This is mit-scheme-blowfish.info, produced by makeinfo version 6.5 from
mit-scheme-blowfish.texi.

This manual documents MIT/GNU Scheme Blowfish 1.1.

   Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018,
2019 Massachusetts Institute of Technology

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.2 or any later version published by the Free Software
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     section entitled "GNU Free Documentation License."
INFO-DIR-SECTION Programming Languages
START-INFO-DIR-ENTRY
* MIT/GNU Scheme Blowfish: (mit-scheme-blowfish).
                                Blowfish plugin.
END-INFO-DIR-ENTRY


File: mit-scheme-blowfish.info,  Node: Top,  Next: Introduction,  Up: (dir)

Blowfish Plugin Manual
**********************

This manual documents MIT/GNU Scheme Blowfish 1.1.

   Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018,
2019 Massachusetts Institute of Technology

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.2 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with no Front-Cover Texts
     and no Back-Cover Texts.  A copy of the license is included in the
     section entitled "GNU Free Documentation License."

* Menu:

* Introduction::
* Procedures::
* DES Modes::
* GNU Free Documentation License::


File: mit-scheme-blowfish.info,  Node: Introduction,  Next: Procedures,  Prev: Top,  Up: Top

1 Introduction
**************

This plugin is a dynamically loadable wrapper of the Blowfish block
cipher C API as implemented by libssl (OpenSSL).

   The cipher operates on 64 bit (8 byte) blocks of data and uses a
variable size key.  Keys with 128 bits (16 bytes) are considered good
for modest encryption.  Blowfish can be used in the same modes as DES,
is quite a bit faster than DES, and much faster than IDEA or RC2.

   The plugin includes a Scheme procedure to feed bytes from a binary
input port to the library, and write the encrypted bytes to a binary
output port.


File: mit-scheme-blowfish.info,  Node: Procedures,  Next: DES Modes,  Prev: Introduction,  Up: Top

2 Procedures
************

Blowfish consists of a key setup phase and the actual encryption or
decryption phase.

 -- Procedure: blowfish-set-key bytes
     Generate a Blowfish key from BYTES, which must be 72 bytes or less
     in length.  For text keys (strings), apply 'md5-string' and use the
     digest for BYTES.

 -- Procedure: blowfish-ecb input output key encyrpt?
     Apply Blowfish in Electronic Code Book mode.  INPUT is an 8-byte
     byte vector.  OUTPUT is an 8-byte byte vector.  KEY is a Blowfish
     key.  ENCRYPT? specifies whether to encrypt (when '#t') or decrypt
     (when '#f').

   The mode functions below all operate on variable length data.  They
all take an initialization vector which needs to be passed along into
the next call of the same function for the same message.  The vector may
be initialized with anything, but the recipient needs to know what it
was initialized with, or it won't be able to decrypt.  Some programs and
protocols simplify this, like SSH, where the vector is simply
initialized to zero.  'Blowfish-cbc' operates on data that is a multiple
of 8 bytes long, while 'blowfish-cfb64' and 'blowfish-ofb64' are used to
encrypt any number of bytes.  The purpose of the latter two is to
simulate stream ciphers, and therefore, they have a parameter 'num', the
current offset in the initialization vector, which should start at zero
and be stored between calls.

 -- Procedure: blowfish-cbc input output key init encrypt?
     Apply Blowfish in Cipher Block Chaining mode.  INPUT is a multiple
     of 8 bytes.  OUTPUT is the same number of bytes as in Input.  KEY
     is a Blowfish key.  INIT is an 8 byte initialization vector; it is
     modified after each call.  The value from any call may be passed in
     to a later call.  ENCRYPT? specifies whether to encrypt (when '#t')
     or decrypt (when '#f').

 -- Procedure: blowfish-cfb64 input istart iend output ostart key init
          num encrypt?
     Apply Blowfish in Cipher Feed-Back mode.  ISTART and IEND specify a
     range of bytes in INPUT.  OSTART specifies the first byte to write
     in OUTPUT.  KEY is a Blowfish key.  INIT is an 8 byte
     initialization vector; it is modified after each call.  The value
     from any call may be passed in to a later call.  The initial value
     must be unique for each message/key pair.  NUM is an integer from 0
     to 7 inclusive, the low 3 bits of the number of bytes that have
     previously been processed in this stream.  ENCRYPT? specifies
     whether to encrypt (when '#t') or decrypt (when '#f').  The
     returned value is the new value of Num.

 -- Procedure: blowfish-ofb64 input istart iend output ostart key init
          num
     Apply Blowfish in Output Feed-Back mode.  ISTART and IEND specify a
     range of bytes in INPUT.  OSTART specifies the first byte to write
     in OUTPUT.  KEY is a Blowfish key.  INIT is an 8 byte
     initialization vector; it is modified after each call.  The value
     from any call may be passed in to a later call.  The initial value
     must be unique for each message/key pair.  NUM is an integer from 0
     to 7 inclusive, the low 3 bits of the number of bytes that have
     previously been processed in this stream.  The returned value is
     the new value of Num.

