
101              nerable to known plaintext attacks.
102
103       Cipher Block Chaining (CBC)
104              CBC mode uses the output of the last block encryption to  affect
105              the  current block. An initialization vector of the same size as
106              the cipher block size is used to handle  the  first  block.  The
107              initialization  vector should be chosen randomly and transmitted
108              as the first block of the output. Errors  in  encryption  affect
109              the current block and the next block after which the cipher will
110              correct itself. CBC is the most commonly used mode  in  software
111              encryption.
112

EXAMPLES

114       % blowfish::blowfish -hex -mode ecb -dir encrypt -key secret01 "hello, world!"
115       d0d8f27e7a374b9e2dbd9938dd04195a
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117
118        set Key [blowfish::Init cbc $eight_bytes_key_data $eight_byte_iv]
119        append ciphertext [blowfish::Encrypt $Key $plaintext]
120        append ciphertext [blowfish::Encrypt $Key $additional_plaintext]
121        blowfish::Final $Key
122
123

REFERENCES

125       [1]    Schneier,  B.  "Applied  Cryptography,  2nd edition", 1996, ISBN
126              0-471-11709-9, pub. John Wiley & Sons.
127

AUTHORS

129       Frank Pilhofer, Pat Thoyts
130

BUGS, IDEAS, FEEDBACK

132       This document, and the package it describes, will  undoubtedly  contain
133       bugs  and  other problems.  Please report such in the category blowfish
134       of       the       Tcllib       SF       Trackers       [http://source
135       forge.net/tracker/?group_id=12883].   Please  also report any ideas for
136       enhancements you may have for either package and/or documentation.
137

SEE ALSO

139       3des, des, rc4
140

KEYWORDS

142       block cipher, blowfish, cryptography, encryption, security
143
145       Copyright (c) 2003, Pat Thoyts <patthoyts@users.sourceforge.net>
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150blowfish                             1.0.3                         blowfish(n)
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