blowfish -
Implementation of the Blowfish block cipher
package require Tcl 8.4
package require blowfish ? 1.0.4 ?
::blowfish::blowfish ? -mode [ecb|cbc] ? ? -dir [encrypt|decrypt] ? -key keydata ? -iv vector ? ? -out channel ? ? -chunksize size ? ? -pad padchar ? [ -in channel | ? -- ? data ]
::blowfish::Init mode keydata iv
::blowfish::Encrypt Key data
::blowfish::Decrypt Key data
::blowfish::Reset Key iv
::blowfish::Final Key
This package is an implementation in Tcl of the Blowfish algorithm
developed by Bruce Schneier [1]. Blowfish is a 64-bit block cipher
designed to operate quickly on 32 bit architectures and accepting a
variable key length. This implementation supports ECB and CBC mode
blowfish encryption.
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::blowfish::blowfish ? -mode [ecb|cbc] ? ? -dir [encrypt|decrypt] ? -key keydata ? -iv vector ? ? -out channel ? ? -chunksize size ? ? -pad padchar ? [ -in channel | ? -- ? data ]
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Perform the blowfish algorithm on either the data provided
by the argument or on the data read from the -in channel. If
an -out channel is given then the result will be written to
this channel.
The -key option must be given. This parameter takes a binary
string of variable length and is used to generate the blowfish
key schedule. You should be aware that creating a key
schedule is quite an expensive operation in blowfish so it is worth
reusing the key where possible. See Reset.
The -mode and -dir options are optional and default to cbc
mode and encrypt respectively. The initialization vector -iv
takes an 8 byte binary argument which defaults to 8 zeros.
See MODES OF OPERATION for more about available modes and
their uses.
Blowfish is a 64-bit block cipher. This means that the data must be
provided in units that are a multiple of 8 bytes. The blowfish
command will by default add nul characters to pad the input data to a
multiple of 8 bytes if necessary. The programming api commands will
never add padding and instead will raise an error if the input is not
a multiple of the block size. The -pad option can be used to
change the padding character or to disable padding if the empty string
is provided as the argument.
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::blowfish::Init mode keydata iv
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Construct a new blowfish key schedule using the specified key data and
the given initialization vector. The initialization vector is not used
with ECB mode but is important for CBC mode.
See MODES OF OPERATION for details about cipher modes.
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::blowfish::Encrypt Key data
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Use a prepared key acquired by calling Init to encrypt the
provided data. The data argument should be a binary array that is a
multiple of the block size of 8 bytes. The result is a binary
array the same size as the input of encrypted data.
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::blowfish::Decrypt Key data
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Decipher data using the key. Note that the same key may be used to
encrypt and decrypt data provided that the initialization vector is
reset appropriately for CBC mode.
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::blowfish::Reset Key iv
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Reset the initialization vector. This permits the programmer to re-use
a key and avoid the cost of re-generating the key schedule where the
same key data is being used multiple times.
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::blowfish::Final Key
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This should be called to clean up resources associated with Key.
Once this function has been called the key may not be used again.
- Electronic Code Book (ECB)
-
ECB is the basic mode of all block ciphers. Each block is encrypted
independently and so identical plain text will produce identical
output when encrypted with the same key. Any encryption errors will
only affect a single block however this is vulnerable to known
plaintext attacks.
- Cipher Block Chaining (CBC)
-
CBC mode uses the output of the last block encryption to affect the
current block. An initialization vector of the same size as the cipher
block size is used to handle the first block. The initialization
vector should be chosen randomly and transmitted as the first block of
the output. Errors in encryption affect the current block and the next
block after which the cipher will correct itself. CBC is the most
commonly used mode in software encryption.
% blowfish::blowfish -hex -mode ecb -dir encrypt -key secret01 "hello, world!"
d0d8f27e7a374b9e2dbd9938dd04195a
set Key [blowfish::Init cbc $eight_bytes_key_data $eight_byte_iv]
append ciphertext [blowfish::Encrypt $Key $plaintext]
append ciphertext [blowfish::Encrypt $Key $additional_plaintext]
blowfish::Final $Key
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Schneier, B. "Applied Cryptography, 2nd edition", 1996,
ISBN 0-471-11709-9, pub. John Wiley & Sons.
Frank Pilhofer, Pat Thoyts
This document, and the package it describes, will undoubtedly contain
bugs and other problems.
Please report such in the category
blowfish of the
http://sourceforge.net/tracker/?group_id=12883.
Please also report any ideas for enhancements you may have for either
package and/or documentation.
des, 3des, rc4
blowfish, block cipher, security, encryption, cryptography