   Two convenience procedures are also provided.

 -- Procedure: blowfish-encrypt-port input output key init encrypt?
     Reads bytes from INPUT, which should be in blocking mode, until the
     end.  Feeds the bytes to 'blowfish-cfb64' and writes the resulting,
     encrypted bytes to OUTPUT.  KEY and INIT are passed to
     'blowfish-cfb64' (which modifies the latter).  ENCRYPT? specifies
     whether to encrypt (when '#t') or decrypt (when '#f').

 -- Procedure: compute-blowfish-init-vector
     Returns a new initialization vector that includes a timestamp with
     a resolution of milliseconds, plus 20 random bits.  This should
     make it very likely unique.

   The Blowfish cipher was invented and described by Counterpane (see
<http://www.counterpane.com/blowfish.html>).  Most of this manual was
adapted from the OpenSSL manual pages.


File: mit-scheme-blowfish.info,  Node: DES Modes,  Next: GNU Free Documentation License,  Prev: Procedures,  Up: Top

3 DES Modes
***********

This chapter was written in large parts by Eric Young in his original
documentation for SSLeay, the predecessor of OpenSSL. In turn, he
attributed it to:

     AS 2805.5.2
     Australian Standard
     Electronic funds transfer - Requirements for interfaces,
     Part 5.2: Modes of operation for an n-bit block cipher algorithm
     Appendix A

3.1 Electronic Codebook Mode (ECB)
==================================

64 bits are enciphered at a time.

   The order of the blocks can be rearranged without detection.

   The same plain text block always produces the same cipher text block
(for the same key) making it vulnerable to a dictionary attack.

   An error will only affect one cipher text block.

3.2 Cipher Block Chaining Mode (CBC)
====================================

A multiple of 64 bits are enciphered at a time.

   The CBC mode produces the same cipher text whenever the same plain
text is encrypted using the same key and starting variable.

   The chaining operation makes the cipher text blocks dependent on the
current and all preceding plain text blocks and therefore blocks can not
be rearranged.

   The use of different starting variables prevents the same plain text
enciphering to the same cipher text.

   An error will affect the current and the following cipher text
blocks.

3.3 Cipher Feedback Mode (CFB)
==============================

Any number of bits, j, up to 64, are enciphered at a time.

   The CFB mode produces the same cipher text whenever the same plain
text is encrypted using the same key and starting variable.

   The chaining operation makes the cipher text variables dependent on
the current and all preceding variables and therefore j-bit variables
are chained together and can not be rearranged.

   The use of different starting variables prevents the same plain text
enciphering to the same cipher text.

   The strength of the CFB mode depends on the size of k (maximal if j =
k).  In my implementation this is always the case.

   Selection of a small value for j will require more cycles through the
encipherment algorithm per unit of plain text and thus cause greater
processing overheads.

   Only multiples of j bits can be enciphered.

   An error will affect the current and the following cipher text
variables.

3.4 Output Feedback Mode (OFB)
==============================

Any number of bits, j, up to 64, are enciphered at a time.

   The OFB mode produces the same cipher text whenever the same plain
text enciphered using the same key and starting variable.  More over, in
the OFB mode the same key stream is produced when the same key and start
variable are used.  Consequently, for security reasons a specific start
variable should be used only once for a given key.

   The absence of chaining makes the OFB more vulnerable to specific
attacks.

   The use of different start variables values prevents the same plain
text enciphering to the same cipher text, by producing different key
streams.

   Selection of a small value for j will require more cycles through the
encipherment algorithm per unit of plain text and thus cause greater
processing overheads.

   Only multiples of j bits can be enciphered.

   OFB mode of operation does not extend cipher text errors in the
resultant plain text output.  Every bit error in the cipher text causes
only one bit to be in error in the deciphered plain text.

   OFB mode is not self-synchronizing.  If the two operations of
encipherment and decipherment get out of synchronism, the system needs
to be re-initialized.

   Each re-initialization should use a value of the start variable
different from the start variable values used before with the same key.
The reason for this is that an identical bit stream would be produced
each time from the same parameters.  This would be susceptible to a
'known plain text' attack.


File: mit-scheme-blowfish.info,  Node: GNU Free Documentation License,  Prev: DES Modes,  Up: Top

Appendix A GNU Free Documentation License
*****************************************

                      Version 1.2, November 2002

     Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
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     This License is a kind of "copyleft", which means that derivative
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     It complements the GNU General Public License, which is a copyleft
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     We have designed this License in order to use it for manuals for
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A.1 ADDENDUM: How to use this License for your documents
========================================================

To use this License in a document you have written, include a copy of
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   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of free
software license, such as the GNU General Public License, to permit
their use in free software.



Tag Table:
Node: Top992
Node: Introduction1924
Node: Procedures2598
Node: DES Modes6851
Node: GNU Free Documentation License10841

End Tag Table
